| Rfc | 3720 |
|---|
| Title | Internet Small Computer Systems Interface (iSCSI) |
|---|
| Author | J. Satran, K.
Meth, C. Sapuntzakis, M. Chadalapaka, E. Zeidner |
|---|
| Date | April 2004 |
|---|
| Format: | TXT, HTML |
|---|
| Obsoleted by | RFC7143 |
|---|
| Updated by | RFC3980,
RFC4850, RFC5048, RFC7146 |
|---|
| Status: | PROPOSED STANDARD |
|---|
|
Network Working Group J. Satran
Request for Comments: 3720 K. Meth
Category: Standards Track IBM
C. Sapuntzakis
Cisco Systems
M. Chadalapaka
Hewlett-Packard Co.
E. Zeidner
IBM
April 2004
Internet Small Computer Systems Interface (iSCSI)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes a transport protocol for Internet Small
Computer Systems Interface (iSCSI) that works on top of TCP. The
iSCSI protocol aims to be fully compliant with the standardized SCSI
architecture model.
SCSI is a popular family of protocols that enable systems to
communicate with I/O devices, especially storage devices. SCSI
protocols are request/response application protocols with a common
standardized architecture model and basic command set, as well as
standardized command sets for different device classes (disks, tapes,
media-changers etc.).
As system interconnects move from the classical bus structure to a
network structure, SCSI has to be mapped to network transport
protocols. IP networks now meet the performance requirements of fast
system interconnects and as such are good candidates to "carry" SCSI.
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 9
2. Definitions and Acronyms. . . . . . . . . . . . . . . . . . . 10
2.1. Definitions. . . . . . . . . . . . . . . . . . . . . . 10
2.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . 14
2.3. Conventions. . . . . . . . . . . . . . . . . . . . . . 16
2.3.1. Word Rule. . . . . . . . . . . . . . . . . . 16
2.3.2. Half-Word Rule . . . . . . . . . . . . . . . 17
2.3.3. Byte Rule. . . . . . . . . . . . . . . . . . 17
3. Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1. SCSI Concepts. . . . . . . . . . . . . . . . . . . . . 17
3.2. iSCSI Concepts and Functional Overview . . . . . . . . 18
3.2.1. Layers and Sessions. . . . . . . . . . . . . 19
3.2.2. Ordering and iSCSI Numbering . . . . . . . . 19
3.2.2.1. Command Numbering and
Acknowledging . . . . . . . . . . 20
3.2.2.2. Response/Status Numbering and
Acknowledging . . . . . . . . . . 23
3.2.2.3. Data Sequencing . . . . . . . . 24
3.2.3. iSCSI Login. . . . . . . . . . . . . . . . . 24
3.2.4. iSCSI Full Feature Phase . . . . . . . . . . 25
3.2.4.1. Command Connection Allegiance . . 26
3.2.4.2. Data Transfer Overview. . . . . . 27
3.2.4.3. Tags and Integrity Checks . . . . 28
3.2.4.4. Task Management . . . . . . . . . 28
3.2.5. iSCSI Connection Termination . . . . . . . . 29
3.2.6. iSCSI Names. . . . . . . . . . . . . . . . . 29
3.2.6.1. iSCSI Name Properties . . . . . . 30
3.2.6.2. iSCSI Name Encoding . . . . . . . 31
3.2.6.3. iSCSI Name Structure. . . . . . . 32
3.2.6.3.1. Type "iqn." (iSCSI
Qualified Name) . . . 32
3.2.6.3.2. Type "eui." (IEEE
EUI-64 format). . . . 34
3.2.7. Persistent State . . . . . . . . . . . . . . 34
3.2.8. Message Synchronization and Steering . . . . 35
3.2.8.1. Sync/Steering and iSCSI PDU
Length . . . . . . . . . . . . . 36
3.3. iSCSI Session Types. . . . . . . . . . . . . . . . . . 36
3.4. SCSI to iSCSI Concepts Mapping Model . . . . . . . . . 37
3.4.1. iSCSI Architecture Model . . . . . . . . . . 37
3.4.2. SCSI Architecture Model. . . . . . . . . . . 39
3.4.3. Consequences of the Model. . . . . . . . . . 41
3.4.3.1. I_T Nexus State . . . . . . . . . 42
3.5. Request/Response Summary . . . . . . . . . . . . . . . 42
3.5.1. Request/Response Types Carrying SCSI Payload 43
3.5.1.1. SCSI-Command . . . . . . . . . . 43
3.5.1.2. SCSI-Response . . . . . . . . . 43
3.5.1.3. Task Management Function Request. 44
3.5.1.4. Task Management Function Response 44
3.5.1.5. SCSI Data-Out and SCSI Data-In. . 44
3.5.1.6. Ready To Transfer (R2T) . . . . . 45
3.5.2. Requests/Responses carrying SCSI and iSCSI
Payload. . . . . . . . . . . . . . . . . . . 46
3.5.2.1. Asynchronous Message. . . . . . . 46
3.5.3. Requests/Responses Carrying iSCSI Only
Payload. . . . . . . . . . . . . . . . . . . 46
3.5.3.1. Text Request and Text Response. . 46
3.5.3.2. Login Request and Login Response. 47
3.5.3.3. Logout Request and Response . . . 47
3.5.3.4. SNACK Request . . . . . . . . . . 48
3.5.3.5. Reject. . . . . . . . . . . . . . 48
3.5.3.6. NOP-Out Request and NOP-In
Response . . . . . . . . . . . . 48
4. SCSI Mode Parameters for iSCSI. . . . . . . . . . . . . . . . 48
5. Login and Full Feature Phase Negotiation. . . . . . . . . . . 48
5.1. Text Format. . . . . . . . . . . . . . . . . . . . . . 50
5.2. Text Mode Negotiation. . . . . . . . . . . . . . . . . 53
5.2.1. List negotiations. . . . . . . . . . . . . . 56
5.2.2. Simple-value Negotiations. . . . . . . . . . 56
5.3. Login Phase. . . . . . . . . . . . . . . . . . . . . . 57
5.3.1. Login Phase Start. . . . . . . . . . . . . . 60
5.3.2. iSCSI Security Negotiation . . . . . . . . . 62
5.3.3. Operational Parameter Negotiation During
the Login Phase. . . . . . . . . . . . . . . 63
5.3.4. Connection Reinstatement . . . . . . . . . . 64
5.3.5. Session Reinstatement, Closure, and Timeout. 64
5 5.3.5.1. Loss of Nexus
Notification. . . . . 65
5.3.6. Session Continuation and Failure . . . . . . 65
5.4. Operational Parameter Negotiation Outside the Login
Phase. . . . . . . . . . . . . . . . . . . . . . . . . 66
6. iSCSI Error Handling and Recovery . . . . . . . . . . . . . . 67
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 67
6.1.1. Background . . . . . . . . . . . . . . . . . 67
6.1.2. Goals. . . . . . . . . . . . . . . . . . . . 67
6.1.3. Protocol Features and State Expectations . . 68
6.1.4. Recovery Classes . . . . . . . . . . . . . . 69
6.1.4.1. Recovery Within-command . . . . . 69
6.1.4.2. Recovery Within-connection. . . . 70
6.1.4.3. Connection Recovery . . . . . . . 71
6.1.4.4. Session Recovery. . . . . . . . . 72
6.1.5. Error Recovery Hierarchy . . . . . . . . . . . 72
6.2. Retry and Reassign in Recovery . . . . . . . . . . . . 74
6.2.1. Usage of Retry . . . . . . . . . . . . . . . 74
6.2.2. Allegiance Reassignment. . . . . . . . . . . 75
6.3. Usage Of Reject PDU in Recovery. . . . . . . . . . . . 76
6.4. Connection Timeout Management. . . . . . . . . . . . . 76
6.4.1. Timeouts on Transport Exception Events . . . 77
6.4.2. Timeouts on Planned Decommissioning. . . . . 77
6.5. Implicit Termination of Tasks. . . . . . . . . . . . . 77
6.6. Format Errors. . . . . . . . . . . . . . . . . . . . . 78
6.7. Digest Errors. . . . . . . . . . . . . . . . . . . . . 78
6.8. Sequence Errors. . . . . . . . . . . . . . . . . . . . 80
6.9. SCSI Timeouts. . . . . . . . . . . . . . . . . . . . . 81
6.10. Negotiation Failures . . . . . . . . . . . . . . . . . 81
6.11. Protocol Errors. . . . . . . . . . . . . . . . . . . . 82
6.12. Connection Failures. . . . . . . . . . . . . . . . . . 82
6.13. Session Errors . . . . . . . . . . . . . . . . . . . . 83
7. State Transitions . . . . . . . . . . . . . . . . . . . . . . 84
7.1. Standard Connection State Diagrams . . . . . . . . . . 84
7.1.1. State Descriptions for Initiators and
Targets. . . . . . . . . . . . . . . . . . . 84
7.1.2. State Transition Descriptions for Initiators
and Targets. . . . . . . . . . . . . . . . . 85
7.1.3. Standard Connection State Diagram for an
Initiator. . . . . . . . . . . . . . . . . . 88
7.1.4. Standard Connection State Diagram for a
Target . . . . . . . . . . . . . . . . . . . 90
7.2. Connection Cleanup State Diagram for Initiators and
Targets. . . . . . . . . . . . . . . . . . . . . . . . 92
7.2.1. State Descriptions for Initiators and
Targets. . . . . . . . . . . . . . . . . . . 94
7.2.2. State Transition Descriptions for Initiators
and Targets. . . . . . . . . . . . . . . . . 94
7.3. Session State Diagrams . . . . . . . . . . . . . . . . 95
7.3.1. Session State Diagram for an Initiator . . . 95
7.3.2. Session State Diagram for a Target . . . . . 96
7.3.3. State Descriptions for Initiators and
Targets. . . . . . . . . . . . . . . . . . . 97
7.3.4. State Transition Descriptions for Initiators
and Targets. . . . . . . . . . . . . . . . . 98
8. Security Considerations . . . . . . . . . . . . . . . . . . . 99
8.1. iSCSI Security Mechanisms. . . . . . . . . . . . . . . 100
8.2. In-band Initiator-Target Authentication. . . . . . . . 100
8.2.1. CHAP Considerations. . . . . . . . . . . . . 101
8.2.2. SRP Considerations . . . . . . . . . . . . . 103
8.3. IPsec. . . . . . . . . . . . . . . . . . . . . . . . . 104
8.3.1. Data Integrity and Authentication. . . . . . 104
8.3.2. Confidentiality. . . . . . . . . . . . . . . 105
8.3.3. Policy, Security Associations, and
Cryptographic Key Management . . . . . . . . 105
9. Notes to Implementers . . . . . . . . . . . . . . . . . . . . 106
10.4.8. ExpDataSN. . . . . . . . . . . . . . . . . . 127
10.4.9. StatSN - Status Sequence Number. . . . . . . 127
10.4.10. ExpCmdSN - Next Expected CmdSN from this
Initiator. . . . . . . . . . . . . . . . . . 128
10.4.11. MaxCmdSN - Maximum CmdSN from this Initiator 128
10.5. Task Management Function Request . . . . . . . . . . . 129
10.5.1. Function . . . . . . . . . . . . . . . . . . 129
10.5.2. TotalAHSLength and DataSegmentLength . . . . 132
10.5.3. LUN. . . . . . . . . . . . . . . . . . . . . 132
10.5.4. Referenced Task Tag. . . . . . . . . . . . . 132
10.5.5. RefCmdSN . . . . . . . . . . . . . . . . . . 132
10.5.6. ExpDataSN. . . . . . . . . . . . . . . . . . 133
10.6. Task Management Function Response. . . . . . . . . . . 134
10.6.1. Response . . . . . . . . . . . . . . . . . . 134
10.6.2. Task Management Actions on Task Sets . . . . 136
10.6.3. TotalAHSLength and DataSegmentLength . . . . 137
10.7. SCSI Data-Out & SCSI Data-In . . . . . . . . . . . . . 137
10.7.1. F (Final) Bit. . . . . . . . . . . . . . . . 139
10.7.2. A (Acknowledge) Bit. . . . . . . . . . . . . 139
10.7.3. Flags (byte 1) . . . . . . . . . . . . . . . 140
10.7.4. Target Transfer Tag and LUN. . . . . . . . . 140
10.7.5. DataSN . . . . . . . . . . . . . . . . . . . 141
10.7.6. Buffer Offset. . . . . . . . . . . . . . . . 141
10.7.7. DataSegmentLength. . . . . . . . . . . . . . 141
10.8. Ready To Transfer (R2T). . . . . . . . . . . . . . . . 142
10.8.1. TotalAHSLength and DataSegmentLength . . . . 143
10.8.2. R2TSN. . . . . . . . . . . . . . . . . . . . 143
10.8.3. StatSN . . . . . . . . . . . . . . . . . . . 144
10.8.4. Desired Data Transfer Length and Buffer
Offset . . . . . . . . . . . . . . . . . . . 144
10.8.5. Target Transfer Tag. . . . . . . . . . . . . 144
10.9. Asynchronous Message . . . . . . . . . . . . . . . . . 145
10.9.1. AsyncEvent . . . . . . . . . . . . . . . . . 146
10.9.2. AsyncVCode . . . . . . . . . . . . . . . . . 147
10.9.3. LUN. . . . . . . . . . . . . . . . . . . . . 147
10.9.4. Sense Data and iSCSI Event Data. . . . . . . 148
10.9.4.1. SenseLength . . . . . . . . . . . 148
10.10. Text Request . . . . . . . . . . . . . . . . . . . . . 149
10.10.1. F (Final) Bit. . . . . . . . . . . . . . . . 150
10.10.2. C (Continue) Bit . . . . . . . . . . . . . . 150
10.10.3. Initiator Task Tag . . . . . . . . . . . . . 150
10.10.4. Target Transfer Tag. . . . . . . . . . . . . 150
10.10.5. Text . . . . . . . . . . . . . . . . . . . . 151
10.11. Text Response. . . . . . . . . . . . . . . . . . . . . 152
10.11.1. F (Final) Bit. . . . . . . . . . . . . . . . 152
10.11.2. C (Continue) Bit . . . . . . . . . . . . . . 153
10.11.3. Initiator Task Tag . . . . . . . . . . . . . 153
10.11.4. Target Transfer Tag. . . . . . . . . . . . . 153
10.11.5. StatSN . . . . . . . . . . . . . . . . . . . 154
10.11.6. Text Response Data . . . . . . . . . . . . . 154
10.12. Login Request. . . . . . . . . . . . . . . . . . . . . 154
10.12.1. T (Transit) Bit. . . . . . . . . . . . . . . 155
10.12.2. C (Continue) Bit . . . . . . . . . . . . . . 155
10.12.3. CSG and NSG. . . . . . . . . . . . . . . . . 156
10.12.4. Version. . . . . . . . . . . . . . . . . . . 156
10.12.4.1. Version-max. . . . . . . . . . . 156
10.12.4.2. Version-min. . . . . . . . . . . 156
10.12.5. ISID . . . . . . . . . . . . . . . . . . . . 157
10.12.6. TSIH . . . . . . . . . . . . . . . . . . . . 158
10.12.7. Connection ID - CID. . . . . . . . . . . . . 158
10.12.8. CmdSN. . . . . . . . . . . . . . . . . . . . 159
10.12.9. ExpStatSN. . . . . . . . . . . . . . . . . . 159
10.12.10. Login Parameters . . . . . . . . . . . . . . 159
10.13. Login Response . . . . . . . . . . . . . . . . . . . . 160
10.13.1. Version-max. . . . . . . . . . . . . . . . . 160
10.13.2. Version-active . . . . . . . . . . . . . . . 161
10.13.3. TSIH . . . . . . . . . . . . . . . . . . . . 161
10.13.4. StatSN . . . . . . . . . . . . . . . . . . . 161
10.13.5. Status-Class and Status-Detail . . . . . . . 161
10.13.6. T (Transit) Bit. . . . . . . . . . . . . . . 164
10.13.7. C (Continue) Bit . . . . . . . . . . . . . . 164
10.13.8. Login Parameters . . . . . . . . . . . . . . 164
10.14. Logout Request . . . . . . . . . . . . . . . . . . . . 165
10.14.1. Reason Code. . . . . . . . . . . . . . . . . 167
10.14.2. TotalAHSLength and DataSegmentLength . . . . 168
10.14.3. CID. . . . . . . . . . . . . . . . . . . . . 168
10.14.4. ExpStatSN. . . . . . . . . . . . . . . . . . 168
10.14.5. Implicit termination of tasks. . . . . . . . 168
10.15. Logout Response. . . . . . . . . . . . . . . . . . . . 169
10.15.1. Response . . . . . . . . . . . . . . . . . . 170
10.15.2. TotalAHSLength and DataSegmentLength . . . . 170
10.15.3. Time2Wait. . . . . . . . . . . . . . . . . . 170
10.15.4. Time2Retain. . . . . . . . . . . . . . . . . 170
10.16. SNACK Request. . . . . . . . . . . . . . . . . . . . . 171
10.16.1. Type . . . . . . . . . . . . . . . . . . . . 172
10.16.2. Data Acknowledgement . . . . . . . . . . . . 173
10.16.3. Resegmentation . . . . . . . . . . . . . . . 173
10.16.4. Initiator Task Tag . . . . . . . . . . . . . 174
10.16.5. Target Transfer Tag or SNACK Tag . . . . . . 174
10.16.6. BegRun . . . . . . . . . . . . . . . . . . . 174
10.16.7. RunLength. . . . . . . . . . . . . . . . . . 174
10.17. Reject . . . . . . . . . . . . . . . . . . . . . . . . 175
10.17.1. Reason . . . . . . . . . . . . . . . . . . . 176
10.17.2. DataSN/R2TSN . . . . . . . . . . . . . . . . 177
10.17.3. StatSN, ExpCmdSN and MaxCmdSN. . . . . . . . 177
10.17.4. Complete Header of Bad PDU . . . . . . . . . 177
10.18. NOP-Out. . . . . . . . . . . . . . . . . . . . . . . . 178
10.18.1. Initiator Task Tag . . . . . . . . . . . . . 179
10.18.2. Target Transfer Tag. . . . . . . . . . . . . 179
10.18.3. Ping Data. . . . . . . . . . . . . . . . . . 179
10.19. NOP-In . . . . . . . . . . . . . . . . . . . . . . . . 180
10.19.1. Target Transfer Tag. . . . . . . . . . . . . 181
10.19.2. StatSN . . . . . . . . . . . . . . . . . . . 181
10.19.3. LUN. . . . . . . . . . . . . . . . . . . . . 181
11. iSCSI Security Text Keys and Authentication Methods . . . . . 181
11.1. AuthMethod . . . . . . . . . . . . . . . . . . . . . . 182
11.1.1. Kerberos . . . . . . . . . . . . . . . . . . 184
11.1.2. Simple Public-Key Mechanism (SPKM) . . . . . 184
11.1.3. Secure Remote Password (SRP) . . . . . . . . 185
11.1.4. Challenge Handshake Authentication Protocol
(CHAP) . . . . . . . . . . . . . . . . . . . 186
12. Login/Text Operational Text Keys. . . . . . . . . . . . . . . 187
12.1. HeaderDigest and DataDigest. . . . . . . . . . . . . . 188
12.2. MaxConnections . . . . . . . . . . . . . . . . . . . . 190
12.3. SendTargets. . . . . . . . . . . . . . . . . . . . . . 191
12.4. TargetName . . . . . . . . . . . . . . . . . . . . . . 191
12.5. InitiatorName. . . . . . . . . . . . . . . . . . . . . 192
12.6. TargetAlias. . . . . . . . . . . . . . . . . . . . . . 192
12.7. InitiatorAlias . . . . . . . . . . . . . . . . . . . . 193
12.8. TargetAddress. . . . . . . . . . . . . . . . . . . . . 193
12.9. TargetPortalGroupTag . . . . . . . . . . . . . . . . . 194
12.10. InitialR2T . . . . . . . . . . . . . . . . . . . . . . 194
12.11. ImmediateData. . . . . . . . . . . . . . . . . . . . . 195
12.12. MaxRecvDataSegmentLength . . . . . . . . . . . . . . . 196
12.13. MaxBurstLength . . . . . . . . . . . . . . . . . . . . 196
12.14. FirstBurstLength . . . . . . . . . . . . . . . . . . . 197
12.15. DefaultTime2Wait . . . . . . . . . . . . . . . . . . . 197
12.16. DefaultTime2Retain . . . . . . . . . . . . . . . . . . 198
12.17. MaxOutstandingR2T. . . . . . . . . . . . . . . . . . . 198
12.18. DataPDUInOrder . . . . . . . . . . . . . . . . . . . . 198
12.19. DataSequenceInOrder. . . . . . . . . . . . . . . . . . 199
12.20. ErrorRecoveryLevel . . . . . . . . . . . . . . . . . . 199
12.21. SessionType. . . . . . . . . . . . . . . . . . . . . . 200
12.22. The Private or Public Extension Key Format . . . . . . 200
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 201
13.1. Naming Requirements. . . . . . . . . . . . . . . . . . 203
13.2. Mechanism Specification Requirements . . . . . . . . . 203
13.3. Publication Requirements . . . . . . . . . . . . . . . 203
13.4. Security Requirements. . . . . . . . . . . . . . . . . 203
13.5. Registration Procedure . . . . . . . . . . . . . . . . 204
13.5.1. Present the iSCSI extension item to the
Community. . . . . . . . . . . . . . . . . . 204
13.5.2. iSCSI extension item review and IESG
approval . . . . . . . . . . . . . . . . . . 204
13.5.3. IANA Registration. . . . . . . . . . . . . . 204
13.5.4. Standard iSCSI extension item-label format . 204
13.6. IANA Procedures for Registering iSCSI extension items. 205
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
Appendix A. Sync and Steering with Fixed Interval Markers . . . . 209
A.1. Markers At Fixed Intervals . . . . . . . . . . . . . . 209
A.2. Initial Marker-less Interval . . . . . . . . . . . . . 210
A.3. Negotiation. . . . . . . . . . . . . . . . . . . . . . 210
A.3.1. OFMarker, IFMarker . . . . . . . . . . . . . 210
A.3.2. OFMarkInt, IFMarkInt . . . . . . . . . . . . 211
Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 212
B.1. Read Operation Example . . . . . . . . . . . . . . . . 212
B.2. Write Operation Example. . . . . . . . . . . . . . . . 213
B.3. R2TSN/DataSN Use Examples. . . . . . . . . . . . . . . 214
B.4. CRC Examples . . . . . . . . . . . . . . . . . . . . . 217
Appendix C. Login Phase Examples . . . . . . . . . . . . . . . . 219
Appendix D. SendTargets Operation. . . . . . . . . . . . . . . . 229
Appendix E. Algorithmic Presentation of Error Recovery Classes . 233
E.1. General Data Structure and Procedure Description . . . 233
E.2. Within-command Error Recovery Algorithms . . . . . . . 234
E.2.1. Procedure Descriptions . . . . . . . . . . . 234
E.2.2. Initiator Algorithms . . . . . . . . . . . . 235
E.2.3. Target Algorithms. . . . . . . . . . . . . . 237
E.3. Within-connection Recovery Algorithms. . . . . . . . . 240
E.3.1. Procedure Descriptions . . . . . . . . . . . 240
E.3.2. Initiator Algorithms . . . . . . . . . . . . 241
E.3.3. Target Algorithms. . . . . . . . . . . . . . 243
E.4. Connection Recovery Algorithms . . . . . . . . . . . . 243
E.4.1. Procedure Descriptions . . . . . . . . . . . 243
E.4.2. Initiator Algorithms . . . . . . . . . . . . 244
E.4.3. Target Algorithms. . . . . . . . . . . . . . 246
Appendix F. Clearing Effects of Various Events on Targets. . . . 249
F.1. Clearing Effects on iSCSI Objects. . . . . . . . . . . 249
F.2. Clearing Effects on SCSI Objects . . . . . . . . . . . 253
Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . 254
Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 256
Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 257
1. Introduction
The Small Computer Systems Interface (SCSI) is a popular family of
protocols for communicating with I/O devices, especially storage
devices. SCSI is a client-server architecture. Clients of a SCSI
interface are called "initiators". Initiators issue SCSI "commands"
to request services from components, logical units of a server known
as a "target". A "SCSI transport" maps the client-server SCSI
protocol to a specific interconnect. An Initiator is one endpoint of
a SCSI transport and a target is the other endpoint.
The SCSI protocol has been mapped over various transports, including
Parallel SCSI, IPI, IEEE-1394 (firewire) and Fibre Channel. These
transports are I/O specific and have limited distance capabilities.
The iSCSI protocol defined in this document describes a means of
transporting SCSI packets over TCP/IP (see [RFC791], [RFC793],
[RFC1035], [RFC1122]), providing for an interoperable solution which
can take advantage of existing Internet infrastructure, Internet
management facilities, and address distance limitations.
2. Definitions and Acronyms
2.1. Definitions
- Alias: An alias string can also be associated with an iSCSI Node.
The alias allows an organization to associate a user-friendly
string with the iSCSI Name. However, the alias string is not a
substitute for the iSCSI Name.
- CID (Connection ID): Connections within a session are identified by
a connection ID. It is a unique ID for this connection within the
session for the initiator. It is generated by the initiator and
presented to the target during login requests and during logouts
that close connections.
- Connection: A connection is a TCP connection. Communication
between the initiator and target occurs over one or more TCP
connections. The TCP connections carry control messages, SCSI
commands, parameters, and data within iSCSI Protocol Data Units
(iSCSI PDUs).
- iSCSI Device: A SCSI Device using an iSCSI service delivery
subsystem. Service Delivery Subsystem is defined by [SAM2] as a
transport mechanism for SCSI commands and responses.
- iSCSI Initiator Name: The iSCSI Initiator Name specifies the
worldwide unique name of the initiator.
- iSCSI Initiator Node: The "initiator". The word "initiator" has
been appropriately qualified as either a port or a device in the
rest of the document when the context is ambiguous. All
unqualified usages of "initiator" refer to an initiator port (or
device) depending on the context.
- iSCSI Layer: This layer builds/receives iSCSI PDUs and
relays/receives them to/from one or more TCP connections that form
an initiator-target "session".
- iSCSI Name: The name of an iSCSI initiator or iSCSI target.
- iSCSI Node: The iSCSI Node represents a single iSCSI initiator or
iSCSI target. There are one or more iSCSI Nodes within a Network
Entity. The iSCSI Node is accessible via one or more Network
Portals. An iSCSI Node is identified by its iSCSI Name. The
separation of the iSCSI Name from the addresses used by and for the
iSCSI Node allows multiple iSCSI Nodes to use the same address, and
the same iSCSI Node to use multiple addresses.
- iSCSI Target Name: The iSCSI Target Name specifies the worldwide
unique name of the target.
- iSCSI Target Node: The "target".
- iSCSI Task: An iSCSI task is an iSCSI request for which a response
is expected.
- iSCSI Transfer Direction: The iSCSI transfer direction is defined
with regard to the initiator. Outbound or outgoing transfers are
transfers from the initiator to the target, while inbound or
incoming transfers are from the target to the initiator.
- ISID: The initiator part of the Session Identifier. It is
explicitly specified by the initiator during Login.
- I_T nexus: According to [SAM2], the I_T nexus is a relationship
between a SCSI Initiator Port and a SCSI Target Port. For iSCSI,
this relationship is a session, defined as a relationship between
an iSCSI Initiator's end of the session (SCSI Initiator Port) and
the iSCSI Target's Portal Group. The I_T nexus can be identified
by the conjunction of the SCSI port names; that is, the I_T nexus
identifier is the tuple (iSCSI Initiator Name + ',i,'+ ISID, iSCSI
Target Name + ',t,'+ Portal Group Tag).
- Network Entity: The Network Entity represents a device or gateway
that is accessible from the IP network. A Network Entity must have
one or more Network Portals, each of which can be used to gain
access to the IP network by some iSCSI Nodes contained in that
Network Entity.
- Network Portal: The Network Portal is a component of a Network
Entity that has a TCP/IP network address and that may be used by an
iSCSI Node within that Network Entity for the connection(s) within
one of its iSCSI sessions. A Network Portal in an initiator is
identified by its IP address. A Network Portal in a target is
identified by its IP address and its listening TCP port.
- Originator: In a negotiation or exchange, the party that initiates
the negotiation or exchange.
- PDU (Protocol Data Unit): The initiator and target divide their
communications into messages. The term "iSCSI protocol data unit"
(iSCSI PDU) is used for these messages.
- Portal Groups: iSCSI supports multiple connections within the same
session; some implementations will have the ability to combine
connections in a session across multiple Network Portals. A Portal
Group defines a set of Network Portals within an iSCSI Network
Entity that collectively supports the capability of coordinating a
session with connections spanning these portals. Not all Network
Portals within a Portal Group need participate in every session
connected through that Portal Group. One or more Portal Groups may
provide access to an iSCSI Node. Each Network Portal, as utilized
by a given iSCSI Node, belongs to exactly one portal group within
that node.
- Portal Group Tag: This 16-bit quantity identifies a Portal Group
within an iSCSI Node. All Network Portals with the same portal
group tag in the context of a given iSCSI Node are in the same
Portal Group.
- Recovery R2T: An R2T generated by a target upon detecting the loss
of one or more Data-Out PDUs through one of the following means: a
digest error, a sequence error, or a sequence reception timeout. A
recovery R2T carries the next unused R2TSN, but requests all or
part of the data burst that an earlier R2T (with a lower R2TSN) had
already requested.
- Responder: In a negotiation or exchange, the party that responds to
the originator of the negotiation or exchange.
- SCSI Device: This is the SAM2 term for an entity that contains one
or more SCSI ports that are connected to a service delivery
subsystem and supports a SCSI application protocol. For example, a
SCSI Initiator Device contains one or more SCSI Initiator Ports and
zero or more application clients. A Target Device contains one or
more SCSI Target Ports and one or more device servers and
associated logical units. For iSCSI, the SCSI Device is the
component within an iSCSI Node that provides the SCSI
functionality. As such, there can be at most, one SCSI Device
within a given iSCSI Node. Access to the SCSI Device can only be
achieved in an iSCSI normal operational session. The SCSI Device
Name is defined to be the iSCSI Name of the node.
- SCSI Layer: This builds/receives SCSI CDBs (Command Descriptor
Blocks) and relays/receives them with the remaining command execute
[SAM2] parameters to/from the iSCSI Layer.
- Session: The group of TCP connections that link an initiator with a
target form a session (loosely equivalent to a SCSI I-T nexus).
TCP connections can be added and removed from a session. Across
all connections within a session, an initiator sees one and the
same target.
- SCSI Initiator Port: This maps to the endpoint of an iSCSI normal
operational session. An iSCSI normal operational session is
negotiated through the login process between an iSCSI initiator
node and an iSCSI target node. At successful completion of this
process, a SCSI Initiator Port is created within the SCSI Initiator
Device. The SCSI Initiator Port Name and SCSI Initiator Port
Identifier are both defined to be the iSCSI Initiator Name together
with (a) a label that identifies it as an initiator port
name/identifier and (b) the ISID portion of the session identifier.
- SCSI Port: This is the SAM2 term for an entity in a SCSI Device
that provides the SCSI functionality to interface with a service
delivery subsystem. For iSCSI, the definition of the SCSI
Initiator Port and the SCSI Target Port are different.
- SCSI Port Name: A name made up as UTF-8 [RFC2279] characters and
includes the iSCSI Name + 'i' or 't' + ISID or Portal Group Tag.
- SCSI Target Port: This maps to an iSCSI Target Portal Group.
- SCSI Target Port Name and SCSI Target Port Identifier: These are
both defined to be the iSCSI Target Name together with (a) a label
that identifies it as a target port name/identifier and (b) the
portal group tag.
- SSID (Session ID): A session between an iSCSI initiator and an
iSCSI target is defined by a session ID that is a tuple composed of
an initiator part (ISID) and a target part (Target Portal Group
Tag). The ISID is explicitly specified by the initiator at session
establishment. The Target Portal Group Tag is implied by the
initiator through the selection of the TCP endpoint at connection
establishment. The TargetPortalGroupTag key must also be returned
by the target as a confirmation during connection establishment
when TargetName is given.
- Target Portal Group Tag: A numerical identifier (16-bit) for an
iSCSI Target Portal Group.
- TSIH (Target Session Identifying Handle): A target assigned tag for
a session with a specific named initiator. The target generates it
during session establishment. Its internal format and content are
not defined by this protocol, except for the value 0 that is
reserved and used by the initiator to indicate a new session. It
is given to the target during additional connection establishment
for the same session.
2.2. Acronyms
Acronym Definition
------------------------------------------------------------
3DES Triple Data Encryption Standard
ACA Auto Contingent Allegiance
AEN Asynchronous Event Notification
AES Advanced Encryption Standard
AH Additional Header (not the IPsec AH!)
AHS Additional Header Segment
API Application Programming Interface
ASC Additional Sense Code
ASCII American Standard Code for Information Interchange
ASCQ Additional Sense Code Qualifier
BHS Basic Header Segment
CBC Cipher Block Chaining
CD Compact Disk
CDB Command Descriptor Block
CHAP Challenge Handshake Authentication Protocol
CID Connection ID
CO Connection Only
CRC Cyclic Redundancy Check
CRL Certificate Revocation List
CSG Current Stage
CSM Connection State Machine
DES Data Encryption Standard
DNS Domain Name Server
DOI Domain of Interpretation
DVD Digital Versatile Disk
ESP Encapsulating Security Payload
EUI Extended Unique Identifier
FFP Full Feature Phase
FFPO Full Feature Phase Only
FIM Fixed Interval Marker
Gbps Gigabits per Second
HBA Host Bus Adapter
HMAC Hashed Message Authentication Code
I_T Initiator_Target
I_T_L Initiator_Target_LUN
IANA Internet Assigned Numbers Authority
ID Identifier
IDN Internationalized Domain Name
IEEE Institute of Electrical & Electronics Engineers
IETF Internet Engineering Task Force
IKE Internet Key Exchange
I/O Input - Output
IO Initialize Only
IP Internet Protocol
IPsec Internet Protocol Security
IPv4 Internet Protocol Version 4
IPv6 Internet Protocol Version 6
IQN iSCSI Qualified Name
ISID Initiator Session ID
ITN iSCSI Target Name
ITT Initiator Task Tag
KRB5 Kerberos V5
LFL Lower Functional Layer
LTDS Logical-Text-Data-Segment
LO Leading Only
LU Logical Unit
LUN Logical Unit Number
MAC Message Authentication Codes
NA Not Applicable
NIC Network Interface Card
NOP No Operation
NSG Next Stage
OS Operating System
PDU Protocol Data Unit
PKI Public Key Infrastructure
R2T Ready To Transfer
R2TSN Ready To Transfer Sequence Number
RDMA Remote Direct Memory Access
RFC Request For Comments
SAM SCSI Architecture Model
SAM2 SCSI Architecture Model - 2
SAN Storage Area Network
SCSI Small Computer Systems Interface
SN Sequence Number
SNACK Selective Negative Acknowledgment - also
Sequence Number Acknowledgement for data
SPKM Simple Public-Key Mechanism
SRP Secure Remote Password
SSID Session ID
SW Session Wide
TCB Task Control Block
TCP Transmission Control Protocol
TPGT Target Portal Group Tag
TSIH Target Session Identifying Handle
TTT Target Transfer Tag
UFL Upper Functional Layer
ULP Upper Level Protocol
URN Uniform Resource Names [RFC2396]
UTF Universal Transformation Format
WG Working Group
2.3. Conventions
In examples, "I->" and "T->" show iSCSI PDUs sent by the initiator
and target respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 [RFC2119].
iSCSI messages - PDUs - are represented by diagrams as in the
following example:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| Basic Header Segment (BHS) |
+---------------+---------------+---------------+---------------+
----------
+| |
+---------------+---------------+---------------+---------------+
The diagrams include byte and bit numbering.
The following representation and ordering rules are observed in this
document:
- Word Rule
- Half-word Rule
- Byte Rule
2.3.1. Word Rule
A word holds four consecutive bytes. Whenever a word has numeric
content, it is considered an unsigned number in base 2 positional
representation with the lowest numbered byte (e.g., byte 0) bit 0
representing 2**31 and bit 1 representing 2**30 through lowest
numbered byte + 3 (e.g., byte 3) bit 7 representing 2**0.
Decimal and hexadecimal representation of word values map this
representation to decimal or hexadecimal positional notation.
2.3.2. Half-Word Rule
A half-word holds two consecutive bytes. Whenever a half-word has
numeric content it is considered an unsigned number in base 2
positional representation with the lowest numbered byte (e.g., byte
0), bit 0 representing 2**15 and bit 1 representing 2**14 through
lowest numbered byte + 1 (e.g., byte 1), bit 7 representing 2**0.
Decimal and hexadecimal representation of half-word values map this
representation to decimal or hexadecimal positional notation.
2.3.3. Byte Rule
For every PDU, bytes are sent and received in increasing numbered
order (network order).
Whenever a byte has numerical content, it is considered an unsigned
number in base 2 positional representation with bit 0 representing
2**7 and bit 1 representing 2**6 through bit 7 representing 2**0.
3. Overview
3.1. SCSI Concepts
The SCSI Architecture Model-2 [SAM2] describes in detail the
architecture of the SCSI family of I/O protocols. This section
provides a brief background of the SCSI architecture and is intended
to familiarize readers with its terminology.
At the highest level, SCSI is a family of interfaces for requesting
services from I/O devices, including hard drives, tape drives, CD and
DVD drives, printers, and scanners. In SCSI terminology, an
individual I/O device is called a "logical unit" (LU).
SCSI is a client-server architecture. Clients of a SCSI interface
are called "initiators". Initiators issue SCSI "commands" to request
services from components, logical units, of a server known as a
"target". The "device server" on the logical unit accepts SCSI
commands and processes them.
A "SCSI transport" maps the client-server SCSI protocol to a specific
interconnect. Initiators are one endpoint of a SCSI transport. The
"target" is the other endpoint. A target can contain multiple
Logical Units (LUs). Each Logical Unit has an address within a
target called a Logical Unit Number (LUN).
A SCSI task is a SCSI command or possibly a linked set of SCSI
commands. Some LUs support multiple pending (queued) tasks, but the
queue of tasks is managed by the logical unit. The target uses an
initiator provided "task tag" to distinguish between tasks. Only one
command in a task can be outstanding at any given time.
Each SCSI command results in an optional data phase and a required
response phase. In the data phase, information can travel from the
initiator to target (e.g., WRITE), target to initiator (e.g., READ),
or in both directions. In the response phase, the target returns the
final status of the operation, including any errors.
Command Descriptor Blocks (CDB) are the data structures used to
contain the command parameters that an initiator sends to a target.
The CDB content and structure is defined by [SAM2] and device-type
specific SCSI standards.
3.2. iSCSI Concepts and Functional Overview
The iSCSI protocol is a mapping of the SCSI remote procedure
invocation model (see [SAM2]) over the TCP protocol. SCSI commands
are carried by iSCSI requests and SCSI responses and status are
carried by iSCSI responses. iSCSI also uses the request response
mechanism for iSCSI protocol mechanisms.
For the remainder of this document, the terms "initiator" and
"target" refer to "iSCSI initiator node" and "iSCSI target node",
respectively (see Section 3.4.1 iSCSI Architecture Model) unless
otherwise qualified.
In keeping with similar protocols, the initiator and target divide
their communications into messages. This document uses the term
"iSCSI protocol data unit" (iSCSI PDU) for these messages.
For performance reasons, iSCSI allows a "phase-collapse". A command
and its associated data may be shipped together from initiator to
target, and data and responses may be shipped together from targets.
The iSCSI transfer direction is defined with respect to the
initiator. Outbound or outgoing transfers are transfers from an
initiator to a target, while inbound or incoming transfers are from a
target to an initiator.
An iSCSI task is an iSCSI request for which a response is expected.
In this document "iSCSI request", "iSCSI command", request, or
(unqualified) command have the same meaning. Also, unless otherwise
specified, status, response, or numbered response have the same
meaning.
3.2.1. Layers and Sessions
The following conceptual layering model is used to specify initiator
and target actions and the way in which they relate to transmitted
and received Protocol Data Units:
a) the SCSI layer builds/receives SCSI CDBs (Command Descriptor
Blocks) and passes/receives them with the remaining command
execute parameters ([SAM2]) to/from
b) the iSCSI layer that builds/receives iSCSI PDUs and
relays/receives them to/from one or more TCP connections; the
group of connections form an initiator-target "session".
Communication between the initiator and target occurs over one or
more TCP connections. The TCP connections carry control messages,
SCSI commands, parameters, and data within iSCSI Protocol Data Units
(iSCSI PDUs). The group of TCP connections that link an initiator
with a target form a session (loosely equivalent to a SCSI I_T nexus,
see Section 3.4.2 SCSI Architecture Model). A session is defined by
a session ID that is composed of an initiator part and a target part.
TCP connections can be added and removed from a session. Each
connection within a session is identified by a connection ID (CID).
Across all connections within a session, an initiator sees one
"target image". All target identifying elements, such as LUN, are
the same. A target also sees one "initiator image" across all
connections within a session. Initiator identifying elements, such
as the Initiator Task Tag, are global across the session regardless
of the connection on which they are sent or received.
iSCSI targets and initiators MUST support at least one TCP connection
and MAY support several connections in a session. For error recovery
purposes, targets and initiators that support a single active
connection in a session SHOULD support two connections during
recovery.
3.2.2. Ordering and iSCSI Numbering
iSCSI uses Command and Status numbering schemes and a Data sequencing
scheme.
Command numbering is session-wide and is used for ordered command
delivery over multiple connections. It can also be used as a
mechanism for command flow control over a session.
Status numbering is per connection and is used to enable missing
status detection and recovery in the presence of transient or
permanent communication errors.
Data sequencing is per command or part of a command (R2T triggered
sequence) and is used to detect missing data and/or R2T PDUs due to
header digest errors.
Typically, fields in the iSCSI PDUs communicate the Sequence Numbers
between the initiator and target. During periods when traffic on a
connection is unidirectional, iSCSI NOP-Out/In PDUs may be utilized
to synchronize the command and status ordering counters of the target
and initiator.
The iSCSI session abstraction is equivalent to the SCSI I_T nexus,
and the iSCSI session provides an ordered command delivery from the
SCSI initiator to the SCSI target. For detailed design
considerations that led to the iSCSI session model as it is defined
here and how it relates the SCSI command ordering features defined in
SCSI specifications to the iSCSI concepts see [CORD].
3.2.2.1. Command Numbering and Acknowledging
iSCSI performs ordered command delivery within a session. All
commands (initiator-to-target PDUs) in transit from the initiator to
the target are numbered.
iSCSI considers a task to be instantiated on the target in response
to every request issued by the initiator. A set of task management
operations including abort and reassign (see Section 10.5 Task
Management Function Request) may be performed on any iSCSI task.
Some iSCSI tasks are SCSI tasks, and many SCSI activities are related
to a SCSI task ([SAM2]). In all cases, the task is identified by the
Initiator Task Tag for the life of the task.
The command number is carried by the iSCSI PDU as CmdSN
(Command Sequence Number). The numbering is session-wide. Outgoing
iSCSI PDUs carry this number. The iSCSI initiator allocates CmdSNs
with a 32-bit unsigned counter (modulo 2**32). Comparisons and
arithmetic on CmdSN use Serial Number Arithmetic as defined in
[RFC1982] where SERIAL_BITS = 32.
Commands meant for immediate delivery are marked with an immediate
delivery flag; they MUST also carry the current CmdSN. CmdSN does
not advance after a command marked for immediate delivery is sent.
Command numbering starts with the first login request on the first
connection of a session (the leading login on the leading connection)
and command numbers are incremented by 1 for every non-immediate
command issued afterwards.
If immediate delivery is used with task management commands, these
commands may reach the target before the tasks on which they are
supposed to act. However their CmdSN serves as a marker of their
position in the stream of commands. The initiator and target must
ensure that the task management commands act as specified by [SAM2].
For example, both commands and responses appear as if delivered in
order. Whenever CmdSN for an outgoing PDU is not specified by an
explicit rule, CmdSN will carry the current value of the local CmdSN
variable (see later in this section).
The means by which an implementation decides to mark a PDU for
immediate delivery or by which iSCSI decides by itself to mark a PDU
for immediate delivery are beyond the scope of this document.
The number of commands used for immediate delivery is not limited and
their delivery for execution is not acknowledged through the
numbering scheme. Immediate commands MAY be rejected by the iSCSI
target layer due to a lack of resources. An iSCSI target MUST be
able to handle at least one immediate task management command and one
immediate non-task-management iSCSI command per connection at any
time.
In this document, delivery for execution means delivery to the SCSI
execution engine or an iSCSI protocol specific execution engine
(e.g., for text requests with public or private extension keys
involving an execution component). With the exception of the
commands marked for immediate delivery, the iSCSI target layer MUST
deliver the commands for execution in the order specified by CmdSN.
Commands marked for immediate delivery may be delivered by the iSCSI
target layer for execution as soon as detected. iSCSI may avoid
delivering some commands to the SCSI target layer if required by a
prior SCSI or iSCSI action (e.g., CLEAR TASK SET Task Management
request received before all the commands on which it was supposed to
act).
On any connection, the iSCSI initiator MUST send the commands in
increasing order of CmdSN, except for commands that are retransmitted
due to digest error recovery and connection recovery.
For the numbering mechanism, the initiator and target maintain the
following three variables for each session:
- CmdSN - the current command Sequence Number, advanced by 1 on
each command shipped except for commands marked for immediate
delivery. CmdSN always contains the number to be assigned to
the next Command PDU.
- ExpCmdSN - the next expected command by the target. The target
acknowledges all commands up to, but not including, this
number. The initiator treats all commands with CmdSN less than
ExpCmdSN as acknowledged. The target iSCSI layer sets the
ExpCmdSN to the largest non-immediate CmdSN that it can deliver
for execution plus 1 (no holes in the CmdSN sequence).
- MaxCmdSN - the maximum number to be shipped. The queuing
capacity of the receiving iSCSI layer is MaxCmdSN - ExpCmdSN +
1.
The initiator's ExpCmdSN and MaxCmdSN are derived from
target-to-initiator PDU fields. Comparisons and arithmetic on
ExpCmdSN and MaxCmdSN MUST use Serial Number Arithmetic as defined in
[RFC1982] where SERIAL_BITS = 32.
The target MUST NOT transmit a MaxCmdSN that is less than
ExpCmdSN-1. For non-immediate commands, the CmdSN field can take any
value from ExpCmdSN to MaxCmdSN inclusive. The target MUST silently
ignore any non-immediate command outside of this range or non-
immediate duplicates within the range. The CmdSN carried by
immediate commands may lie outside the ExpCmdSN to MaxCmdSN range.
For example, if the initiator has previously sent a non-immediate
command carrying the CmdSN equal to MaxCmdSN, the target window is
closed. For group task management commands issued as immediate
commands, CmdSN indicates the scope of the group action (e.g., on
ABORT TASK SET indicates which commands are aborted).
MaxCmdSN and ExpCmdSN fields are processed by the initiator as
follows:
- If the PDU MaxCmdSN is less than the PDU ExpCmdSN-1 (in Serial
Arithmetic Sense), they are both ignored.
- If the PDU MaxCmdSN is greater than the local MaxCmdSN (in
Serial Arithmetic Sense), it updates the local MaxCmdSN;
otherwise, it is ignored.
- If the PDU ExpCmdSN is greater than the local ExpCmdSN (in
Serial Arithmetic Sense), it updates the local ExpCmdSN;
otherwise, it is ignored.
This sequence is required because updates may arrive out of order
(e.g., the updates are sent on different TCP connections).
iSCSI initiators and targets MUST support the command numbering
scheme.
A numbered iSCSI request will not change its allocated CmdSN,
regardless of the number of times and circumstances in which it is
reissued (see Section 6.2.1 Usage of Retry). At the target, CmdSN is
only relevant when the command has not created any state related to
its execution (execution state); afterwards, CmdSN becomes
irrelevant. Testing for the execution state (represented by
identifying the Initiator Task Tag) MUST precede any other action at
the target. If no execution state is found, it is followed by
ordering and delivery. If an execution state is found, it is
followed by delivery.
If an initiator issues a command retry for a command with CmdSN R on
a connection when the session CmdSN value is Q, it MUST NOT advance
the CmdSN past R + 2**31 -1 unless the connection is no longer
operational (i.e., it has returned to the FREE state, see Section
7.1.3 Standard Connection State Diagram for an Initiator), the
connection has been reinstated (see Section 5.3.4 Connection
Reinstatement), or a non-immediate command with CmdSN equal or
greater than Q was issued subsequent to the command retry on the same
connection and the reception of that command is acknowledged by the
target (see Section 9.4 Command Retry and Cleaning Old Command
Instances).
A target MUST NOT issue a command response or Data-In PDU with status
before acknowledging the command. However, the acknowledgement can
be included in the response or Data-In PDU.
3.2.2.2. Response/Status Numbering and Acknowledging
Responses in transit from the target to the initiator are numbered.
The StatSN (Status Sequence Number) is used for this purpose. StatSN
is a counter maintained per connection. ExpStatSN is used by the
initiator to acknowledge status. The status sequence number space is
32-bit unsigned-integers and the arithmetic operations are the
regular mod(2**32) arithmetic.
Status numbering starts with the Login response to the first Login
request of the connection. The Login response includes an initial
value for status numbering (any initial value is valid).
To enable command recovery, the target MAY maintain enough state
information for data and status recovery after a connection failure.
A target doing so can safely discard all of the state information
maintained for recovery of a command after the delivery of the status
for the command (numbered StatSN) is acknowledged through ExpStatSN.
A large absolute difference between StatSN and ExpStatSN may indicate
a failed connection. Initiators MUST undertake recovery actions if
the difference is greater than an implementation defined constant
that MUST NOT exceed 2**31-1.
Initiators and Targets MUST support the response-numbering scheme.
3.2.2.3. Data Sequencing
Data and R2T PDUs transferred as part of some command execution MUST
be sequenced. The DataSN field is used for data sequencing. For
input (read) data PDUs, DataSN starts with 0 for the first data PDU
of an input command and advances by 1 for each subsequent data PDU.
For output data PDUs, DataSN starts with 0 for the first data PDU of
a sequence (the initial unsolicited sequence or any data PDU sequence
issued to satisfy an R2T) and advances by 1 for each subsequent data
PDU. R2Ts are also sequenced per command. For example, the first
R2T has an R2TSN of 0 and advances by 1 for each subsequent R2T. For
bidirectional commands, the target uses the DataSN/R2TSN to sequence
Data-In and R2T PDUs in one continuous sequence (undifferentiated).
Unlike command and status, data PDUs and R2Ts are not acknowledged by
a field in regular outgoing PDUs. Data-In PDUs can be acknowledged
on demand by a special form of the SNACK PDU. Data and R2T PDUs are
implicitly acknowledged by status for the command. The DataSN/R2TSN
field enables the initiator to detect missing data or R2T PDUs.
For any read or bidirectional command, a target MUST issue less than
2**32 combined R2T and Data-In PDUs. Any output data sequence MUST
contain less than 2**32 Data-Out PDUs.
3.2.3. iSCSI Login
The purpose of the iSCSI login is to enable a TCP connection for
iSCSI use, authentication of the parties, negotiation of the
session's parameters and marking of the connection as belonging to an
iSCSI session.
A session is used to identify to a target all the connections with a
given initiator that belong to the same I_T nexus. (For more details
on how a session relates to an I_T nexus, see Section 3.4.2 SCSI
Architecture Model).
The targets listen on a well-known TCP port or other TCP port for
incoming connections. The initiator begins the login process by
connecting to one of these TCP ports.
As part of the login process, the initiator and target SHOULD
authenticate each other and MAY set a security association protocol
for the session. This can occur in many different ways and is
subject to negotiation.
To protect the TCP connection, an IPsec security association MAY be
established before the Login request. For information on using IPsec
security for iSCSI see Chapter 8 and [RFC3723].
The iSCSI Login Phase is carried through Login requests and
responses. Once suitable authentication has occurred and operational
parameters have been set, the session transitions to the Full Feature
Phase and the initiator may start to send SCSI commands. The
security policy for whether, and by what means, a target chooses to
authorize an initiator is beyond the scope of this document. For a
more detailed description of the Login Phase, see Chapter 5.
The login PDU includes the ISID part of the session ID (SSID). The
target portal group that services the login is implied by the
selection of the connection endpoint. For a new session, the TSIH is
zero. As part of the response, the target generates a TSIH.
During session establishment, the target identifies the SCSI
initiator port (the "I" in the "I_T nexus") through the value pair
(InitiatorName, ISID). We describe InitiatorName later in this
section. Any persistent state (e.g., persistent reservations) on the
target that is associated with a SCSI initiator port is identified
based on this value pair. Any state associated with the SCSI target
port (the "T" in the "I_T nexus") is identified externally by the
TargetName and portal group tag (see Section 3.4.1 iSCSI Architecture
Model). ISID is subject to reuse restrictions because it is used to
identify a persistent state (see Section 3.4.3 Consequences of the
Model).
Before the Full Feature Phase is established, only Login Request and
Login Response PDUs are allowed. Login requests and responses MUST
be used exclusively during Login. On any connection, the login phase
MUST immediately follow TCP connection establishment and a subsequent
Login Phase MUST NOT occur before tearing down a connection.
A target receiving any PDU except a Login request before the Login
phase is started MUST immediately terminate the connection on which
the PDU was received. Once the Login phase has started, if the
target receives any PDU except a Login request, it MUST send a Login
reject (with Status "invalid during login") and then disconnect. If
the initiator receives any PDU except a Login response, it MUST
immediately terminate the connection.
3.2.4. iSCSI Full Feature Phase
Once the initiator is authorized to do so, the iSCSI session is in
the iSCSI Full Feature Phase. A session is in Full Feature Phase
after successfully finishing the Login Phase on the first (leading)
connection of a session. A connection is in Full Feature Phase if
the session is in Full Feature Phase and the connection login has
completed successfully. An iSCSI connection is not in Full Feature
Phase
a) when it does not have an established transport connection,
OR
b) when it has a valid transport connection, but a successful
login was not performed or the connection is currently logged
out.
In a normal Full Feature Phase, the initiator may send SCSI commands
and data to the various LUs on the target by encapsulating them in
iSCSI PDUs that go over the established iSCSI session.
3.2.4.1. Command Connection Allegiance
For any iSCSI request issued over a TCP connection, the corresponding
response and/or other related PDU(s) MUST be sent over the same
connection. We call this "connection allegiance". If the original
connection fails before the command is completed, the connection
allegiance of the command may be explicitly reassigned to a different
transport connection as described in detail in Section 6.2 Retry and
Reassign in Recovery.
Thus, if an initiator issues a READ command, the target MUST send the
requested data, if any, followed by the status to the initiator over
the same TCP connection that was used to deliver the SCSI command.
If an initiator issues a WRITE command, the initiator MUST send the
data, if any, for that command over the same TCP connection that was
used to deliver the SCSI command. The target MUST return Ready To
Transfer (R2T), if any, and the status over the same TCP connection
that was used to deliver the SCSI command. Retransmission requests
(SNACK PDUs) and the data and status that they generate MUST also use
the same connection.
However, consecutive commands that are part of a SCSI linked
command-chain task (see [SAM2]) MAY use different connections.
Connection allegiance is strictly per-command and not per-task.
During the iSCSI Full Feature Phase, the initiator and target MAY
interleave unrelated SCSI commands, their SCSI Data, and responses
over the session.
3.2.4.2. Data Transfer Overview
Outgoing SCSI data (initiator to target user data or command
parameters) is sent as either solicited data or unsolicited data.
Solicited data are sent in response to R2T PDUs. Unsolicited data
can be sent as part of an iSCSI command PDU ("immediate data") or in
separate iSCSI data PDUs.
Immediate data are assumed to originate at offset 0 in the initiator
SCSI write-buffer (outgoing data buffer). All other Data PDUs have
the buffer offset set explicitly in the PDU header.
An initiator may send unsolicited data up to FirstBurstLength as
immediate (up to the negotiated maximum PDU length), in a separate
PDU sequence or both. All subsequent data MUST be solicited. The
maximum length of an individual data PDU or the immediate-part of the
first unsolicited burst MAY be negotiated at login.
The maximum amount of unsolicited data that can be sent with a
command is negotiated at login through the FirstBurstLength key. A
target MAY separately enable immediate data (through the
ImmediateData key) without enabling the more general (separate data
PDUs) form of unsolicited data (through the InitialR2T key).
Unsolicited data on write are meant to reduce the effect of latency
on throughput (no R2T is needed to start sending data). In addition,
immediate data is meant to reduce the protocol overhead (both
bandwidth and execution time).
An iSCSI initiator MAY choose not to send unsolicited data, only
immediate data or FirstBurstLength bytes of unsolicited data with a
command. If any non-immediate unsolicited data is sent, the total
unsolicited data MUST be either FirstBurstLength, or all of the data
if the total amount is less than the FirstBurstLength.
It is considered an error for an initiator to send unsolicited data
PDUs to a target that operates in R2T mode (only solicited data are
allowed). It is also an error for an initiator to send more
unsolicited data, whether immediate or as separate PDUs, than
FirstBurstLength.
An initiator MUST honor an R2T data request for a valid outstanding
command (i.e., carrying a valid Initiator Task Tag) and deliver all
the requested data provided the command is supposed to deliver
outgoing data and the R2T specifies data within the command bounds.
The initiator action is unspecified for receiving an R2T request that
specifies data, all or part, outside of the bounds of the command.
A target SHOULD NOT silently discard data and then request
retransmission through R2T. Initiators SHOULD NOT keep track of the
data transferred to or from the target (scoreboarding). SCSI targets
perform residual count calculation to check how much data was
actually transferred to or from the device by a command. This may
differ from the amount the initiator sent and/or received for reasons
such as retransmissions and errors. Read or bidirectional commands
implicitly solicit the transmission of the entire amount of data
covered by the command. SCSI data packets are matched to their
corresponding SCSI commands by using tags specified in the protocol.
In addition, iSCSI initiators and targets MUST enforce some ordering
rules. When unsolicited data is used, the order of the unsolicited
data on each connection MUST match the order in which the commands on
that connection are sent. Command and unsolicited data PDUs may be
interleaved on a single connection as long as the ordering
requirements of each are maintained (e.g., command N+1 MAY be sent
before the unsolicited Data-Out PDUs for command N, but the
unsolicited Data-Out PDUs for command N MUST precede the unsolicited
Data-Out PDUs of command N+1). A target that receives data out of
order MAY terminate the session.
3.2.4.3. Tags and Integrity Checks
Initiator tags for pending commands are unique initiator-wide for a
session. Target tags are not strictly specified by the protocol. It
is assumed that target tags are used by the target to tag (alone or
in combination with the LUN) the solicited data. Target tags are
generated by the target and "echoed" by the initiator. These
mechanisms are designed to accomplish efficient data delivery along
with a large degree of control over the data flow.
As the Initiator Task Tag is used to identify a task during its
execution, the iSCSI initiator and target MUST verify that all other
fields used in task-related PDUs have values that are consistent with
the values used at the task instantiation based on the Initiator Task
Tag (e.g., the LUN used in an R2T PDU MUST be the same as the one
used in the SCSI command PDU used to instantiate the task). Using
inconsistent field values is considered a protocol error.
3.2.4.4. Task Management
SCSI task management assumes that individual tasks and task groups
can be aborted solely based on the task tags (for individual tasks)
or the timing of the task management command (for task groups), and
that the task management action is executed synchronously - i.e., no
message involving an aborted task will be seen by the SCSI initiator
after receiving the task management response. In iSCSI initiators
and targets interact asynchronously over several connections. iSCSI
specifies the protocol mechanism and implementation requirements
needed to present a synchronous view while using an asynchronous
infrastructure.
3.2.5. iSCSI Connection Termination
An iSCSI connection may be terminated by use of a transport
connection shutdown or a transport reset. Transport reset is assumed
to be an exceptional event.
Graceful TCP connection shutdowns are done by sending TCP FINs. A
graceful transport connection shutdown SHOULD only be initiated by
either party when the connection is not in iSCSI Full Feature Phase.
A target MAY terminate a Full Feature Phase connection on internal
exception events, but it SHOULD announce the fact through an
Asynchronous Message PDU. Connection termination with outstanding
commands may require recovery actions.
If a connection is terminated while in Full Feature Phase, connection
cleanup (see section 7) is required prior to recovery. By doing
connection cleanup before starting recovery, the initiator and target
will avoid receiving stale PDUs after recovery.
3.2.6. iSCSI Names
Both targets and initiators require names for the purpose of
identification. In addition, names enable iSCSI storage resources to
be managed regardless of location (address). An iSCSI node name is
also the SCSI device name of an iSCSI device. The iSCSI name of a
SCSI device is the principal object used in authentication of targets
to initiators and initiators to targets. This name is also used to
identify and manage iSCSI storage resources.
iSCSI names must be unique within the operational domain of the end
user. However, because the operational domain of an IP network is
potentially worldwide, the iSCSI name formats are architected to be
worldwide unique. To assist naming authorities in the construction
of worldwide unique names, iSCSI provides two name formats for
different types of naming authorities.
iSCSI names are associated with iSCSI nodes, and not iSCSI network
adapter cards, to ensure that the replacement of network adapter
cards does not require reconfiguration of all SCSI and iSCSI resource
allocation information.
Some SCSI commands require that protocol-specific identifiers be
communicated within SCSI CDBs. See Section 3.4.2 SCSI Architecture
Model for the definition of the SCSI port name/identifier for iSCSI
ports.
An initiator may discover the iSCSI Target Names to which it has
access, along with their addresses, using the SendTargets text
request, or other techniques discussed in [RFC3721].
3.2.6.1. iSCSI Name Properties
Each iSCSI node, whether an initiator or target, MUST have an iSCSI
name.
Initiators and targets MUST support the receipt of iSCSI names of up
to the maximum length of 223 bytes.
The initiator MUST present both its iSCSI Initiator Name and the
iSCSI Target Name to which it wishes to connect in the first login
request of a new session or connection. The only exception is if a
discovery session (see Section 2.3 iSCSI Session Types) is to be
established. In this case, the iSCSI Initiator Name is still
required, but the iSCSI Target Name MAY be omitted.
iSCSI names have the following properties:
a) iSCSI names are globally unique. No two initiators or targets
can have the same name.
b) iSCSI names are permanent. An iSCSI initiator node or target
node has the same name for its lifetime.
c) iSCSI names do not imply a location or address. An iSCSI
initiator or target can move, or have multiple addresses. A
change of address does not imply a change of name.
d) iSCSI names do not rely on a central name broker; the naming
authority is distributed.
e) iSCSI names support integration with existing unique naming
schemes.
f) iSCSI names rely on existing naming authorities. iSCSI does
not create any new naming authority.
The encoding of an iSCSI name has the following properties:
a) iSCSI names have the same encoding method regardless of the
underlying protocols.
b) iSCSI names are relatively simple to compare. The algorithm
for comparing two iSCSI names for equivalence does not rely on
an external server.
c) iSCSI names are composed only of displayable characters. iSCSI
names allow the use of international character sets but are not
case sensitive. No whitespace characters are used in iSCSI
names.
d) iSCSI names may be transported using both binary and
ASCII-based protocols.
An iSCSI name really names a logical software entity, and is not tied
to a port or other hardware that can be changed. For instance, an
initiator name should name the iSCSI initiator node, not a particular
NIC or HBA. When multiple NICs are used, they should generally all
present the same iSCSI initiator name to the targets, because they
are simply paths to the same SCSI layer. In most operating systems,
the named entity is the operating system image.
Similarly, a target name should not be tied to hardware interfaces
that can be changed. A target name should identify the logical
target and must be the same for the target regardless of the physical
portion being addressed. This assists iSCSI initiators in
determining that the two targets it has discovered are really two
paths to the same target.
The iSCSI name is designed to fulfill the functional requirements for
Uniform Resource Names (URN) [RFC1737]. For example, it is required
that the name have a global scope, be independent of address or
location, and be persistent and globally unique. Names must be
extensible and scalable with the use of naming authorities. The name
encoding should be both human and machine readable. See [RFC1737]
for further requirements.
3.2.6.2. iSCSI Name Encoding
An iSCSI name MUST be a UTF-8 encoding of a string of Unicode
characters with the following properties:
- It is in Normalization Form C (see "Unicode Normalization
Forms" [UNICODE]).
- It only contains characters allowed by the output of the iSCSI
stringprep template (described in [RFC3722]).
- The following characters are used for formatting iSCSI names:
- dash ('-'=U+002d)
- dot ('.'=U+002e)
- colon (':'=U+003a)
- The UTF-8 encoding of the name is not larger than 223 bytes.
The stringprep process is described in [RFC3454]; iSCSI's use of the
stringprep process is described in [RFC3722]. Stringprep is a method
designed by the Internationalized Domain Name (IDN) working group to
translate human-typed strings into a format that can be compared as
opaque strings. Strings MUST NOT include punctuation, spacing,
diacritical marks, or other characters that could get in the way of
readability. The stringprep process also converts strings into
equivalent strings of lower-case characters.
The stringprep process does not need to be implemented if the names
are only generated using numeric and lower-case (any character set)
alphabetic characters.
Once iSCSI names encoded in UTF-8 are "normalized" they may be safely
compared byte-for-byte.
3.2.6.3. iSCSI Name Structure
An iSCSI name consists of two parts--a type designator followed by a
unique name string.
The iSCSI name does not define any new naming authorities. Instead,
it supports two existing ways of designating naming authorities: an
iSCSI-Qualified Name, using domain names to identify a naming
authority, and the EUI format, where the IEEE Registration Authority
assists in the formation of worldwide unique names (EUI-64 format).
The type designator strings currently defined are:
iqn. - iSCSI Qualified name
eui. - Remainder of the string is an IEEE EUI-64
identifier, in ASCII-encoded hexadecimal.
These two naming authority designators were considered sufficient at
the time of writing this document. The creation of additional naming
type designators for iSCSI may be considered by the IETF and detailed
in separate RFCs.
3.2.6.3.1. Type "iqn." (iSCSI Qualified Name)
This iSCSI name type can be used by any organization that owns a
domain name. This naming format is useful when an end user or
service provider wishes to assign iSCSI names for targets and/or
initiators.
To generate names of this type, the person or organization generating
the name must own a registered domain name. This domain name does
not have to be active, and does not have to resolve to an address; it
just needs to be reserved to prevent others from generating iSCSI
names using the same domain name.
Since a domain name can expire, be acquired by another entity, or may
be used to generate iSCSI names by both owners, the domain name must
be additionally qualified by a date during which the naming authority
owned the domain name. For this reason, a date code is provided as
part of the "iqn." format.
The iSCSI qualified name string consists of:
- The string "iqn.", used to distinguish these names from "eui."
formatted names.
- A date code, in yyyy-mm format. This date MUST be a date
during which the naming authority owned the domain name used in
this format, and SHOULD be the first month in which the domain
name was owned by this naming authority at 00:01 GMT of the
first day of the month. This date code uses the Gregorian
calendar. All four digits in the year must be present. Both
digits of the month must be present, with January == "01" and
December == "12". The dash must be included.
- A dot "."
- The reversed domain name of the naming authority (person or
organization) creating this iSCSI name.
- An optional, colon (:) prefixed, string within the character
set and length boundaries that the owner of the domain name
deems appropriate. This may contain product types, serial
numbers, host identifiers, or software keys (e.g., it may
include colons to separate organization boundaries). With the
exception of the colon prefix, the owner of the domain name can
assign everything after the reversed domain name as desired.
It is the responsibility of the entity that is the naming
authority to ensure that the iSCSI names it assigns are
worldwide unique. For example, "Example Storage Arrays, Inc.",
might own the domain name "example.com".
The following are examples of iSCSI qualified names that might be
generated by "EXAMPLE Storage Arrays, Inc."
Naming String defined by
Type Date Auth "example.com" naming authority
+--++-----+ +---------+ +--------------------------------+
| || | | | | |
iqn.2001-04.com.example:storage:diskarrays-sn-a8675309
iqn.2001-04.com.example
iqn.2001-04.com.example:storage.tape1.sys1.xyz
iqn.2001-04.com.example:storage.disk2.sys1.xyz
3.2.6.3.2. Type "eui." (IEEE EUI-64 format)
The IEEE Registration Authority provides a service for assigning
globally unique identifiers [EUI]. The EUI-64 format is used to
build a global identifier in other network protocols. For example,
Fibre Channel defines a method of encoding it into a WorldWideName.
For more information on registering for EUI identifiers, see [OUI].
The format is "eui." followed by an EUI-64 identifier (16
ASCII-encoded hexadecimal digits).
Example iSCSI name:
Type EUI-64 identifier (ASCII-encoded hexadecimal)
+--++--------------+
| || |
eui.02004567A425678D
The IEEE EUI-64 iSCSI name format might be used when a manufacturer
is already registered with the IEEE Registration Authority and uses
EUI-64 formatted worldwide unique names for its products.
More examples of name construction are discussed in [RFC3721].
3.2.7. Persistent State
iSCSI does not require any persistent state maintenance across
sessions. However, in some cases, SCSI requires persistent
identification of the SCSI initiator port name (See Section 3.4.2
SCSI Architecture Model and Section 3.4.3 Consequences of the Model).
iSCSI sessions do not persist through power cycles and boot
operations.
All iSCSI session and connection parameters are re-initialized upon
session and connection creation.
Commands persist beyond connection termination if the session
persists and command recovery within the session is supported.
However, when a connection is dropped, command execution, as
perceived by iSCSI (i.e., involving iSCSI protocol exchanges for the
affected task), is suspended until a new allegiance is established by
the 'task reassign' task management function. (See Section 10.5 Task
Management Function Request.)
3.2.8. Message Synchronization and Steering
iSCSI presents a mapping of the SCSI protocol onto TCP. This
encapsulation is accomplished by sending iSCSI PDUs of varying
lengths. Unfortunately, TCP does not have a built-in mechanism for
signaling message boundaries at the TCP layer. iSCSI overcomes this
obstacle by placing the message length in the iSCSI message header.
This serves to delineate the end of the current message as well as
the beginning of the next message.
In situations where IP packets are delivered in order from the
network, iSCSI message framing is not an issue and messages are
processed one after the other. In the presence of IP packet
reordering (i.e., frames being dropped), legacy TCP implementations
store the "out of order" TCP segments in temporary buffers until the
missing TCP segments arrive, upon which the data must be copied to
the application buffers. In iSCSI, it is desirable to steer the SCSI
data within these out of order TCP segments into the pre-allocated
SCSI buffers rather than store them in temporary buffers. This
decreases the need for dedicated reassembly buffers as well as the
latency and bandwidth related to extra copies.
Relying solely on the "message length" information from the iSCSI
message header may make it impossible to find iSCSI message
boundaries in subsequent TCP segments due to the loss of a TCP
segment that contains the iSCSI message length. The missing TCP
segment(s) must be received before any of the following segments can
be steered to the correct SCSI buffers (due to the inability to
determine the iSCSI message boundaries). Since these segments cannot
be steered to the correct location, they must be saved in temporary
buffers that must then be copied to the SCSI buffers.
Different schemes can be used to recover synchronization. To make
these schemes work, iSCSI implementations have to make sure that the
appropriate protocol layers are provided with enough information to
implement a synchronization and/or data steering mechanism. One of
these schemes is detailed in Appendix A. - Sync and Steering with
Fixed Interval Markers -.
The Fixed Interval Markers (FIM) scheme works by inserting markers in
the payload stream at fixed intervals that contain the offset for the
start of the next iSCSI PDU.
Under normal circumstances (no PDU loss or data reception out of
order), iSCSI data steering can be accomplished by using the
identifying tag and the data offset fields in the iSCSI header in
addition to the TCP sequence number from the TCP header. The
identifying tag helps associate the PDU with a SCSI buffer address
while the data offset and TCP sequence number are used to determine
the offset within the buffer.
When the part of the TCP data stream containing an iSCSI PDU header
is delayed or lost, markers may be used to minimize the damage as
follows:
- Markers indicate where the next iSCSI PDU starts and enable
continued processing when iSCSI headers have to be dropped due to
data errors discovered at the iSCSI level (e.g., iSCSI header CRC
errors).
- Markers help minimize the amount of data that has to be kept by
the TCP/iSCSI layer while waiting for a late TCP packet arrival
or recovery, because later they might help find iSCSI PDU headers
and use the information contained in those to steer data to SCSI
buffers.
3.2.8.1. Sync/Steering and iSCSI PDU Length
When a large iSCSI message is sent, the TCP segment(s) that contain
the iSCSI header may be lost. The remaining TCP segment(s), up to
the next iSCSI message, must be buffered (in temporary buffers)
because the iSCSI header that indicates to which SCSI buffers the
data are to be steered was lost. To minimize the amount of
buffering, it is recommended that the iSCSI PDU length be restricted
to a small value (perhaps a few TCP segments in length). During
login, each end of the iSCSI session specifies the maximum iSCSI PDU
length it will accept.
3.3. iSCSI Session Types
iSCSI defines two types of sessions:
a) Normal operational session - an unrestricted session.
b) Discovery-session - a session only opened for target
discovery. The target MUST ONLY accept text requests with the
SendTargets key and a logout request with the reason "close
the session". All other requests MUST be rejected.
The session type is defined during login with the key=value parameter
in the login command.
3.4. SCSI to iSCSI Concepts Mapping Model
The following diagram shows an example of how multiple iSCSI Nodes
(targets in this case) can coexist within the same Network Entity and
can share Network Portals (IP addresses and TCP ports). Other more
complex configurations are also possible. For detailed descriptions
of the components of these diagrams, see Section 3.4.1 iSCSI
Architecture Model.
+-----------------------------------+
| Network Entity (iSCSI Client) |
| |
| +-------------+ |
| | iSCSI Node | |
| | (Initiator) | |
| +-------------+ |
| | | |
| +--------------+ +--------------+ |
| |Network Portal| |Network Portal| |
| | 10.1.30.4 | | 10.1.40.6 | |
+-+--------------+-+--------------+-+
| |
| IP Networks |
| |
+-+--------------+-+--------------+-+
| |Network Portal| |Network Portal| |
| | 10.1.30.21 | | 10.1.40.3 | |
| | TCP Port 3260| | TCP Port 3260| |
| +--------------+ +--------------+ |
| | | |
| ----------------- |
| | | |
| +-------------+ +--------------+ |
| | iSCSI Node | | iSCSI Node | |
| | (Target) | | (Target) | |
| +-------------+ +--------------+ |
| |
| Network Entity (iSCSI Server) |
+-----------------------------------+
3.4.1. iSCSI Architecture Model
This section describes the part of the iSCSI architecture model that
has the most bearing on the relationship between iSCSI and the SCSI
Architecture Model.
a) Network Entity - represents a device or gateway that is
accessible from the IP network. A Network Entity must have
one or more Network Portals (see item d), each of which can be
used by some iSCSI Nodes (see item (b)) contained in that
Network Entity to gain access to the IP network.
b) iSCSI Node - represents a single iSCSI initiator or iSCSI
target. There are one or more iSCSI Nodes within a Network
Entity. The iSCSI Node is accessible via one or more Network
Portals (see item d). An iSCSI Node is identified by its
iSCSI Name (see Section 3.2.6 iSCSI Names and Chapter 12).
The separation of the iSCSI Name from the addresses used by
and for the iSCSI node allows multiple iSCSI nodes to use the
same addresses, and the same iSCSI node to use multiple
addresses.
c) An alias string may also be associated with an iSCSI Node.
The alias allows an organization to associate a user friendly
string with the iSCSI Name. However, the alias string is not
a substitute for the iSCSI Name.
d) Network Portal - a component of a Network Entity that has a
TCP/IP network address and that may be used by an iSCSI Node
within that Network Entity for the connection(s) within one of
its iSCSI sessions. In an initiator, it is identified by its
IP address. In a target, it is identified by its IP address
and its listening TCP port.
e) Portal Groups - iSCSI supports multiple connections within the
same session; some implementations will have the ability to
combine connections in a session across multiple Network
Portals. A Portal Group defines a set of Network Portals
within an iSCSI Node that collectively supports the capability
of coordinating a session with connections that span these
portals. Not all Network Portals within a Portal Group need
to participate in every session connected through that Portal
Group. One or more Portal Groups may provide access to an
iSCSI Node. Each Network Portal, as utilized by a given iSCSI
Node, belongs to exactly one portal group within that node.
Portal Groups are identified within an iSCSI Node by a portal
group tag, a simple unsigned-integer between 0 and 65535 (see
Section 12.3 SendTargets). All Network Portals with the same
portal group tag in the context of a given iSCSI Node are in
the same Portal Group.
Both iSCSI Initiators and iSCSI Targets have portal groups,
though only the iSCSI Target Portal Groups are used directly
in the iSCSI protocol (e.g., in SendTargets). For references
to the initiator Portal Groups, see Section 9.1.1 Conservative
Reuse of ISIDs.
f) Portals within a Portal Group should support similar session
parameters, because they may participate in a common session.
The following diagram shows an example of one such configuration on a
target and how a session that shares Network Portals within a Portal
Group may be established.
----------------------------IP Network---------------------
| | |
+----|---------------|-----+ +----|---------+
| +---------+ +---------+ | | +---------+ |
| | Network | | Network | | | | Network | |
| | Portal | | Portal | | | | Portal | |
| +--|------+ +---------+ | | +---------+ |
| | | | | | |
| | Portal | | | | Portal |
| | Group 1 | | | | Group 2 |
+--------------------------+ +--------------+
| | |
+--------|---------------|--------------------|--------------------+
| | | | |
| +----------------------------+ +-----------------------------+ |
| | iSCSI Session (Target side)| | iSCSI Session (Target side) | |
| | | | | |
| | (TSIH = 56) | | (TSIH = 48) | |
| +----------------------------+ +-----------------------------+ |
| |
| iSCSI Target Node |
| (within Network Entity, not shown) |
+------------------------------------------------------------------+
3.4.2. SCSI Architecture Model
This section describes the relationship between the SCSI Architecture
Model [SAM2] and the constructs of the SCSI device, SCSI port and I_T
nexus, and the iSCSI constructs described in Section 3.4.1 iSCSI
Architecture Model.
This relationship implies implementation requirements in order to
conform to the SAM2 model and other SCSI operational functions.
These requirements are detailed in Section 3.4.3 Consequences of the
Model.
The following list outlines mappings of SCSI architectural elements
to iSCSI.
a) SCSI Device - the SAM2 term for an entity that contains one or
more SCSI ports that are connected to a service delivery
subsystem and supports a SCSI application protocol. For
example, a SCSI Initiator Device contains one or more SCSI
Initiator Ports and zero or more application clients. A SCSI
Target Device contains one or more SCSI Target Ports and one
or more logical units. For iSCSI, the SCSI Device is the
component within an iSCSI Node that provides the SCSI
functionality. As such, there can be one SCSI Device, at
most, within an iSCSI Node. Access to the SCSI Device can
only be achieved in an iSCSI normal operational session (see
Section 3.3 iSCSI Session Types). The SCSI Device Name is
defined to be the iSCSI Name of the node and MUST be used in
the iSCSI protocol.
b) SCSI Port - the SAM2 term for an entity in a SCSI Device that
provides the SCSI functionality to interface with a service
delivery subsystem or transport. For iSCSI, the definition of
SCSI Initiator Port and SCSI Target Port are different.
SCSI Initiator Port: This maps to one endpoint of an iSCSI
normal operational session (see Section 3.3 iSCSI Session
Types). An iSCSI normal operational session is negotiated
through the login process between an iSCSI initiator node and
an iSCSI target node. At successful completion of this
process, a SCSI Initiator Port is created within the SCSI
Initiator Device. The SCSI Initiator Port Name and SCSI
Initiator Port Identifier are both defined to be the iSCSI
Initiator Name together with (a) a label that identifies it as
an initiator port name/identifier and (b) the ISID portion of
the session identifier.
SCSI Target Port: This maps to an iSCSI Target Portal Group.
The SCSI Target Port Name and the SCSI Target Port Identifier
are both defined to be the iSCSI Target Name together with (a)
a label that identifies it as a target port name/identifier
and (b) the portal group tag.
The SCSI Port Name MUST be used in iSCSI. When used in SCSI
parameter data, the SCSI port name MUST be encoded as:
- The iSCSI Name in UTF-8 format, followed by
- a comma separator (1 byte), followed by
- the ASCII character 'i' (for SCSI Initiator Port) or the
ASCII character 't' (for SCSI Target Port) (1 byte),
followed by
- a comma separator (1 byte), followed by
- a text encoding as a hex-constant (see Section 5.1 Text
Format) of the ISID (for SCSI initiator port) or the portal
group tag (for SCSI target port) including the initial 0X
or 0x and the terminating null (15 bytes).
The ASCII character 'i' or 't' is the label that identifies
this port as either a SCSI Initiator Port or a SCSI Target
Port.
c) I_T nexus - a relationship between a SCSI Initiator Port and a
SCSI Target Port, according to [SAM2]. For iSCSI, this
relationship is a session, defined as a relationship between
an iSCSI Initiator's end of the session (SCSI Initiator Port)
and the iSCSI Target's Portal Group. The I_T nexus can be
identified by the conjunction of the SCSI port names or by the
iSCSI session identifier SSID. iSCSI defines the I_T nexus
identifier to be the tuple (iSCSI Initiator Name + 'i' + ISID,
iSCSI Target Name + 't' + Portal Group Tag).
NOTE: The I_T nexus identifier is not equal to the session
identifier (SSID).
3.4.3. Consequences of the Model
This section describes implementation and behavioral requirements
that result from the mapping of SCSI constructs to the iSCSI
constructs defined above. Between a given SCSI initiator port and a
given SCSI target port, only one I_T nexus (session) can exist. No
more than one nexus relationship (parallel nexus) is allowed by
[SAM2]. Therefore, at any given time, only one session can exist
between a given iSCSI initiator node and an iSCSI target node, with
the same session identifier (SSID).
These assumptions lead to the following conclusions and requirements:
ISID RULE: Between a given iSCSI Initiator and iSCSI Target Portal
Group (SCSI target port), there can only be one session with a given
value for ISID that identifies the SCSI initiator port. See Section
10.12.5 ISID.
The structure of the ISID that contains a naming authority component
(see Section 10.12.5 ISID and [RFC3721]) provides a mechanism to
facilitate compliance with the ISID rule. (See Section 9.1.1
Conservative Reuse of ISIDs.)
The iSCSI Initiator Node should manage the assignment of ISIDs prior
to session initiation. The "ISID RULE" does not preclude the use of
the same ISID from the same iSCSI Initiator with different Target
Portal Groups on the same iSCSI target or on other iSCSI targets (see
Section 9.1.1 Conservative Reuse of ISIDs). Allowing this would be
analogous to a single SCSI Initiator Port having relationships
(nexus) with multiple SCSI target ports on the same SCSI target
device or SCSI target ports on other SCSI target devices. It is also
possible to have multiple sessions with different ISIDs to the same
Target Portal Group. Each such session would be considered to be
with a different initiator even when the sessions originate from the
same initiator device. The same ISID may be used by a different
iSCSI initiator because it is the iSCSI Name together with the ISID
that identifies the SCSI Initiator Port.
NOTE: A consequence of the ISID RULE and the specification for the
I_T nexus identifier is that two nexus with the same identifier
should never exist at the same time.
TSIH RULE: The iSCSI Target selects a non-zero value for the TSIH at
session creation (when an initiator presents a 0 value at Login).
After being selected, the same TSIH value MUST be used whenever the
initiator or target refers to the session and a TSIH is required.
3.4.3.1. I_T Nexus State
Certain nexus relationships contain an explicit state (e.g.,
initiator-specific mode pages) that may need to be preserved by the
device server [SAM2] in a logical unit through changes or failures in
the iSCSI layer (e.g., session failures). In order for that state to
be restored, the iSCSI initiator should reestablish its session
(re-login) to the same Target Portal Group using the previous ISID.
That is, it should perform session recovery as described in Chapter
6. This is because the SCSI initiator port identifier and the SCSI
target port identifier (or relative target port) form the datum that
the SCSI logical unit device server uses to identify the I_T nexus.
3.5. Request/Response Summary
This section lists and briefly describes all the iSCSI PDU types
(request and responses).
All iSCSI PDUs are built as a set of one or more header segments
(basic and auxiliary) and zero or one data segments. The header
group and the data segment may each be followed by a CRC (digest).
The basic header segment has a fixed length of 48 bytes.
3.5.1. Request/Response Types Carrying SCSI Payload
3.5.1.1. SCSI-Command
This request carries the SCSI CDB and all the other SCSI execute
command procedure call (see [SAM2]) IN arguments such as task
attributes, Expected Data Transfer Length for one or both transfer
directions (the latter for bidirectional commands), and Task Tag (as
part of the I_T_L_x nexus). The I_T_L nexus is derived by the
initiator and target from the LUN field in the request and the I_T
nexus is implicit in the session identification.
In addition, the SCSI-command PDU carries information required for
the proper operation of the iSCSI protocol - the command sequence
number (CmdSN) for the session and the expected status number
(ExpStatSN) for the connection.
All or part of the SCSI output (write) data associated with the SCSI
command may be sent as part of the SCSI-Command PDU as a data
segment.
3.5.1.2. SCSI-Response
The SCSI-Response carries all the SCSI execute-command procedure call
(see [SAM2]) OUT arguments and the SCSI execute-command procedure
call return value.
The SCSI-Response contains the residual counts from the operation, if
any, an indication of whether the counts represent an overflow or an
underflow, and the SCSI status if the status is valid or a response
code (a non-zero return value for the execute-command procedure call)
if the status is not valid.
For a valid status that indicates that the command has been
processed, but resulted in an exception (e.g., a SCSI CHECK
CONDITION), the PDU data segment contains the associated sense data.
The use of Autosense ([SAM2]) is REQUIRED by iSCSI.
Some data segment content may also be associated (in the data
segment) with a non-zero response code.
In addition, the SCSI-Response PDU carries information required for
the proper operation of the iSCSI protocol:
- The number of Data-In PDUs that a target has sent (to enable
the initiator to check that all have arrived).
- StatSN - the Status Sequence Number on this connection.
- ExpCmdSN - the next Expected Command Sequence Number at the
target.
- MaxCmdSN - the maximum CmdSN acceptable at the target from
this initiator.
3.5.1.3 Task Management Function Request
The Task Management function request provides an initiator with a way
to explicitly control the execution of one or more SCSI Tasks or
iSCSI functions. The PDU carries a function identifier (which task
management function to perform) and enough information to
unequivocally identify the task or task-set on which to perform the
action, even if the task(s) to act upon has not yet arrived or has
been discarded due to an error.
The referenced tag identifies an individual task if the function
refers to an individual task.
The I_T_L nexus identifies task sets. In iSCSI the I_T_L nexus is
identified by the LUN and the session identification (the session
identifies an I_T nexus).
For task sets, the CmdSN of the Task Management function request
helps identify the tasks upon which to act, namely all tasks
associated with a LUN and having a CmdSN preceding the Task
Management function request CmdSN.
For a Task Management function, the coordination between responses to
the tasks affected and the Task Management function response is done
by the target.
3.5.1.4. Task Management Function Response
The Task Management function response carries an indication of
function completion for a Task Management function request including
how it was completed (response and qualifier) and additional
information for failure responses.
After the Task Management response indicates Task Management function
completion, the initiator will not receive any additional responses
from the affected tasks.
3.5.1.5. SCSI Data-Out and SCSI Data-In
SCSI Data-Out and SCSI Data-In are the main vehicles by which SCSI
data payload is carried between initiator and target. Data payload
is associated with a specific SCSI command through the Initiator Task
Tag. For target convenience, outgoing solicited data also carries a
Target Transfer Tag (copied from R2T) and the LUN. Each PDU contains
the payload length and the data offset relative to the buffer address
contained in the SCSI execute command procedure call.
In each direction, the data transfer is split into "sequences". An
end-of-sequence is indicated by the F bit.
An outgoing sequence is either unsolicited (only the first sequence
can be unsolicited) or consists of all the Data-Out PDUs sent in
response to an R2T.
Input sequences are built to enable the direction switching for
bidirectional commands.
For input, the target may request positive acknowledgement of input
data. This is limited to sessions that support error recovery and is
implemented through the A bit in the SCSI Data-In PDU header.
Data-In and Data-Out PDUs also carry the DataSN to enable the
initiator and target to detect missing PDUs (discarded due to an
error).
In addition, StatSN is carried by the Data-In PDUs.
To enable a SCSI command to be processed while involving a minimum
number of messages, the last SCSI Data-In PDU passed for a command
may also contain the status if the status indicates termination with
no exceptions (no sense or response involved).
3.5.1.6. Ready To Transfer (R2T)
R2T is the mechanism by which the SCSI target "requests" the
initiator for output data. R2T specifies to the initiator the offset
of the requested data relative to the buffer address from the execute
command procedure call and the length of the solicited data.
To help the SCSI target associate the resulting Data-Out with an R2T,
the R2T carries a Target Transfer Tag that will be copied by the
initiator in the solicited SCSI Data-Out PDUs. There are no protocol
specific requirements with regard to the value of these tags, but it
is assumed that together with the LUN, they will enable the target to
associate data with an R2T.
R2T also carries information required for proper operation of the
iSCSI protocol, such as:
- R2TSN (to enable an initiator to detect a missing R2T)
- StatSN
- ExpCmdSN
- MaxCmdSN
3.5.2. Requests/Responses carrying SCSI and iSCSI Payload
3.5.2.1. Asynchronous Message
Asynchronous Messages are used to carry SCSI asynchronous events
(AEN) and iSCSI asynchronous messages.
When carrying an AEN, the event details are reported as sense data in
the data segment.
3.5.3. Requests/Responses Carrying iSCSI Only Payload
3.5.3.1. Text Request and Text Response
Text requests and responses are designed as a parameter negotiation
vehicle and as a vehicle for future extension.
In the data segment, Text Requests/Responses carry text information
using a simple "key=value" syntax.
Text Request/Responses may form extended sequences using the same
Initiator Task Tag. The initiator uses the F (Final) flag bit in the
text request header to indicate its readiness to terminate a
sequence. The target uses the F (Final) flag bit in the text
response header to indicate its consent to sequence termination.
Text Request and Responses also use the Target Transfer Tag to
indicate continuation of an operation or a new beginning. A target
that wishes to continue an operation will set the Target Transfer Tag
in a Text Response to a value different from the default 0xffffffff.
An initiator willing to continue will copy this value into the Target
Transfer Tag of the next Text Request. If the initiator wants to
restart the current target negotiation (start fresh) will set the
Target Transfer Tag to 0xffffffff.
Although a complete exchange is always started by the initiator,
specific parameter negotiations may be initiated by the initiator or
target.
3.5.3.2. Login Request and Login Response
Login Requests and Responses are used exclusively during the Login
Phase of each connection to set up the session and connection
parameters. (The Login Phase consists of a sequence of login
requests and responses carrying the same Initiator Task Tag.)
A connection is identified by an arbitrarily selected connection-ID
(CID) that is unique within a session.
Similar to the Text Requests and Responses, Login Requests/Responses
carry key=value text information with a simple syntax in the data
segment.
The Login Phase proceeds through several stages (security
negotiation, operational parameter negotiation) that are selected
with two binary coded fields in the header -- the "current stage"
(CSG) and the "next stage" (NSG) with the appearance of the latter
being signaled by the "transit" flag (T).
The first Login Phase of a session plays a special role, called the
leading login, which determines some header fields (e.g., the version
number, the maximum number of connections, and the session
identification).
The CmdSN initial value is also set by the leading login.
StatSN for each connection is initiated by the connection login.
A login request may indicate an implied logout (cleanup) of the
connection to be logged in (a connection restart) by using the same
Connection ID (CID) as an existing connection, as well as the same
session identifying elements of the session to which the old
connection was associated.
3.5.3.3. Logout Request and Response
Logout Requests and Responses are used for the orderly closing of
connections for recovery or maintenance. The logout request may be
issued following a target prompt (through an asynchronous message) or
at an initiators initiative. When issued on the connection to be
logged out, no other request may follow it.
The Logout Response indicates that the connection or session cleanup
is completed and no other responses will arrive on the connection (if
received on the logging out connection). In addition, the Logout
Response indicates how long the target will continue to hold
resources for recovery (e.g., command execution that continues on a
new connection) in the text key Time2Retain and how long the
initiator must wait before proceeding with recovery in the text key
Time2Wait.
3.5.3.4. SNACK Request
With the SNACK Request, the initiator requests retransmission of
numbered-responses or data from the target. A single SNACK request
covers a contiguous set of missing items, called a run, of a given
type of items. The type is indicated in a type field in the PDU
header. The run is composed of an initial item (StatSN, DataSN,
R2TSN) and the number of missed Status, Data, or R2T PDUs. For long
Data-In sequences, the target may request (at predefined minimum
intervals) a positive acknowledgement for the data sent. A SNACK
request with a type field that indicates ACK and the number of
Data-In PDUs acknowledged conveys this positive acknowledgement.
3.5.3.5. Reject
Reject enables the target to report an iSCSI error condition (e.g.,
protocol, unsupported option) that uses a Reason field in the PDU
header and includes the complete header of the bad PDU in the Reject
PDU data segment.
3.5.3.6. NOP-Out Request and NOP-In Response
This request/response pair may be used by an initiator and target as
a "ping" mechanism to verify that a connection/session is still
active and all of its components are operational. Such a ping may be
triggered by the initiator or target. The triggering party indicates
that it wants a reply by setting a value different from the default
0xffffffff in the corresponding Initiator/Target Transfer Tag.
NOP-In/NOP-Out may also be used "unidirectional" to convey to the
initiator/target command, status or data counter values when there is
no other "carrier" and there is a need to update the initiator/
target.
4. SCSI Mode Parameters for iSCSI
There are no iSCSI specific mode pages.
5. Login and Full Feature Phase Negotiation
iSCSI parameters are negotiated at session or connection
establishment by using Login Requests and Responses (see Section
3.2.3 iSCSI Login) and during the Full Feature Phase (Section 3.2.4
iSCSI Full Feature Phase) by using Text Requests and Responses. In
both cases the mechanism used is an exchange of iSCSI-text-key=value
pairs. For brevity iSCSI-text-keys are called just keys in the rest
of this document.
Keys are either declarative or require negotiation and the key
description indicates if the key is declarative or requires
negotiation.
For the declarative keys, the declaring party sets a value for the
key. The key specification indicates if the key can be declared by
the initiator, target or both.
For the keys that require negotiation one of the parties (the
proposing party) proposes a value or set of values by including the
key=value in the data part of a Login or Text Request or Response
PDUs. The other party (the accepting party) makes a selection based
on the value or list of values proposed and includes the selected
value in a key=value in the data part of one of the following Login
or Text Response or Request PDUs. For most of the keys both the
initiator and target can be proposing parties.
The login process proceeds in two stages - the security negotiation
stage and the operational parameter negotiation stage. Both stages
are optional but at least one of them has to be present to enable the
setting of some mandatory parameters.
If present, the security negotiation stage precedes the operational
parameter negotiation stage.
Progression from stage to stage is controlled by the T (Transition)
bit in the Login Request/Response PDU header. Through the T bit set
to 1, the initiator indicates that it would like to transition. The
target agrees to the transition (and selects the next stage) when
ready. A field in the Login PDU header indicates the current stage
(CSG) and during transition, another field indicates the next stage
(NSG) proposed (initiator) and selected (target).
The text negotiation process is used to negotiate or declare
operational parameters. The negotiation process is controlled by the
F (final) bit in the PDU header. During text negotiations, the F bit
is used by the initiator to indicate that it is ready to finish the
negotiation and by the Target to acquiesce the end of negotiation.
Since some key=value pairs may not fit entirely in a single PDU, the
C (continuation) bit is used (both in Login and Text) to indicate
that "more follows".
The text negotiation uses an additional mechanism by which a target
may deliver larger amounts of data to an enquiring initiator. The
target sets a Target Task Tag to be used as a bookmark that when
returned by the initiator, means "go on". If reset to a "neutral
value", it means "forget about the rest".
This chapter details types of keys and values used, the syntax rules
for parameter formation, and the negotiation schemes to be used with
different types of parameters.
5.1. Text Format
The initiator and target send a set of key=value pairs encoded in
UTF-8 Unicode. All the text keys and text values specified in this
document are to be presented and interpreted in the case in which
they appear in this document. They are case sensitive.
The following character symbols are used in this document for text
items (the hexadecimal values represent Unicode code points):
(a-z, A-Z) - letters
(0-9) - digits
" " (0x20) - space
"." (0x2e) - dot
"-" (0x2d) - minus
"+" (0x2b) - plus
"@" (0x40) - commercial at
"_" (0x5f) - underscore
"=" (0x3d) - equal
":" (0x3a) - colon
"/" (0x2f) - solidus or slash
"[" (0x5b) - left bracket
"]" (0x5d) - right bracket
null (0x00) - null separator
"," (0x2c) - comma
"~" (0x7e) - tilde
Key=value pairs may span PDU boundaries. An initiator or target that
sends partial key=value text within a PDU indicates that more text
follows by setting the C bit in the Text or Login Request or Text or
Login Response to 1. Data segments in a series of PDUs that have the
C bit set to 1 and end with a PDU that have the C bit set to 0, or
include a single PDU that has the C bit set to 0, have to be
considered as forming a single logical-text-data-segment (LTDS).
Every key=value pair, including the last or only pair in a LTDS, MUST
be followed by one null (0x00) delimiter.
A key-name is whatever precedes the first "=" in the key=value pair.
The term key is used frequently in this document in place of
key-name.
A value is whatever follows the first "=" in the key=value pair up to
the end of the key=value pair, but not including the null delimiter.
The following definitions will be used in the rest of this document:
standard-label: A string of one or more characters that consist of
letters, digits, dot, minus, plus, commercial at, or underscore.
A standard-label MUST begin with a capital letter and must not
exceed 63 characters.
key-name: A standard-label.
text-value: A string of zero or more characters that consist of
letters, digits, dot, minus, plus, commercial at, underscore,
slash, left bracket, right bracket, or colon.
iSCSI-name-value: A string of one or more characters that consist
of minus, dot, colon, or any character allowed by the output of
the iSCSI string-prep template as specified in [RFC3722] (see
also Section 3.2.6.2 iSCSI Name Encoding).
iSCSI-local-name-value: A UTF-8 string; no null characters are
allowed in the string. This encoding is to be used for localized
(internationalized) aliases.
boolean-value: The string "Yes" or "No".
hex-constant: A hexadecimal constant encoded as a string that
starts with "0x" or "0X" followed by one or more digits or the
letters a, b, c, d, e, f, A, B, C, D, E, or F. Hex-constants are
used to encode numerical values or binary strings. When used to
encode numerical values, the excessive use of leading 0 digits is
discouraged. The string following 0X (or 0x) represents a base16
number that starts with the most significant base16 digit,
followed by all other digits in decreasing order of significance
and ending with the least-significant base16 digit. When used to
encode binary strings, hexadecimal constants have an implicit
byte-length that includes four bits for every hexadecimal digit
of the constant, including leading zeroes. For example, a
hex-constant of n hexadecimal digits has a byte-length of (the
integer part of) (n+1)/2.
decimal-constant: An unsigned decimal number with the digit 0 or a
string of one or more digits that start with a non-zero digit.
Decimal-constants are used to encode numerical values or binary
strings. Decimal constants can only be used to encode binary
strings if the string length is explicitly specified. There is
no implicit length for decimal strings. Decimal-constant MUST
NOT be used for parameter values if the values can be equal or
greater than 2**64 (numerical) or for binary strings that can be
longer than 64 bits.
base64-constant: base64 constant encoded as a string that starts
with "0b" or "0B" followed by 1 or more digits or letters or plus
or slash or equal. The encoding is done according to [RFC2045]
and each character, except equal, represents a base64 digit or a
6-bit binary string. Base64-constants are used to encode
numerical-values or binary strings. When used to encode
numerical values, the excessive use of leading 0 digits (encoded
as A) is discouraged. The string following 0B (or 0b) represents
a base64 number that starts with the most significant base64
digit, followed by all other digits in decreasing order of
significance and ending with the least-significant base64 digit;
the least significant base64 digit may be optionally followed by
pad digits (encoded as equal) that are not considered as part of
the number. When used to encode binary strings, base64-constants
have an implicit
byte-length that includes six bits for every character of the
constant, excluding trailing equals (i.e., a base64-constant of n
base64 characters excluding the trailing equals has a byte-length
of ((the integer part of) (n*3/4)). Correctly encoded base64
strings cannot have n values of 1, 5 ... k*4+1.
numerical-value: An unsigned integer always less than 2**64 encoded
as a decimal-constant or a hex-constant. Unsigned integer
arithmetic applies to numerical-values.
large-numerical-value: An unsigned integer that can be larger than
or equal to 2**64 encoded as a hex constant, or
base64-constant. Unsigned integer arithmetic applies to
large-numeric-values.
numeric-range: Two numerical-values separated by a tilde where the
value to the right of tilde must not be lower than the value to
the left.
regular-binary-value: A binary string not longer than 64 bits
encoded as a decimal constant, hex constant, or base64-constant.
The length of the string is either specified by the key
definition or is the implicit byte-length of the encoded string.
large-binary-value: A binary string longer than 64 bits encoded as
a hex-constant or base64-constant. The length of the string is
either specified by the key definition or is the implicit
byte-length of the encoded string.
binary-value: A regular-binary-value or a large-binary-value.
Operations on binary values are key specific.
simple-value: Text-value, iSCSI-name-value, boolean-value,
numeric-value, a numeric-range, or a binary-value.
list-of-values: A sequence of text-values separated by a comma.
If not otherwise specified, the maximum length of a simple-value (not
its encoded representation) is 255 bytes, not including the delimiter
(comma or zero byte).
Any iSCSI target or initiator MUST support receiving at least 8192
bytes of key=value data in a negotiation sequence. When proposing or
accepting authentication methods that explicitly require support for
very long authentication items, the initiator and target MUST support
receiving of at least 64 kilobytes of key=value data (see Appendix
11.1.2 - Simple Public-Key Mechanism (SPKM) - that require support
for public key certificates).
5.2. Text Mode Negotiation
During login, and thereafter, some session or connection parameters
are either declared or negotiated through an exchange of textual
information.
The initiator starts the negotiation and/or declaration through a
Text or Login Request and indicates when it is ready for completion
(by setting the F bit to 1 and keeping it to 1 in a Text Request or
the T bit in the Login Request). As negotiation text may span PDU
boundaries, a Text or Login Request or Text or Login Response PDU
that has the C bit set to 1 MUST NOT have the F/T bit set to 1.
A target receiving a Text or Login Request with the C bit set to 1
MUST answer with a Text or Login Response with no data segment
(DataSegmentLength 0). An initiator receiving a Text or Login
Response with the C bit set to 1 MUST answer with a Text or Login
Request with no data segment (DataSegmentLength 0).
A target or initiator SHOULD NOT use a Text or Login Response or Text
or Login Request with no data segment (DataSegmentLength 0) unless
explicitly required by a general or a key-specific negotiation rule.
The format of a declaration is:
Declarer-> <key>=<valuex>
The general format of text negotiation is:
Proposer-> <key>=<valuex>
Acceptor-> <key>={<valuey>|NotUnderstood|Irrelevant|Reject}
Thus a declaration is a one-way textual exchange while a negotiation
is a two-way exchange.
The proposer or declarer can either be the initiator or the target,
and the acceptor can either be the target or initiator, respectively.
Targets are not limited to respond to key=value pairs as proposed by
the initiator. The target may propose key=value pairs of its own.
All negotiations are explicit (i.e., the result MUST only be based on
newly exchanged or declared values). There are no implicit
proposals. If a proposal is not made, then a reply cannot be
expected. Conservative design also requires that default values
should not be relied upon when use of some other value has serious
consequences.
The value proposed or declared can be a numerical-value, a
numerical-range defined by lower and upper values with both integers
separated by a tilde, a binary value, a text-value, an
iSCSI-name-value, an iSCSI-local-name-value, a boolean-value (Yes or
No), or a list of comma separated text-values. A range, a
large-numerical-value, an iSCSI-name-value and an
iSCSI-local-name-value MAY ONLY be used if it is explicitly allowed.
An accepted value can be a numerical-value, a large-numerical-value,
a text-value, or a boolean-value.
If a specific key is not relevant for the current negotiation, the
acceptor may answer with the constant "Irrelevant" for all types of
negotiation. However the negotiation is not considered as failed if
the answer is "Irrelevant". The "Irrelevant" answer is meant for
those cases in which several keys are presented by a proposing party
but the selection made by the acceptor for one of the keys makes
other keys irrelevant. The following example illustrates the use of
"Irrelevant":
I->T OFMarker=Yes,OFMarkInt=2048~8192
T->I OFMarker=No,OFMarkInt=Irrelevant
I->T X#vkey1=(bla,alb,None),X#vkey2=(bla,alb)
T->I X#vkey1=None,X#vkey2=Irrelevant
Any key not understood by the acceptor may be ignored by the acceptor
without affecting the basic function. However, the answer for a key
not understood MUST be key=NotUnderstood.
The constants "None", "Reject", "Irrelevant", and "NotUnderstood" are
reserved and MUST ONLY be used as described here. Violation of this
rule is a protocol error (in particular the use of "Reject",
"Irrelevant", and "NotUnderstood" as proposed values).
Reject or Irrelevant are legitimate negotiation options where allowed
but their excessive use is discouraged. A negotiation is considered
complete when the acceptor has sent the key value pair even if the
value is "Reject", "Irrelevant", or "NotUnderstood. Sending the key
again would be a re-negotiation and is forbidden for many keys.
If the acceptor sends "Reject" as an answer the negotiated key is
left at its current value (or default if no value was set). If the
current value is not acceptable to the proposer on the connection or
to the session it is sent, the proposer MAY choose to terminate the
connection or session.
All keys in this document, except for the X extension formats, MUST
be supported by iSCSI initiators and targets when used as specified
here. If used as specified, these keys MUST NOT be answered with
NotUnderstood.
Implementers may introduce new keys by prefixing them with
"X-", followed by their (reversed) domain name, or with new keys
registered with IANA prefixing them with X#. For example, the entity
owning the domain example.com can issue:
X-com.example.bar.foo.do_something=3
or a new registered key may be used as in:
X#SuperCalyPhraGilistic=Yes
Implementers MAY also introduce new values, but ONLY for new keys or
authentication methods (see Section 11 iSCSI Security Text Keys and
Authentication Methods), or digests (see Section 12.1 HeaderDigest
and DataDigest).
Whenever parameter action or acceptance is dependent on other
parameters, the dependency rules and parameter sequence must be
specified with the parameters.
In the Login Phase (see Section 5.3 Login Phase), every stage is a
separate negotiation. In the FullFeaturePhase, a Text Request
Response sequence is a negotiation. Negotiations MUST be handled as
atomic operations. For example, all negotiated values go into effect
after the negotiation concludes in agreement or are ignored if the
negotiation fails.
Some parameters may be subject to integrity rules (e.g., parameter-x
must not exceed parameter-y or parameter-u not 1 implies parameter-v
be Yes). Whenever required, integrity rules are specified with the
keys. Checking for compliance with the integrity rule must only be
performed after all the parameters are available (the existent and
the newly negotiated). An iSCSI target MUST perform integrity
checking before the new parameters take effect. An initiator MAY
perform integrity checking.
An iSCSI initiator or target MAY terminate a negotiation that does
not end within a reasonable time or number of exchanges.
5.2.1. List negotiations
In list negotiation, the originator sends a list of values (which may
include "None") in its order of preference.
The responding party MUST respond with the same key and the first
value that it supports (and is allowed to use for the specific
originator) selected from the originator list.
The constant "None" MUST always be used to indicate a missing
function. However, "None" is only a valid selection if it is
explicitly proposed.
If an acceptor does not understand any particular value in a list, it
MUST ignore it. If an acceptor does not support, does not
understand, or is not allowed to use any of the proposed options with
a specific originator, it may use the constant "Reject" or terminate
the negotiation. The selection of a value not proposed MUST be
handled as a protocol error.
5.2.2. Simple-value Negotiations
For simple-value negotiations, the accepting party MUST answer with
the same key. The value it selects becomes the negotiation result.
Proposing a value not admissible (e.g., not within the specified
bounds) MAY be answered with the constant "Reject" or the acceptor
MAY select an admissible value.
The selection by the acceptor, of a value not admissible under the
selection rules is considered a protocol error. The selection rules
are key-specific.
For a numerical range, the value selected must be an integer within
the proposed range or "Reject" (if the range is unacceptable).
In Boolean negotiations (i.e., those that result in keys taking the
values Yes or No), the accepting party MUST answer with the same key
and the result of the negotiation when the received value does not
determine that result by itself. The last value transmitted becomes
the negotiation result. The rules for selecting the value to answer
with are expressed as Boolean functions of the value received, and
the value that the accepting party would have selected if given a
choice.
Specifically, the two cases in which answers are OPTIONAL are:
- The Boolean function is "AND" and the value "No" is received.
The outcome of the negotiation is "No".
- The Boolean function is "OR" and the value "Yes" is received.
The outcome of the negotiation is "Yes".
Responses are REQUIRED in all other cases, and the value chosen and
sent by the acceptor becomes the outcome of the negotiation.
5.3. Login Phase
The Login Phase establishes an iSCSI connection between an initiator
and a target; it also creates a new session or associates the
connection to an existing session. The Login Phase sets the iSCSI
protocol parameters, security parameters, and authenticates the
initiator and target to each other.
The Login Phase is only implemented via Login Request and Responses.
The whole Login Phase is considered as a single task and has a single
Initiator Task Tag (similar to the linked SCSI commands).
The default MaxRecvDataSegmentLength is used during Login.
The Login Phase sequence of requests and responses proceeds as
follows:
- Login initial request
- Login partial response (optional)
- More Login Requests and Responses (optional)
- Login Final-Response (mandatory)
The initial Login Request of any connection MUST include the
InitiatorName key=value pair. The initial Login Request of the first
connection of a session MAY also include the SessionType key=value
pair. For any connection within a session whose type is not
"Discovery", the first Login Request MUST also include the TargetName
key=value pair.
The Login Final-response accepts or rejects the Login Request.
The Login Phase MAY include a SecurityNegotiation stage and a
LoginOperationalNegotiation stage or both, but MUST include at least
one of them. The included stage MAY be empty except for the
mandatory names.
The Login Requests and Responses contain a field (CSG) that indicates
the current negotiation stage (SecurityNegotiation or
LoginOperationalNegotiation). If both stages are used, the
SecurityNegotiation MUST precede the LoginOperationalNegotiation.
Some operational parameters can be negotiated outside the login
through Text Requests and Responses.
Security MUST be completely negotiated within the Login Phase. The
use of underlying IPsec security is specified in Chapter 8 and in
[RFC3723]. iSCSI support for security within the protocol only
consists of authentication in the Login Phase.
In some environments, a target or an initiator is not interested in
authenticating its counterpart. It is possible to bypass
authentication through the Login Request and Response.
The initiator and target MAY want to negotiate iSCSI authentication
parameters. Once this negotiation is completed, the channel is
considered secure.
Most of the negotiation keys are only allowed in a specific stage.
The SecurityNegotiation keys appear in Chapter 11 and the
LoginOperationalNegotiation keys appear in Chapter 12. Only a
limited set of keys (marked as Any-Stage in Chapter 12) may be used
in any of the two stages.
Any given Login Request or Response belongs to a specific stage; this
determines the negotiation keys allowed with the request or response.
It is considered to be a protocol error to send a key that is not
allowed in the current stage.
Stage transition is performed through a command exchange (request/
response) that carries the T bit and the same CSG code. During this
exchange, the next stage is selected by the target through the "next
stage" code (NSG). The selected NSG MUST NOT exceed the value stated
by the initiator. The initiator can request a transition whenever it
is ready, but a target can only respond with a transition after one
is proposed by the initiator.
In a negotiation sequence, the T bit settings in one pair of Login
Request-Responses have no bearing on the T bit settings of the next
pair. An initiator that has a T bit set to 1 in one pair and is
answered with a T bit setting of 0, may issue the next request with
the T bit set to 0.
When a transition is requested by the initiator and acknowledged by
the target, both the initiator and target switch to the selected
stage.
Targets MUST NOT submit parameters that require an additional
initiator Login Request in a Login Response with the T bit set to 1.
Stage transitions during login (including entering and exit) are only
possible as outlined in the following table:
+-----------------------------------------------------------+
|From To -> | Security | Operational | FullFeature |
| | | | | |
| V | | | |
+-----------------------------------------------------------+
| (start) | yes | yes | no |
+-----------------------------------------------------------+
| Security | no | yes | yes |
+-----------------------------------------------------------+
| Operational | no | no | yes |
+-----------------------------------------------------------+
The Login Final-Response that accepts a Login Request can only come
as a response to a Login Request with the T bit set to 1, and both
the request and response MUST indicate FullFeaturePhase as the next
phase via the NSG field.
Neither the initiator nor the target should attempt to declare or
negotiate a parameter more than once during login except for
responses to specific keys that explicitly allow repeated key
declarations (e.g., TargetAddress). An attempt to
renegotiate/redeclare parameters not specifically allowed MUST be
detected by the initiator and target. If such an attempt is detected
by the target, the target MUST respond with Login reject (initiator
error); if detected by the initiator, the initiator MUST drop the
connection.
5.3.1. Login Phase Start
The Login Phase starts with a Login Request from the initiator to the
target. The initial Login Request includes:
- Protocol version supported by the initiator.
- iSCSI Initiator Name and iSCSI Target Name
- ISID, TSIH, and connection Ids
- Negotiation stage that the initiator is ready to enter.
A login may create a new session or it may add a connection to an
existing session. Between a given iSCSI Initiator Node (selected
only by an InitiatorName) and a given iSCSI target defined by an
iSCSI TargetName and a Target Portal Group Tag, the login results are
defined by the following table:
+------------------------------------------------------------------+
|ISID | TSIH | CID | Target action |
+------------------------------------------------------------------+
|new | non-zero | any | fail the login |
| | | | ("session does not exist") |
+------------------------------------------------------------------+
|new | zero | any | instantiate a new session |
+------------------------------------------------------------------+
|existing | zero | any | do session reinstatement |
| | | | (see section 5.3.5) |
+------------------------------------------------------------------+
|existing | non-zero | new | add a new connection to |
| | existing | | the session |
+------------------------------------------------------------------+
|existing | non-zero |existing| do connection reinstatement|
| | existing | | (see section 5.3.4) |
+------------------------------------------------------------------+
|existing | non-zero | any | fail the login |
| | new | | ("session does not exist") |
+------------------------------------------------------------------+
Determination of "existing" or "new" are made by the target.
Optionally, the Login Request may include:
- Security parameters
OR
- iSCSI operational parameters
AND/OR
- The next negotiation stage that the initiator is ready to
enter.
The target can answer the login in the following ways:
- Login Response with Login reject. This is an immediate rejection
from the target that causes the connection to terminate and the
session to terminate if this is the first (or only) connection of
a new session. The T bit and the CSG and NSG fields are
reserved.
- Login Response with Login Accept as a final response (T bit set
to 1 and the NSG in both request and response are set to
FullFeaturePhase). The response includes the protocol version
supported by the target and the session ID, and may include iSCSI
operational or security parameters (that depend on the current
stage).
- Login Response with Login Accept as a partial response (NSG not
set to FullFeaturePhase in both request and response) that
indicates the start of a negotiation sequence. The response
includes the protocol version supported by the target and either
security or iSCSI parameters (when no security mechanism is
chosen) supported by the target.
If the initiator decides to forego the SecurityNegotiation stage, it
issues the Login with the CSG set to LoginOperationalNegotiation and
the target may reply with a Login Response that indicates that it is
unwilling to accept the connection (see Section 10.13 Login Response)
without SecurityNegotiation and will terminate the connection with a
response of Authentication failure (see Section 10.13.5 Status-Class
and Status-Detail).
If the initiator is willing to negotiate iSCSI security, but is
unwilling to make the initial parameter proposal and may accept a
connection without iSCSI security, it issues the Login with the T bit
set to 1, the CSG set to SecurityNegotiation, and the NSG set to
LoginOperationalNegotiation. If the target is also ready to skip
security, the Login Response only contains the TargetPortalGroupTag
key (see Section 12.9 TargetPortalGroupTag), the T bit set to 1, the
CSG set to SecurityNegotiation, and the NSG set to
LoginOperationalNegotiation.
An initiator that chooses to operate without iSCSI security, with all
the operational parameters taking the default values, issues the
Login with the T bit set to 1, the CSG set to
LoginOperationalNegotiation, and the NSG set to FullFeaturePhase. If
the target is also ready to forego security and can finish its
LoginOperationalNegotiation, the Login Response has T bit set to 1,
the CSG set to LoginOperationalNegotiation, and the NSG set to
FullFeaturePhase in the next stage.
During the Login Phase the iSCSI target MUST return the
TargetPortalGroupTag key with the first Login Response PDU with which
it is allowed to do so (i.e., the first Login Response issued after
the first Login Request with the C bit set to 0) for all session
types when TargetName is given and the response is not a redirection.
The TargetPortalGroupTag key value indicates the iSCSI portal group
servicing the Login Request PDU. If the reconfiguration of iSCSI
portal groups is a concern in a given environment, the iSCSI
initiator should use this key to ascertain that it had indeed
initiated the Login Phase with the intended target portal group.
5.3.2. iSCSI Security Negotiation
The security exchange sets the security mechanism and authenticates
the initiator user and the target to each other. The exchange
proceeds according to the authentication method chosen in the
negotiation phase and is conducted using the Login Requests' and
responses' key=value parameters.
An initiator directed negotiation proceeds as follows:
- The initiator sends a Login Request with an ordered list of the
options it supports (authentication algorithm). The options are
listed in the initiator's order of preference. The initiator MAY
also send private or public extension options.
- The target MUST reply with the first option in the list it
supports and is allowed to use for the specific initiator unless
it does not support any, in which case it MUST answer with
"Reject" (see Section 5.2 Text Mode Negotiation). The parameters
are encoded in UTF8 as key=value. For security parameters, see
Chapter 11.
- When the initiator considers that it is ready to conclude the
SecurityNegotiation stage, it sets the T bit to 1 and the NSG to
what it would like the next stage to be. The target will then
set the T bit to 1 and set the NSG to the next stage in the Login
Response when it finishes sending its security keys. The next
stage selected will be the one the target selected. If the next
stage is FullFeaturePhase, the target MUST respond with a Login
Response with the TSIH value.
If the security negotiation fails at the target, then the target MUST
send the appropriate Login Response PDU. If the security negotiation
fails at the initiator, the initiator SHOULD close the connection.
It should be noted that the negotiation might also be directed by the
target if the initiator does support security, but is not ready to
direct the negotiation (propose options).
5.3.3. Operational Parameter Negotiation During the Login Phase
Operational parameter negotiation during the login MAY be done:
- Starting with the first Login Request if the initiator does not
propose any security/integrity option.
- Starting immediately after the security negotiation if the
initiator and target perform such a negotiation.
Operational parameter negotiation MAY involve several Login
Request-Response exchanges started and terminated by the initiator.
The initiator MUST indicate its intent to terminate the negotiation
by setting the T bit to 1; the target sets the T bit to 1 on the last
response.
If the target responds to a Login Request that has the T bit set to 1
with a Login Response that has the T bit set to 0, the initiator
should keep sending the Login Request (even empty) with the T bit set
to 1, while it still wants to switch stage, until it receives the
Login Response that has the T bit set to 1 or it receives a key that
requires it to set the T bit to 0.
Some session specific parameters can only be specified during the
Login Phase of the first connection of a session (i.e., begun by a
Login Request that contains a zero-valued TSIH) - the leading Login
Phase (e.g., the maximum number of connections that can be used for
this session).
A session is operational once it has at least one connection in
FullFeaturePhase. New or replacement connections can only be added
to a session after the session is operational.
For operational parameters, see Chapter 12.
5.3.4. Connection Reinstatement
Connection reinstatement is the process of an initiator logging in
with an ISID-TSIH-CID combination that is possibly active from the
target's perspective, which causes the implicit logging out of the
connection corresponding to the CID, and reinstating a new Full
Feature Phase iSCSI connection in its place (with the same CID).
Thus, the TSIH in the Login PDU MUST be non-zero and the CID does not
change during a connection reinstatement. The Login Request performs
the logout function of the old connection if an explicit logout was
not performed earlier. In sessions with a single connection, this
may imply the opening of a second connection with the sole purpose of
cleaning up the first. Targets MUST support opening a second
connection even when they do not support multiple connections in Full
Feature Phase if ErrorRecoveryLevel is 2 and SHOULD support opening a
second connection if ErrorRecoveryLevel is less than 2.
If the operational ErrorRecoveryLevel is 2, connection reinstatement
enables future task reassignment. If the operational
ErrorRecoveryLevel is less than 2, connection reinstatement is the
replacement of the old CID without enabling task reassignment. In
this case, all the tasks that were active on the old CID must be
immediately terminated without further notice to the initiator.
The initiator connection state MUST be CLEANUP_WAIT (section 7.1.3)
when the initiator attempts a connection reinstatement.
In practical terms, in addition to the implicit logout of the old
connection, reinstatement is equivalent to a new connection login.
5.3.5. Session Reinstatement, Closure, and Timeout
Session reinstatement is the process of the initiator logging in with
an ISID that is possibly active from the target's perspective. Thus
implicitly logging out the session that corresponds to the ISID and
reinstating a new iSCSI session in its place (with the same ISID).
Therefore, the TSIH in the Login PDU MUST be zero to signal session
reinstatement. Session reinstatement causes all the tasks that were
active on the old session to be immediately terminated by the target
without further notice to the initiator.
The initiator session state MUST be FAILED (Section 7.3 Session State
Diagrams) when the initiator attempts a session reinstatement.
Session closure is an event defined to be one of the following:
- A successful "session close" logout.
- A successful "connection close" logout for the last Full Feature
Phase connection when no other connection in the session is
waiting for cleanup (Section 7.2 Connection Cleanup State Diagram
for Initiators and Targets) and no tasks in the session are
waiting for reassignment.
Session timeout is an event defined to occur when the last connection
state timeout expires and no tasks are waiting for reassignment.
This takes the session to the FREE state (N6 transition in the
session state diagram).
5.3.5.1. Loss of Nexus Notification
The iSCSI layer provides the SCSI layer with the "I_T nexus loss"
notification when any one of the following events happens:
a) Successful completion of session reinstatement.
b) Session closure event.
c) Session timeout event.
Certain SCSI object clearing actions may result due to the
notification in the SCSI end nodes, as documented in Appendix F.
- Clearing Effects of Various Events on Targets -.
5.3.6. Session Continuation and Failure
Session continuation is the process by which the state of a
preexisting session continues to be used by connection reinstatement
(Section 5.3.4 Connection Reinstatement), or by adding a connection
with a new CID. Either of these actions associates the new transport
connection with the session state.
Session failure is an event where the last Full Feature Phase
connection reaches the CLEANUP_WAIT state (Section 7.2 Connection
Cleanup State Diagram for Initiators and Targets), or completes a
successful recovery logout, thus causing all active tasks (that are
formerly allegiant to the connection) to start waiting for task
reassignment.
5.4. Operational Parameter Negotiation Outside the Login Phase
Some operational parameters MAY be negotiated outside (after) the
Login Phase.
Parameter negotiation in Full Feature Phase is done through Text
requests and responses. Operational parameter negotiation MAY
involve several Text request-response exchanges, which the initiator
always starts and terminates using the same Initiator Task Tag. The
initiator MUST indicate its intent to terminate the negotiation by
setting the F bit to 1; the target sets the F bit to 1 on the last
response.
If the target responds to a Text request with the F bit set to 1 and
with a Text response with the F bit set to 0, the initiator should
keep sending the Text request (even empty) with the F bit set to 1,
while it still wants to finish the negotiation, until it receives the
Text response with the F bit set to 1. Responding to a Text request
with the F bit set to 1 with an empty (no key=value pairs) response
with the F bit set to 0 is discouraged.
Targets MUST NOT submit parameters that require an additional
initiator Text request in a Text response with the F bit set to 1.
In a negotiation sequence, the F bit settings in one pair of Text
request-responses have no bearing on the F bit settings of the next
pair. An initiator that has the F bit set to 1 in a request and is
being answered with an F bit setting of 0 may issue the next request
with the F bit set to 0.
Whenever the target responds with the F bit set to 0, it MUST set the
Target Transfer Tag to a value other than the default 0xffffffff.
An initiator MAY reset an operational parameter negotiation by
issuing a Text request with the Target Transfer Tag set to the value
0xffffffff after receiving a response with the Target Transfer Tag
set to a value other than 0xffffffff. A target may reset an
operational parameter negotiation by answering a Text request with a
Reject PDU.
Neither the initiator nor the target should attempt to declare or
negotiate a parameter more than once during any negotiation sequence
without an intervening operational parameter negotiation reset,
except for responses to specific keys that explicitly allow repeated
key declarations (e.g., TargetAddress). If detected by the target,
this MUST result in a Reject PDU with a reason of "protocol error".
The initiator MUST reset the negotiation as outlined above.
Parameters negotiated by a text exchange negotiation sequence only
become effective after the negotiation sequence is completed.
6. iSCSI Error Handling and Recovery
6.1. Overview
6.1.1. Background
The following two considerations prompted the design of much of the
error recovery functionality in iSCSI:
i) An iSCSI PDU may fail the digest check and be dropped, despite
being received by the TCP layer. The iSCSI layer must
optionally be allowed to recover such dropped PDUs.
ii) A TCP connection may fail at any time during the data
transfer. All the active tasks must optionally be allowed to
continue on a different TCP connection within the same
session.
Implementations have considerable flexibility in deciding what degree
of error recovery to support, when to use it and by which mechanisms
to achieve the required behavior. Only the externally visible
actions of the error recovery mechanisms must be standardized to
ensure interoperability.
This chapter describes a general model for recovery in support of
interoperability. See Appendix E. - Algorithmic Presentation of
Error Recovery Classes - for further detail on how the described
model may be implemented. Compliant implementations do not have to
match the implementation details of this model as presented, but the
external behavior of such implementations must correspond to the
externally observable characteristics of the presented model.
6.1.2. Goals
The major design goals of the iSCSI error recovery scheme are as
follows:
a) Allow iSCSI implementations to meet different requirements by
defining a collection of error recovery mechanisms that
implementations may choose from.
b) Ensure interoperability between any two implementations
supporting different sets of error recovery capabilities.
c) Define the error recovery mechanisms to ensure command
ordering even in the face of errors, for initiators that
demand ordering.
d) Do not make additions in the fast path, but allow moderate
complexity in the error recovery path.
e) Prevent both the initiator and target from attempting to
recover the same set of PDUs at the same time. For example,
there must be a clear "error recovery functionality
distribution" between the initiator and target.
6.1.3. Protocol Features and State Expectations
The initiator mechanisms defined in connection with error recovery
are:
a) NOP-OUT to probe sequence numbers of the target (section
10.18)
b) Command retry (section 6.2.1)
c) Recovery R2T support (section 6.7)
d) Requesting retransmission of status/data/R2T using the SNACK
facility (section 10.16)
e) Acknowledging the receipt of the data (section 10.16)
f) Reassigning the connection allegiance of a task to a different
TCP connection (section 6.2.2)
g) Terminating the entire iSCSI session to start afresh (section
6.1.4.4)
The target mechanisms defined in connection with error recovery are:
a) NOP-IN to probe sequence numbers of the initiator (section
10.19)
b) Requesting retransmission of data using the recovery R2T
feature (section 6.7)
c) SNACK support (section 10.16) d) Requesting that parts of
read data be acknowledged (section 10.7.2)
e) Allegiance reassignment support (section 6.2.2)
f) Terminating the entire iSCSI session to force the initiator to
start over (section 6.1.4.4)
For any outstanding SCSI command, it is assumed that iSCSI, in
conjunction with SCSI at the initiator, is able to keep enough
information to be able to rebuild the command PDU, and that outgoing
data is available (in host memory) for retransmission while the
command is outstanding. It is also assumed that at the target,
incoming data (read data) MAY be kept for recovery or it can be
reread from a device server.
It is further assumed that a target will keep the "status & sense"
for a command it has executed if it supports status retransmission.
A target that agrees to support data retransmission is expected to be
prepared to retransmit the outgoing data (i.e., Data-In) on request
until either the status for the completed command is acknowledged, or
the data in question has been separately acknowledged.
6.1.4. Recovery Classes
iSCSI enables the following classes of recovery (in the order of
increasing scope of affected iSCSI tasks):
- Within a command (i.e., without requiring command restart).
- Within a connection (i.e., without requiring the connection to
be rebuilt, but perhaps requiring command restart).
- Connection recovery (i.e., perhaps requiring connections to be
rebuilt and commands to be reissued).
- Session recovery.
The recovery scenarios detailed in the rest of this section are
representative rather than exclusive. In every case, they detail the
lowest class recovery that MAY be attempted. The implementer is left
to decide under which circumstances to escalate to the next recovery
class and/or what recovery classes to implement. Both the iSCSI
target and initiator MAY escalate the error handling to an error
recovery class, which impacts a larger number of iSCSI tasks in any
of the cases identified in the following discussion.
In all classes, the implementer has the choice of deferring errors to
the SCSI initiator (with an appropriate response code), in which case
the task, if any, has to be removed from the target and all the side
effects, such as ACA, must be considered.
Use of within-connection and within-command recovery classes MUST NOT
be attempted before the connection is in Full Feature Phase.
In the detailed description of the recovery classes, the mandating
terms (MUST, SHOULD, MAY, etc.) indicate normative actions to be
executed if the recovery class is supported and used.
6.1.4.1. Recovery Within-command
At the target, the following cases lend themselves to
within-command recovery:
- Lost data PDU - realized through one of the following:
a) Data digest error - dealt with as specified in Section 6.7
Digest Errors, using the option of a recovery R2T.
b) Sequence reception timeout (no data or
partial-data-and-no-F-bit) - considered an implicit sequence
error and dealt with as specified in Section 6.8 Sequence
Errors, using the option of a recovery R2T.
c) Header digest error, which manifests as a sequence reception
timeout or a sequence error - dealt with as specified in
Section 6.8 Sequence Errors, using the option of a recovery
R2T.
At the initiator, the following cases lend themselves to
within-command recovery:
Lost data PDU or lost R2T - realized through one of the
following:
a) Data digest error - dealt with as specified in Section 6.7
Digest Errors, using the option of a SNACK.
b) Sequence reception timeout (no status) or response reception
timeout - dealt with as specified in Section 6.8 Sequence
Errors, using the option of a SNACK.
c) Header digest error, which manifests as a sequence reception
timeout or a sequence error - dealt with as specified in
Section 6.8 Sequence Errors, using the option of a SNACK.
To avoid a race with the target, which may already have a recovery
R2T or a termination response on its way, an initiator SHOULD NOT
originate a SNACK for an R2T based on its internal timeouts (if any).
Recovery in this case is better left to the target.
The timeout values used by the initiator and target are outside the
scope of this document. Sequence reception timeout is generally a
large enough value to allow the data sequence transfer to be
complete.
6.1.4.2. Recovery Within-connection
At the initiator, the following cases lend themselves to
within-connection recovery:
- Requests not acknowledged for a long time. Requests are
acknowledged explicitly through ExpCmdSN or implicitly by
receiving data and/or status. The initiator MAY retry
non-acknowledged commands as specified in Section 6.2 Retry and
Reassign in Recovery.
- Lost iSCSI numbered Response. It is recognized by either
identifying a data digest error on a Response PDU or a Data-In
PDU carrying the status, or by receiving a Response PDU with a
higher StatSN than expected. In the first case, digest error
handling is done as specified in Section 6.7 Digest Errors using
the option of a SNACK. In the second case, sequence error
handling is done as specified in Section 6.8 Sequence Errors,
using the option of a SNACK.
At the target, the following cases lend themselves to
within-connection recovery:
- Status/Response not acknowledged for a long time. The target MAY
issue a NOP-IN (with a valid Target Transfer Tag or otherwise)
that carries the next status sequence number it is going to use
in the StatSN field. This helps the initiator detect any missing
StatSN(s) and issue a SNACK for the status.
The timeout values used by the initiator and the target are outside
the scope of this document.
6.1.4.3. Connection Recovery
At an iSCSI initiator, the following cases lend themselves to
connection recovery:
- TCP connection failure: The initiator MUST close the connection.
It then MUST either implicitly or explicitly logout the failed
connection with the reason code "remove the connection for
recovery" and reassign connection allegiance for all commands
still in progress associated with the failed connection on one or
more connections (some or all of which MAY be newly established
connections) using the "Task reassign" task management function
(see Section 10.5.1 Function). For an initiator, a command is in
progress as long as it has not received a response or a Data-In
PDU including status.
Note: The logout function is mandatory. However, a new connection
establishment is only mandatory if the failed connection was the
last or only connection in the session.
- Receiving an Asynchronous Message that indicates one or all
connections in a session has been dropped. The initiator MUST
handle it as a TCP connection failure for the connection(s)
referred to in the Message.
At an iSCSI target, the following cases lend themselves to connection
recovery:
- TCP connection failure. The target MUST close the connection and,
if more than one connection is available, the target SHOULD send
an Asynchronous Message that indicates it has dropped the
connection. Then, the target will wait for the initiator to
continue recovery.
6.1.4.4. Session Recovery
Session recovery should be performed when all other recovery attempts
have failed. Very simple initiators and targets MAY perform session
recovery on all iSCSI errors and rely on recovery on the SCSI layer
and above.
Session recovery implies the closing of all TCP connections,
internally aborting all executing and queued tasks for the given
initiator at the target, terminating all outstanding SCSI commands
with an appropriate SCSI service response at the initiator, and
restarting a session on a new set of connection(s) (TCP connection
establishment and login on all new connections).
For possible clearing effects of session recovery on SCSI and iSCSI
objects, refer to Appendix F. - Clearing Effects of Various Events on
Targets -.
6.1.5. Error Recovery Hierarchy
The error recovery classes described so far are organized into a
hierarchy for ease in understanding and to limit the implementation
complexity. With few and well defined recovery levels
interoperability is easier to achieve. The attributes of this
hierarchy are as follows:
a) Each level is a superset of the capabilities of the previous
level. For example, Level 1 support implies supporting all
capabilities of Level 0 and more.
b) As a corollary, supporting a higher error recovery level means
increased sophistication and possibly an increase in resource
requirements.
c) Supporting error recovery level "n" is advertised and
negotiated by each iSCSI entity by exchanging the text key
"ErrorRecoveryLevel=n". The lower of the two exchanged values
is the operational ErrorRecoveryLevel for the session.
The following diagram represents the error recovery hierarchy.
+
/
/ 2 \ <-- Connection recovery
+-----+
/ 1 \ <-- Digest failure recovery
+---------+
/ 0 \ <-- Session failure recovery
+-------------+
The following table lists the error recovery capabilities expected
from the implementations that support each error recovery level.
+-------------------+--------------------------------------------+
|ErrorRecoveryLevel | Associated Error recovery capabilities |
+-------------------+--------------------------------------------+
| 0 | Session recovery class |
| | (Section 6.1.4.4 Session Recovery) |
+-------------------+--------------------------------------------+
| 1 | Digest failure recovery (See Note below.) |
| | plus the capabilities of ER Level 0 |
+-------------------+--------------------------------------------+
| 2 | Connection recovery class |
| | (Section 6.1.4.3 Connection Recovery) |
| | plus the capabilities of ER Level 1 |
+-------------------+--------------------------------------------+
Note: Digest failure recovery is comprised of two recovery classes:
Within-Connection recovery class (Section 6.1.4.2 Recovery Within-
connection) and Within-Command recovery class (Section 6.1.4.1
Recovery Within-command).
When a defined value of ErrorRecoveryLevel is proposed by an
originator in a text negotiation, the originator MUST support the
functionality defined for the proposed value and additionally, the
functionality corresponding to any defined value numerically less
than the proposed. When a defined value of ErrorRecoveryLevel is
returned by a responder in a text negotiation, the responder MUST
support the functionality corresponding to the ErrorRecoveryLevel it
is accepting.
When either party attempts to use error recovery functionality beyond
what is negotiated, the recovery attempts MAY fail unless an a priori
agreement outside the scope of this document exists between the two
parties to provide such support.
Implementations MUST support error recovery level "0", while the rest
are OPTIONAL to implement. In implementation terms, the above
striation means that the following incremental sophistication with
each level is required.
+-------------------+---------------------------------------------+
|Level transition | Incremental requirement |
+-------------------+---------------------------------------------+
| 0->1 | PDU retransmissions on the same connection |
+-------------------+---------------------------------------------+
| 1->2 | Retransmission across connections and |
| | allegiance reassignment |
+-------------------+---------------------------------------------+
6.2. Retry and Reassign in Recovery
This section summarizes two important and somewhat related iSCSI
protocol features used in error recovery.
6.2.1. Usage of Retry
By resending the same iSCSI command PDU ("retry") in the absence of a
command acknowledgement (by way of an ExpCmdSN update) or a response,
an initiator attempts to "plug" (what it thinks are) the
discontinuities in CmdSN ordering on the target end. Discarded
command PDUs, due to digest errors, may have created these
discontinuities.
Retry MUST NOT be used for reasons other than plugging command
sequence gaps, and in particular, cannot be used for requesting PDU
retransmissions from a target. Any such PDU retransmission requests
for a currently allegiant command in progress may be made using the
SNACK mechanism described in section 10.16, although the usage of
SNACK is OPTIONAL.
If initiators, as part of plugging command sequence gaps as described
above, inadvertently issue retries for allegiant commands already in
progress (i.e., targets did not see the discontinuities in CmdSN
ordering), the duplicate commands are silently ignored by targets as
specified in section 3.2.2.1.
When an iSCSI command is retried, the command PDU MUST carry the
original Initiator Task Tag and the original operational attributes
(e.g., flags, function names, LUN, CDB etc.) as well as the original
CmdSN. The command being retried MUST be sent on the same connection
as the original command unless the original connection was already
successfully logged out.
6.2.2. Allegiance Reassignment
By issuing a "task reassign" task management request (Section 10.5.1
Function), the initiator signals its intent to continue an already
active command (but with no current connection allegiance) as part of
connection recovery. This means that a new connection allegiance is
requested for the command, which seeks to associate it to the
connection on which the task management request is being issued.
Before the allegiance reassignment is attempted for a task, an
implicit or explicit Logout with the reason code "remove the
connection for recovery" ( see section 10.14) MUST be successfully
completed for the previous connection to which the task was
allegiant.
In reassigning connection allegiance for a command, the targets
SHOULD continue the command from its current state. For example,
when reassigning read commands, the target SHOULD take advantage of
the ExpDataSN field provided by the Task Management function request
(which must be set to zero if there was no data transfer) and bring
the read command to completion by sending the remaining data and
sending (or resending) the status. ExpDataSN acknowledges all data
sent up to, but not including, the Data-In PDU and or R2T with DataSN
(or R2TSN) equal to ExpDataSN. However, targets may choose to
send/receive all unacknowledged data or all of the data on a
reassignment of connection allegiance if unable to recover or
maintain an accurate state. Initiators MUST not subsequently request
data retransmission through Data SNACK for PDUs numbered less than
ExpDataSN (i.e., prior to the acknowledged sequence number). For all
types of commands, a reassignment request implies that the task is
still considered in progress by the initiator and the target must
conclude the task appropriately if the target returns the "Function
Complete" response to the reassignment request. This might possibly
involve retransmission of data/R2T/status PDUs as necessary, but MUST
involve the (re)transmission of the status PDU.
It is OPTIONAL for targets to support the allegiance reassignment.
This capability is negotiated via the ErrorRecoveryLevel text key
during the login time. When a target does not support allegiance
reassignment, it MUST respond with a Task Management response code of
"Allegiance reassignment not supported". If allegiance reassignment
is supported by the target, but the task is still allegiant to a
different connection, or a successful recovery Logout of the
previously allegiant connection was not performed, the target MUST
respond with a Task Management response code of "Task still
allegiant".
If allegiance reassignment is supported by the target, the Task
Management response to the reassignment request MUST be issued before
the reassignment becomes effective.
If a SCSI Command that involves data input is reassigned, any SNACK
Tag it holds for a final response from the original connection is
deleted and the default value of 0 MUST be used instead.
6.3. Usage Of Reject PDU in Recovery
Targets MUST NOT implicitly terminate an active task by sending a
Reject PDU for any PDU exchanged during the life of the task. If the
target decides to terminate the task, a Response PDU (SCSI, Text,
Task, etc.) must be returned by the target to conclude the task. If
the task had never been active before the Reject (i.e., the Reject is
on the command PDU), targets should not send any further responses
because the command itself is being discarded.
The above rule means that the initiator can eventually expect a
response on receiving Rejects, if the received Reject is for a PDU
other than the command PDU itself. The non-command Rejects only have
diagnostic value in logging the errors, and they can be used for
retransmission decisions by the initiators.
The CmdSN of the rejected command PDU (if it is a non-immediate
command) MUST NOT be considered received by the target (i.e., a
command sequence gap must be assumed for the CmdSN), even though the
CmdSN of the rejected command PDU may be reliably ascertained. Upon
receiving the Reject, the initiator MUST plug the CmdSN gap in order
to continue to use the session. The gap may be plugged either by
transmitting a command PDU with the same CmdSN, or by aborting the
task (see section 6.9 on how an abort may plug a CmdSN gap).
When a data PDU is rejected and its DataSN can be ascertained, a
target MUST advance ExpDataSN for the current data burst if a
recovery R2T is being generated. The target MAY advance its
ExpDataSN if it does not attempt to recover the lost data PDU.
6.4. Connection Timeout Management
iSCSI defines two session-global timeout values (in seconds)
- Time2Wait and Time2Retain - that are applicable when an iSCSI Full
Feature Phase connection is taken out of service either intentionally
or by an exception. Time2Wait is the initial "respite time" before
attempting an explicit/implicit Logout for the CID in question or
task reassignment for the affected tasks (if any). Time2Retain is
the maximum time after the initial respite interval that the task
and/or connection state(s) is/are guaranteed to be maintained on the
target to cater to a possible recovery attempt. Recovery attempts
for the connection and/or task(s) SHOULD NOT be made before Time2Wait
seconds, but MUST be completed within Time2Retain seconds after that
initial Time2Wait waiting period.
6.4.1. Timeouts on Transport Exception Events
A transport connection shutdown or a transport reset without any
preceding iSCSI protocol interactions informing the end-points of the
fact causes a Full Feature Phase iSCSI connection to be abruptly
terminated. The timeout values to be used in this case are the
negotiated values of defaultTime2Wait (Section 12.15
DefaultTime2Wait) and DefaultTime2Retain (Section 12.16
DefaultTime2Retain) text keys for the session.
6.4.2. Timeouts on Planned Decommissioning
Any planned decommissioning of a Full Feature Phase iSCSI connection
is preceded by either a Logout Response PDU, or an Async Message PDU.
The Time2Wait and Time2Retain field values (section 10.15) in a
Logout Response PDU, and the Parameter2 and Parameter3 fields of an
Async Message (AsyncEvent types "drop the connection" or "drop all
the connections"; section 10.9.1) specify the timeout values to be
used in each of these cases.
These timeout values are only applicable for the affected connection,
and the tasks active on that connection. These timeout values have
no bearing on initiator timers (if any) that are already running on
connections or tasks associated with that session.
6.5. Implicit Termination of Tasks
A target implicitly terminates the active tasks due to iSCSI protocol
dynamics in the following cases:
a) When a connection is implicitly or explicitly logged out with
the reason code of "Close the connection" and there are active
tasks allegiant to that connection.
b) When a connection fails and the connection state eventually
times out (state transition M1 in Section 7.2.2 State
Transition Descriptions for Initiators and Targets) and there
are active tasks allegiant to that connection.
c) When a successful Logout with the reason code of "remove the
connection for recovery" is performed while there are active
tasks allegiant to that connection, and those tasks eventually
time out after the Time2Wait and Time2Retain periods without
allegiance reassignment.
d) When a connection is implicitly or explicitly logged out with
the reason code of "Close the session" and there are active
tasks in that session.
If the tasks terminated in the above cases a), b, c) and d)are SCSI
tasks, they must be internally terminated as if with CHECK CONDITION
status. This status is only meaningful for appropriately handling
the internal SCSI state and SCSI side effects with respect to
ordering because this status is never communicated back as a
terminating status to the initiator. However additional actions may
have to be taken at SCSI level depending on the SCSI context as
defined by the SCSI standards (e.g., queued commands and ACA, in
cases a), b), and c), after the tasks are terminated, the target MUST
report a Unit Attention condition on the next command processed on
any connection for each affected I_T_L nexus with the status of CHECK
CONDITION, and the ASC/ASCQ value of 47h/7Fh - "SOME COMMANDS CLEARED
BY ISCSI PROTOCOL EVENT" , etc. - see [SAM2] and [SPC3]).
6.6. Format Errors
The following two explicit violations of PDU layout rules are format
errors:
a) Illegal contents of any PDU header field except the Opcode
(legal values are specified in Section 10 iSCSI PDU Formats).
b) Inconsistent field contents (consistent field contents are
specified in Section 10 iSCSI PDU Formats).
Format errors indicate a major implementation flaw in one of the
parties.
When a target or an initiator receives an iSCSI PDU with a format
error, it MUST immediately terminate all transport connections in the
session either with a connection close or with a connection reset and
escalate the format error to session recovery (see Section 6.1.4.4
Session Recovery).
6.7. Digest Errors
The discussion of the legal choices in handling digest errors below
excludes session recovery as an explicit option, but either party
detecting a digest error may choose to escalate the error to session
recovery.
When a target or an initiator receives any iSCSI PDU, with a header
digest error, it MUST either discard the header and all data up to
the beginning of a later PDU or close the connection. Because the
digest error indicates that the length field of the header may have
been corrupted, the location of the beginning of a later PDU needs to
be reliably ascertained by other means such as the operation of a
sync and steering layer.
When a target receives any iSCSI PDU with a payload digest error, it
MUST answer with a Reject PDU with a reason code of
Data-Digest-Error and discard the PDU.
- If the discarded PDU is a solicited or unsolicited iSCSI data
PDU (for immediate data in a command PDU, non-data PDU rule
below applies), the target MUST do one of the following:
a) Request retransmission with a recovery R2T.
b) Terminate the task with a response PDU with a CHECK
CONDITION Status and an iSCSI Condition of "protocol service
CRC error" (Section 10.4.7.2 Sense Data). If the target
chooses to implement this option, it MUST wait to receive
all the data (signaled by a Data PDU with the final bit set
for all outstanding R2Ts) before sending the response PDU.
A task management command (such as an abort task) from the
initiator during this wait may also conclude the task.
- No further action is necessary for targets if the discarded PDU
is a non-data PDU. In case of immediate data being present on
a discarded command, the immediate data is implicitly recovered
when the task is retried (see section 6.2.1), followed by the
entire data transfer for the task.
When an initiator receives any iSCSI PDU with a payload digest error,
it MUST discard the PDU.
- If the discarded PDU is an iSCSI data PDU, the initiator MUST do
one of the following:
a) Request the desired data PDU through SNACK. In response to the
SNACK, the target MUST either resend the data PDU or reject the
SNACK with a Reject PDU with a reason code of "SNACK reject" in
which case:
i) If the status has not already been sent for the command,
the target MUST terminate the command with a CHECK
CONDITION Status and an iSCSI Condition of "SNACK rejected"
(Section 10.4.7.2 Sense Data).
ii) If the status was already sent, no further action is
necessary for the target. The initiator in this case MUST
wait for the status to be received and then discard it, so
as to internally signal the completion with CHECK CONDITION
Status and an iSCSI Condition of "protocol service CRC
error" (Section 10.4.7.2 Sense Data).
b) Abort the task and terminate the command with an error.
- If the discarded PDU is a response PDU, the initiator MUST do one
of the following:
a) Request PDU retransmission with a status SNACK.
b) Logout the connection for recovery and continue the tasks on a
different connection instance as described in Section 6.2 Retry
and Reassign in Recovery.
c) Logout to close the connection (abort all the commands
associated with the connection).
- No further action is necessary for initiators if the discarded PDU
is an unsolicited PDU (e.g., Async, Reject). Task timeouts as in
the initiator waiting for a command completion, or process
timeouts, as in the target waiting for a Logout, will ensure that
the correct operational behavior will result in these cases
despite the discarded PDU.
6.8. Sequence Errors
When an initiator receives an iSCSI R2T/data PDU with an out of order
R2TSN/DataSN or a SCSI response PDU with an ExpDataSN that implies
missing data PDU(s), it means that the initiator must have detected a
header or payload digest error on one or more earlier R2T/data PDUs.
The initiator MUST address these implied digest errors as described
in Section 6.7 Digest Errors. When a target receives a data PDU with
an out of order DataSN, it means that the target must have hit a
header or payload digest error on at least one of the earlier data
PDUs. The target MUST address these implied digest errors as
described in Section 6.7 Digest Errors.
When an initiator receives an iSCSI status PDU with an out of order
StatSN that implies missing responses, it MUST address the one or
more missing status PDUs as described in Section 6.7 Digest Errors.
As a side effect of receiving the missing responses, the initiator
may discover missing data PDUs. If the initiator wants to recover
the missing data for a command, it MUST NOT acknowledge the received
responses that start from the StatSN of the relevant command, until
it has completed receiving all the data PDUs of the command.
When an initiator receives duplicate R2TSNs (due to proactive
retransmission of R2Ts by the target) or duplicate DataSNs (due to
proactive SNACKs by the initiator), it MUST discard the duplicates.
6.9. SCSI Timeouts
An iSCSI initiator MAY attempt to plug a command sequence gap on the
target end (in the absence of an acknowledgement of the command by
way of ExpCmdSN) before the ULP timeout by retrying the
unacknowledged command, as described in Section 6.2 Retry and
Reassign in Recovery.
On a ULP timeout for a command (that carried a CmdSN of n), if the
iSCSI initiator intends to continue the session, it MUST abort the
command by either using an appropriate Task Management function
request for the specific command, or a "close the connection" Logout.
When using an ABORT TASK, if the ExpCmdSN is still less than (n+1),
the target may see the abort request while missing the original
command itself due to one of the following reasons:
- Original command was dropped due to digest error.
- Connection on which the original command was sent was
successfully logged out. Upon logout, the unacknowledged
commands issued on the connection being logged out are
discarded.
If the abort request is received and the original command is missing,
targets MUST consider the original command with that RefCmdSN to be
received and issue a Task Management response with the response code:
"Function Complete". This response concludes the task on both ends.
If the abort request is received and the target can determine (based
on the Referenced Task Tag) that the command was received and
executed and also that the response was sent prior to the abort, then
the target MUST respond with the response code of "Task Does Not
Exist".
6.10. Negotiation Failures
Text request and response sequences, when used to set/negotiate
operational parameters, constitute the negotiation/parameter setting.
A negotiation failure is considered to be one or more of the
following:
- None of the choices, or the stated value, is acceptable to one
of the sides in the negotiation.
- The text request timed out and possibly terminated.
- The text request was answered with a Reject PDU.
The following two rules should be used to address negotiation
failures:
- During Login, any failure in negotiation MUST be considered a
login process failure and the Login Phase must be terminated,
and with it, the connection. If the target detects the
failure, it must terminate the login with the appropriate Login
Response code.
- A failure in negotiation, while in the Full Feature Phase, will
terminate the entire negotiation sequence that may consist of a
series of text requests that use the same Initiator Task Tag.
The operational parameters of the session or the connection
MUST continue to be the values agreed upon during an earlier
successful negotiation (i.e., any partial results of this
unsuccessful negotiation MUST NOT take effect and MUST be
discarded).
6.11. Protocol Errors
Mapping framed messages over a "stream" connection, such as TCP,
makes the proposed mechanisms vulnerable to simple software framing
errors. On the other hand, the introduction of framing mechanisms to
limit the effects of these errors may be onerous on performance for
simple implementations. Command Sequence Numbers and the above
mechanisms for connection drop and reestablishment help handle this
type of mapping errors.
All violations of iSCSI PDU exchange sequences specified in this
document are also protocol errors. This category of errors can only
be addressed by fixing the implementations; iSCSI defines Reject and
response codes to enable this.
6.12. Connection Failures
iSCSI can keep a session in operation if it is able to
keep/establish at least one TCP connection between the initiator and
the target in a timely fashion. Targets and/or initiators may
recognize a failing connection by either transport level means (TCP),
a gap in the command sequence number, a response stream that is not
filled for a long time, or by a failing iSCSI NOP (acting as a ping).
The latter MAY be used periodically to increase the speed and
likelihood of detecting connection failures. Initiators and targets
MAY also use the keep-alive option on the TCP connection to enable
early link failure detection on otherwise idle links.
On connection failure, the initiator and target MUST do one of the
following:
- Attempt connection recovery within the session (Section 6.1.4.3
Connection Recovery).
- Logout the connection with the reason code "closes the
connection" (Section 10.14.5 Implicit termination of tasks),
re-issue missing commands, and implicitly terminate all active
commands. This option requires support for the
within-connection recovery class (Section 6.1.4.2 Recovery
Within-connection).
- Perform session recovery (Section 6.1.4.4 Session Recovery).
Either side may choose to escalate to session recovery (via the
initiator dropping all the connections, or via an Async Message that
announces the similar intent from a target), and the other side MUST
give it precedence. On a connection failure, a target MUST terminate
and/or discard all of the active immediate commands regardless of
which of the above options is used (i.e., immediate commands are not
recoverable across connection failures).
6.13. Session Errors
If all of the connections of a session fail and cannot be
reestablished in a short time, or if initiators detect protocol
errors repeatedly, an initiator may choose to terminate a session and
establish a new session.
In this case, the initiator takes the following actions:
- Resets or closes all the transport connections.
- Terminates all outstanding requests with an appropriate
response before initiating a new session. If the same I_T
nexus is intended to be reestablished, the initiator MUST
employ session reinstatement (see section 5.3.5).
When the session timeout (the connection state timeout for the last
failed connection) happens on the target, it takes the following
actions:
- Resets or closes the TCP connections (closes the session).
- Terminates all active tasks that were allegiant to the
connection(s) that constituted the session.
A target MUST also be prepared to handle a session reinstatement
request from the initiator, that may be addressing session errors.
7. State Transitions
iSCSI connections and iSCSI sessions go through several well-defined
states from the time they are created to the time they are cleared.
The connection state transitions are described in two separate but
dependent state diagrams for ease in understanding. The first
diagram, "standard connection state diagram", describes the
connection state transitions when the iSCSI connection is not waiting
for, or undergoing, a cleanup by way of an explicit or implicit
Logout. The second diagram, "connection cleanup state diagram",
describes the connection state transitions while performing the iSCSI
connection cleanup.
The "session state diagram" describes the state transitions an iSCSI
session would go through during its lifetime, and it depends on the
states of possibly multiple iSCSI connections that participate in the
session.
States and state transitions are described in the text, tables and
diagrams. The diagrams are used for illustration. The text and the
tables are the governing specification.
7.1. Standard Connection State Diagrams
7.1.1. State Descriptions for Initiators and Targets
State descriptions for the standard connection state diagram are as
follows:
-S1: FREE
-initiator: State on instantiation, or after successful
connection closure.
-target: State on instantiation, or after successful connection
closure.
-S2: XPT_WAIT
-initiator: Waiting for a response to its transport connection
establishment request.
-target: Illegal
-S3: XPT_UP
-initiator: Illegal
-target: Waiting for the Login process to commence.
-S4: IN_LOGIN
-initiator: Waiting for the Login process to conclude, possibly
involving several PDU exchanges.
-target: Waiting for the Login process to conclude, possibly
involving several PDU exchanges.
-S5: LOGGED_IN
-initiator: In Full Feature Phase, waiting for all internal,
iSCSI, and transport events.
-target: In Full Feature Phase, waiting for all internal, iSCSI,
and transport events.
-S6: IN_LOGOUT
-initiator: Waiting for a Logout response.
-target: Waiting for an internal event signaling completion of
logout processing.
-S7: LOGOUT_REQUESTED
-initiator: Waiting for an internal event signaling readiness to
proceed with Logout.
-target: Waiting for the Logout process to start after having
requested a Logout via an Async Message.
-S8: CLEANUP_WAIT
-initiator: Waiting for the context and/or resources to initiate
the cleanup processing for this CSM.
-target: Waiting for the cleanup process to start for this CSM.
7.1.2. State Transition Descriptions for Initiators and Targets
-T1:
-initiator: Transport connect request was made (e.g., TCP SYN
sent).
-target: Illegal
-T2:
-initiator: Transport connection request timed out, a transport
reset was received, or an internal event of receiving a
Logout response (success) on another connection for a
"close the session" Logout request was received.
-target:Illegal
-T3:
-initiator: Illegal
-target: Received a valid transport connection request that
establishes the transport connection.
-T4:
-initiator: Transport connection established, thus prompting the
initiator to start the iSCSI Login.
-target: Initial iSCSI Login Request was received.
-T5:
-initiator: The final iSCSI Login Response with a Status-Class
of zero was received.
-target: The final iSCSI Login Request to conclude the Login
Phase was received, thus prompting the target to send the
final iSCSI Login Response with a Status-Class of zero.
-T6:
-initiator: Illegal
-target: Timed out waiting for an iSCSI Login, transport
disconnect indication was received, transport reset was
received, or an internal event indicating a transport
timeout was received. In all these cases, the connection is
to be closed.
-T7:
-initiator - one of the following events caused the transition:
- The final iSCSI Login Response was received with a
non-zero Status-Class.
- Login timed out.
- A transport disconnect indication was received.
- A transport reset was received.
- An internal event was received indicating a transport
timeout.
- An internal event of receiving a Logout response (success)
on another connection for a "close the session" Logout
request was received.
In all these cases, the transport connection is closed.
-target - one of the following events caused the transition:
- The final iSCSI Login Request to conclude the Login Phase
was received, prompting the target to send the final iSCSI
Login Response with a non-zero Status-Class.
- Login timed out.
- Transport disconnect indication was received.
- Transport reset was received.
- An internal event indicating a transport timeout was
received.
- On another connection a "close the session" Logout request
was received.
In all these cases, the connection is to be closed.
-T8:
-initiator: An internal event of receiving a Logout response
(success) on another connection for a "close the session"
Logout request was received, thus closing this connection
requiring no further cleanup.
-target: An internal event of sending a Logout response
(success) on another connection for a "close the session"
Logout request was received, or an internal event of a
successful connection/session reinstatement is received,
thus prompting the target to close this connection cleanly.
-T9, T10:
-initiator: An internal event that indicates the readiness to
start the Logout process was received, thus prompting an
iSCSI Logout to be sent by the initiator.
-target: An iSCSI Logout request was received.
-T11, T12:
-initiator: Async PDU with AsyncEvent "Request Logout" was
received.
-target: An internal event that requires the decommissioning of
the connection is received, thus causing an Async PDU with
an AsyncEvent "Request Logout" to be sent.
-T13:
-initiator: An iSCSI Logout response (success) was received, or
an internal event of receiving a Logout response (success)
on another connection for a "close the session" Logout
request was received.
-target: An internal event was received that indicates
successful processing of the Logout, which prompts an iSCSI
Logout response (success) to be sent; an internal event of
sending a Logout response (success) on another connection
for a "close the session" Logout request was received; or an
internal event of a successful connection/session
reinstatement is received. In all these cases, the
transport connection is closed.
-T14:
-initiator: Async PDU with AsyncEvent "Request Logout" was
received again.
-target: Illegal
-T15, T16:
-initiator: One or more of the following events caused this
transition:
-Internal event that indicates a transport connection
timeout was received thus prompting transport RESET or
transport connection closure.
-A transport RESET.
-A transport disconnect indication.
-Async PDU with AsyncEvent "Drop connection" (for this CID).
-Async PDU with AsyncEvent "Drop all connections".
-target: One or more of the following events caused this
transition:
-Internal event that indicates a transport connection
timeout was received, thus prompting transport RESET or
transport connection closure.
-An internal event of a failed connection/session
reinstatement is received.
-A transport RESET.
-A transport disconnect indication.
-Internal emergency cleanup event was received which prompts
an Async PDU with AsyncEvent "Drop connection" (for this
CID), or event "Drop all connections".
-T17:
-initiator: One or more of the following events caused this
transition:
-Logout response, (failure i.e., a non-zero status) was
received, or Logout timed out.
-Any of the events specified for T15 and T16.
-target: One or more of the following events caused this
transition:
-Internal event that indicates a failure of the Logout
processing was received, which prompts a Logout response
(failure, i.e., a non-zero status) to be sent.
-Any of the events specified for T15 and T16.
-T18:
-initiator: An internal event of receiving a Logout response
(success) on another connection for a "close the session"
Logout request was received.
-target: An internal event of sending a Logout response
(success) on another connection for a "close the session"
Logout request was received, or an internal event of a
successful connection/session reinstatement is received. In
both these cases, the connection is closed.
The CLEANUP_WAIT state (S8) implies that there are possible iSCSI
tasks that have not reached conclusion and are still considered busy.
7.1.3. Standard Connection State Diagram for an Initiator
Symbolic names for States:
S1: FREE
S2: XPT_WAIT
S4: IN_LOGIN
S5: LOGGED_IN
S6: IN_LOGOUT
S7: LOGOUT_REQUESTED
S8: CLEANUP_WAIT
States S5, S6, and S7 constitute the Full Feature Phase operation of
the connection.
The state diagram is as follows:
-------<-------------+
+--------->/ S1 \<----+ |
T13| +->\ /<-+ \ |
| / ---+--- \ \ |
| / | T2 \ | |
| T8 | |T1 | | |
| | | / |T7 |
| | | / | |
| | | / | |
| | V / / |
| | ------- / / |
| | / S2 \ / |
| | \ / / |
| | ---+--- / |
| | |T4 / |
| | V / | T18
| | ------- / |
| | / S4 \ |
| | \ / |
| | ---+--- | T15
| | |T5 +--------+---------+
| | | /T16+-----+------+ |
| | | / -+-----+--+ | |
| | | / / S7 \ |T12| |
| | | / +->\ /<-+ V V
| | | / / -+----- -------
| | | / /T11 |T10 / S8 \
| | V / / V +----+ \ /
| | ---+-+- ----+-- | -------
| | / S5 \T9 / S6 \<+ ^
| +-----\ /--->\ / T14 |
| ------- --+----+------+T17
+---------------------------+
The following state transition table represents the above diagram.
Each row represents the starting state for a given transition, which
after taking a transition marked in a table cell would end in the
state represented by the column of the cell. For example, from state
S1, the connection takes the T1 transition to arrive at state S2.
The fields marked "-" correspond to undefined transitions.
+----+---+---+---+---+----+---+
|S1 |S2 |S4 |S5 |S6 |S7 |S8 |
---+----+---+---+---+---+----+---+
S1| - |T1 | - | - | - | - | - |
---+----+---+---+---+---+----+---+
S2|T2 |- |T4 | - | - | - | - |
---+----+---+---+---+---+----+---+
S4|T7 |- |- |T5 | - | - | - |
---+----+---+---+---+---+----+---+
S5|T8 |- |- | - |T9 |T11 |T15|
---+----+---+---+---+---+----+---+
S6|T13 |- |- | - |T14|- |T17|
---+----+---+---+---+---+----+---+
S7|T18 |- |- | - |T10|T12 |T16|
---+----+---+---+---+---+----+---+
S8| - |- |- | - | - | - | - |
---+----+---+---+---+---+----+---+
7.1.4. Standard Connection State Diagram for a Target
Symbolic names for States:
S1: FREE
S3: XPT_UP
S4: IN_LOGIN
S5: LOGGED_IN
S6: IN_LOGOUT
S7: LOGOUT_REQUESTED
S8: CLEANUP_WAIT
States S5, S6, and S7 constitute the Full Feature Phase operation of
the connection.
The state diagram is as follows:
-------<-------------+
+--------->/ S1 \<----+ |
T13| +->\ /<-+ \ |
| / ---+--- \ \ |
| / | T6 \ | |
| T8 | |T3 | | |
| | | / |T7 |
| | | / | |
| | | / | |
| | V / / |
| | ------- / / |
| | / S3 \ / |
| | \ / / | T18
| | ---+--- / |
| | |T4 / |
| | V / |
| | ------- / |
| | / S4 \ |
| | \ / |
| | ---+--- T15 |
| | |T5 +--------+---------+
| | | /T16+-----+------+ |
| | | / -+-----+---+ | |
| | | / / S7 \ |T12| |
| | | / +->\ /<-+ V V
| | | / / -+----- -------
| | | / /T11 |T10 / S8 \
| | V / / V \ /
| | ---+-+- ------- -------
| | / S5 \T9 / S6 \ ^
| +-----\ /--->\ / |
| ------- --+----+--------+T17
+---------------------------+
The following state transition table represents the above diagram,
and follows the conventions described for the initiator diagram.
+----+---+---+---+---+----+---+
|S1 |S3 |S4 |S5 |S6 |S7 |S8 |
---+----+---+---+---+---+----+---+
S1| - |T3 | - | - | - | - | - |
---+----+---+---+---+---+----+---+
S3|T6 |- |T4 | - | - | - | - |
---+----+---+---+---+---+----+---+
S4|T7 |- |- |T5 | - | - | - |
---+----+---+---+---+---+----+---+
S5|T8 |- |- | - |T9 |T11 |T15|
---+----+---+---+---+---+----+---+
S6|T13 |- |- | - |- |- |T17|
---+----+---+---+---+---+----+---+
S7|T18 |- |- | - |T10|T12 |T16|
---+----+---+---+---+---+----+---+
S8| - |- |- | - | - | - | - |
---+----+---+---+---+---+----+---+
7.2. Connection Cleanup State Diagram for Initiators and Targets
Symbolic names for states:
R1: CLEANUP_WAIT (same as S8)
R2: IN_CLEANUP
R3: FREE (same as S1)
Whenever a connection state machine (e.g., CSM-C) enters the
CLEANUP_WAIT state (S8), it must go through the state transitions
described in the connection cleanup state diagram either a) using a
separate full-feature phase connection (let's call it CSM-E) in the
LOGGED_IN state in the same session, or b) using a new transport
connection (let's call it CSM-I) in the FREE state that is to be
added to the same session. In the CSM-E case, an explicit logout for
the CID that corresponds to CSM-C (either as a connection or session
logout) needs to be performed to complete the cleanup. In the CSM-I
case, an implicit logout for the CID that corresponds to CSM-C needs
to be performed by way of connection reinstatement (section 5.3.4)
for that CID. In either case, the protocol exchanges on CSM-E or
CSM-I determine the state transitions for CSM-C. Therefore, this
cleanup state diagram is only applicable to the instance of the
connection in cleanup (i.e., CSM-C). In the case of an implicit
logout for example, CSM-C reaches FREE (R3) at the time CSM-I reaches
LOGGED_IN. In the case of an explicit logout, CSM-C reaches FREE
(R3) when CSM-E receives a successful logout response while
continuing to be in the LOGGED_IN state.
An initiator must initiate an explicit or implicit connection logout
for a connection in the CLEANUP_WAIT state, if the initiator intends
to continue using the associated iSCSI session.
The following state diagram applies to both initiators and targets.
-------
/ R1 \
+--\ /<-+
/ ---+---
/ | \ M3
M1 | |M2 |
| | /
| | /
| | /
| V /
| ------- /
| / R2 \
| \ /
| -------
| |
| |M4
| |
| |
| |
| V
| -------
| / R3 \
+---->\ /
-------
The following state transition table represents the above diagram,
and follows the same conventions as in earlier sections.
+----+----+----+
|R1 |R2 |R3 |
-----+----+----+----+
R1 | - |M2 |M1 |
-----+----+----+----+
R2 |M3 | - |M4 |
-----+----+----+----+
R3 | - | - | - |
-----+----+----+----+
7.2.1. State Descriptions for Initiators and Targets
-R1: CLEANUP_WAIT (Same as S8)
-initiator: Waiting for the internal event to initiate the
cleanup processing for CSM-C.
-target: Waiting for the cleanup process to start for CSM-C.
-R2: IN_CLEANUP
-initiator: Waiting for the connection cleanup process to
conclude for CSM-C.
-target: Waiting for the connection cleanup process to conclude
for CSM-C.
-R3: FREE (Same as S1)
-initiator: End state for CSM-C.
-target: End state for CSM-C.
7.2.2. State Transition Descriptions for Initiators and Targets
-M1: One or more of the following events was received:
-initiator:
-An internal event that indicates connection state timeout.
-An internal event of receiving a successful Logout response
on a different connection for a "close the session"
Logout.
-target:
-An internal event that indicates connection state timeout.
-An internal event of sending a Logout response (success) on
a different connection for a "close the session" Logout
request.
-M2: An implicit/explicit logout process was initiated by the
initiator.
-In CSM-I usage:
-initiator: An internal event requesting the connection (or
session) reinstatement was received, thus prompting a
connection (or session) reinstatement Login to be sent
transitioning CSM-I to state IN_LOGIN.
-target: A connection/session reinstatement Login was
received while in state XPT_UP.
-In CSM-E usage:
-initiator: An internal event that indicates that an
explicit logout was sent for this CID in state LOGGED_IN.
-target: An explicit logout was received for this CID in
state LOGGED_IN.
-M3: Logout failure detected
-In CSM-I usage:
-initiator: CSM-I failed to reach LOGGED_IN and arrived into
FREE instead.
-target: CSM-I failed to reach LOGGED_IN and arrived into
FREE instead.
-In CSM-E usage:
-initiator: CSM-E either moved out of LOGGED_IN, or Logout
timed out and/or aborted, or Logout response (failure)
was received.
-target: CSM-E either moved out of LOGGED_IN, Logout timed
out and/or aborted, or an internal event that indicates a
failed Logout processing was received. A Logout response
(failure) was sent in the last case.
-M4: Successful implicit/explicit logout was performed.
- In CSM-I usage:
-initiator: CSM-I reached state LOGGED_IN, or an internal
event of receiving a Logout response (success) on another
connection for a "close the session" Logout request was
received.
-target: CSM-I reached state LOGGED_IN, or an internal event
of sending a Logout response (success) on a different
connection for a "close the session" Logout request was
received.
- In CSM-E usage:
-initiator: CSM-E stayed in LOGGED_IN and received a Logout
response (success), or an internal event of receiving a
Logout response (success) on another connection for a
"close the session" Logout request was received.
-target: CSM-E stayed in LOGGED_IN and an internal event
indicating a successful Logout processing was received,
or an internal event of sending a Logout response
(success) on a different connection for a "close the
session" Logout request was received.
7.3. Session State Diagrams
7.3.1. Session State Diagram for an Initiator
Symbolic Names for States:
Q1: FREE
Q3: LOGGED_IN
Q4: FAILED
State Q3 represents the Full Feature Phase operation of the session.
The state diagram is as follows:
-------
/ Q1 \
+------>\ /<-+
/ ---+--- |
/ | |N3
N6 | |N1 |
| | |
| N4 | |
| +--------+ | /
| | | | /
| | | | /
| | V V /
-+--+-- -----+-
/ Q4 \ N5 / Q3 \
\ /<---\ /
------- -------
The state transition table is as follows:
+----+----+----+
|Q1 |Q3 |Q4 |
-----+----+----+----+
Q1 | - |N1 | - |
-----+----+----+----+
Q3 |N3 | - |N5 |
-----+----+----+----+
Q4 |N6 |N4 | - |
-----+----+----+----+
7.3.2. Session State Diagram for a Target
Symbolic Names for States:
Q1: FREE
Q2: ACTIVE
Q3: LOGGED_IN
Q4: FAILED
Q5: IN_CONTINUE
State Q3 represents the Full Feature Phase operation of the session.
The state diagram is as follows:
-------
+------------------>/ Q1 \
/ +-------------->\ /<-+
| | ---+--- |
| | ^ | |N3
N6 | |N11 N9| V N1 |
| | +------ |
| | / Q2 \ |
| | \ / |
| --+---- +--+--- |
| / Q5 \ | |
| \ / N10 | |
| +-+---+------------+ |N2 /
| ^ | | | /
|N7| |N8 | | /
| | | | V /
-+--+-V V----+-
/ Q4 \ N5 / Q3 \
\ /<-------------\ /
------- -------
The state transition table is as follows:
+----+----+----+----+----+
|Q1 |Q2 |Q3 |Q4 |Q5 |
-----+----+----+----+----+----+
Q1 | - |N1 | - | - | - |
-----+----+----+----+----+----+
Q2 |N9 | - |N2 | - | - |
-----+----+----+----+----+----+
Q3 |N3 | - | - |N5 | - |
-----+----+----+----+----+----+
Q4 |N6 | - | - | - |N7 |
-----+----+----+----+----+----+
Q5 |N11 | - |N10 |N8 | - |
-----+----+----+----+----+----+
7.3.3. State Descriptions for Initiators and Targets
-Q1: FREE
-initiator: State on instantiation or after cleanup.
-target: State on instantiation or after cleanup.
-Q2: ACTIVE
-initiator: Illegal.
-target: The first iSCSI connection in the session transitioned
to IN_LOGIN, waiting for it to complete the login process.
-Q3: LOGGED_IN
-initiator: Waiting for all session events.
-target: Waiting for all session events.
-Q4: FAILED
-initiator: Waiting for session recovery or session
continuation.
-target: Waiting for session recovery or session continuation.
-Q5: IN_CONTINUE
-initiator: Illegal.
-target: Waiting for session continuation attempt to reach a
conclusion.
7.3.4. State Transition Descriptions for Initiators and Targets
-N1:
-initiator: At least one transport connection reached the
LOGGED_IN state.
-target: The first iSCSI connection in the session had reached
the IN_LOGIN state.
-N2:
-initiator: Illegal.
-target: At least one iSCSI connection reached the LOGGED_IN
state.
-N3:
-initiator: Graceful closing of the session via session closure
(Section 5.3.6 Session Continuation and Failure).
-target: Graceful closing of the session via session closure
(Section 5.3.6 Session Continuation and Failure) or a
successful session reinstatement cleanly closed the session.
-N4:
-initiator: A session continuation attempt succeeded.
-target: Illegal.
-N5:
-initiator: Session failure (Section 5.3.6 Session Continuation
and Failure) occurred.
-target: Session failure (Section 5.3.6 Session Continuation and
Failure) occurred.
-N6:
-initiator: Session state timeout occurred, or a session
reinstatement cleared this session instance. This results
in the freeing of all associated resources and the session
state is discarded.
-target: Session state timeout occurred, or a session
reinstatement cleared this session instance. This results
in the freeing of all associated resources and the session
state is discarded.
-N7:
-initiator: Illegal.
-target: A session continuation attempt is initiated.
-N8:
-initiator: Illegal.
-target: The last session continuation attempt failed.
-N9:
-initiator: Illegal.
-target: Login attempt on the leading connection failed.
-N10:
-initiator: Illegal.
-target: A session continuation attempt succeeded.
-N11:
-initiator: Illegal.
-target: A successful session reinstatement cleanly closed the
session.
8. Security Considerations
Historically, native storage systems have not had to consider
security because their environments offered minimal security risks.
That is, these environments consisted of storage devices either
directly attached to hosts or connected via a Storage Area Network
(SAN) distinctly separate from the communications network. The use
of storage protocols, such as SCSI, over IP-networks requires that
security concerns be addressed. iSCSI implementations MUST provide
means of protection against active attacks (e.g., pretending to be
another identity, message insertion, deletion, modification, and
replaying) and passive attacks (e.g., eavesdropping, gaining
advantage by analyzing the data sent over the line).
Although technically possible, iSCSI SHOULD NOT be configured without
security. iSCSI configured without security should be confined, in
extreme cases, to closed environments without any security risk.
[RFC3723] specifies the mechanisms that must be used in order to
mitigate risks fully described in that document.
The following section describes the security mechanisms provided by
an iSCSI implementation.
8.1. iSCSI Security Mechanisms
The entities involved in iSCSI security are the initiator, target,
and the IP communication end points. iSCSI scenarios in which
multiple initiators or targets share a single communication end point
are expected. To accommodate such scenarios, iSCSI uses two separate
security mechanisms: In-band authentication between the initiator and
the target at the iSCSI connection level (carried out by exchange of
iSCSI Login PDUs), and packet protection (integrity, authentication,
and confidentiality) by IPsec at the IP level. The two security
mechanisms complement each other. The in-band authentication
provides end-to-end trust (at login time) between the iSCSI initiator
and the target while IPsec provides a secure channel between the IP
communication end points.
Further details on typical iSCSI scenarios and the relation between
the initiators, targets, and the communication end points can be
found in [RFC3723].
8.2. In-band Initiator-Target Authentication
During login, the target MAY authenticate the initiator and the
initiator MAY authenticate the target. The authentication is
performed on every new iSCSI connection by an exchange of iSCSI Login
PDUs using a negotiated authentication method.
The authentication method cannot assume an underlying IPsec
protection, because IPsec is optional to use. An attacker should
gain as little advantage as possible by inspecting the authentication
phase PDUs. Therefore, a method using clear text (or equivalent)
passwords is not acceptable; on the other hand, identity protection
is not strictly required.
The authentication mechanism protects against an unauthorized login
to storage resources by using a false identity (spoofing). Once the
authentication phase is completed, if the underlying IPsec is not
used, all PDUs are sent and received in clear. The authentication
mechanism alone (without underlying IPsec) should only be used when
there is no risk of eavesdropping, message insertion, deletion,
modification, and replaying.
Section 11 iSCSI Security Text Keys and Authentication Methods
defines several authentication methods and the exact steps that must
be followed in each of them, including the iSCSI-text-keys and their
allowed values in each step. Whenever an iSCSI initiator gets a
response whose keys, or their values, are not according to the step
definition, it MUST abort the connection. Whenever an iSCSI target
gets a response whose keys, or their values, are not according to the
step definition, it MUST answer with a Login reject with the
"Initiator Error" or "Missing Parameter" status. These statuses are
not intended for cryptographically incorrect values such as the CHAP
response, for which "Authentication Failure" status MUST be
specified. The importance of this rule can be illustrated in CHAP
with target authentication (see Section 11.1.4 Challenge Handshake
Authentication Protocol (CHAP)) where the initiator would have been
able to conduct a reflection attack by omitting his response key
(CHAP_R) using the same CHAP challenge as the target and reflecting
the target's response back to the target. In CHAP, this is prevented
because the target must answer the missing CHAP_R key with a Login
reject with the "Missing Parameter" status.
For some of the authentication methods, a key specifies the identity
of the iSCSI initiator or target for authentication purposes. The
value associated with that key MAY be different from the iSCSI name
and SHOULD be configurable. (CHAP_N, see Section 11.1.4 Challenge
Handshake Authentication Protocol (CHAP) and SRP_U, see Section
11.1.3 Secure Remote Password (SRP)).
8.2.1. CHAP Considerations
Compliant iSCSI initiators and targets MUST implement the CHAP
authentication method [RFC1994] (according to Section 11.1.4
Challenge Handshake Authentication Protocol (CHAP) including the
target authentication option).
When CHAP is performed over a non-encrypted channel, it is vulnerable
to an off-line dictionary attack. Implementations MUST support use
of up to 128 bit random CHAP secrets, including the means to generate
such secrets and to accept them from an external generation source.
Implementations MUST NOT provide secret generation (or expansion)
means other than random generation.
An administrative entity of an environment in which CHAP is used with
a secret that has less than 96 random bits MUST enforce IPsec
encryption (according to the implementation requirements in Section
8.3.2 Confidentiality) to protect the connection. Moreover, in this
case IKE authentication with group pre-shared cryptographic keys
SHOULD NOT be used unless it is not essential to protect group
members against off-line dictionary attacks by other members.
CHAP secrets MUST be an integral number of bytes (octets). A
compliant implementation SHOULD NOT continue with the login step in
which it should send a CHAP response (CHAP_R, Section 11.1.4
Challenge Handshake Authentication Protocol (CHAP)) unless it can
verify that the CHAP secret is at least 96 bits, or that IPsec
encryption is being used to protect the connection.
Any CHAP secret used for initiator authentication MUST NOT be
configured for authentication of any target, and any CHAP secret used
for target authentication MUST NOT be configured for authentication
of any initiator. If the CHAP response received by one end of an
iSCSI connection is the same as the CHAP response that the receiving
endpoint would have generated for the same CHAP challenge, the
response MUST be treated as an authentication failure and cause the
connection to close (this ensures that the same CHAP secret is not
used for authentication in both directions). Also, if an iSCSI
implementation can function as both initiator and target, different
CHAP secrets and identities MUST be configured for these two roles.
The following is an example of the attacks prevented by the above
requirements:
Rogue wants to impersonate Storage to Alice, and knows that a
single secret is used for both directions of Storage-Alice
authentication.
Rogue convinces Alice to open two connections to Rogue, and Rogue
identifies itself as Storage on both connections.
Rogue issues a CHAP challenge on connection 1, waits for Alice to
respond, and then reflects Alice's challenge as the initial
challenge to Alice on connection 2.
If Alice doesn't check for the reflection across connections,
Alice's response on connection 2 enables Rogue to impersonate
Storage on connection 1, even though Rogue does not know the
Alice-Storage CHAP secret.
Originators MUST NOT reuse the CHAP challenge sent by the Responder
for the other direction of a bidirectional authentication.
Responders MUST check for this condition and close the iSCSI TCP
connection if it occurs.
The same CHAP secret SHOULD NOT be configured for authentication of
multiple initiators or multiple targets, as this enables any of them
to impersonate any other one of them, and compromising one of them
enables the attacker to impersonate any of them. It is recommended
that iSCSI implementations check for use of identical CHAP secrets by
different peers when this check is feasible, and take appropriate
measures to warn users and/or administrators when this is detected.
When an iSCSI initiator or target authenticates itself to
counterparts in multiple administrative domains, it SHOULD use a
different CHAP secret for each administrative domain to avoid
propagating security compromises across domains.
Within a single administrative domain:
- A single CHAP secret MAY be used for authentication of an initiator
to multiple targets.
- A single CHAP secret MAY be used for an authentication of a target
to multiple initiators when the initiators use an external server
(e.g., RADIUS) to verify the target's CHAP responses and do not know
the target's CHAP secret.
If an external response verification server (e.g., RADIUS) is not
used, employing a single CHAP secret for authentication of a target
to multiple initiators requires that all such initiators know that
target secret. Any of these initiators can impersonate the target to
any other such initiator, and compromise of such an initiator enables
an attacker to impersonate the target to all such initiators.
Targets SHOULD use separate CHAP secrets for authentication to each
initiator when such risks are of concern; in this situation it may be
useful to configure a separate logical iSCSI target with its own
iSCSI Node Name for each initiator or group of initiators among which
such separation is desired.
8.2.2. SRP Considerations
The strength of the SRP authentication method (specified in
[RFC2945]) is dependent on the characteristics of the group being
used (i.e., the prime modulus N and generator g). As described in
[RFC2945], N is required to be a Sophie-German prime (of the form
N = 2q + 1, where q is also prime) and the generator g is a primitive
root of GF(n). In iSCSI authentication, the prime modulus N MUST be
at least 768 bits.
The list of allowed SRP groups is provided in [RFC3723].
8.3. IPsec
iSCSI uses the IPsec mechanism for packet protection (cryptographic
integrity, authentication, and confidentiality) at the IP level
between the iSCSI communicating end points. The following sections
describe the IPsec protocols that must be implemented for data
integrity and authentication, confidentiality, and cryptographic key
management.
An iSCSI initiator or target may provide the required IPsec support
fully integrated or in conjunction with an IPsec front-end device.
In the latter case, the compliance requirements with regard to IPsec
support apply to the "combined device". Only the "combined device"
is to be considered an iSCSI device.
Detailed considerations and recommendations for using IPsec for iSCSI
are provided in [RFC3723].
8.3.1. Data Integrity and Authentication
Data authentication and integrity is provided by a cryptographic
keyed Message Authentication Code in every sent packet. This code
protects against message insertion, deletion, and modification.
Protection against message replay is realized by using a sequence
counter.
An iSCSI compliant initiator or target MUST provide data integrity
and authentication by implementing IPsec [RFC2401] with ESP [RFC2406]
in tunnel mode and MAY provide data integrity and authentication by
implementing IPsec with ESP in transport mode. The IPsec
implementation MUST fulfill the following iSCSI specific
requirements:
- HMAC-SHA1 MUST be implemented [RFC2404].
- AES CBC MAC with XCBC extensions SHOULD be implemented
[RFC3566].
The ESP anti-replay service MUST also be implemented.
At the high speeds iSCSI is expected to operate, a single IPsec SA
could rapidly cycle through the 32-bit IPsec sequence number space.
In view of this, it may be desirable in the future for an iSCSI
implementation that operates at speeds of 1 Gbps or greater to
implement the IPsec sequence number extension [SEQ-EXT].
8.3.2. Confidentiality
Confidentiality is provided by encrypting the data in every packet.
When confidentiality is used it MUST be accompanied by data integrity
and authentication to provide comprehensive protection against
eavesdropping, message insertion, deletion, modification, and
replaying.
An iSCSI compliant initiator or target MUST provide confidentiality
by implementing IPsec [RFC2401] with ESP [RFC2406] in tunnel mode and
MAY provide confidentiality by implementing IPsec with ESP in
transport mode, with the following iSCSI specific requirements:
- 3DES in CBC mode MUST be implemented [RFC2451].
- AES in Counter mode SHOULD be implemented [RFC3686].
DES in CBC mode SHOULD NOT be used due to its inherent weakness. The
NULL encryption algorithm MUST also be implemented.
8.3.3. Policy, Security Associations, and Cryptographic Key Management
A compliant iSCSI implementation MUST meet the cryptographic key
management requirements of the IPsec protocol suite. Authentication,
security association negotiation, and cryptographic key management
MUST be provided by implementing IKE [RFC2409] using the IPsec DOI
[RFC2407] with the following iSCSI specific requirements:
- Peer authentication using a pre-shared cryptographic key MUST be
supported. Certificate-based peer authentication using digital
signatures MAY be supported. Peer authentication using the
public key encryption methods outlined in IKE sections 5.2 and
5.3[7] SHOULD NOT be used.
- When digital signatures are used to achieve authentication, an
IKE negotiator SHOULD use IKE Certificate Request Payload(s) to
specify the certificate authority. IKE negotiators SHOULD check
the pertinent Certificate Revocation List (CRL) before accepting
a PKI certificate for use in IKE authentication procedures.
- Conformant iSCSI implementations MUST support IKE Main Mode and
SHOULD support Aggressive Mode. IKE main mode with pre-shared
key authentication method SHOULD NOT be used when either the
initiator or the target uses dynamically assigned IP addresses.
While in many cases pre-shared keys offer good security,
situations in which dynamically assigned addresses are used force
the use of a group pre-shared key, which creates vulnerability to
a man-in-the-middle attack.
- In the IKE Phase 2 Quick Mode, exchanges for creating the Phase 2
SA, the Identity Payload, fields MUST be present. ID_IPV4_ADDR,
ID_IPV6_ADDR (if the protocol stack supports IPv6) and ID_FQDN
Identity payloads MUST be supported; ID_USER_FQDN SHOULD be
supported. The IP Subnet, IP Address Range, ID_DER_ASN1_DN, and
ID_DER_ASN1_GN formats SHOULD NOT be used. The ID_KEY_ID
Identity Payload MUST NOT be used.
Manual cryptographic keying MUST NOT be used because it does not
provide the necessary re-keying support.
When IPsec is used, the receipt of an IKE Phase 2 delete message
SHOULD NOT be interpreted as a reason for tearing down the iSCSI TCP
connection. If additional traffic is sent on it, a new IKE Phase 2
SA will be created to protect it.
The method used by the initiator to determine whether the target
should be connected using IPsec is regarded as an issue of IPsec
policy administration, and thus not defined in the iSCSI standard.
If an iSCSI target is discovered via a SendTargets request in a
discovery session not using IPsec, the initiator should assume that
it does not need IPsec to establish a session to that target. If an
iSCSI target is discovered using a discovery session that does use
IPsec, the initiator SHOULD use IPsec when establishing a session to
that target.
9. Notes to Implementers
This section notes some of the performance and reliability
considerations of the iSCSI protocol. This protocol was designed to
allow efficient silicon and software implementations. The iSCSI task
tag mechanism was designed to enable Direct Data Placement (DDP - a
DMA form) at the iSCSI level or lower.
The guiding assumption made throughout the design of this protocol is
that targets are resource constrained relative to initiators.
Implementers are also advised to consider the implementation
consequences of the iSCSI to SCSI mapping model as outlined in
Section 3.4.3 Consequences of the Model.
9.1. Multiple Network Adapters
The iSCSI protocol allows multiple connections, not all of which need
to go over the same network adapter. If multiple network connections
are to be utilized with hardware support, the iSCSI protocol
command-data-status allegiance to one TCP connection ensures that
there is no need to replicate information across network adapters or
otherwise require them to cooperate.
However, some task management commands may require some loose form of
cooperation or replication at least on the target.
9.1.1. Conservative Reuse of ISIDs
Historically, the SCSI model (and implementations and applications
based on that model) has assumed that SCSI ports are static, physical
entities. Recent extensions to the SCSI model have taken advantage
of persistent worldwide unique names for these ports. In iSCSI
however, the SCSI initiator ports are the endpoints of dynamically
created sessions, so the presumptions of "static and physical" do not
apply. In any case, the model clauses (particularly, Section 3.4.2
SCSI Architecture Model) provide for persistent, reusable names for
the iSCSI-type SCSI initiator ports even though there does not need
to be any physical entity bound to these names.
To both minimize the disruption of legacy applications and to better
facilitate the SCSI features that rely on persistent names for SCSI
ports, iSCSI implementations SHOULD attempt to provide a stable
presentation of SCSI Initiator Ports (both to the upper OS-layers and
to the targets to which they connect). This can be achieved in an
initiator implementation by conservatively reusing ISIDs. In other
words, the same ISID should be used in the Login process to multiple
target portal groups (of the same iSCSI Target or different iSCSI
Targets). The ISID RULE (Section 3.4.3 Consequences of the Model)
only prohibits reuse to the same target portal group. It does not
"preclude" reuse to other target portal groups. The principle of
conservative reuse "encourages" reuse to other target portal groups.
When a SCSI target device sees the same (InitiatorName, ISID) pair in
different sessions to different target portal groups, it can identify
the underlying SCSI Initiator Port on each session as the same SCSI
port. In effect, it can recognize multiple paths from the same
source.
9.1.2. iSCSI Name, ISID, and TPGT Use
The designers of the iSCSI protocol envisioned there being one iSCSI
Initiator Node Name per operating system image on a machine. This
enables SAN resource configuration and authentication schemes based
on a system's identity. It supports the notion that it should be
possible to assign access to storage resources based on "initiator
device" identity.
When there are multiple hardware or software components coordinated
as a single iSCSI Node, there must be some (logical) entity that
represents the iSCSI Node that makes the iSCSI Node Name available to
all components involved in session creation and login. Similarly,
this entity that represents the iSCSI Node must be able to coordinate
session identifier resources (ISID for initiators) to enforce both
the ISID and TSIH RULES (see Section 3.4.3 Consequences of the
Model).
For targets, because of the closed environment, implementation of
this entity should be straightforward. However, vendors of iSCSI
hardware (e.g., NICs or HBAs) intended for targets, SHOULD provide
mechanisms for configuration of the iSCSI Node Name across the portal
groups instantiated by multiple instances of these components within
a target.
However, complex targets making use of multiple Target Portal Group
Tags may reconfigure them to achieve various quality goals. The
initiators have two mechanisms at their disposal to discover and/or
check reconfiguring targets - the discovery session type and a key
returned by the target during login to confirm the TPGT. An
initiator should attempt to "rediscover" the target configuration
anytime a session is terminated unexpectedly.
For initiators, in the long term, it is expected that operating
system vendors will take on the role of this entity and provide
standard APIs that can inform components of their iSCSI Node Name and
can configure and/or coordinate ISID allocation, use, and reuse.
Recognizing that such initiator APIs are not available today, other
implementations of the role of this entity are possible. For
example, a human may instantiate the (common) Node name as part of
the installation process of each iSCSI component involved in session
creation and login. This may be done either by pointing the
component to a vendor-specific location for this datum or to a
system-wide location. The structure of the ISID namespace (see
Section 10.12.5 ISID and [RFC3721]) facilitates implementation of the
ISID coordination by allowing each component vendor to independently
(of other vendor's components) coordinate allocation, use, and reuse
of its own partition of the ISID namespace in a vendor-specific
manner. Partitioning of the ISID namespace within initiator portal
groups managed by that vendor allows each such initiator portal group
to act independently of all other portal groups when selecting an
ISID for a login; this facilitates enforcement of the ISID RULE (see
Section 3.4.3 Consequences of the Model) at the initiator.
A vendor of iSCSI hardware (e.g., NICs or HBAs) intended for use in
initiators MUST implement a mechanism for configuring the iSCSI Node
Name. Vendors, and administrators must ensure that iSCSI Node Names
are unique worldwide. It is therefore important that when one
chooses to reuse the iSCSI Node Name of a disabled unit, not to
re-assign that name to the original unit unless its worldwide
uniqueness can be ascertained again.
In addition, a vendor of iSCSI hardware must implement a mechanism to
configure and/or coordinate ISIDs for all sessions managed by
multiple instances of that hardware within a given iSCSI Node. Such
configuration might be either permanently pre-assigned at the factory
(in a necessarily globally unique way), statically assigned (e.g.,
partitioned across all the NICs at initialization in a locally unique
way), or dynamically assigned (e.g., on-line allocator, also in a
locally unique way). In the latter two cases, the configuration may
be via public APIs (perhaps driven by an independent vendor's
software, such as the OS vendor) or via private APIs driven by the
vendor's own software.
9.2. Autosense and Auto Contingent Allegiance (ACA)
Autosense refers to the automatic return of sense data to the
initiator in case a command did not complete successfully. iSCSI
initiators and targets MUST support and use autosense.
ACA helps preserve ordered command execution in the presence of
errors. As iSCSI can have many commands in-flight between initiator
and target, iSCSI initiators and targets SHOULD support ACA.
9.3. iSCSI Timeouts
iSCSI recovery actions are often dependent on iSCSI time-outs being
recognized and acted upon before SCSI time-outs. Determining the
right time-outs to use for various iSCSI actions (command
acknowledgements expected, status acknowledgements, etc.) is very
much dependent on infrastructure (hardware, links, TCP/IP stack,
iSCSI driver). As a guide, the implementer may use an average
Nop-Out/Nop-In turnaround delay multiplied by a "safety factor"
(e.g., 4) as a good estimate for the basic delay of the iSCSI stack
for a given connection. The safety factor should account for the
network load variability. For connection teardown the implementer
may want to consider also the TCP common practice for the given
infrastructure.
Text negotiations MAY also be subject to either time-limits or limits
in the number of exchanges. Those SHOULD be generous enough to avoid
affecting interoperability (e.g., allowing each key to be negotiated
on a separate exchange).
The relation between iSCSI timeouts and SCSI timeouts should also be
considered. SCSI timeouts should be longer than iSCSI timeouts plus
the time required for iSCSI recovery whenever iSCSI recovery is
planned. Alternatively, an implementer may choose to interlock iSCSI
timeouts and recovery with SCSI timeouts so that SCSI recovery will
become active only where iSCSI is not planned to, or failed to,
recover.
The implementer may also want to consider the interaction between
various iSCSI exception events - such as a digest failure - and
subsequent timeouts. When iSCSI error recovery is active, a digest
failure is likely to result in discovering a missing command or data
PDU. In these cases, an implementer may want to lower the timeout
values to enable faster initiation for recovery procedures.
9.4. Command Retry and Cleaning Old Command Instances
To avoid having old, retried command instances appear in a valid
command window after a command sequence number wrap around, the
protocol requires (see Section 3.2.2.1 Command Numbering and
Acknowledging) that on every connection on which a retry has been
issued, a non-immediate command be issued and acknowledged within a
2**31-1 commands interval from the CmdSN of the retried command.
This requirement can be fulfilled by an implementation in several
ways.
The simplest technique to use is to send a (non-retry) non-immediate
SCSI command (or a NOP if no SCSI command is available for a while)
after every command retry on the connection on which the retry was
attempted. As errors are deemed rare events, this technique is
probably the most effective, as it does not involve additional checks
at the initiator when issuing commands.
9.5. Synch and Steering Layer and Performance
While a synch and steering layer is optional, an initiator/target
that does not have it working against a target/initiator that demands
synch and steering may experience performance degradation caused by
packet reordering and loss. Providing a synch and steering mechanism
is recommended for all high-speed implementations.
9.6. Considerations for State-dependent Devices and Long-lasting SCSI
Operations
Sequential access devices operate on the principle that the position
of the device is based on the last command processed. As such,
command processing order and knowledge of whether or not the previous
command was processed is of the utmost importance to maintain data
integrity. For example, inadvertent retries of SCSI commands when it
is not known if the previous SCSI command was processed is a
potential data integrity risk.
For a sequential access device, consider the scenario in which a SCSI
SPACE command to backspace one filemark is issued and then re-issued
due to no status received for the command. If the first SPACE
command was actually processed, the re-issued SPACE command, if
processed, will cause the position to change. Thus, a subsequent
write operation will write data to the wrong position and any
previous data at that position will be overwritten.
For a medium changer device, consider the scenario in which an
EXCHANGE MEDIUM command (the SOURCE ADDRESS and DESTINATION ADDRESS
are the same thus performing a swap) is issued and then re-issued due
to no status received for the command. If the first EXCHANGE MEDIUM
command was actually processed, the re-issued EXCHANGE MEDIUM
command, if processed, will perform the swap again. The net effect
is that a swap was not performed thus leaving a data integrity
exposure.
All commands that change the state of the device (as in SPACE
commands for sequential access devices, and EXCHANGE MEDIUM for
medium changer device), MUST be issued as non-immediate commands for
deterministic and in order delivery to iSCSI targets.
For many of those state changing commands, the execution model also
assumes that the command is executed exactly once. Devices
implementing READ POSITION and LOCATE provide a means for SCSI level
command recovery and new tape-class devices should support those
commands. In their absence a retry at SCSI level is difficult and
error recovery at iSCSI level is advisable.
Devices operating on long latency delivery subsystems and performing
long lasting SCSI operations may need mechanisms that enable
connection replacement while commands are running (e.g., during an
extended copy operation).
9.6.1. Determining the Proper ErrorRecoveryLevel
The implementation and use of a specific ErrorRecoveryLevel should be
determined based on the deployment scenarios of a given iSCSI
implementation. Generally, the following factors must be considered
before deciding on the proper level of recovery:
a) Application resilience to I/O failures.
b) Required level of availability in the face of transport
connection failures.
c) Probability of transport layer "checksum escape". This in
turn decides the iSCSI digest failure frequency, and thus the
criticality of iSCSI-level error recovery. The details of
estimating this probability are outside the scope of this
document.
A consideration of the above factors for SCSI tape devices as an
example suggests that implementations SHOULD use ErrorRecoveryLevel=1
when transport connection failure is not a concern and SCSI level
recovery is unavailable, and ErrorRecoveryLevel=2 when the connection
failure is also of high likelihood during a backup/retrieval.
For extended copy operations, implementations SHOULD use
ErrorRecoveryLevel=2 whenever there is a relatively high likelihood
of connection failure.
10. iSCSI PDU Formats
All multi-byte integers that are specified in formats defined in this
document are to be represented in network byte order (i.e., big
endian). Any field that appears in this document assumes that the
most significant byte is the lowest numbered byte and the most
significant bit (within byte or field) is the lowest numbered bit
unless specified otherwise.
Any compliant sender MUST set all bits not defined and all reserved
fields to zero unless specified otherwise. Any compliant receiver
MUST ignore any bit not defined and all reserved fields unless
specified otherwise. Receipt of reserved code values in defined
fields MUST be reported as a protocol error.
Reserved fields are marked by the word "reserved", some abbreviation
of "reserved", or by "." for individual bits when no other form of
marking is technically feasible.
10.1. iSCSI PDU Length and Padding
iSCSI PDUs are padded to the closest integer number of four byte
words. The padding bytes SHOULD be sent as 0.
10.2. PDU Template, Header, and Opcodes
All iSCSI PDUs have one or more header segments and, optionally, a
data segment. After the entire header segment group a header-digest
MAY follow. The data segment MAY also be followed by a data-digest.
The Basic Header Segment (BHS) is the first segment in all of the
iSCSI PDUs. The BHS is a fixed-length 48-byte header segment. It
MAY be followed by Additional Header Segments (AHS), a Header-Digest,
a Data Segment, and/or a Data-Digest.
The overall structure of an iSCSI PDU is as follows:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0/ Basic Header Segment (BHS) /
+/ /
+---------------+---------------+---------------+---------------+
48/ Additional Header Segment 1 (AHS) (optional) /
+/ /
+---------------+---------------+---------------+---------------+
/ Additional Header Segment 2 (AHS) (optional) /
+/ /
+---------------+---------------+---------------+---------------+
----
+---------------+---------------+---------------+---------------+
/ Additional Header Segment n (AHS) (optional) /
+/ /
+---------------+---------------+---------------+---------------+
----
+---------------+---------------+---------------+---------------+
k/ Header-Digest (optional) /
+/ /
+---------------+---------------+---------------+---------------+
l/ Data Segment(optional) /
+/ /
+---------------+---------------+---------------+---------------+
m/ Data-Digest (optional) /
+/ /
+---------------+---------------+---------------+---------------+
All PDU segments and digests are padded to the closest integer number
of four byte words. For example, all PDU segments and digests start
at a four byte word boundary and the padding ranges from 0 to 3
bytes. The padding bytes SHOULD be sent as 0.
iSCSI response PDUs do not have AH Segments.
10.2.1. Basic Header Segment (BHS)
The BHS is 48 bytes long. The Opcode and DataSegmentLength fields
appear in all iSCSI PDUs. In addition, when used, the Initiator Task
Tag and Logical Unit Number always appear in the same location in the
header.
The format of the BHS is:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|I| Opcode |F| Opcode-specific fields |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Opcode-specific fields |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20/ Opcode-specific fields /
+/ /
+---------------+---------------+---------------+---------------+
48
10.2.1.1 I
For request PDUs, the I bit set to 1 is an immediate delivery marker.
10.2.1.2. Opcode
The Opcode indicates the type of iSCSI PDU the header encapsulates.
The Opcodes are divided into two categories: initiator opcodes and
target opcodes. Initiator opcodes are in PDUs sent by the initiator
(request PDUs). Target opcodes are in PDUs sent by the target
(response PDUs).
Initiators MUST NOT use target opcodes and targets MUST NOT use
initiator opcodes.
Initiator opcodes defined in this specification are:
0x00 NOP-Out
0x01 SCSI Command (encapsulates a SCSI Command Descriptor Block)
0x02 SCSI Task Management function request
0x03 Login Request
0x04 Text Request
0x05 SCSI Data-Out (for WRITE operations)
0x06 Logout Request
0x10 SNACK Request
0x1c-0x1e Vendor specific codes
Target opcodes are:
0x20 NOP-In
0x21 SCSI Response - contains SCSI status and possibly sense
information or other response information.
0x22 SCSI Task Management function response
0x23 Login Response
0x24 Text Response
0x25 SCSI Data-In - for READ operations.
0x26 Logout Response
0x31 Ready To Transfer (R2T) - sent by target when it is ready
to receive data.
0x32 Asynchronous Message - sent by target to indicate certain
special conditions.
0x3c-0x3e Vendor specific codes
0x3f Reject
All other opcodes are reserved.
10.2.1.3. Final (F) bit
When set to 1 it indicates the final (or only) PDU of a sequence.
10.2.1.4. Opcode-specific Fields
These fields have different meanings for different opcode types.
10.2.1.5. TotalAHSLength
Total length of all AHS header segments in units of four byte words
including padding, if any.
The TotalAHSLength is only used in PDUs that have an AHS and MUST be
0 in all other PDUs.
10.2.1.6. DataSegmentLength
This is the data segment payload length in bytes (excluding padding).
The DataSegmentLength MUST be 0 whenever the PDU has no data segment.
10.2.1.7. LUN
Some opcodes operate on a specific Logical Unit. The Logical Unit
Number (LUN) field identifies which Logical Unit. If the opcode does
not relate to a Logical Unit, this field is either ignored or may be
used in an opcode specific way. The LUN field is 64-bits and should
be formatted in accordance with [SAM2]. For example, LUN[0] from
[SAM2] is BHS byte 8 and so on up to LUN[7] from [SAM2], which is BHS
byte 15.
10.2.1.8. Initiator Task Tag
The initiator assigns a Task Tag to each iSCSI task it issues. While
a task exists, this tag MUST uniquely identify the task session-wide.
SCSI may also use the initiator task tag as part of the SCSI task
identifier when the timespan during which an iSCSI initiator task tag
must be unique extends over the timespan during which a SCSI task tag
must be unique. However, the iSCSI Initiator Task Tag must exist and
be unique even for untagged SCSI commands.
10.2.2. Additional Header Segment (AHS)
The general format of an AHS is:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| AHSLength | AHSType | AHS-Specific |
+---------------+---------------+---------------+---------------+
4/ AHS-Specific /
+/ /
+---------------+---------------+---------------+---------------+
x
10.2.2.1. AHSType
The AHSType field is coded as follows:
bit 0-1 - Reserved
bit 2-7 - AHS code
0 - Reserved
1 - Extended CDB
2 - Expected Bidirectional Read Data Length
3 - 63 Reserved
10.2.2.2. AHSLength
This field contains the effective length in bytes of the AHS
excluding AHSType and AHSLength and padding, if any. The AHS is
padded to the smallest integer number of 4 byte words (i.e., from 0
up to 3 padding bytes).
10.2.2.3. Extended CDB AHS
The format of the Extended CDB AHS is:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| AHSLength (CDBLength-15) | 0x01 | Reserved |
+---------------+---------------+---------------+---------------+
4/ ExtendedCDB...+padding /
+/ /
+---------------+---------------+---------------+---------------+
x
This type of AHS MUST NOT be used if the CDBLength is less than 17.
The length includes the reserved byte 3.
10.2.2.4. Bidirectional Expected Read-Data Length AHS
The format of the Bidirectional Read Expected Data Transfer Length
AHS is:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| AHSLength (0x0005) | 0x02 | Reserved |
+---------------+---------------+---------------+---------------+
4| Expected Read-Data Length |
+---------------+---------------+---------------+---------------+
8
10.2.3. Header Digest and Data Digest
Optional header and data digests protect the integrity of the header
and data, respectively. The digests, if present, are located,
respectively, after the header and PDU-specific data, and cover
respectively the header and the PDU data, each including the padding
bytes, if any.
The existence and type of digests are negotiated during the Login
Phase.
The separation of the header and data digests is useful in iSCSI
routing applications, in which only the header changes when a message
is forwarded. In this case, only the header digest should be
recalculated.
Digests are not included in data or header length fields.
A zero-length Data Segment also implies a zero-length data-digest.
10.2.4. Data Segment
The (optional) Data Segment contains PDU associated data. Its
payload effective length is provided in the BHS field -
DataSegmentLength. The Data Segment is also padded to an integer
number of 4 byte words.
10.3. SCSI Command
The format of the SCSI Command PDU is:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|I| 0x01 |F|R|W|. .|ATTR | Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| Logical Unit Number (LUN) |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Expected Data Transfer Length |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ SCSI Command Descriptor Block (CDB) /
+/ /
+---------------+---------------+---------------+---------------+
48/ AHS (Optional) /
+---------------+---------------+---------------+---------------+
x/ Header Digest (Optional) /
+---------------+---------------+---------------+---------------+
y/ (DataSegment, Command Data) (Optional) /
+/ /
+---------------+---------------+---------------+---------------+
z/ Data Digest (Optional) /
+---------------+---------------+---------------+---------------+
10.3.1. Flags and Task Attributes (byte 1)
The flags for a SCSI Command are:
bit 0 (F) is set to 1 when no unsolicited SCSI Data-Out PDUs follow
this PDU. When F=1 for a write and if Expected Data
Transfer Length is larger than the DataSegmentLength, the
target may solicit additional data through R2T.
bit 1 (R) is set to 1 when the command is expected to input data.
bit 2 (W) is set to 1 when the command is expected to output data.
bit 3-4 Reserved.
bit 5-7 contains Task Attributes.
Task Attributes (ATTR) have one of the following integer values (see
[SAM2] for details):
0 - Untagged
1 - Simple
2 - Ordered
3 - Head of Queue
4 - ACA
5-7 - Reserved
Setting both the W and the F bit to 0 is an error. Either or both of
R and W MAY be 1 when either the Expected Data Transfer Length and/or
Bidirectional Read Expected Data Transfer Length are 0, but they MUST
NOT both be 0 when the Expected Data Transfer Length and/or
Bidirectional Read Expected Data Transfer Length are not 0 (i.e.,
when some data transfer is expected the transfer direction is
indicated by the R and/or W bit).
10.3.2. CmdSN - Command Sequence Number
Enables ordered delivery across multiple connections in a single
session.
10.3.3. ExpStatSN
Command responses up to ExpStatSN-1 (mod 2**32) have been received
(acknowledges status) on the connection.
10.3.4. Expected Data Transfer Length
For unidirectional operations, the Expected Data Transfer Length
field contains the number of bytes of data involved in this SCSI
operation. For a unidirectional write operation (W flag set to 1 and
R flag set to 0), the initiator uses this field to specify the number
of bytes of data it expects to transfer for this operation. For a
unidirectional read operation (W flag set to 0 and R flag set to 1),
the initiator uses this field to specify the number of bytes of data
it expects the target to transfer to the initiator. It corresponds
to the SAM2 byte count.
For bidirectional operations (both R and W flags are set to 1), this
field contains the number of data bytes involved in the write
transfer. For bidirectional operations, an additional header segment
MUST be present in the header sequence that indicates the
Bidirectional Read Expected Data Transfer Length. The Expected Data
Transfer Length field and the Bidirectional Read Expected Data
Transfer Length field correspond to the SAM2 byte count
If the Expected Data Transfer Length for a write and the length of
the immediate data part that follows the command (if any) are the
same, then no more data PDUs are expected to follow. In this case,
the F bit MUST be set to 1.
If the Expected Data Transfer Length is higher than the
FirstBurstLength (the negotiated maximum amount of unsolicited data
the target will accept), the initiator MUST send the maximum amount
of unsolicited data OR ONLY the immediate data, if any.
Upon completion of a data transfer, the target informs the initiator
(through residual counts) of how many bytes were actually processed
(sent and/or received) by the target.
10.3.5. CDB - SCSI Command Descriptor Block
There are 16 bytes in the CDB field to accommodate the commonly used
CDBs. Whenever the CDB is larger than 16 bytes, an Extended CDB AHS
MUST be used to contain the CDB spillover.
10.3.6. Data Segment - Command Data
Some SCSI commands require additional parameter data to accompany the
SCSI command. This data may be placed beyond the boundary of the
iSCSI header in a data segment. Alternatively, user data (e.g., from
a WRITE operation) can be placed in the data segment (both cases are
referred to as immediate data). These data are governed by the rules
for solicited vs. unsolicited data outlined in Section 3.2.4.2 Data
Transfer Overview.
10.4. SCSI Response
The format of the SCSI Response PDU is:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x21 |1|. .|o|u|O|U|.| Response | Status |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| SNACK Tag or Reserved |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| ExpDataSN or Reserved |
+---------------+---------------+---------------+---------------+
40| Bidirectional Read Residual Count or Reserved |
+---------------+---------------+---------------+---------------+
44| Residual Count or Reserved |
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
/ Data Segment (Optional) /
+/ /
+---------------+---------------+---------------+---------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
10.4.1. Flags (byte 1)
bit 1-2 Reserved.
bit 3 - (o) set for Bidirectional Read Residual Overflow. In this
case, the Bidirectional Read Residual Count indicates the number
of bytes that were not transferred to the initiator because the
initiator's Expected Bidirectional Read Data Transfer Length was
not sufficient.
bit 4 - (u) set for Bidirectional Read Residual Underflow. In this
case, the Bidirectional Read Residual Count indicates the number
of bytes that were not transferred to the initiator out of the
number of bytes expected to be transferred.
bit 5 - (O) set for Residual Overflow. In this case, the Residual
Count indicates the number of bytes that were not transferred
because the initiator's Expected Data Transfer Length was not
sufficient. For a bidirectional operation, the Residual Count
contains the residual for the write operation.
bit 6 - (U) set for Residual Underflow. In this case, the Residual
Count indicates the number of bytes that were not transferred out
of the number of bytes that were expected to be transferred. For
a bidirectional operation, the Residual Count contains the
residual for the write operation.
bit 7 - (0) Reserved.
Bits O and U and bits o and u are mutually exclusive (i.e., having
both o and u or O and U set to 1 is a protocol error). For a
response other than "Command Completed at Target", bits 3-6 MUST be
0.
10.4.2. Status
The Status field is used to report the SCSI status of the command (as
specified in [SAM2]) and is only valid if the Response Code is
Command Completed at target.
Some of the status codes defined in [SAM2] are:
0x00 GOOD
0x02 CHECK CONDITION
0x08 BUSY
0x18 RESERVATION CONFLICT
0x28 TASK SET FULL
0x30 ACA ACTIVE
0x40 TASK ABORTED
See [SAM2] for the complete list and definitions.
If a SCSI device error is detected while data from the initiator is
still expected (the command PDU did not contain all the data and the
target has not received a Data PDU with the final bit Set), the
target MUST wait until it receives a Data PDU with the F bit set in
the last expected sequence before sending the Response PDU.
10.4.3. Response
This field contains the iSCSI service response.
iSCSI service response codes defined in this specification are:
0x00 - Command Completed at Target
0x01 - Target Failure
0x80-0xff - Vendor specific
All other response codes are reserved.
The Response is used to report a Service Response. The mapping of
the response code into a SCSI service response code value, if needed,
is outside the scope of this document. However, in symbolic terms
response value 0x00 maps to the SCSI service response (see [SAM2] and
[SPC3]) of TASK COMPLETE or LINKED COMMAND COMPLETE. All other
Response values map to the SCSI service response of SERVICE DELIVERY
OR TARGET FAILURE.
If a PDU that includes SCSI status (Response PDU or Data-In PDU
including status) does not arrive before the session is terminated,
the SCSI service response is SERVICE DELIVERY OR TARGET FAILURE.
A non-zero Response field indicates a failure to execute the command
in which case the Status and Flag fields are undefined.
10.4.4. SNACK Tag
This field contains a copy of the SNACK Tag of the last SNACK Tag
accepted by the target on the same connection and for the command for
which the response is issued. Otherwise it is reserved and should be
set to 0.
After issuing a R-Data SNACK the initiator must discard any SCSI
status unless contained in an SCSI Response PDU carrying the same
SNACK Tag as the last issued R-Data SNACK for the SCSI command on the
current connection.
For a detailed discussion on R-Data SNACK see Section 10.16 SNACK
Request.
10.4.5. Residual Count
The Residual Count field MUST be valid in the case where either the U
bit or the O bit is set. If neither bit is set, the Residual Count
field is reserved. Targets may set the residual count and initiators
may use it when the response code is "completed at target" (even if
the status returned is not GOOD). If the O bit is set, the Residual
Count indicates the number of bytes that were not transferred because
the initiator's Expected Data Transfer Length was not sufficient. If
the U bit is set, the Residual Count indicates the number of bytes
that were not transferred out of the number of bytes expected to be
transferred.
10.4.6. Bidirectional Read Residual Count
The Bidirectional Read Residual Count field MUST be valid in the case
where either the u bit or the o bit is set. If neither bit is set,
the Bidirectional Read Residual Count field is reserved. Targets may
set the Bidirectional Read Residual Count and initiators may use it
when the response code is "completed at target". If the o bit is
set, the Bidirectional Read Residual Count indicates the number of
bytes that were not transferred to the initiator because the
initiator's Expected Bidirectional Read Transfer Length was not
sufficient. If the u bit is set, the Bidirectional Read Residual
Count indicates the number of bytes that were not transferred to the
initiator out of the number of bytes expected to be transferred.
10.4.7. Data Segment - Sense and Response Data Segment
iSCSI targets MUST support and enable autosense. If Status is CHECK
CONDITION (0x02), then the Data Segment MUST contain sense data for
the failed command.
For some iSCSI responses, the response data segment MAY contain some
response related information, (e.g., for a target failure, it may
contain a vendor specific detailed description of the failure).
If the DataSegmentLength is not 0, the format of the Data Segment is
as follows:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|SenseLength | Sense Data |
+---------------+---------------+---------------+---------------+
x/ Sense Data /
+---------------+---------------+---------------+---------------+
y/ Response Data /
/ /
+---------------+---------------+---------------+---------------+
z|
10.4.7.1. SenseLength
Length of Sense Data.
10.4.7.2. Sense Data
The Sense Data contains detailed information about a check condition
and [SPC3] specifies the format and content of the Sense Data.
Certain iSCSI conditions result in the command being terminated at
the target (response Command Completed at Target) with a SCSI Check
Condition Status as outlined in the next table:
+--------------------------+----------+---------------------------+
| iSCSI Condition |Sense | Additional Sense Code & |
| |Key | Qualifier |
+--------------------------+----------+---------------------------+
| Unexpected unsolicited |Aborted | ASC = 0x0c ASCQ = 0x0c |
| data |Command-0B| Write Error |
+--------------------------+----------+---------------------------+
| Incorrect amount of data |Aborted | ASC = 0x0c ASCQ = 0x0d |
| |Command-0B| Write Error |
+--------------------------+----------+---------------------------+
| Protocol Service CRC |Aborted | ASC = 0x47 ASCQ = 0x05 |
| error |Command-0B| CRC Error Detected |
+--------------------------+----------+---------------------------+
| SNACK rejected |Aborted | ASC = 0x11 ASCQ = 0x13 |
| |Command-0B| Read Error |
+--------------------------+----------+---------------------------+
The target reports the "Incorrect amount of data" condition if during
data output the total data length to output is greater than
FirstBurstLength and the initiator sent unsolicited non-immediate
data but the total amount of unsolicited data is different than
FirstBurstLength. The target reports the same error when the amount
of data sent as a reply to an R2T does not match the amount
requested.
10.4.8. ExpDataSN
The number of R2T and Data-In (read) PDUs the target has sent for the
command.
This field MUST be 0 if the response code is not Command Completed at
Target or the target sent no Data-In PDUs for the command.
10.4.9. StatSN - Status Sequence Number
StatSN is a Sequence Number that the target iSCSI layer generates per
connection and that in turn, enables the initiator to acknowledge
status reception. StatSN is incremented by 1 for every
response/status sent on a connection except for responses sent as a
result of a retry or SNACK. In the case of responses sent due to a
retransmission request, the StatSN MUST be the same as the first time
the PDU was sent unless the connection has since been restarted.
10.4.10. ExpCmdSN - Next Expected CmdSN from this Initiator
ExpCmdSN is a Sequence Number that the target iSCSI returns to the
initiator to acknowledge command reception. It is used to update a
local variable with the same name. An ExpCmdSN equal to MaxCmdSN+1
indicates that the target cannot accept new commands.
10.4.11. MaxCmdSN - Maximum CmdSN from this Initiator
MaxCmdSN is a Sequence Number that the target iSCSI returns to the
initiator to indicate the maximum CmdSN the initiator can send. It
is used to update a local variable with the same name. If MaxCmdSN
is equal to ExpCmdSN-1, this indicates to the initiator that the
target cannot receive any additional commands. When MaxCmdSN changes
at the target while the target has no pending PDUs to convey this
information to the initiator, it MUST generate a NOP-IN to carry the
new MaxCmdSN.
10.5. Task Management Function Request
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|I| 0x02 |1| Function | Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| Logical Unit Number (LUN) or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Referenced Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32| RefCmdSN or Reserved |
+---------------+---------------+---------------+---------------+
36| ExpDataSN or Reserved |
+---------------+---------------+---------------+---------------+
40/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
10.5.1. Function
The Task Management functions provide an initiator with a way to
explicitly control the execution of one or more Tasks (SCSI and iSCSI
tasks). The Task Management function codes are listed below. For a
more detailed description of SCSI task management, see [SAM2].
1 - ABORT TASK - aborts the task identified by the Referenced Task
Tag field.
2 - ABORT TASK SET - aborts all Tasks issued via this session on the
logical unit.
3 - CLEAR ACA - clears the Auto Contingent Allegiance condition.
4 - CLEAR TASK SET - aborts all Tasks in the appropriate task set as
defined by the TST field in the Control mode page (see [SPC3]).
5 - LOGICAL UNIT RESET
6 - TARGET WARM RESET
7 - TARGET COLD RESET
8 - TASK REASSIGN - reassigns connection allegiance for the task
identified by the Referenced Task Tag field to this connection,
thus resuming the iSCSI exchanges for the task.
For all these functions, the Task Management function response MUST
be returned as detailed in Section 10.6 Task Management Function
Response. All these functions apply to the referenced tasks
regardless of whether they are proper SCSI tasks or tagged iSCSI
operations. Task management requests must act on all the commands
from the same session having a CmdSN lower than the task management
CmdSN. LOGICAL UNIT RESET, TARGET WARM RESET and TARGET COLD RESET
may affect commands from other sessions or commands from the same
session with CmdSN equal or exceeding CmdSN.
If the task management request is marked for immediate delivery, it
must be considered immediately for execution, but the operations
involved (all or part of them) may be postponed to allow the target
to receive all relevant tasks. According to [SAM2], for all the
tasks covered by the Task Management response (i.e., with CmdSN lower
than the task management command CmdSN) but except the Task
Management response to a TASK REASSIGN, additional responses MUST NOT
be delivered to the SCSI layer after the Task Management response.
The iSCSI initiator MAY deliver to the SCSI layer all responses
received before the Task Management response (i.e., it is a matter of
implementation if the SCSI responses, received before the Task
Management response but after the task management request was issued,
are delivered to the SCSI layer by the iSCSI layer in the initiator).
The iSCSI target MUST ensure that no responses for the tasks covered
by a task management function are delivered to the iSCSI initiator
after the Task Management response except for a task covered by a
TASK REASSIGN.
For ABORT TASK SET and CLEAR TASK SET, the issuing initiator MUST
continue to respond to all valid target transfer tags (received via
R2T, Text Response, NOP-In, or SCSI Data-In PDUs) related to the
affected task set, even after issuing the task management request.
The issuing initiator SHOULD however terminate (i.e., by setting the
F-bit to 1) these response sequences as quickly as possible. The
target on its part MUST wait for responses on all affected target
transfer tags before acting on either of these two task management
requests. In case all or part of the response sequence is not
received (due to digest errors) for a valid TTT, the target MAY treat
it as a case of within-command error recovery class (see Section
6.1.4.1 Recovery Within-command) if it is supporting
ErrorRecoveryLevel >= 1, or alternatively may drop the connection to
complete the requested task set function.
If an ABORT TASK is issued for a task created by an immediate command
then RefCmdSN MUST be that of the Task Management request itself
(i.e., CmdSN and RefCmdSN are equal); otherwise RefCmdSN MUST be set
to the CmdSN of the task to be aborted (lower than CmdSN).
If the connection is still active (it is not undergoing an implicit
or explicit logout), ABORT TASK MUST be issued on the same connection
to which the task to be aborted is allegiant at the time the Task
Management Request is issued. If the connection is implicitly or
explicitly logged out (i.e., no other request will be issued on the
failing connection and no other response will be received on the
failing connection), then an ABORT TASK function request may be
issued on another connection. This Task Management request will then
establish a new allegiance for the command to be aborted as well as
abort it (i.e., the task to be aborted will not have to be retried or
reassigned, and its status, if issued but not acknowledged, will be
reissued followed by the Task Management response).
At the target an ABORT TASK function MUST NOT be executed on a Task
Management request; such a request MUST result in Task Management
response of "Function rejected".
For the LOGICAL UNIT RESET function, the target MUST behave as
dictated by the Logical Unit Reset function in [SAM2].
The implementation of the TARGET WARM RESET function and the TARGET
COLD RESET function is OPTIONAL and when implemented, should act as
described below. The TARGET WARM RESET is also subject to SCSI
access controls on the requesting initiator as defined in [SPC3].
When authorization fails at the target, the appropriate response as
described in Section 10.6 Task Management Function Response MUST be
returned by the target. The TARGET COLD RESET function is not
subject to SCSI access controls, but its execution privileges may be
managed by iSCSI mechanisms such as login authentication.
When executing the TARGET WARM RESET and TARGET COLD RESET functions,
the target cancels all pending operations on all Logical Units known
by the issuing initiator. Both functions are equivalent to the
Target Reset function specified by [SAM2]. They can affect many
other initiators logged in with the servicing SCSI target port.
The target MUST treat the TARGET COLD RESET function additionally as
a power on event, thus terminating all of its TCP connections to all
initiators (all sessions are terminated). For this reason, the
Service Response (defined by [SAM2]) for this SCSI task management
function may not be reliably delivered to the issuing initiator port.
For the TASK REASSIGN function, the target should reassign the
connection allegiance to this new connection (and thus resume iSCSI
exchanges for the task). TASK REASSIGN MUST ONLY be received by the
target after the connection on which the command was previously
executing has been successfully logged-out. The Task Management
response MUST be issued before the reassignment becomes effective.
For additional usage semantics see Section 6.2 Retry and Reassign in
Recovery.
At the target a TASK REASSIGN function request MUST NOT be executed
to reassign the connection allegiance of a Task Management function
request, an active text negotiation task, or a Logout task; such a
request MUST result in Task Management response of "Function
rejected".
TASK REASSIGN MUST be issued as an immediate command.
10.5.2. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
10.5.3. LUN
This field is required for functions that address a specific LU
(ABORT TASK, CLEAR TASK SET, ABORT TASK SET, CLEAR ACA, LOGICAL UNIT
RESET) and is reserved in all others.
10.5.4. Referenced Task Tag
The Initiator Task Tag of the task to be aborted for the ABORT TASK
function or reassigned for the TASK REASSIGN function. For all the
other functions this field MUST be set to the reserved value
0xffffffff.
10.5.5. RefCmdSN
If an ABORT TASK is issued for a task created by an immediate command
then RefCmdSN MUST be that of the Task Management request itself
(i.e., CmdSN and RefCmdSN are equal).
For an ABORT TASK of a task created by non-immediate command RefCmdSN
MUST be set to the CmdSN of the task identified by the Referenced
Task Tag field. Targets must use this field as described in section
10.6.1 when the task identified by the Referenced Task Tag field is
not with the target.
Otherwise, this field is reserved.
10.5.6. ExpDataSN
For recovery purposes, the iSCSI target and initiator maintain a data
acknowledgement reference number - the first input DataSN number
unacknowledged by the initiator. When issuing a new command, this
number is set to 0. If the function is TASK REASSIGN, which
establishes a new connection allegiance for a previously issued Read
or Bidirectional command, ExpDataSN will contain an updated data
acknowledgement reference number or the value 0; the latter
indicating that the data acknowledgement reference number is
unchanged. The initiator MUST discard any data PDUs from the
previous execution that it did not acknowledge and the target MUST
transmit all Data-In PDUs (if any) starting with the data
acknowledgement reference number. The number of retransmitted PDUs
may or may not be the same as the original transmission depending on
if there was a change in MaxRecvDataSegmentLength in the
reassignment. The target MAY also send no more Data-In PDUs if all
data has been acknowledged.
The value of ExpDataSN MUST be 0 or higher than the DataSN of the
last acknowledged Data-In PDU, but not larger than DataSN+1 of the
last Data-In PDU sent by the target. Any other value MUST be ignored
by the target.
For other functions this field is reserved.
10.6. Task Management Function Response
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x22 |1| Reserved | Response | Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------------------------------------------------------+
8/ Reserved /
/ /
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Reserved |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
For the functions ABORT TASK, ABORT TASK SET, CLEAR ACA, CLEAR TASK
SET, LOGICAL UNIT RESET, TARGET COLD RESET, TARGET WARM RESET and
TASK REASSIGN, the target performs the requested Task Management
function and sends a Task Management response back to the initiator.
For TASK REASSIGN, the new connection allegiance MUST ONLY become
effective at the target after the target issues the Task Management
Response.
10.6.1. Response
The target provides a Response, which may take on the following
values:
a) 0 - Function complete.
b) 1 - Task does not exist.
c) 2 - LUN does not exist.
d) 3 - Task still allegiant.
e) 4 - Task allegiance reassignment not supported.
f) 5 - Task management function not supported.
g) 6 - Function authorization failed.
h) 255 - Function rejected.
All other values are reserved.
For a discussion on usage of response codes 3 and 4, see Section
6.2.2 Allegiance Reassignment.
For the TARGET COLD RESET and TARGET WARM RESET functions, the target
cancels all pending operations across all Logical Units known to the
issuing initiator. For the TARGET COLD RESET function, the target
MUST then close all of its TCP connections to all initiators
(terminates all sessions).
The mapping of the response code into a SCSI service response code
value, if needed, is outside the scope of this document. However, in
symbolic terms Response values 0 and 1 map to the SCSI service
response of FUNCTION COMPLETE. All other Response values map to the
SCSI service response of FUNCTION REJECTED. If a Task Management
function response PDU does not arrive before the session is
terminated, the SCSI service response is SERVICE DELIVERY OR TARGET
FAILURE.
The response to ABORT TASK SET and CLEAR TASK SET MUST only be issued
by the target after all of the commands affected have been received
by the target, the corresponding task management functions have been
executed by the SCSI target, and the delivery of all responses
delivered until the task management function completion have been
confirmed (acknowledged through ExpStatSN) by the initiator on all
connections of this session. For the exact timeline of events, refer
to Section 10.6.2 Task Management Actions on Task Sets.
For the ABORT TASK function,
a) If the Referenced Task Tag identifies a valid task leading to
a successful termination, then targets must return the
"Function complete" response.
b) If the Referenced Task Tag does not identify an existing task,
but if the CmdSN indicated by the RefCmdSN field in the Task
Management function request is within the valid CmdSN window
and less than the CmdSN of the Task Management function
request itself, then targets must consider the CmdSN received
and return the "Function complete" response.
c) If the Referenced Task Tag does not identify an existing task
and if the CmdSN indicated by the RefCmdSN field in the Task
Management function request is outside the valid CmdSN window,
then targets must return the "Task does not exist" response.
10.6.2. Task Management Actions on Task Sets
The execution of ABORT TASK SET and CLEAR TASK SET Task Management
function requests consists of the following sequence of events in the
specified order on each of the entities.
The initiator:
a) Issues ABORT TASK SET/CLEAR TASK SET request.
b) Continues to respond to each target transfer tag received
for the affected task set.
c) Receives any responses for the tasks in the affected task
set (may process them as usual because they are guaranteed
to be valid).
d) Receives the task set management response, thus concluding
all the tasks in the affected task set.
The target:
a) Receives the ABORT TASK SET/CLEAR TASK SET request.
b) Waits for all target transfer tags to be responded to and
for all affected tasks in the task set to be received.
c) Propagates the command to and receives the response from the
target SCSI layer.
d) Takes note of last-sent StatSN on each of the connections in
the iSCSI sessions (one or more) sharing the affected task
set, and waits for acknowledgement of each StatSN (may
solicit for acknowledgement by way of a NOP-In). If some
tasks originate from non-iSCSI I_T_L nexi then the means by
which the target insures that all affected tasks have
returned their status to the initiator are defined by the
specific protocol.
e) Sends the task set management response to the issuing
initiator.
10.6.3. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
10.7. SCSI Data-Out & SCSI Data-In
The SCSI Data-Out PDU for WRITE operations has the following format:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x05 |F| Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| Reserved |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32| Reserved |
+---------------+---------------+---------------+---------------+
36| DataSN |
+---------------+---------------+---------------+---------------+
40| Buffer Offset |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
/ DataSegment /
+/ /
+---------------+---------------+---------------+---------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
The SCSI Data-In PDU for READ operations has the following format:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x25 |F|A|0 0 0|O|U|S| Reserved |Status or Rsvd |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| StatSN or Reserved |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| DataSN |
+---------------+---------------+---------------+---------------+
40| Buffer Offset |
+---------------+---------------+---------------+---------------+
44| Residual Count |
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
/ DataSegment /
+/ /
+---------------+---------------+---------------+---------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
Status can accompany the last Data-In PDU if the command did not end
with an exception (i.e., the status is "good status" - GOOD,
CONDITION MET or INTERMEDIATE CONDITION MET). The presence of status
(and of a residual count) is signaled though the S flag bit.
Although targets MAY choose to send even non-exception status in
separate responses, initiators MUST support non-exception status in
Data-In PDUs.
10.7.1. F (Final) Bit
For outgoing data, this bit is 1 for the last PDU of unsolicited data
or the last PDU of a sequence that answers an R2T.
For incoming data, this bit is 1 for the last input (read) data PDU
of a sequence. Input can be split into several sequences, each
having its own F bit. Splitting the data stream into sequences does
not affect DataSN counting on Data-In PDUs. It MAY be used as a
"change direction" indication for Bidirectional operations that need
such a change.
DataSegmentLength MUST not exceed MaxRecvDataSegmentLength for the
direction it is sent and the total of all the DataSegmentLength of
all PDUs in a sequence MUST not exceed MaxBurstLength (or
FirstBurstLength for unsolicited data). However the number of
individual PDUs in a sequence (or in total) may be higher than the
MaxBurstLength (or FirstBurstLength) to MaxRecvDataSegmentLength
ratio (as PDUs may be limited in length by the sender capabilities).
Using DataSegmentLength of 0 may increase beyond what is reasonable
for the number of PDUs and should therefore be avoided.
For Bidirectional operations, the F bit is 1 for both the end of the
input sequences and the end of the output sequences.
10.7.2. A (Acknowledge) Bit
For sessions with ErrorRecoveryLevel 1 or higher, the target sets
this bit to 1 to indicate that it requests a positive acknowledgement
from the initiator for the data received. The target should use the
A bit moderately; it MAY only set the A bit to 1 once every
MaxBurstLength bytes, or on the last Data-In PDU that concludes the
entire requested read data transfer for the task from the target's
perspective, and it MUST NOT do so more frequently. The target MUST
NOT set to 1 the A bit for sessions with ErrorRecoveryLevel=0. The
initiator MUST ignore the A bit set to 1 for sessions with
ErrorRecoveryLevel=0.
On receiving a Data-In PDU with the A bit set to 1 on a session with
ErrorRecoveryLevel greater than 0, if there are no holes in the read
data until that Data-In PDU, the initiator MUST issue a SNACK of type
DataACK except when it is able to acknowledge the status for the task
immediately via ExpStatSN on other outbound PDUs if the status for
the task is also received. In the latter case (acknowledgement
through ExpStatSN), sending a SNACK of type DataACK in response to
the A bit is OPTIONAL, but if it is done, it must not be sent after
the status acknowledgement through ExpStatSN. If the initiator has
detected holes in the read data prior to that Data-In PDU, it MUST
postpone issuing the SNACK of type DataACK until the holes are
filled. An initiator also MUST NOT acknowledge the status for the
task before those holes are filled. A status acknowledgement for a
task that generated the Data-In PDUs is considered by the target as
an implicit acknowledgement of the Data-In PDUs if such an
acknowledgement was requested by the target.
10.7.3. Flags (byte 1)
The last SCSI Data packet sent from a target to an initiator for a
SCSI command that completed successfully (with a status of GOOD,
CONDITION MET, INTERMEDIATE or INTERMEDIATE CONDITION MET) may also
optionally contain the Status for the data transfer. As Sense Data
cannot be sent together with the Command Status, if the command is
completed with an error, then the response and sense data MUST be
sent in a SCSI Response PDU (i.e., MUST NOT be sent in a SCSI Data
packet). If Status is sent with the data, then a SCSI Response PDU
MUST NOT be sent as this would violate SCSI rules (a single status).
For Bidirectional commands, the status MUST be sent in a SCSI
Response PDU.
bit 2-4 - Reserved.
bit 5-6 - used the same as in a SCSI Response. These bits are
only valid when S is set to 1. For details see Section
10.4.1 Flags (byte 1).
bit 7 S (status)- set to indicate that the Command Status field
contains status. If this bit is set to 1, the F bit
MUST also be set to 1.
The fields StatSN, Status, and Residual Count only have meaningful
content if the S bit is set to 1 and their values are defined in
Section 10.4 SCSI Response.
10.7.4. Target Transfer Tag and LUN
On outgoing data, the Target Transfer Tag is provided to the target
if the transfer is honoring an R2T. In this case, the Target
Transfer Tag field is a replica of the Target Transfer Tag provided
with the R2T.
On incoming data, the Target Transfer Tag and LUN MUST be provided by
the target if the A bit is set to 1; otherwise they are reserved.
The Target Transfer Tag and LUN are copied by the initiator into the
SNACK of type DataACK that it issues as a result of receiving a SCSI
Data-In PDU with the A bit set to 1.
The Target Transfer Tag values are not specified by this protocol
except that the value 0xffffffff is reserved and means that the
Target Transfer Tag is not supplied. If the Target Transfer Tag is
provided, then the LUN field MUST hold a valid value and be
consistent with whatever was specified with the command; otherwise,
the LUN field is reserved.
10.7.5. DataSN
For input (read) or bidirectional Data-In PDUs, the DataSN is the
input PDU number within the data transfer for the command identified
by the Initiator Task Tag.
R2T and Data-In PDUs, in the context of bidirectional commands, share
the numbering sequence (see Section 3.2.2.3 Data Sequencing).
For output (write) data PDUs, the DataSN is the Data-Out PDU number
within the current output sequence. The current output sequence is
either identified by the Initiator Task Tag (for unsolicited data) or
is a data sequence generated for one R2T (for data solicited through
R2T).
10.7.6. Buffer Offset
The Buffer Offset field contains the offset of this PDU payload data
within the complete data transfer. The sum of the buffer offset and
length should not exceed the expected transfer length for the
command.
The order of data PDUs within a sequence is determined by
DataPDUInOrder. When set to Yes, it means that PDUs have to be in
increasing Buffer Offset order and overlays are forbidden.
The ordering between sequences is determined by DataSequenceInOrder.
When set to Yes, it means that sequences have to be in increasing
Buffer Offset order and overlays are forbidden.
10.7.7. DataSegmentLength
This is the data payload length of a SCSI Data-In or SCSI Data-Out
PDU. The sending of 0 length data segments should be avoided, but
initiators and targets MUST be able to properly receive 0 length data
segments.
The Data Segments of Data-In and Data-Out PDUs SHOULD be filled to
the integer number of 4 byte words (real payload) unless the F bit is
set to 1.
10.8. Ready To Transfer (R2T)
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x31 |1| Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| R2TSN |
+---------------+---------------+---------------+---------------+
40| Buffer Offset |
+---------------+---------------+---------------+---------------+
44| Desired Data Transfer Length |
+---------------------------------------------------------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
When an initiator has submitted a SCSI Command with data that passes
from the initiator to the target (WRITE), the target may specify
which blocks of data it is ready to receive. The target may request
that the data blocks be delivered in whichever order is convenient
for the target at that particular instant. This information is
passed from the target to the initiator in the Ready To Transfer
(R2T) PDU.
In order to allow write operations without an explicit initial R2T,
the initiator and target MUST have negotiated the key InitialR2T to
No during Login.
An R2T MAY be answered with one or more SCSI Data-Out PDUs with a
matching Target Transfer Tag. If an R2T is answered with a single
Data-Out PDU, the Buffer Offset in the Data PDU MUST be the same as
the one specified by the R2T, and the data length of the Data PDU
MUST be the same as the Desired Data Transfer Length specified in the
R2T. If the R2T is answered with a sequence of Data PDUs, the Buffer
Offset and Length MUST be within the range of those specified by R2T,
and the last PDU MUST have the F bit set to 1. If the last PDU
(marked with the F bit) is received before the Desired Data Transfer
Length is transferred, a target MAY choose to Reject that
PDU with "Protocol error" reason code. DataPDUInOrder governs the
Data-Out PDU ordering. If DataPDUInOrder is set to Yes, the Buffer
Offsets and Lengths for consecutive PDUs MUST form a continuous
non-overlapping range and the PDUs MUST be sent in increasing offset
order.
The target may send several R2T PDUs. It, therefore, can have a
number of pending data transfers. The number of outstanding R2T PDUs
are limited by the value of the negotiated key MaxOutstandingR2T.
Within a connection, outstanding R2Ts MUST be fulfilled by the
initiator in the order in which they were received.
R2T PDUs MAY also be used to recover Data Out PDUs. Such an R2T
(Recovery-R2T) is generated by a target upon detecting the loss of
one or more Data-Out PDUs due to:
- Digest error
- Sequence error
- Sequence reception timeout
A Recovery-R2T carries the next unused R2TSN, but requests part of or
the entire data burst that an earlier R2T (with a lower R2TSN) had
already requested.
DataSequenceInOrder governs the buffer offset ordering in consecutive
R2Ts. If DataSequenceInOrder is Yes, then consecutive R2Ts MUST
refer to continuous non-overlapping ranges except for Recovery-R2Ts.
10.8.1. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
10.8.2. R2TSN
R2TSN is the R2T PDU input PDU number within the command identified
by the Initiator Task Tag.
For bidirectional commands R2T and Data-In PDUs share the input PDU
numbering sequence (see Section 3.2.2.3 Data Sequencing).
10.8.3. StatSN
The StatSN field will contain the next StatSN. The StatSN for this
connection is not advanced after this PDU is sent.
10.8.4. Desired Data Transfer Length and Buffer Offset
The target specifies how many bytes it wants the initiator to send
because of this R2T PDU. The target may request the data from the
initiator in several chunks, not necessarily in the original order of
the data. The target, therefore, also specifies a Buffer Offset that
indicates the point at which the data transfer should begin, relative
to the beginning of the total data transfer. The Desired Data
Transfer Length MUST NOT be 0 and MUST not exceed MaxBurstLength.
10.8.5. Target Transfer Tag
The target assigns its own tag to each R2T request that it sends to
the initiator. This tag can be used by the target to easily identify
the data it receives. The Target Transfer Tag and LUN are copied in
the outgoing data PDUs and are only used by the target. There is no
protocol rule about the Target Transfer Tag except that the value
0xffffffff is reserved and MUST NOT be sent by a target in an R2T.
10.9. Asynchronous Message
An Asynchronous Message may be sent from the target to the initiator
without correspondence to a particular command. The target specifies
the reason for the event and sense data.
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x32 |1| Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| 0xffffffff |
+---------------+---------------+---------------+---------------+
20| Reserved |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| AsyncEvent | AsyncVCode | Parameter1 or Reserved |
+---------------+---------------+---------------+---------------+
40| Parameter2 or Reserved | Parameter3 or Reserved |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
/ DataSegment - Sense Data and iSCSI Event Data /
+/ /
+---------------+---------------+---------------+---------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
Some Asynchronous Messages are strictly related to iSCSI while others
are related to SCSI [SAM2].
StatSN counts this PDU as an acknowledgeable event (StatSN is
advanced), which allows for initiator and target state
synchronization.
10.9.1. AsyncEvent
The codes used for iSCSI Asynchronous Messages (events) are:
0 - a SCSI Asynchronous Event is reported in the sense data.
Sense Data that accompanies the report, in the data segment,
identifies the condition. The sending of a SCSI Event
(Asynchronous Event Reporting in SCSI terminology) is
dependent on the target support for SCSI asynchronous event
reporting (see [SAM2]) as indicated in the standard INQUIRY
data (see [SPC3]). Its use may be enabled by parameters in
the SCSI Control mode page (see [SPC3]).
1 - target requests Logout. This Async Message MUST be sent on
the same connection as the one requesting to be logged out.
The initiator MUST honor this request by issuing a Logout as
early as possible, but no later than Parameter3 seconds.
Initiator MUST send a Logout with a reason code of "Close the
connection" OR "Close the session" to close all the
connections. Once this message is received, the initiator
SHOULD NOT issue new iSCSI commands on the connection to be
logged out. The target MAY reject any new I/O requests that
it receives after this Message with the reason code "Waiting
for Logout". If the initiator does not Logout in Parameter3
seconds, the target should send an Async PDU with iSCSI event
code "Dropped the connection" if possible, or simply terminate
the transport connection. Parameter1 and Parameter2 are
reserved.
2 - target indicates it will drop the connection. The Parameter1
field indicates the CID of the connection that is going to be
dropped.
The Parameter2 field (Time2Wait) indicates, in seconds, the
minimum time to wait before attempting to reconnect or
reassign.
The Parameter3 field (Time2Retain) indicates the maximum time
allowed to reassign commands after the initial wait (in
Parameter2).
If the initiator does not attempt to reconnect and/or reassign
the outstanding commands within the time specified by
Parameter3, or if Parameter3 is 0, the target will terminate
all outstanding commands on this connection. In this case, no
other responses should be expected from the target for the
outstanding commands on this connection.
A value of 0 for Parameter2 indicates that reconnect can be
attempted immediately.
3 - target indicates it will drop all the connections of this
session.
Parameter1 field is reserved.
The Parameter2 field (Time2Wait) indicates, in seconds, the
minimum time to wait before attempting to reconnect. The
Parameter3 field (Time2Retain) indicates the maximum time
allowed to reassign commands after the initial wait (in
Parameter2).
If the initiator does not attempt to reconnect and/or reassign
the outstanding commands within the time specified by
Parameter3, or if Parameter3 is 0, the session is terminated.
In this case, the target will terminate all outstanding
commands in this session; no other responses should be
expected from the target for the outstanding commands in this
session. A value of 0 for Parameter2 indicates that reconnect
can be attempted immediately.
4 - target requests parameter negotiation on this connection. The
initiator MUST honor this request by issuing a Text Request
(that can be empty) on the same connection as early as
possible, but no later than Parameter3 seconds, unless a Text
Request is already pending on the connection, or by issuing a
Logout Request. If the initiator does not issue a Text
Request the target may reissue the Asynchronous Message
requesting parameter negotiation.
255 - vendor specific iSCSI Event. The AsyncVCode details the
vendor code, and data MAY accompany the report.
All other event codes are reserved.
10.9.2. AsyncVCode
AsyncVCode is a vendor specific detail code that is only valid if the
AsyncEvent field indicates a vendor specific event. Otherwise, it is
reserved.
10.9.3. LUN
The LUN field MUST be valid if AsyncEvent is 0. Otherwise, this
field is reserved.
10.9.4. Sense Data and iSCSI Event Data
For a SCSI event, this data accompanies the report in the data
segment and identifies the condition.
For an iSCSI event, additional vendor-unique data MAY accompany the
Async event. Initiators MAY ignore the data when not understood
while processing the rest of the PDU.
If the DataSegmentLength is not 0, the format of the DataSegment is
as follows:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|SenseLength | Sense Data |
+---------------+---------------+---------------+---------------+
x/ Sense Data /
+---------------+---------------+---------------+---------------+
y/ iSCSI Event Data /
/ /
+---------------+---------------+---------------+---------------+
z|
10.9.4.1. SenseLength
This is the length of Sense Data. When the Sense Data field is empty
(e.g., the event is not a SCSI event) SenseLength is 0.
10.10. Text Request
The Text Request is provided to allow for the exchange of information
and for future extensions. It permits the initiator to inform a
target of its capabilities or to request some special operations.
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|I| 0x04 |F|C| Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
/ DataSegment (Text) /
+/ /
+---------------+---------------+---------------+---------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
An initiator MUST have at most one outstanding Text Request on a
connection at any given time.
On a connection failure, an initiator must either explicitly abort
any active allegiant text negotiation task or must cause such a task
to be implicitly terminated by the target.
10.10.1. F (Final) Bit
When set to 1, indicates that this is the last or only text request
in a sequence of Text Requests; otherwise, it indicates that more
Text Requests will follow.
10.10.2. C (Continue) Bit
When set to 1, indicates that the text (set of key=value pairs) in
this Text Request is not complete (it will be continued on subsequent
Text Requests); otherwise, it indicates that this Text Request ends a
set of key=value pairs. A Text Request with the C bit set to 1 MUST
have the F bit set to 0.
10.10.3. Initiator Task Tag
The initiator assigned identifier for this Text Request. If the
command is sent as part of a sequence of text requests and responses,
the Initiator Task Tag MUST be the same for all the requests within
the sequence (similar to linked SCSI commands). The I bit for all
requests in a sequence also MUST be the same.
10.10.4. Target Transfer Tag
When the Target Transfer Tag is set to the reserved value 0xffffffff,
it tells the target that this is a new request and the target resets
any internal state associated with the Initiator Task Tag (resets the
current negotiation state).
The target sets the Target Transfer Tag in a text response to a value
other than the reserved value 0xffffffff whenever it indicates that
it has more data to send or more operations to perform that are
associated with the specified Initiator Task Tag. It MUST do so
whenever it sets the F bit to 0 in the response. By copying the
Target Transfer Tag from the response to the next Text Request, the
initiator tells the target to continue the operation for the specific
Initiator Task Tag. The initiator MUST ignore the Target Transfer
Tag in the Text Response when the F bit is set to 1.
This mechanism allows the initiator and target to transfer a large
amount of textual data over a sequence of text-command/text-response
exchanges, or to perform extended negotiation sequences.
If the Target Transfer Tag is not 0xffffffff, the LUN field MUST be
sent by the target in the Text Response.
A target MAY reset its internal negotiation state if an exchange is
stalled by the initiator for a long time or if it is running out of
resources.
Long text responses are handled as in the following example:
I->T Text SendTargets=All (F=1,TTT=0xffffffff)
T->I Text <part 1> (F=0,TTT=0x12345678)
I->T Text <empty> (F=1, TTT=0x12345678)
T->I Text <part 2> (F=0, TTT=0x12345678)
I->T Text <empty> (F=1, TTT=0x12345678)
...
T->I Text <part n> (F=1, TTT=0xffffffff)
10.10.5. Text
The data lengths of a text request MUST NOT exceed the iSCSI target
MaxRecvDataSegmentLength (a per connection and per direction
negotiated parameter). The text format is specified in Section 5.2
Text Mode Negotiation.
Chapter 11 and Chapter 12 list some basic Text key=value pairs, some
of which can be used in Login Request/Response and some in Text
Request/Response.
A key=value pair can span Text request or response boundaries. A
key=value pair can start in one PDU and continue on the next. In
other words the end of a PDU does not necessarily signal the end of a
key=value pair.
The target responds by sending its response back to the initiator.
The response text format is similar to the request text format. The
text response MAY refer to key=value pairs presented in an earlier
text request and the text in the request may refer to earlier
responses.
Chapter 5 details the rules for the Text Requests and Responses.
Text operations are usually meant for parameter setting/
negotiations, but can also be used to perform some long lasting
operations.
Text operations that take a long time should be placed in their own
Text request.
10.11. Text Response
The Text Response PDU contains the target's responses to the
initiator's Text request. The format of the Text field matches that
of the Text request.
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x24 |F|C| Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
/ DataSegment (Text) /
+/ /
+---------------+---------------+---------------+---------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
10.11.1. F (Final) Bit
When set to 1, in response to a Text Request with the Final bit set
to 1, the F bit indicates that the target has finished the whole
operation. Otherwise, if set to 0 in response to a Text Request with
the Final Bit set to 1, it indicates that the target has more work to
do (invites a follow-on text request). A Text Response with the F
bit set to 1 in response to a Text Request with the F bit set to 0 is
a protocol error.
A Text Response with the F bit set to 1 MUST NOT contain key=value
pairs that may require additional answers from the initiator.
A Text Response with the F bit set to 1 MUST have a Target Transfer
Tag field set to the reserved value of 0xffffffff.
A Text Response with the F bit set to 0 MUST have a Target Transfer
Tag field set to a value other than the reserved 0xffffffff.
10.11.2. C (Continue) Bit
When set to 1, indicates that the text (set of key=value pairs) in
this Text Response is not complete (it will be continued on
subsequent Text Responses); otherwise, it indicates that this Text
Response ends a set of key=value pairs. A Text Response with the C
bit set to 1 MUST have the F bit set to 0.
10.11.3. Initiator Task Tag
The Initiator Task Tag matches the tag used in the initial Text
Request.
10.11.4. Target Transfer Tag
When a target has more work to do (e.g., cannot transfer all the
remaining text data in a single Text Response or has to continue the
negotiation) and has enough resources to proceed, it MUST set the
Target Transfer Tag to a value other than the reserved value of
0xffffffff. Otherwise, the Target Transfer Tag MUST be set to
0xffffffff.
When the Target Transfer Tag is not 0xffffffff, the LUN field may be
significant.
The initiator MUST copy the Target Transfer Tag and LUN in its next
request to indicate that it wants the rest of the data.
When the target receives a Text Request with the Target Transfer Tag
set to the reserved value of 0xffffffff, it resets its internal
information (resets state) associated with the given Initiator Task
Tag (restarts the negotiation).
When a target cannot finish the operation in a single Text Response,
and does not have enough resources to continue, it rejects the Text
Request with the appropriate Reject code.
A target may reset its internal state associated with an Initiator
Task Tag (the current negotiation state), state expressed through the
Target Transfer Tag if the initiator fails to continue the exchange
for some time. The target may reject subsequent Text Requests with
the Target Transfer Tag set to the "stale" value.
10.11.5. StatSN
The target StatSN variable is advanced by each Text Response sent.
10.11.6. Text Response Data
The data lengths of a text response MUST NOT exceed the iSCSI
initiator MaxRecvDataSegmentLength (a per connection and per
direction negotiated parameter).
The text in the Text Response Data is governed by the same rules as
the text in the Text Request Data (see Section 10.10.5 Text).
Although the initiator is the requesting party and controls the
request-response initiation and termination, the target can offer
key=value pairs of its own as part of a sequence and not only in
response to the initiator.
10.12. Login Request
After establishing a TCP connection between an initiator and a
target, the initiator MUST start a Login Phase to gain further access
to the target's resources.
The Login Phase (see Chapter 5) consists of a sequence of Login
Requests and Responses that carry the same Initiator Task Tag.
Login Requests are always considered as immediate.
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|1| 0x03 |T|C|.|.|CSG|NSG| Version-max | Version-min |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| ISID |
+ +---------------+---------------+
12| | TSIH |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| CID | Reserved |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN or Reserved |
+---------------+---------------+---------------+---------------+
32| Reserved |
+---------------+---------------+---------------+---------------+
36| Reserved |
+---------------+---------------+---------------+---------------+
40/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48/ DataSegment - Login Parameters in Text request Format /
+/ /
+---------------+---------------+---------------+---------------+
10.12.1. T (Transit) Bit
If set to 1, indicates that the initiator is ready to transit to the
next stage.
If the T bit is set to 1 and NSG is FullFeaturePhase, then this also
indicates that the initiator is ready for the Final Login Response
(see Chapter 5).
10.12.2. C (Continue) Bit
When set to 1, indicates that the text (set of key=value pairs) in
this Login Request is not complete (it will be continued on
subsequent Login Requests); otherwise, it indicates that this Login
Request ends a set of key=value pairs. A Login Request with the C
bit set to 1 MUST have the T bit set to 0.
10.12.3. CSG and NSG
Through these fields, Current Stage (CSG) and Next Stage (NSG), the
Login negotiation requests and responses are associated with a
specific stage in the session (SecurityNegotiation,
LoginOperationalNegotiation, FullFeaturePhase) and may indicate the
next stage to which they want to move (see Chapter 5). The next
stage value is only valid when the T bit is 1; otherwise, it is
reserved.
The stage codes are:
- 0 - SecurityNegotiation
- 1 - LoginOperationalNegotiation
- 3 - FullFeaturePhase
All other codes are reserved.
10.12.4. Version
The version number of the current draft is 0x00. As such, all
devices MUST carry version 0x00 for both Version-min and Version-max.
10.12.4.1. Version-max
Maximum Version number supported.
All Login Requests within the Login Phase MUST carry the same
Version-max.
The target MUST use the value presented with the first Login Request.
10.12.4.2. Version-min
All Login Requests within the Login Phase MUST carry the same
Version-min. The target MUST use the value presented with the first
Login Request.
10.12.5. ISID
This is an initiator-defined component of the session identifier and
is structured as follows (see [RFC3721] and Section 9.1.1
Conservative Reuse of ISIDs for details):
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
8| T | A | B | C |
+---------------+---------------+---------------+---------------+
12| D |
+---------------+---------------+
The T field identifies the format and usage of A, B, C, and D as
indicated below:
T
00b OUI-Format
A&B are a 22 bit OUI
(the I/G & U/L bits are omitted)
C&D 24 bit qualifier
01b EN - Format (IANA Enterprise Number)
A - Reserved
B&C EN (IANA Enterprise Number)
D - Qualifier
10b "Random"
A - Reserved
B&C Random
D - Qualifier
11b A,B,C&D Reserved
For the T field values 00b and 01b, a combination of A and B (for
00b) or B and C (for 01b) identifies the vendor or organization whose
component (software or hardware) generates this ISID. A vendor or
organization with one or more OUIs, or one or more Enterprise
Numbers, MUST use at least one of these numbers and select the
appropriate value for the T field when its components generate ISIDs.
An OUI or EN MUST be set in the corresponding fields in network byte
order (byte big-endian).
If the T field is 10b, B and C are set to a random 24-bit unsigned
integer value in network byte order (byte big-endian). See [RFC3721]
for how this affects the principle of "conservative reuse".
The Qualifier field is a 16 or 24-bit unsigned integer value that
provides a range of possible values for the ISID within the selected
namespace. It may be set to any value within the constraints
specified in the iSCSI protocol (see Section 3.4.3 Consequences of
the Model and Section 9.1.1 Conservative Reuse of ISIDs).
The T field value of 11b is reserved.
If the ISID is derived from something assigned to a hardware adapter
or interface by a vendor, as a preset default value, it MUST be
configurable to a value assigned according to the SCSI port behavior
desired by the system in which it is installed (see Section 9.1.1
Conservative Reuse of ISIDs and Section 9.1.2 iSCSI Name, ISID, and
TPGT Use). The resultant ISID MUST also be persistent over power
cycles, reboot, card swap, etc.
10.12.6. TSIH
TSIH must be set in the first Login Request. The reserved value 0
MUST be used on the first connection for a new session. Otherwise,
the TSIH sent by the target at the conclusion of the successful login
of the first connection for this session MUST be used. The TSIH
identifies to the target the associated existing session for this new
connection.
All Login Requests within a Login Phase MUST carry the same TSIH.
The target MUST check the value presented with the first Login
Request and act as specified in Section 5.3.1 Login Phase Start.
10.12.7. Connection ID - CID
A unique ID for this connection within the session.
All Login Requests within the Login Phase MUST carry the same CID.
The target MUST use the value presented with the first Login Request.
A Login Request with a non-zero TSIH and a CID equal to that of an
existing connection implies a logout of the connection followed by a
Login (see Section 5.3.4 Connection Reinstatement). For the details
of the implicit Logout Request, see Section 10.14 Logout Request.
10.12.8. CmdSN
CmdSN is either the initial command sequence number of a session (for
the first Login Request of a session - the "leading" login), or the
command sequence number in the command stream if the login is for a
new connection in an existing session.
Examples:
- Login on a leading connection - if the leading login carries
the CmdSN 123, all other Login Requests in the same Login Phase
carry the CmdSN 123 and the first non-immediate command in
FullFeaturePhase also carries the CmdSN 123.
- Login on other than a leading connection - if the current CmdSN
at the time the first login on the connection is issued is 500,
then that PDU carries CmdSN=500. Subsequent Login Requests
that are needed to complete this Login Phase may carry a CmdSN
higher than 500 if non-immediate requests that were issued on
other connections in the same session advance CmdSN.
If the Login Request is a leading Login Request, the target MUST use
the value presented in CmdSN as the target value for ExpCmdSN.
10.12.9. ExpStatSN
For the first Login Request on a connection this is ExpStatSN for the
old connection and this field is only valid if the Login Request
restarts a connection (see Section 5.3.4 Connection Reinstatement).
For subsequent Login Requests it is used to acknowledge the Login
Responses with their increasing StatSN values.
10.12.10. Login Parameters
The initiator MUST provide some basic parameters in order to enable
the target to determine if the initiator may use the target's
resources and the initial text parameters for the security exchange.
All the rules specified in Section 10.10.5 Text for text requests
also hold for Login Requests. Keys and their explanations are listed
in Chapter 11 (security negotiation keys) and Chapter 12 (operational
parameter negotiation keys). All keys in Chapter 12, except for the
X extension formats, MUST be supported by iSCSI initiators and
targets. Keys in Chapter 11 only need to be supported when the
function to which they refer is mandatory to implement.
10.13. Login Response
The Login Response indicates the progress and/or end of the Login
Phase.
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x23 |T|C|.|.|CSG|NSG| Version-max | Version-active|
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| ISID |
+ +---------------+---------------+
12| | TSIH |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Reserved |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| Status-Class | Status-Detail | Reserved |
+---------------+---------------+---------------+---------------+
40/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48/ DataSegment - Login Parameters in Text request Format /
+/ /
+---------------+---------------+---------------+---------------+
10.13.1. Version-max
This is the highest version number supported by the target.
All Login Responses within the Login Phase MUST carry the same
Version-max.
The initiator MUST use the value presented as a response to the first
Login Request.
10.13.2. Version-active
Indicates the highest version supported by the target and initiator.
If the target does not support a version within the range specified
by the initiator, the target rejects the login and this field
indicates the lowest version supported by the target.
All Login Responses within the Login Phase MUST carry the same
Version-active.
The initiator MUST use the value presented as a response to the first
Login Request.
10.13.3. TSIH
The TSIH is the target assigned session identifying handle. Its
internal format and content are not defined by this protocol except
for the value 0 that is reserved. With the exception of the Login
Final-Response in a new session, this field should be set to the TSIH
provided by the initiator in the Login Request. For a new session,
the target MUST generate a non-zero TSIH and ONLY return it in the
Login Final-Response (see Section 5.3 Login Phase).
10.13.4. StatSN
For the first Login Response (the response to the first Login
Request), this is the starting status Sequence Number for the
connection. The next response of any kind, including the next Login
Response, if any, in the same Login Phase, will carry this number +
1. This field is only valid if the Status-Class is 0.
10.13.5. Status-Class and Status-Detail
The Status returned in a Login Response indicates the execution
status of the Login Phase. The status includes:
Status-Class
Status-Detail
0 Status-Class indicates success.
A non-zero Status-Class indicates an exception. In this case,
Status-Class is sufficient for a simple initiator to use when
handling exceptions, without having to look at the Status-Detail.
The Status-Detail allows finer-grained exception handling for more
sophisticated initiators and for better information for logging.
The status classes are as follows:
0 - Success - indicates that the iSCSI target successfully
received, understood, and accepted the request. The numbering
fields (StatSN, ExpCmdSN, MaxCmdSN) are only valid if
Status-Class is 0.
1 - Redirection - indicates that the initiator must take further
action to complete the request. This is usually due to the
target moving to a different address. All of the redirection
status class responses MUST return one or more text key
parameters of the type "TargetAddress", which indicates the
target's new address. A redirection response MAY be issued by
a target prior or after completing a security negotiation if a
security negotiation is required. A redirection SHOULD be
accepted by an initiator even without having the target
complete a security negotiation if any security negotiation is
required, and MUST be accepted by the initiator after the
completion of the security negotiation if any security
negotiation is required.
2 - Initiator Error (not a format error) - indicates that the
initiator most likely caused the error. This MAY be due to a
request for a resource for which the initiator does not have
permission. The request should not be tried again.
3 - Target Error - indicates that the target sees no errors in the
initiator's Login Request, but is currently incapable of
fulfilling the request. The initiator may re-try the same
Login Request later.
The table below shows all of the currently allocated status codes.
The codes are in hexadecimal; the first byte is the status class and
the second byte is the status detail.
-----------------------------------------------------------------
Status | Code | Description
|(hex) |
-----------------------------------------------------------------
Success | 0000 | Login is proceeding OK (*1).
-----------------------------------------------------------------
Target moved | 0101 | The requested iSCSI Target Name (ITN)
temporarily | | has temporarily moved
| | to the address provided.
-----------------------------------------------------------------
Target moved | 0102 | The requested ITN has permanently moved
permanently | | to the address provided.
-----------------------------------------------------------------
Initiator | 0200 | Miscellaneous iSCSI initiator
error | | errors.
----------------------------------------------------------------
Authentication| 0201 | The initiator could not be
failure | | successfully authenticated or target
| | authentication is not supported.
-----------------------------------------------------------------
Authorization | 0202 | The initiator is not allowed access
failure | | to the given target.
-----------------------------------------------------------------
Not found | 0203 | The requested ITN does not
| | exist at this address.
-----------------------------------------------------------------
Target removed| 0204 | The requested ITN has been removed and
| |no forwarding address is provided.
-----------------------------------------------------------------
Unsupported | 0205 | The requested iSCSI version range is
version | | not supported by the target.
-----------------------------------------------------------------
Too many | 0206 | Too many connections on this SSID.
connections | |
-----------------------------------------------------------------
Missing | 0207 | Missing parameters (e.g., iSCSI
parameter | | Initiator and/or Target Name).
-----------------------------------------------------------------
Can't include | 0208 | Target does not support session
in session | | spanning to this connection (address).
-----------------------------------------------------------------
Session type | 0209 | Target does not support this type of
not supported | | of session or not from this Initiator.
-----------------------------------------------------------------
Session does | 020a | Attempt to add a connection
not exist | | to a non-existent session.
-----------------------------------------------------------------
Invalid during| 020b | Invalid Request type during Login.
login | |
-----------------------------------------------------------------
Target error | 0300 | Target hardware or software error.
-----------------------------------------------------------------
Service | 0301 | The iSCSI service or target is not
unavailable | | currently operational.
-----------------------------------------------------------------
Out of | 0302 | The target has insufficient session,
resources | | connection, or other resources.
-----------------------------------------------------------------
(*1) If the response T bit is 1 in both the request and the matching
response, and the NSG is FullFeaturePhase in both the request and the
matching response, the Login Phase is finished and the initiator may
proceed to issue SCSI commands.
If the Status Class is not 0, the initiator and target MUST close the
TCP connection.
If the target wishes to reject the Login Request for more than one
reason, it should return the primary reason for the rejection.
10.13.6. T (Transit) bit
The T bit is set to 1 as an indicator of the end of the stage. If
the T bit is set to 1 and NSG is FullFeaturePhase, then this is also
the Final Login Response (see Chapter 5). A T bit of 0 indicates a
"partial" response, which means "more negotiation needed".
A Login Response with a T bit set to 1 MUST NOT contain key=value
pairs that may require additional answers from the initiator within
the same stage.
If the status class is 0, the T bit MUST NOT be set to 1 if the T bit
in the request was set to 0.
10.13.7. C (Continue) Bit
When set to 1, indicates that the text (set of key=value pairs) in
this Login Response is not complete (it will be continued on
subsequent Login Responses); otherwise, it indicates that this Login
Response ends a set of key=value pairs. A Login Response with the C
bit set to 1 MUST have the T bit set to 0.
10.13.8. Login Parameters
The target MUST provide some basic parameters in order to enable the
initiator to determine if it is connected to the correct port and the
initial text parameters for the security exchange.
All the rules specified in Section 10.11.6 Text Response Data for
text responses also hold for Login Responses. Keys and their
explanations are listed in Chapter 11 (security negotiation keys) and
Chapter 12 (operational parameter negotiation keys). All keys in
Chapter 12, except for the X extension formats, MUST be supported by
iSCSI initiators and targets. Keys in Chapter 11, only need to be
supported when the function to which they refer is mandatory to
implement.
10.14. Logout Request
The Logout Request is used to perform a controlled closing of a
connection.
An initiator MAY use a Logout Request to remove a connection from a
session or to close an entire session.
After sending the Logout Request PDU, an initiator MUST NOT send any
new iSCSI requests on the closing connection. If the Logout Request
is intended to close the session, new iSCSI requests MUST NOT be sent
on any of the connections participating in the session.
When receiving a Logout Request with the reason code of "close the
connection" or "close the session", the target MUST terminate all
pending commands, whether acknowledged via ExpCmdSN or not, on that
connection or session respectively.
When receiving a Logout Request with the reason code "remove
connection for recovery", the target MUST discard all requests not
yet acknowledged via ExpCmdSN that were issued on the specified
connection, and suspend all data/status/R2T transfers on behalf of
pending commands on the specified connection.
The target then issues the Logout Response and half-closes the TCP
connection (sends FIN). After receiving the Logout Response and
attempting to receive the FIN (if still possible), the initiator MUST
completely close the logging-out connection. For the terminated
commands, no additional responses should be expected.
A Logout for a CID may be performed on a different transport
connection when the TCP connection for the CID has already been
terminated. In such a case, only a logical "closing" of the iSCSI
connection for the CID is implied with a Logout.
All commands that were not terminated or not completed (with status)
and acknowledged when the connection is closed completely can be
reassigned to a new connection if the target supports connection
recovery.
If an initiator intends to start recovery for a failing connection,
it MUST use the Logout Request to "clean-up" the target end of a
failing connection and enable recovery to start, or the Login Request
with a non-zero TSIH and the same CID on a new connection for the
same effect (see Section 10.14.3 CID). In sessions with a single
connection, the connection can be closed and then a new connection
reopened. A connection reinstatement login can be used for recovery
(see Section 5.3.4 Connection Reinstatement).
A successful completion of a Logout Request with the reason code of
"close the connection" or "remove the connection for recovery"
results at the target in the discarding of unacknowledged commands
received on the connection being logged out. These are commands that
have arrived on the connection being logged out, but have not been
delivered to SCSI because one or more commands with a smaller CmdSN
has not been received by iSCSI. See Section 3.2.2.1 Command
Numbering and Acknowledging. The resulting holes the in command
sequence numbers will have to be handled by appropriate recovery (see
Chapter 6) unless the session is also closed.
The entire logout discussion in this section is also applicable for
an implicit Logout realized via a connection reinstatement or session
reinstatement. When a Login Request performs an implicit Logout, the
implicit Logout is performed as if having the reason codes specified
below:
Reason code Type of implicit Logout
-------------------------------------------
0 session reinstatement
1 connection reinstatement when
the operational ErrorRecoveryLevel < 2
2 connection reinstatement when
the operational ErrorRecoveryLevel = 2
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|I| 0x06 |1| Reason Code | Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------------------------------------------------------+
8/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| CID or Reserved | Reserved |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
10.14.1. Reason Code
Reason Code indicates the reason for Logout as follows:
0 - close the session. All commands associated with the session
(if any) are terminated.
1 - close the connection. All commands associated with connection
(if any) are terminated.
2 - remove the connection for recovery. Connection is closed and
all commands associated with it, if any, are to be prepared
for a new allegiance.
All other values are reserved.
10.14.2. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
10.14.3. CID
This is the connection ID of the connection to be closed (including
closing the TCP stream). This field is only valid if the reason code
is not "close the session".
10.14.4. ExpStatSN
This is the last ExpStatSN value for the connection to be closed.
10.14.5. Implicit termination of tasks
A target implicitly terminates the active tasks due to the iSCSI
protocol in the following cases:
a) When a connection is implicitly or explicitly logged out with
the reason code of "Close the connection" and there are active
tasks allegiant to that connection.
b) When a connection fails and eventually the connection state
times out (state transition M1 in Section 7.2.2 State
Transition Descriptions for Initiators and Targets) and there
are active tasks allegiant to that connection.
c) When a successful recovery Logout is performed while there are
active tasks allegiant to that connection, and those tasks
eventually time out after the Time2Wait and Time2Retain
periods without allegiance reassignment.
d) When a connection is implicitly or explicitly logged out with
the reason code of "Close the session" and there are active
tasks in that session.
If the tasks terminated in any of the above cases are SCSI tasks,
they must be internally terminated as if with CHECK CONDITION status.
This status is only meaningful for appropriately handling the
internal SCSI state and SCSI side effects with respect to ordering
because this status is never communicated back as a terminating
status to the initiator. However additional actions may have to be
taken at SCSI level depending on the SCSI context as defined by the
SCSI standards (e.g., queued commands and ACA, in cases a), b), and
c), after the tasks are terminated, the target MUST report a Unit
Attention condition on the next command processed on any connection
for each affected I_T_L nexus with the status of CHECK CONDITION, and
the ASC/ASCQ value of 47h/7Fh - "SOME COMMANDS CLEARED BY ISCSI
PROTOCOL EVENT" - etc. - see [SAM2] and [SPC3]).
10.15. Logout Response
The Logout Response is used by the target to indicate if the cleanup
operation for the connection(s) has completed.
After Logout, the TCP connection referred by the CID MUST be closed
at both ends (or all connections must be closed if the logout reason
was session close).
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x26 |1| Reserved | Response | Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------------------------------------------------------+
8/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Reserved |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| Reserved |
+---------------------------------------------------------------+
40| Time2Wait | Time2Retain |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
10.15.1. Response
Logout Response:
0 - connection or session closed successfully.
1 - CID not found.
2 - connection recovery is not supported. If Logout reason code
was recovery and target does not support it as indicated by the
ErrorRecoveryLevel.
3 - cleanup failed for various reasons.
10.15.2. TotalAHSLength and DataSegmentLength
For this PDU TotalAHSLength and DataSegmentLength MUST be 0.
10.15.3. Time2Wait
If the Logout Response code is 0 and if the operational
ErrorRecoveryLevel is 2, this is the minimum amount of time, in
seconds, to wait before attempting task reassignment. If the Logout
Response code is 0 and if the operational ErrorRecoveryLevel is less
than 2, this field is to be ignored.
This field is invalid if the Logout Response code is 1.
If the Logout response code is 2 or 3, this field specifies the
minimum time to wait before attempting a new implicit or explicit
logout.
If Time2Wait is 0, the reassignment or a new Logout may be attempted
immediately.
10.15.4. Time2Retain
If the Logout response code is 0 and if the operational
ErrorRecoveryLevel is 2, this is the maximum amount of time, in
seconds, after the initial wait (Time2Wait), the target waits for the
allegiance reassignment for any active task after which the task
state is discarded. If the Logout response code is 0 and if the
operational ErrorRecoveryLevel is less than 2, this field is to be
ignored.
This field is invalid if the Logout response code is 1.
If the Logout response code is 2 or 3, this field specifies the
maximum amount of time, in seconds, after the initial wait
(Time2Wait), the target waits for a new implicit or explicit logout.
If it is the last connection of a session, the whole session state is
discarded after Time2Retain.
If Time2Retain is 0, the target has already discarded the connection
(and possibly the session) state along with the task states. No
reassignment or Logout is required in this case.
10.16. SNACK Request
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x10 |1|.|.|.| Type | Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or SNACK Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| Reserved |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
40| BegRun |
+---------------------------------------------------------------+
44| RunLength |
+---------------------------------------------------------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
If the implementation supports ErrorRecoveryLevel greater than zero,
it MUST support all SNACK types.
The SNACK is used by the initiator to request the retransmission of
numbered-responses, data, or R2T PDUs from the target. The SNACK
request indicates the numbered-responses or data "runs" whose
retransmission is requested by the target, where the run starts with
the first StatSN, DataSN, or R2TSN whose retransmission is requested
and indicates the number of Status, Data, or R2T PDUs requested
including the first. 0 has special meaning when used as a starting
number and length:
- When used in RunLength, it means all PDUs starting with the
initial.
- When used in both BegRun and RunLength, it means all
unacknowledged PDUs.
The numbered-response(s) or R2T(s), requested by a SNACK, MUST be
delivered as exact replicas of the ones that the target transmitted
originally except for the fields ExpCmdSN, MaxCmdSN, and ExpDataSN,
which MUST carry the current values. R2T(s)requested by SNACK MUST
also carry the current value of StatSN.
The numbered Data-In PDUs, requested by a Data SNACK MUST be
delivered as exact replicas of the ones that the target transmitted
originally except for the fields ExpCmdSN and MaxCmdSN, which MUST
carry the current values and except for resegmentation (see Section
10.16.3 Resegmentation).
Any SNACK that requests a numbered-response, Data, or R2T that was
not sent by the target or was already acknowledged by the initiator,
MUST be rejected with a reason code of "Protocol error".
10.16.1. Type
This field encodes the SNACK function as follows:
0-Data/R2T SNACK - requesting retransmission of one or more Data-
In or R2T PDUs.
1-Status SNACK - requesting retransmission of one or more numbered
responses.
2-DataACK - positively acknowledges Data-In PDUs.
3-R-Data SNACK - requesting retransmission of Data-In PDUs with
possible resegmentation and status tagging.
All other values are reserved.
Data/R2T SNACK, Status SNACK, or R-Data SNACK for a command MUST
precede status acknowledgement for the given command.
10.16.2. Data Acknowledgement
If an initiator operates at ErrorRecoveryLevel 1 or higher, it MUST
issue a SNACK of type DataACK after receiving a Data-In PDU with the
A bit set to 1. However, if the initiator has detected holes in the
input sequence, it MUST postpone issuing the SNACK of type DataACK
until the holes are filled. An initiator MAY ignore the A bit if it
deems that the bit is being set aggressively by the target (i.e.,
before the MaxBurstLength limit is reached).
The DataACK is used to free resources at the target and not to
request or imply data retransmission.
An initiator MUST NOT request retransmission for any data it had
already acknowledged.
10.16.3. Resegmentation
If the initiator MaxRecvDataSegmentLength changed between the
original transmission and the time the initiator requests
retransmission, the initiator MUST issue a R-Data SNACK (see Section
10.16.1 Type). With R-Data SNACK, the initiator indicates that it
discards all the unacknowledged data and expects the target to resend
it. It also expects resegmentation. In this case, the retransmitted
Data-In PDUs MAY be different from the ones originally sent in order
to reflect changes in MaxRecvDataSegmentLength. Their DataSN starts
with the BegRun of the last DataACK received by the target if any was
received; otherwise it starts with 0 and is increased by 1 for each
resent Data-In PDU.
A target that has received a R-Data SNACK MUST return a SCSI Response
that contains a copy of the SNACK Tag field from the R-Data SNACK in
the SCSI Response SNACK Tag field as its last or only Response. For
example, if it has already sent a response containing another value
in the SNACK Tag field or had the status included in the last Data-In
PDU, it must send a new SCSI Response PDU. If a target sends more
than one SCSI Response PDU due to this rule, all SCSI responses must
carry the same StatSN (see Section 10.4.4 SNACK Tag). If an
initiator attempts to recover a lost SCSI Response (with a
Status SNACK, see Section 10.16.1 Type) when more than one response
has been sent, the target will send the SCSI Response with the latest
content known to the target, including the last SNACK Tag for the
command.
For considerations in allegiance reassignment of a task to a
connection with a different MaxRecvDataSegmentLength, refer to
Section 6.2.2 Allegiance Reassignment.
10.16.4. Initiator Task Tag
For Status SNACK and DataACK, the Initiator Task Tag MUST be set to
the reserved value 0xffffffff. In all other cases, the Initiator
Task Tag field MUST be set to the Initiator Task Tag of the
referenced command.
10.16.5. Target Transfer Tag or SNACK Tag
For an R-Data SNACK, this field MUST contain a value that is
different from 0 or 0xffffffff and is unique for the task (identified
by the Initiator Task Tag). This value MUST be copied by the iSCSI
target in the last or only SCSI Response PDU it issues for the
command.
For DataACK, the Target Transfer Tag MUST contain a copy of the
Target Transfer Tag and LUN provided with the SCSI Data-In PDU with
the A bit set to 1.
In all other cases, the Target Transfer Tag field MUST be set to the
reserved value of 0xffffffff.
10.16.6. BegRun
The DataSN, R2TSN, or StatSN of the first PDU whose retransmission is
requested (Data/R2T and Status SNACK), or the next expected DataSN
(DataACK SNACK).
BegRun 0 when used in conjunction with RunLength 0 means resend all
unacknowledged Data-In, R2T or Response PDUs.
BegRun MUST be 0 for a R-Data SNACK.
10.16.7. RunLength
The number of PDUs whose retransmission is requested.
RunLength 0 signals that all Data-In, R2T, or Response PDUs carrying
the numbers equal to or greater than BegRun have to be resent.
The RunLength MUST also be 0 for a DataACK SNACK in addition to
R-Data SNACK.
10.17. Reject
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x3f |1| Reserved | Reason | Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
16| 0xffffffff |
+---------------+---------------+---------------+---------------+
20| Reserved |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| DataSN/R2TSN or Reserved |
+---------------+---------------+---------------+---------------+
40| Reserved |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
xx/ Complete Header of Bad PDU /
+/ /
+---------------+---------------+---------------+---------------+
yy/Vendor specific data (if any) /
/ /
+---------------+---------------+---------------+---------------+
zz| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
Reject is used to indicate an iSCSI error condition (protocol,
unsupported option, etc.).
10.17.1. Reason
The reject Reason is coded as follows:
+------+----------------------------------------+------------------+
| Code | Explanation | Can the original |
| (hex)| | PDU be re-sent? |
+------+----------------------------------------+------------------+
| 0x01 | Reserved | no |
| | | |
| 0x02 | Data (payload) Digest Error | yes (Note 1) |
| | | |
| 0x03 | SNACK Reject | yes |
| | | |
| 0x04 | Protocol Error (e.g., SNACK request for| no |
| | a status that was already acknowledged)| |
| | | |
| 0x05 | Command not supported | no |
| | | |
| 0x06 | Immediate Command Reject - too many | yes |
| | immediate commands | |
| | | |
| 0x07 | Task in progress | no |
| | | |
| 0x08 | Invalid Data ACK | no |
| | | |
| 0x09 | Invalid PDU field | no (Note 2) |
| | | |
| 0x0a | Long Operation Reject - Can't generate | yes |
| | Target Transfer Tag - out of resources | |
| | | |
| 0x0b | Negotiation Reset | no |
| | | |
| 0x0c | Waiting for Logout | no |
+------+----------------------------------------+------------------+
Note 1: For iSCSI, Data-Out PDU retransmission is only done if the
target requests retransmission with a recovery R2T. However, if this
is the data digest error on immediate data, the initiator may choose
to retransmit the whole PDU including the immediate data.
Note 2: A target should use this reason code for all invalid values
of PDU fields that are meant to describe a task, a response, or a
data transfer. Some examples are invalid TTT/ITT, buffer offset, LUN
qualifying a TTT, and an invalid sequence number in a SNACK.
All other values for Reason are reserved.
In all the cases in which a pre-instantiated SCSI task is terminated
because of the reject, the target MUST issue a proper SCSI command
response with CHECK CONDITION as described in Section 10.4.3
Response. In these cases in which a status for the SCSI task was
already sent before the reject, no additional status is required. If
the error is detected while data from the initiator is still expected
(i.e., the command PDU did not contain all the data and the target
has not received a Data-Out PDU with the Final bit set to 1 for the
unsolicited data, if any, and all outstanding R2Ts, if any), the
target MUST wait until it receives the last expected Data-Out PDUs
with the F bit set to 1 before sending the Response PDU.
For additional usage semantics of Reject PDU, see Section 6.3 Usage
Of Reject PDU in Recovery.
10.17.2. DataSN/R2TSN
This field is only valid if the rejected PDU is a Data/R2T SNACK and
the Reject reason code is "Protocol error" (see Section 10.16 SNACK
Request). The DataSN/R2TSN is the next Data/R2T sequence number that
the target would send for the task, if any.
10.17.3. StatSN, ExpCmdSN and MaxCmdSN
These fields carry their usual values and are not related to the
rejected command. StatSN is advanced after a Reject.
10.17.4. Complete Header of Bad PDU
The target returns the header (not including digest) of the PDU in
error as the data of the response.
10.18. NOP-Out
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|I| 0x00 |1| Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
/ DataSegment - Ping Data (optional) /
+/ /
+---------------+---------------+---------------+---------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
A NOP-Out may be used by an initiator as a "ping request" to verify
that a connection/session is still active and all its components are
operational. The NOP-In response is the "ping echo".
A NOP-Out is also sent by an initiator in response to a NOP-In.
A NOP-Out may also be used to confirm a changed ExpStatSN if another
PDU will not be available for a long time.
Upon receipt of a NOP-In with the Target Transfer Tag set to a valid
value (not the reserved 0xffffffff), the initiator MUST respond with
a NOP-Out. In this case, the NOP-Out Target Transfer Tag MUST
contain a copy of the NOP-In Target Transfer Tag.
10.18.1. Initiator Task Tag
The NOP-Out MUST have the Initiator Task Tag set to a valid value
only if a response in the form of NOP-In is requested (i.e., the
NOP-Out is used as a ping request). Otherwise, the Initiator Task
Tag MUST be set to 0xffffffff.
When a target receives the NOP-Out with a valid Initiator Task Tag,
it MUST respond with a Nop-In Response (see Section 10.19 NOP-In).
If the Initiator Task Tag contains 0xffffffff, the I bit MUST be set
to 1 and the CmdSN is not advanced after this PDU is sent.
10.18.2. Target Transfer Tag
A target assigned identifier for the operation.
The NOP-Out MUST only have the Target Transfer Tag set if it is
issued in response to a NOP-In with a valid Target Transfer Tag. In
this case, it copies the Target Transfer Tag from the NOP-In PDU.
Otherwise, the Target Transfer Tag MUST be set to 0xffffffff.
When the Target Transfer Tag is set to a value other than 0xffffffff,
the LUN field MUST also be copied from the NOP-In.
10.18.3. Ping Data
Ping data are reflected in the NOP-In Response. The length of the
reflected data are limited to MaxRecvDataSegmentLength. The length
of ping data are indicated by the DataSegmentLength. 0 is a valid
value for the DataSegmentLength and indicates the absence of ping
data.
10.19. NOP-In
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0|.|.| 0x20 |1| Reserved |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Header-Digest (Optional) |
+---------------+---------------+---------------+---------------+
/ DataSegment - Return Ping Data /
+/ /
+---------------+---------------+---------------+---------------+
| Data-Digest (Optional) |
+---------------+---------------+---------------+---------------+
NOP-In is either sent by a target as a response to a NOP-Out, as a
"ping" to an initiator, or as a means to carry a changed ExpCmdSN
and/or MaxCmdSN if another PDU will not be available for a long time
(as determined by the target).
When a target receives the NOP-Out with a valid Initiator Task Tag
(not the reserved value 0xffffffff), it MUST respond with a NOP-In
with the same Initiator Task Tag that was provided in the NOP-Out
request. It MUST also duplicate up to the first
MaxRecvDataSegmentLength bytes of the initiator provided Ping Data.
For such a response, the Target Transfer Tag MUST be 0xffffffff.
Otherwise, when a target sends a NOP-In that is not a response to a
Nop-Out received from the initiator, the Initiator Task Tag MUST be
set to 0xffffffff and the Data Segment MUST NOT contain any data
(DataSegmentLength MUST be 0).
10.19.1. Target Transfer Tag
If the target is responding to a NOP-Out, this is set to the reserved
value 0xffffffff.
If the target is sending a NOP-In as a Ping (intending to receive a
corresponding NOP-Out), this field is set to a valid value (not the
reserved 0xffffffff).
If the target is initiating a NOP-In without wanting to receive a
corresponding NOP-Out, this field MUST hold the reserved value of
0xffffffff.
10.19.2. StatSN
The StatSN field will always contain the next StatSN. However, when
the Initiator Task Tag is set to 0xffffffff, StatSN for the
connection is not advanced after this PDU is sent.
10.19.3. LUN
A LUN MUST be set to a correct value when the Target Transfer Tag is
valid (not the reserved value 0xffffffff).
11. iSCSI Security Text Keys and Authentication Methods
Only the following keys are used during the SecurityNegotiation stage
of the Login Phase:
SessionType
InitiatorName
TargetName
TargetAddress
InitiatorAlias
TargetAlias
TargetPortalGroupTag
AuthMethod and the keys used by the authentication methods
specified under Section 11.1 AuthMethod along with all of
their associated keys as well as Vendor Specific
Authentication Methods.
Other keys MUST NOT be used.
SessionType, InitiatorName, TargetName, InitiatorAlias, TargetAlias,
and TargetPortalGroupTag are described in Chapter 12 as they can be
used also in the OperationalNegotiation stage.
All security keys have connection-wide applicability.
11.1. AuthMethod
Use: During Login - Security Negotiation Senders: Initiator and
Target Scope: connection
AuthMethod = <list-of-values>
The main item of security negotiation is the authentication method
(AuthMethod).
The authentication methods that can be used (appear in the
list-of-values) are either those listed in the following table or are
vendor-unique methods:
+------------------------------------------------------------+
| Name | Description |
+------------------------------------------------------------+
| KRB5 | Kerberos V5 - defined in [RFC1510] |
+------------------------------------------------------------+
| SPKM1 | Simple Public-Key GSS-API Mechanism |
| | defined in [RFC2025] |
+------------------------------------------------------------+
| SPKM2 | Simple Public-Key GSS-API Mechanism |
| | defined in [RFC2025] |
+------------------------------------------------------------+
| SRP | Secure Remote Password |
| | defined in [RFC2945] |
+------------------------------------------------------------+
| CHAP | Challenge Handshake Authentication Protocol|
| | defined in [RFC1994] |
+------------------------------------------------------------+
| None | No authentication |
+------------------------------------------------------------+
The AuthMethod selection is followed by an "authentication exchange"
specific to the authentication method selected.
The authentication method proposal may be made by either the
initiator or the target. However the initiator MUST make the first
step specific to the selected authentication method as soon as it is
selected. It follows that if the target makes the authentication
method proposal the initiator sends the first keys(s) of the exchange
together with its authentication method selection.
The authentication exchange authenticates the initiator to the
target, and optionally, the target to the initiator. Authentication
is OPTIONAL to use but MUST be supported by the target and initiator.
The initiator and target MUST implement CHAP. All other
authentication methods are OPTIONAL.
Private or public extension algorithms MAY also be negotiated for
authentication methods. Whenever a private or public extension
algorithm is part of the default offer (the offer made in absence of
explicit administrative action) the implementer MUST ensure that CHAP
is listed as an alternative in the default offer and "None" is not
part of the default offer.
Extension authentication methods MUST be named using one of the
following two formats:
a) Z-reversed.vendor.dns_name.do_something=
b) Z<#><IANA-registered-string>=
Authentication methods named using the Z- format are used as private
extensions. Authentication methods named using the Z# format are
used as public extensions that must be registered with IANA and MUST
be described by an informational RFC.
For all of the public or private extension authentication methods,
the method specific keys MUST conform to the format specified in
Section 5.1 Text Format for standard-label.
To identify the vendor for private extension authentication methods,
we suggest you use the reversed DNS-name as a prefix to the proper
digest names.
The part of digest-name following Z- and Z# MUST conform to the
format for standard-label specified in Section 5.1 Text Format.
Support for public or private extension authentication methods is
OPTIONAL.
The following subsections define the specific exchanges for each of
the standardized authentication methods. As mentioned earlier the
first step is always done by the initiator.
11.1.1. Kerberos
For KRB5 (Kerberos V5) [RFC1510] and [RFC1964], the initiator MUST
use:
KRB_AP_REQ=<KRB_AP_REQ>
where KRB_AP_REQ is the client message as defined in [RFC1510].
The default principal name assumed by an iSCSI initiator or target
(prior to any administrative configuration action) MUST be the iSCSI
Initiator Name or iSCSI Target Name respectively, prefixed by the
string "iscsi/".
If the initiator authentication fails, the target MUST respond with a
Login reject with "Authentication Failure" status. Otherwise, if the
initiator has selected the mutual authentication option (by setting
MUTUAL-REQUIRED in the ap-options field of the KRB_AP_REQ), the
target MUST reply with:
KRB_AP_REP=<KRB_AP_REP>
where KRB_AP_REP is the server's response message as defined in
[RFC1510].
If mutual authentication was selected and target authentication
fails, the initiator MUST close the connection.
KRB_AP_REQ and KRB_AP_REP are binary-values and their binary length
(not the length of the character string that represents them in
encoded form) MUST not exceed 65536 bytes.
11.1.2. Simple Public-Key Mechanism (SPKM)
For SPKM1 and SPKM2 [RFC2025], the initiator MUST use:
SPKM_REQ=<SPKM-REQ>
where SPKM-REQ is the first initiator token as defined in [RFC2025].
[RFC2025] defines situations where each side may send an error token
that may cause the peer to re-generate and resend its last token.
This scheme is followed in iSCSI, and the error token syntax is:
SPKM_ERROR=<SPKM-ERROR>
However, SPKM-DEL tokens that are defined by [RFC2025] for fatal
errors will not be used by iSCSI. If the target needs to send a
SPKM-DEL token, it will, instead, send a Login "login reject" message
with the "Authentication Failure" status and terminate the
connection. If the initiator needs to send a SPKM-DEL token, it will
close the connection.
In the following sections, we assume that no SPKM-ERROR tokens are
required.
If the initiator authentication fails, the target MUST return an
error. Otherwise, if the AuthMethod is SPKM1 or if the initiator has
selected the mutual authentication option (by setting mutual-state
bit in the options field of the REQ-TOKEN in the SPKM-REQ), the
target MUST reply with:
SPKM_REP_TI=<SPKM-REP-TI>
where SPKM-REP-TI is the target token as defined in [RFC2025].
If mutual authentication was selected and target authentication
fails, the initiator MUST close the connection. Otherwise, if the
AuthMethod is SPKM1, the initiator MUST continue with:
SPKM_REP_IT=<SPKM-REP-IT>
where SPKM-REP-IT is the second initiator token as defined in
[RFC2025]. If the initiator authentication fails, the target MUST
answer with a Login reject with "Authentication Failure" status.
SPKM requires support for very long authentication items.
All the SPKM-* tokens are binary-values and their binary length (not
the length of the character string that represents them in encoded
form) MUST not exceed 65536 bytes.
11.1.3. Secure Remote Password (SRP)
For SRP [RFC2945], the initiator MUST use:
SRP_U=<U> TargetAuth=Yes /* or TargetAuth=No */
The target MUST answer with a Login reject with the "Authorization
Failure" status or reply with:
SRP_GROUP=<G1,G2...> SRP_s=<s>
Where G1,G2... are proposed groups, in order of preference.
The initiator MUST either close the connection or continue with:
SRP_A=<A> SRP_GROUP=<G>
Where G is one of G1,G2... that were proposed by the target.
The target MUST answer with a Login reject with the "Authentication
Failure" status or reply with:
SRP_B=<B>
The initiator MUST close the connection or continue with:
SRP_M=<M>
If the initiator authentication fails, the target MUST answer with a
Login reject with "Authentication Failure" status. Otherwise, if the
initiator sent TargetAuth=Yes in the first message (requiring target
authentication), the target MUST reply with:
SRP_HM=<H(A | M | K)>
If the target authentication fails, the initiator MUST close the
connection.
Where U, s, A, B, M, and H(A | M | K) are defined in [RFC2945] (using
the SHA1 hash function, such as SRP-SHA1) and G,Gn (Gn stands for
G1,G2...) are identifiers of SRP groups specified in [RFC3723]. G,
Gn, and U are text strings, s,A,B,M, and H(A | M | K) are
binary-values. The length of s,A,B,M and H(A | M | K) in binary form
(not the length of the character string that represents them in
encoded form) MUST not exceed 1024 bytes.
For the SRP_GROUP, all the groups specified in [RFC3723] up to 1536
bits (i.e., SRP-768, SRP-1024, SRP-1280, SRP-1536) must be supported
by initiators and targets. To guarantee interoperability, targets
MUST always offer "SRP-1536" as one of the proposed groups.
11.1.4. Challenge Handshake Authentication Protocol (CHAP)
For CHAP [RFC1994], in the first step, the initiator MUST send:
CHAP_A=<A1,A2...>
Where A1,A2... are proposed algorithms, in order of preference.
In the second step, the target MUST answer with a Login reject with
the "Authentication Failure" status or reply with:
CHAP_A=<A> CHAP_I=<I> CHAP_C=<C>
Where A is one of A1,A2... that were proposed by the initiator.
In the third step, the initiator MUST continue with:
CHAP_N=<N> CHAP_R=<R>
or, if it requires target authentication, with:
CHAP_N=<N> CHAP_R=<R> CHAP_I=<I> CHAP_C=<C>
If the initiator authentication fails, the target MUST answer with a
Login reject with "Authentication Failure" status. Otherwise, if the
initiator required target authentication, the target MUST either
answer with a Login reject with "Authentication Failure" or reply
with:
CHAP_N=<N> CHAP_R=<R>
If target authentication fails, the initiator MUST close the
connection.
Where N, (A,A1,A2), I, C, and R are (correspondingly) the Name,
Algorithm, Identifier, Challenge, and Response as defined in
[RFC1994], N is a text string, A,A1,A2, and I are numbers, and C and
R are large-binary-values and their binary length (not the length of
the character string that represents them in encoded form) MUST not
exceed 1024 bytes.
For the Algorithm, as stated in [RFC1994], one value is required to
be implemented:
5 (CHAP with MD5)
To guarantee interoperability, initiators MUST always offer it as one
of the proposed algorithms.
12. Login/Text Operational Text Keys
Some session specific parameters MUST only be carried on the leading
connection and cannot be changed after the leading connection login
(e.g., MaxConnections, the maximum number of connections). This
holds for a single connection session with regard to connection
restart. The keys that fall into this category have the use: LO
(Leading Only).
Keys that can only be used during login have the use: IO (initialize
only), while those that can be used in both the Login Phase and Full
Feature Phase have the use: ALL.
Keys that can only be used during Full Feature Phase use FFPO (Full
Feature Phase only).
Keys marked as Any-Stage may also appear in the SecurityNegotiation
stage while all other keys described in this chapter are operational
keys.
Keys that do not require an answer are marked as Declarative.
Key scope is indicated as session-wide (SW) or connection-only (CO).
Result function, wherever mentioned, states the function that can be
applied to check the validity of the responder selection. Minimum
means that the selected value cannot exceed the offered value.
Maximum means that the selected value cannot be lower than the
offered value. AND means that the selected value must be a possible
result of a Boolean "and" function with an arbitrary Boolean value
(e.g., if the offered value is No the selected value must be No). OR
means that the selected value must be a possible result of a Boolean
"or" function with an arbitrary Boolean value (e.g., if the offered
value is Yes the selected value must be Yes).
12.1. HeaderDigest and DataDigest
Use: IO
Senders: Initiator and Target
Scope: CO
HeaderDigest = <list-of-values>
DataDigest = <list-of-values>
Default is None for both HeaderDigest and DataDigest.
Digests enable the checking of end-to-end, non-cryptographic data
integrity beyond the integrity checks provided by the link layers and
the covering of the whole communication path including all elements
that may change the network level PDUs such as routers, switches, and
proxies.
The following table lists cyclic integrity checksums that can be
negotiated for the digests and that MUST be implemented by every
iSCSI initiator and target. These digest options only have error
detection significance.
+---------------------------------------------+
| Name | Description | Generator |
+---------------------------------------------+
| CRC32C | 32 bit CRC |0x11edc6f41|
+---------------------------------------------+
| None | no digest |
+---------------------------------------------+
The generator polynomial for this digest is given in
hex-notation (e.g., 0x3b stands for 0011 1011 and the polynomial is
x**5+X**4+x**3+x+1).
When the Initiator and Target agree on a digest, this digest MUST be
used for every PDU in Full Feature Phase.
Padding bytes, when present in a segment covered by a CRC, SHOULD be
set to 0 and are included in the CRC.
The CRC MUST be calculated by a method that produces the same
results as the following process:
- The PDU bits are considered as the coefficients of a
polynomial M(x) of degree n-1; bit 7 of the lowest numbered
byte is considered the most significant bit (x^n-1), followed
by bit 6 of the lowest numbered byte through bit 0 of the
highest numbered byte (x^0).
- The most significant 32 bits are complemented.
- The polynomial is multiplied by x^32 then divided by G(x). The
generator polynomial produces a remainder R(x) of degree <= 31.
- The coefficients of R(x) are considered a 32 bit sequence.
- The bit sequence is complemented and the result is the CRC.
- The CRC bits are mapped into the digest word. The x^31
coefficient in bit 7 of the lowest numbered byte of the digest
continuing through to the byte up to the x^24 coefficient in
bit 0 of the lowest numbered byte, continuing with the x^23
coefficient in bit 7 of next byte through x^0 in bit 0 of the
highest numbered byte.
- Computing the CRC over any segment (data or header) extended
to include the CRC built using the generator 0x11edc6f41 will
always get the value 0x1c2d19ed as its final remainder (R(x)).
This value is given here in its polynomial form (i.e., not
mapped as the digest word).
For a discussion about selection criteria for the CRC, see
[RFC3385]. For a detailed analysis of the iSCSI polynomial, see
[Castagnoli93].
Private or public extension algorithms MAY also be negotiated for
digests. Whenever a private or public digest extension algorithm is
part of the default offer (the offer made in absence of explicit
administrative action) the implementer MUST ensure that CRC32C is
listed as an alternative in the default offer and "None" is not
part of the default offer.
Extension digest algorithms MUST be named using one of the following
two formats:
a) Y-reversed.vendor.dns_name.do_something=
b) Y<#><IANA-registered-string>=
Digests named using the Y- format are used for private purposes
(unregistered). Digests named using the Y# format (public extension)
must be registered with IANA and MUST be described by an
informational RFC.
For private extension digests, to identify the vendor, we suggest
you use the reversed DNS-name as a prefix to the proper digest
names.
The part of digest-name following Y- and Y# MUST conform to the
format for standard-label specified in Section 5.1 Text Format.
Support for public or private extension digests is OPTIONAL.
12.2. MaxConnections
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
MaxConnections=<numerical-value-from-1-to-65535>
Default is 1.
Result function is Minimum.
Initiator and target negotiate the maximum number of connections
requested/acceptable.
12.3. SendTargets
Use: FFPO
Senders: Initiator
Scope: SW
For a complete description, see Appendix D. - SendTargets
Operation -.
12.4. TargetName
Use: IO by initiator, FFPO by target - only as response to a
SendTargets, Declarative, Any-Stage
Senders: Initiator and Target
Scope: SW
TargetName=<iSCSI-name-value>
Examples:
TargetName=iqn.1993-11.com.disk-vendor:diskarrays.sn.45678
TargetName=eui.020000023B040506
The initiator of the TCP connection MUST provide this key to the
remote endpoint in the first login request if the initiator is not
establishing a discovery session. The iSCSI Target Name specifies
the worldwide unique name of the target.
The TargetName key may also be returned by the "SendTargets" text
request (which is its only use when issued by a target).
TargetName MUST not be redeclared within the login phase.
12.5. InitiatorName
Use: IO, Declarative, Any-Stage
Senders: Initiator
Scope: SW
InitiatorName=<iSCSI-name-value>
Examples:
InitiatorName=iqn.1992-04.com.os-vendor.plan9:cdrom.12345
InitiatorName=iqn.2001-02.com.ssp.users:customer235.host90
The initiator of the TCP connection MUST provide this key to the
remote endpoint at the first Login of the Login Phase for every
connection. The InitiatorName key enables the initiator to identify
itself to the remote endpoint.
InitiatorName MUST not be redeclared within the login phase.
12.6. TargetAlias
Use: ALL, Declarative, Any-Stage
Senders: Target
Scope: SW
TargetAlias=<iSCSI-local-name-value>
Examples:
TargetAlias=Bob-s Disk
TargetAlias=Database Server 1 Log Disk
TargetAlias=Web Server 3 Disk 20
If a target has been configured with a human-readable name or
description, this name SHOULD be communicated to the initiator during
a Login Response PDU if SessionType=Normal (see Section 12.21
SessionType). This string is not used as an identifier, nor is it
meant to be used for authentication or authorization decisions. It
can be displayed by the initiator's user interface in a list of
targets to which it is connected.
12.7. InitiatorAlias
Use: ALL, Declarative, Any-Stage
Senders: Initiator
Scope: SW
InitiatorAlias=<iSCSI-local-name-value>
Examples:
InitiatorAlias=Web Server 4
InitiatorAlias=spyalley.nsa.gov
InitiatorAlias=Exchange Server
If an initiator has been configured with a human-readable name or
description, it SHOULD be communicated to the target during a Login
Request PDU. If not, the host name can be used instead. This string
is not used as an identifier, nor is meant to be used for
authentication or authorization decisions. It can be displayed by
the target's user interface in a list of initiators to which it is
connected.
12.8. TargetAddress
Use: ALL, Declarative, Any-Stage
Senders: Target
Scope: SW
TargetAddress=domainname[:port][,portal-group-tag]
The domainname can be specified as either a DNS host name, a
dotted-decimal IPv4 address, or a bracketed IPv6 address as specified
in [RFC2732].
If the TCP port is not specified, it is assumed to be the
IANA-assigned default port for iSCSI (see Section 13 IANA
Considerations).
If the TargetAddress is returned as the result of a redirect status
in a login response, the comma and portal group tag MUST be omitted.
If the TargetAddress is returned within a SendTargets response, the
portal group tag MUST be included.
Examples:
TargetAddress=10.0.0.1:5003,1
TargetAddress=[1080:0:0:0:8:800:200C:417A],65
TargetAddress=[1080::8:800:200C:417A]:5003,1
TargetAddress=computingcenter.example.com,23
Use of the portal-group-tag is described in Appendix D.
- SendTargets Operation -. The formats for the port and
portal-group-tag are the same as the one specified in Section 12.9
TargetPortalGroupTag.
12.9. TargetPortalGroupTag
Use: IO by target, Declarative, Any-Stage
Senders: Target
Scope: SW
TargetPortalGroupTag=<16-bit-binary-value>
Examples:
TargetPortalGroupTag=1
The target portal group tag is a 16-bit binary-value that uniquely
identifies a portal group within an iSCSI target node. This key
carries the value of the tag of the portal group that is servicing
the Login request. The iSCSI target returns this key to the
initiator in the Login Response PDU to the first Login Request PDU
that has the C bit set to 0 when TargetName is given by the
initiator.
For the complete usage expectations of this key see Section 5.3 Login
Phase.
12.10. InitialR2T
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
InitialR2T=<boolean-value>
Examples:
I->InitialR2T=No
T->InitialR2T=No
Default is Yes.
Result function is OR.
The InitialR2T key is used to turn off the default use of R2T for
unidirectional and the output part of bidirectional commands, thus
allowing an initiator to start sending data to a target as if it has
received an initial R2T with Buffer Offset=Immediate Data Length and
Desired Data Transfer Length=(min(FirstBurstLength, Expected Data
Transfer Length) - Received Immediate Data Length).
The default action is that R2T is required, unless both the initiator
and the target send this key-pair attribute specifying InitialR2T=No.
Only the first outgoing data burst (immediate data and/or separate
PDUs) can be sent unsolicited (i.e., not requiring an explicit R2T).
12.11. ImmediateData
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
ImmediateData=<boolean-value>
Default is Yes.
Result function is AND.
The initiator and target negotiate support for immediate data. To
turn immediate data off, the initiator or target must state its
desire to do so. ImmediateData can be turned on if both the
initiator and target have ImmediateData=Yes.
If ImmediateData is set to Yes and InitialR2T is set to Yes
(default), then only immediate data are accepted in the first burst.
If ImmediateData is set to No and InitialR2T is set to Yes, then the
initiator MUST NOT send unsolicited data and the target MUST reject
unsolicited data with the corresponding response code.
If ImmediateData is set to No and InitialR2T is set to No, then the
initiator MUST NOT send unsolicited immediate data, but MAY send one
unsolicited burst of Data-Out PDUs.
If ImmediateData is set to Yes and InitialR2T is set to No, then the
initiator MAY send unsolicited immediate data and/or one unsolicited
burst of Data-Out PDUs.
The following table is a summary of unsolicited data options:
+----------+-------------+------------------+--------------+
|InitialR2T|ImmediateData| Unsolicited |Immediate Data|
| | | Data Out PDUs | |
+----------+-------------+------------------+--------------+
| No | No | Yes | No |
+----------+-------------+------------------+--------------+
| No | Yes | Yes | Yes |
+----------+-------------+------------------+--------------+
| Yes | No | No | No |
+----------+-------------+------------------+--------------+
| Yes | Yes | No | Yes |
+----------+-------------+------------------+--------------+
12.12. MaxRecvDataSegmentLength
Use: ALL, Declarative
Senders: Initiator and Target
Scope: CO
MaxRecvDataSegmentLength=<numerical-value-512-to-(2**24-1)>
Default is 8192 bytes.
The initiator or target declares the maximum data segment length in
bytes it can receive in an iSCSI PDU.
The transmitter (initiator or target) is required to send PDUs with a
data segment that does not exceed MaxRecvDataSegmentLength of the
receiver.
A target receiver is additionally limited by MaxBurstLength for
solicited data and FirstBurstLength for unsolicited data. An
initiator MUST NOT send solicited PDUs exceeding MaxBurstLength nor
unsolicited PDUs exceeding FirstBurstLength (or
FirstBurstLength-Immediate Data Length if immediate data were sent).
12.13. MaxBurstLength
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
MaxBurstLength=<numerical-value-512-to-(2**24-1)>
Default is 262144 (256 Kbytes).
Result function is Minimum.
The initiator and target negotiate maximum SCSI data payload in bytes
in a Data-In or a solicited Data-Out iSCSI sequence. A sequence
consists of one or more consecutive Data-In or Data-Out PDUs that end
with a Data-In or Data-Out PDU with the F bit set to one.
12.14. FirstBurstLength
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
Irrelevant when: ( InitialR2T=Yes and ImmediateData=No )
FirstBurstLength=<numerical-value-512-to-(2**24-1)>
Default is 65536 (64 Kbytes).
Result function is Minimum.
The initiator and target negotiate the maximum amount in bytes of
unsolicited data an iSCSI initiator may send to the target during the
execution of a single SCSI command. This covers the immediate data
(if any) and the sequence of unsolicited Data-Out PDUs (if any) that
follow the command.
FirstBurstLength MUST NOT exceed MaxBurstLength.
12.15. DefaultTime2Wait
Use: LO
Senders: Initiator and Target
Scope: SW
DefaultTime2Wait=<numerical-value-0-to-3600>
Default is 2.
Result function is Maximum.
The initiator and target negotiate the minimum time, in seconds, to
wait before attempting an explicit/implicit logout or an active task
reassignment after an unexpected connection termination or a
connection reset.
A value of 0 indicates that logout or active task reassignment can be
attempted immediately.
12.16. DefaultTime2Retain
Use: LO Senders: Initiator and Target Scope: SW
DefaultTime2Retain=<numerical-value-0-to-3600>
Default is 20. Result function is Minimum.
The initiator and target negotiate the maximum time, in seconds after
an initial wait (Time2Wait), before which an active task reassignment
is still possible after an unexpected connection termination or a
connection reset.
This value is also the session state timeout if the connection in
question is the last LOGGED_IN connection in the session.
A value of 0 indicates that connection/task state is immediately
discarded by the target.
12.17. MaxOutstandingR2T
Use: LO
Senders: Initiator and Target
Scope: SW
MaxOutstandingR2T=<numerical-value-from-1-to-65535>
Irrelevant when: SessionType=Discovery
Default is 1.
Result function is Minimum.
Initiator and target negotiate the maximum number of outstanding R2Ts
per task, excluding any implied initial R2T that might be part of
that task. An R2T is considered outstanding until the last data PDU
(with the F bit set to 1) is transferred, or a sequence reception
timeout (Section 6.1.4.1 Recovery Within-command) is encountered for
that data sequence.
12.18. DataPDUInOrder
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
DataPDUInOrder=<boolean-value>
Default is Yes.
Result function is OR.
No is used by iSCSI to indicate that the data PDUs within sequences
can be in any order. Yes is used to indicate that data PDUs within
sequences have to be at continuously increasing addresses and
overlays are forbidden.
12.19. DataSequenceInOrder
Use: LO
Senders: Initiator and Target
Scope: SW
Irrelevant when: SessionType=Discovery
DataSequenceInOrder=<boolean-value>
Default is Yes.
Result function is OR.
A Data Sequence is a sequence of Data-In or Data-Out PDUs that end
with a Data-In or Data-Out PDU with the F bit set to one. A Data-Out
sequence is sent either unsolicited or in response to an R2T.
Sequences cover an offset-range.
If DataSequenceInOrder is set to No, Data PDU sequences may be
transferred in any order.
If DataSequenceInOrder is set to Yes, Data Sequences MUST be
transferred using continuously non-decreasing sequence offsets (R2T
buffer offset for writes, or the smallest SCSI Data-In buffer offset
within a read data sequence).
If DataSequenceInOrder is set to Yes, a target may retry at most the
last R2T, and an initiator may at most request retransmission for the
last read data sequence. For this reason, if ErrorRecoveryLevel is
not 0 and DataSequenceInOrder is set to Yes then MaxOustandingR2T
MUST be set to 1.
12.20. ErrorRecoveryLevel
Use: LO
Senders: Initiator and Target
Scope: SW
ErrorRecoveryLevel=<numerical-value-0-to-2>
Default is 0.
Result function is Minimum.
The initiator and target negotiate the recovery level supported.
Recovery levels represent a combination of recovery capabilities.
Each recovery level includes all the capabilities of the lower
recovery levels and adds some new ones to them.
In the description of recovery mechanisms, certain recovery classes
are specified. Section 6.1.5 Error Recovery Hierarchy describes the
mapping between the classes and the levels.
12.21. SessionType
Use: LO, Declarative, Any-Stage
Senders: Initiator
Scope: SW
SessionType= <Discovery|Normal>
Default is Normal.
The initiator indicates the type of session it wants to create. The
target can either accept it or reject it.
A discovery session indicates to the Target that the only purpose of
this Session is discovery. The only requests a target accepts in
this type of session are a text request with a SendTargets key and a
logout request with reason "close the session".
The discovery session implies MaxConnections = 1 and overrides both
the default and an explicit setting.
12.22. The Private or Public Extension Key Format
Use: ALL
Senders: Initiator and Target
Scope: specific key dependent
X-reversed.vendor.dns_name.do_something=
or
X<#><IANA-registered-string>=
Keys with this format are used for public or private extension
purposes. These keys always start with X- if unregistered with IANA
(private) or X# if registered with IANA (public).
For unregistered keys, to identify the vendor, we suggest you use the
reversed DNS-name as a prefix to the key-proper.
The part of key-name following X- and X# MUST conform to the format
for key-name specified in Section 5.1 Text Format.
For IANA registered keys the string following X# must be registered
with IANA and the use of the key MUST be described by an
informational RFC.
Vendor specific keys MUST ONLY be used in normal sessions.
Support for public or private extension keys is OPTIONAL.
13. IANA Considerations
This section conforms to [RFC2434].
The well-known user TCP port number for iSCSI connections assigned by
IANA is 3260 and this is the default iSCSI port. Implementations
needing a system TCP port number may use port 860, the port assigned
by IANA as the iSCSI system port; however in order to use port 860,
it MUST be explicitly specified - implementations MUST NOT default to
use of port 860, as 3260 is the only allowed default.
Extension keys, authentication methods, or digest types for which a
vendor or group of vendors intend to provide publicly available
descriptions MUST be described by an RFC and MUST be registered with
IANA.
The IANA has set up the following three registries:
a) iSCSI extended key registry
b) iSCSI authentication methods registry
c) iSCSI digests registry
[RFC3723] also instructs IANA to maintain a registry for the values
of the SRP_GROUP key. The format of these values must conform to the
one specified for iSCSI extension item-label in Section 13.5.4
Standard iSCSI extension item-label format.
For the iSCSI authentication methods registry and the iSCSI digests
registry, IANA MUST also assign a 16-bit unsigned integer number (the
method number for the authentication method and the digest number for
the digest).
The following initial values for the registry for authentication
methods are specified by the standards action of this document:
Authentication Method | Number |
+----------------------------------------+--------+
| CHAP | 1 |
+----------------------------------------+--------+
| SRP | 2 |
+----------------------------------------+--------+
| KRB5 | 3 |
+----------------------------------------+--------+
| SPKM1 | 4 |
+----------------------------------------+--------+
| SPKM2 | 5 |
+----------------------------------------+--------+
All other record numbers from 0 to 255 are reserved. IANA will
register numbers above 255.
Authentication methods with numbers above 255 MUST be unique within
the registry and MUST be used with the prefix Z#.
The following initial values for the registry for digests are
specified by the standards action of this document:
Digest | Number |
+----------------------------------------+--------+
| CRC32C | 1 |
+----------------------------------------+--------+
All other record numbers from 0 to 255 are reserved. IANA will
register numbers above 255.
Digests with numbers above 255 MUST be unique within the registry and
MUST be used with the prefix Y#.
The RFC that describes the item to be registered MUST indicate in the
IANA Considerations section the string and iSCSI registry to which it
should be recorded.
Extension Keys, Authentication Methods, and digests (iSCSI extension
items) must conform to a number of requirements as described below.
13.1. Naming Requirements
Each iSCSI extension item must have a unique name in its category.
This name will be used as a standard-label for the key, access
method, or digest and must conform to the syntax specified in Section
13.5.4 Standard iSCSI extension item-label format for iSCSI extension
item-labels.
13.2. Mechanism Specification Requirements
For iSCSI extension items all of the protocols and procedures used by
a given iSCSI extension item must be described, either in the
specification of the iSCSI extension item itself or in some other
publicly available specification, in sufficient detail for the iSCSI
extension item to be implemented by any competent implementor. Use
of secret and/or proprietary methods in iSCSI extension items are
expressly prohibited. In addition, the restrictions imposed by
[RFC1602] on the standardization of patented algorithms must be
respected.
13.3. Publication Requirements
All iSCSI extension items must be described by an RFC. The RFC may
be informational rather than Standards-Track, although Standards
Track review and approval are encouraged for all iSCSI extension
items.
13.4. Security Requirements
Any known security issues that arise from the use of the iSCSI
extension item must be completely and fully described. It is not
required that the iSCSI extension item be secure or that it be free
from risks, but that the known risks be identified. Publication of a
new iSCSI extension item does not require an exhaustive security
review, and the security considerations section is subject to
continuing evaluation.
Additional security considerations should be addressed by publishing
revised versions of the iSCSI extension item specification.
For each of these registries, IANA must record the registered string,
which MUST conform to the format rules described in Section 13.5.4
Standard iSCSI extension item-label format for iSCSI extension
item-labels, and the RFC number that describes it. The key prefix
(X#, Y# or Z#) is not part of the recorded string.
13.5. Registration Procedure
Registration of a new iSCSI extension item starts with the
construction of an Internet Draft to become an RFC.
13.5.1. Present the iSCSI extension item to the Community
Send a proposed access type specification to the IPS WG mailing list,
or if the IPS WG is disbanded at the registration time, to a mailing
list designated by the IETF Transport Area Director for a review
period of a month. The intent of the public posting is to solicit
comments and feedback on the iSCSI extension item specification and a
review of any security considerations.
13.5.2. iSCSI extension item review and IESG approval
When the one month period has passed, the IPS WG chair or a person
nominated by the IETF Transport Area Director (the iSCSI extension
item reviewer) forwards the Internet Draft to the IESG for
publication as an informational RFC or rejects it. If the
specification is a standards track document, the usual IETF
procedures for such documents are followed.
Decisions made by the iSCSI extension item reviewer must be published
within two weeks after the month-long review period. Decisions made
by the iSCSI extension item reviewer can be appealed through the IESG
appeal process.
13.5.3. IANA Registration
Provided that the iSCSI extension item has either passed review or
has been successfully appealed to the IESG, and the specification is
published as an RFC, then IANA will register the iSCSI extension item
and make the registration available to the community.
13.5.4. Standard iSCSI extension item-label format
The following character symbols are used iSCSI extension item-labels
(the hexadecimal values represent Unicode code points):
(a-z, A-Z) - letters
(0-9) - digits
"." (0x2e) - dot
"-" (0x2d) - minus
"+" (0x2b) - plus
"@" (0x40) - commercial at
"_" (0x5f) - underscore
An iSCSI extension item-label is a string of one or more characters
that consist of letters, digits, dot, minus, plus, commercial at, or
underscore. An iSCSI extension item-label MUST begin with a capital
letter and must not exceed 63 characters.
13.6. IANA Procedures for Registering iSCSI extension items
The identity of the iSCSI extension item reviewer is communicated to
the IANA by the IESG. Then, the IANA only acts in response to iSCSI
extension item definitions that are approved by the iSCSI extension
item reviewer and forwarded by the reviewer to the IANA for
registration, or in response to a communication from the IESG that an
iSCSI extension item definition appeal has overturned the iSCSI
extension item reviewer's ruling.
References
Normative References
[CAM] ANSI X3.232-199X, Common Access Method-3.
[EUI] "Guidelines for 64-bit Global Identifier (EUI-64)",
http:
//standards.ieee.org/regauth/oui/tutorials/EUI64.html
[OUI] "IEEE OUI and Company_Id Assignments",
http://standards.ieee.org/regauth/oui
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC1035] Mockapetris, P., "Domain Names - Implementation and
Specification", STD 13, RFC 1035, November 1987.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts-
Communication Layer", STD 3, RFC 1122, October 1989.
[RFC1510] Kohl, J. and C. Neuman, "The Kerberos Network
Authentication Service (V5)", RFC 1510, September
1993.
[RFC1737] Sollins, K. and L. Masinter "Functional Requirements
for Uniform Resource Names"RFC 1737, December 1994.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC
1982, August 1996.
[RFC1994] Simpson, W., "PPP Challenge Handshake Authentication
Protocol (CHAP)", RFC 1994, August 1996.
[RFC2025] Adams, C., "The Simple Public-Key GSS-API Mechanism
(SPKM)", RFC 2025, October 1996.
[RFC2045] Borenstein, N. and N. Freed, "MIME (Multipurpose
Internet Mail Extensions) Part One: Mechanisms for
Specifying and Describing the Format of Internet
Message Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S. "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2279] Yergeau, F., "UTF-8, a Transformation Format of ISO
10646", RFC 2279 October 1996.
[RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter "Uniform
Resource Identifiers", RFC 2396, August 1998.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for
the Internet Protocol", RFC 2401, November 1998.
[RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96
within ESP and AH", RFC 2404, November 1998.
[RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating Security
Payload (ESP)", RFC 2406, November 1998.
[RFC2407] Piper, D., "The Internet IP Security Domain of
Interpretation of ISAKMP", RFC 2407, November 1998.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC2409, November 1998.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs.", BCP 26, RFC
2434, October 1998.
[RFC2451] Pereira, R. and R. Adams " The ESP CBC-Mode Cipher
Algorithms", RFC 2451, November 1998.
[RFC2732] Hinden, R., Carpenter, B. and L. Masinter, "Format for
Literal IPv6 Addresses in URL's", RFC 2451, December
1999.
[RFC2945] Wu, T., "The SRP Authentication and Key Exchange
System", RFC 2945, September 2000.
[RFC3066] Alvestrand, H., "Tags for the Identification of
Languages", STD 47, RFC 3066, January 2001.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454,
December 2002.
[RFC3566] Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96
Algorithm and Its Use With IPsec", RFC 3566, September
2003.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode with IPsec Encapsulating Security Payload
(ESP)", RFC 3686, January 2004.
[RFC3722] Bakke, M., "String Profile for Internet Small Computer
Systems Interface (iSCSI) Names", RFC 3722, March
2004.
[RFC3723] Aboba, B., Tseng, J., Walker, J., Rangan, V. and F.
Travostino, "Securing Block Storage Protocols over
IP", RFC 3723, March 2004.
[SAM2] T10/1157D, SCSI Architecture Model - 2 (SAM-2).
[SBC] NCITS.306-1998, SCSI-3 Block Commands (SBC).
[SPC3] T10/1416-D, SCSI Primary Commands-3.
[UNICODE] Unicode Standard Annex #15, "Unicode Normalization
Forms", http://www.unicode.org/unicode/reports/tr15
Informative References
[BOOT] P. Sarkar, et al., "Bootstrapping Clients using the
iSCSI Protocol", Work in Progress, July 2003.
[Castagnoli93] G. Castagnoli, S. Braeuer and M. Herrman "Optimization
of Cyclic Redundancy-Check Codes with 24 and 32 Parity
Bits", IEEE Transact. on Communications, Vol. 41, No.
6, June 1993.
[CORD] Chadalapaka, M. and R. Elliott, "SCSI Command
Ordering Considerations with iSCSI", Work in Progress.
[RFC3347] Krueger, M., Haagens, R., Sapuntzakis, C. and M.
Bakke, "Small Computer Systems Interface protocol over
the Internet (iSCSI) Requirements and Design
Considerations", RFC 3347, July 2002.
[RFC3385] Sheinwald, D., Staran, J., Thaler, P. and V. Cavanna,
"Internet Protocol Small Computer System Interface
(iSCSI) Cyclic Redundancy Check (CRC)/Checksum
Considerations", RFC 3385, September 2002.
[RFC3721] Bakke M., Hafner, J., Hufferd, J., Voruganti, K. and
M. Krueger, "Internet Small Computer Systems Interface
(iSCSI) Naming and Discovery, RFC 3721, March 2004.
[SEQ-EXT] Kent, S., "IP Encapsulating Security Payload (ESP)",
Work in Progress, July 2002.
Appendix A. Sync and Steering with Fixed Interval Markers
This appendix presents a simple scheme for synchronization (PDU
boundary retrieval). It uses markers that include synchronization
information placed at fixed intervals in the TCP stream.
A Marker consists of:
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| Next-iSCSI-PDU-start pointer - copy #1 |
+---------------+---------------+---------------+---------------+
4| Next-iSCSI-PDU-start pointer - copy #2 |
+---------------+---------------+---------------+---------------+
The Marker scheme uses payload byte stream counting that includes
every byte placed by iSCSI in the TCP stream except for the markers
themselves. It also excludes any bytes that TCP counts but are not
originated by iSCSI.
Markers MUST NOT be included in digest calculation.
The Marker indicates the offset to the next iSCSI PDU header. The
Marker is eight bytes in length and contains two 32-bit offset fields
that indicate how many bytes to skip in the TCP stream in order to
find the next iSCSI PDU header. The marker uses two copies of the
pointer so that a marker that spans a TCP packet boundary should
leave at least one valid copy in one of the packets.
The structure and semantics of an inserted marker are independent of
the marker interval.
The use of markers is negotiable. The initiator and target MAY
indicate their readiness to receive and/or send markers during login
separately for each connection. The default is No.
A.1. Markers At Fixed Intervals
A marker is inserted at fixed intervals in the TCP byte stream.
During login, each end of the iSCSI session specifies the interval at
which it is willing to receive the marker, or it disables the marker
altogether. If a receiver indicates that it desires a marker, the
sender MAY agree (during negotiation) and provide the marker at the
desired interval. However, in certain environments, a sender that
does not provide markers to a receiver that wants markers may suffer
an appreciable performance degradation.
The marker interval and the initial marker-less interval are counted
in terms of the bytes placed in the TCP stream data by iSCSI.
When reduced to iSCSI terms, markers MUST indicate the offset to a
4-byte word boundary in the stream. The least significant two bits
of each marker word are reserved and are considered 0 for offset
computation.
Padding iSCSI PDU payloads to 4-byte word boundaries simplifies
marker manipulation.
A.2. Initial Marker-less Interval
To enable the connection setup including the Login Phase negotiation,
marking (if any) is only started at the first marker interval after
the end of the Login Phase. However, in order to enable the marker
inclusion and exclusion mechanism to work without knowledge of the
length of the Login Phase, the first marker will be placed in the TCP
stream as if the Marker-less interval had included markers.
Thus, all markers appear in the stream at locations conforming to the
formula: [(MI + 8) * n - 8] where MI = Marker Interval, n = integer
number.
For example, if the marker interval is 512 bytes and the login ended
at byte 1003 (first iSCSI placed byte is 0), the first marker will be
inserted after byte 1031 in the stream.
A.3. Negotiation
The following operational key=value pairs are used to negotiate the
fixed interval markers. The direction (output or input) is relative
to the initiator.
A.3.1. OFMarker, IFMarker
Use: IO
Senders: Initiator and Target
Scope: CO
OFMarker=<boolean-value>
IFMarker=<boolean-value>
Default is No.
Result function is AND.
OFMarker is used to turn on or off the initiator to target markers
on the connection. IFMarker is used to turn on or off the target to
initiator markers on the connection.
Examples:
I->OFMarker=Yes,IFMarker=Yes
T->OFMarker=Yes,IFMarker=Yes
Results in the Marker being used in both directions while:
I->OFMarker=Yes,IFMarker=Yes
T->OFMarker=Yes,IFMarker=No
Results in Marker being used from the initiator to the target, but
not from the target to initiator.
A.3.2. OFMarkInt, IFMarkInt
Use: IO
Senders: Initiator and Target
Scope: CO
OFMarkInt is Irrelevant when: OFMarker=No
IFMarkInt is Irrelevant when: IFMarker=No
Offering:
OFMarkInt=<numeric-range-from-1-to-65535>
IFMarkInt=<numeric-range-from-1-to-65535>
Responding:
OFMarkInt=<numeric-value-from-1-to-65535>|Reject
IFMarkInt=<numeric-value-from-1-to-65535>|Reject
OFMarkInt is used to set the interval for the initiator to target
markers on the connection. IFMarkInt is used to set the interval for
the target to initiator markers on the connection.
For the offering, the initiator or target indicates the minimum to
maximum interval (in 4-byte words) it wants the markers for one or
both directions. In case it only wants a specific value, only a
single value has to be specified. The responder selects a value
within the minimum and maximum offered or the only value offered or
indicates through the xFMarker key=value its inability to set and/or
receive markers. When the interval is unacceptable the responder
answers with "Reject". Reject is resetting the marker function in
the specified direction (Output or Input) to No.
The interval is measured from the end of a marker to the beginning of
the next marker. For example, a value of 1024 means 1024 words (4096
bytes of iSCSI payload between markers).
The default is 2048.
Appendix B. Examples
B.1. Read Operation Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command (READ)>>> | |
| (read) | | |
+------------------+-----------------------+----------------------+
| | |Prepare Data Transfer |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-In | Send Data |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-In | Send Data |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-In | Send Data |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
B.2. Write Operation Example
+------------------+-----------------------+---------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+---------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) | | and queue it |
+------------------+-----------------------+---------------------+
| | | Process old commands|
+------------------+-----------------------+---------------------+
| | | Ready to process |
| | <<< R2T | WRITE command |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-Out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for data |
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for data |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-Out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-Out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| | <<< SCSI Response |Send Status and Sense|
+------------------+-----------------------+---------------------+
| Command Complete | | |
+------------------+-----------------------+---------------------+
B.3. R2TSN/DataSN Use Examples
Output (write) data DataSN/R2TSN Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type & Content | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) | | and queue it |
+------------------+-----------------------+----------------------+
| | | Process old commands |
+------------------+-----------------------+----------------------+
| | <<< R2T | Ready for data |
| | R2TSN = 0 | |
+------------------+-----------------------+----------------------+
| | <<< R2T | Ready for more data |
| | R2TSN = 1 | |
+------------------+-----------------------+----------------------+
| Send Data | SCSI Data-Out >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=0 | |
+------------------+-----------------------+----------------------+
| Send Data | SCSI Data-Out >>> | Receive Data |
| for R2TSN 0 | DataSN = 1, F=1 | |
+------------------+-----------------------+----------------------+
| Send Data | SCSI Data >>> | Receive Data |
| for R2TSN 1 | DataSN = 0, F=1 | |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
| | ExpDataSN = 0 | |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
Input (read) data DataSN Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command (READ)>>> | |
| (read) | | |
+------------------+-----------------------+----------------------+
| | | Prepare Data Transfer|
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-In | Send Data |
| | DataSN = 0, F=0 | |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-In | Send Data |
| | DataSN = 1, F=0 | |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-In | Send Data |
| | DataSN = 2, F=1 | |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
| | ExpDataSN = 3 | |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
Bidirectional DataSN Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command >>> | |
| (Read-Write) | Read-Write | |
+------------------+-----------------------+----------------------+
| | | Process old commands |
+------------------+-----------------------+----------------------+
| | <<< R2T | Ready to process |
| | R2TSN = 0 | WRITE command |
+------------------+-----------------------+----------------------+
| * Receive Data | <<< SCSI Data-In | Send Data |
| | DataSN = 1, F=0 | |
+------------------+-----------------------+----------------------+
| * Receive Data | <<< SCSI Data-In | Send Data |
| | DataSN = 2, F=1 | |
+------------------+-----------------------+----------------------+
| * Send Data | SCSI Data-Out >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=1 | |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
| | ExpDataSN = 3 | |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
*) Send data and Receive Data may be transferred simultaneously as in
an atomic Read-Old-Write-New or sequentially as in an atomic
Read-Update-Write (in the latter case the R2T may follow the received
data).
Unsolicited and immediate output (write) data with DataSN Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type & Content | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) |F=0 | and data |
|+ Immediate data | | and queue it |
+------------------+-----------------------+----------------------+
| Send Unsolicited | SCSI Write Data >>> | Receive more Data |
| Data | DataSN = 0, F=1 | |
+------------------+-----------------------+----------------------+
| | | Process old commands |
+------------------+-----------------------+----------------------+
| | <<< R2T | Ready for more data |
| | R2TSN = 0 | |
+------------------+-----------------------+----------------------+
| Send Data | SCSI Write Data >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=1 | |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
| | | |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
B.4. CRC Examples
N.B. all Values are Hexadecimal
32 bytes of zeroes:
Byte: 0 1 2 3
0: 00 00 00 00
...
28: 00 00 00 00
CRC: aa 36 91 8a
32 bytes of ones:
Byte: 0 1 2 3
0: ff ff ff ff
...
28: ff ff ff ff
CRC: 43 ab a8 62
32 bytes of incrementing 00..1f:
Byte: 0 1 2 3
0: 00 01 02 03
...
28: 1c 1d 1e 1f
CRC: 4e 79 dd 46
32 bytes of decrementing 1f..00:
Byte: 0 1 2 3
0: 1f 1e 1d 1c
...
28: 03 02 01 00
CRC: 5c db 3f 11
An iSCSI - SCSI Read (10) Command PDU
Byte: 0 1 2 3
0: 01 c0 00 00
4: 00 00 00 00
8: 00 00 00 00
12: 00 00 00 00
16: 14 00 00 00
20: 00 00 04 00
24: 00 00 00 14
28: 00 00 00 18
32: 28 00 00 00
36: 00 00 00 00
40: 02 00 00 00
44: 00 00 00 00
CRC: 56 3a 96 d9
Appendix C. Login Phase Examples
In the first example, the initiator and target authenticate each
other via Kerberos:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,SRP,None
T-> Login (CSG,NSG=0,0 T=0)
AuthMethod=KRB5
I-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REQ=<krb_ap_req>
(krb_ap_req contains the Kerberos V5 ticket and authenticator
with MUTUAL-REQUIRED set in the ap-options field)
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REP=<krb_ap_rep>
(krb_ap_rep is the Kerberos V5 mutual authentication reply)
If the authentication is successful, the initiator may proceed
with:
I-> Login (CSG,NSG=1,0 T=0) FirstBurstLength=8192
T-> Login (CSG,NSG=1,0 T=0) FirstBurstLength=4096
MaxBurstLength=8192
I-> Login (CSG,NSG=1,0 T=0) MaxBurstLength=8192
... more iSCSI Operational Parameters
T-> Login (CSG,NSG=1,0 T=0)
... more iSCSI Operational Parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the initiator's authentication by the target is not
successful, the target responds with:
T-> Login "login reject"
instead of the Login KRB_AP_REP message, and terminates the
connection.
If the target's authentication by the initiator is not
successful, the initiator terminates the connection (without
responding to the Login KRB_AP_REP message).
In the next example only the initiator is authenticated by the
target via Kerberos:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=SRP,KRB5,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=KRB5
I-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REQ=krb_ap_req
(MUTUAL-REQUIRED not set in the ap-options field of krb_ap_req)
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
. . .
T-> Login (CSG,NSG=1,3 T=1)"login accept"
In the next example, the initiator and target authenticate each
other via SPKM1:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=SPKM1,KRB5,None
T-> Login (CSG,NSG=0,0 T=0)
AuthMethod=SPKM1
I-> Login (CSG,NSG=0,0 T=0)
SPKM_REQ=<spkm-req>
(spkm-req is the SPKM-REQ token with the mutual-state bit in the
options field of the REQ-TOKEN set)
T-> Login (CSG,NSG=0,0 T=0)
SPKM_REP_TI=<spkm-rep-ti>
If the authentication is successful, the initiator proceeds:
I-> Login (CSG,NSG=0,1 T=1)
SPKM_REP_IT=<spkm-rep-it>
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
The initiator may proceed:
I-> Login (CSG,NSG=1,0 T=0) ... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0) ... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the target's authentication by the initiator is not
successful, the initiator terminates the connection (without
responding to the Login SPKM_REP_TI message).
If the initiator's authentication by the target is not
successful, the target responds with:
T-> Login "login reject"
instead of the Login "proceed and change stage" message, and
terminates the connection.
In the next example, the initiator and target authenticate each
other via SPKM2:
I-> Login (CSG,NSG=0,0 T=0)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=SPKM1,SPKM2
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=SPKM2
I-> Login (CSG,NSG=0,1 T=1)
SPKM_REQ=<spkm-req>
(spkm-req is the SPKM-REQ token with the mutual-state bit in the
options field of the REQ-TOKEN not set)
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
The initiator may proceed:
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
In the next example, the initiator and target authenticate each
other via SRP:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,SRP,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=SRP
I-> Login (CSG,NSG=0,0 T=0)
SRP_U=<user>
TargetAuth=Yes
T-> Login (CSG,NSG=0,0 T=0)
SRP_GROUP=SRP-1536,SRP-1024
SRP_s=<s>
I-> Login (CSG,NSG=0,0 T=0)
SRP_GROUP=SRP-1536
SRP_A=<A>
T-> Login (CSG,NSG=0,0 T=0)
SRP_B=<B>
I-> Login (CSG,NSG=0,1 T=1)
SRP_M=<M>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
SRP_HM=<H(A | M | K)>
Where N, g, s, A, B, M, and H(A | M | K) are defined in [RFC2945].
If the target authentication is not successful, the initiator
terminates the connection; otherwise, it proceeds.
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the initiator authentication is not successful, the target
responds with:
T-> Login "login reject"
Instead of the T-> Login SRP_HM=<H(A | M | K)> message and
terminates the connection.
In the next example, the initiator and target authenticate each
other via SRP:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,SRP,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=SRP
I-> Login (CSG,NSG=0,0 T=0)
SRP_U=<user>
TargetAuth=No
T-> Login (CSG,NSG=0,0 T=0)
SRP_GROUP=SRP-1536
SRP_s=<s>
I-> Login (CSG,NSG=0,0 T=0)
SRP_GROUP=SRP-1536
SRP_A=<A>
T-> Login (CSG,NSG=0,0 T=0)
SRP_B=<B>
I-> Login (CSG,NSG=0,1 T=1)
SRP_M=<M>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
In the next example the initiator and target authenticate each other
via CHAP:
I-> Login (CSG,NSG=0,0 T=0)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,CHAP,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=CHAP
I-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1,A2>
T-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1>
CHAP_I=<I>
CHAP_C=<C>
I-> Login (CSG,NSG=0,1 T=1)
CHAP_N=<N>
CHAP_R=<R>
CHAP_I=<I>
CHAP_C=<C>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
CHAP_N=<N>
CHAP_R=<R>
If the target authentication is not successful, the initiator
aborts the connection; otherwise, it proceeds.
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the initiator authentication is not successful, the target
responds with:
T-> Login "login reject"
Instead of the Login CHAP_R=<response> "proceed and change
stage" message and terminates the connection.
In the next example, only the initiator is authenticated by the
target via CHAP:
I-> Login (CSG,NSG=0,1 T=0)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,CHAP,None
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=CHAP
I-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1,A2>
T-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1>
CHAP_I=<I>
CHAP_C=<C>
I-> Login (CSG,NSG=0,1 T=1)
CHAP_N=<N>
CHAP_R=<R>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
In the next example, the initiator does not offer any security
parameters. It therefore may offer iSCSI parameters on the Login PDU
with the T bit set to 1, and the target may respond with a final
Login Response PDU immediately:
I-> Login (CSG,NSG=1,3 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
... iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
... ISCSI parameters
In the next example, the initiator does offer security
parameters on the Login PDU, but the target does not choose
any (i.e., chooses the "None" values):
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os:hostid.77
TargetName=iqn.1999-07.com.example:diskarray.sn.88
AuthMethod=KRB5,SRP,None
T-> Login-PR (CSG,NSG=0,1 T=1)
AuthMethod=None
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
Appendix D. SendTargets Operation
To reduce the amount of configuration required on an initiator, iSCSI
provides the SendTargets text request. The initiator uses the
SendTargets request to get a list of targets to which it may have
access, as well as the list of addresses (IP address and TCP port) on
which these targets may be accessed.
To make use of SendTargets, an initiator must first establish one of
two types of sessions. If the initiator establishes the session
using the key "SessionType=Discovery", the session is a discovery
session, and a target name does not need to be specified. Otherwise,
the session is a normal, operational session. The SendTargets
command MUST only be sent during the Full Feature Phase of a normal
or discovery session.
A system that contains targets MUST support discovery sessions on
each of its iSCSI IP address-port pairs, and MUST support the
SendTargets command on the discovery session. In a discovery
session, a target MUST return all path information (target name and
IP address-port pairs and portal group tags) for the targets on the
target network entity which the requesting initiator is authorized to
access.
A target MUST support the SendTargets command on operational
sessions; these will only return path information about the target to
which the session is connected, and do not need to return information
about other target names that may be defined in the responding
system.
An initiator MAY make use of the SendTargets as it sees fit.
A SendTargets command consists of a single Text request PDU. This
PDU contains exactly one text key and value. The text key MUST be
SendTargets. The expected response depends upon the value, as well
as whether the session is a discovery or operational session.
The value must be one of:
All
The initiator is requesting that information on all relevant
targets known to the implementation be returned. This value
MUST be supported on a discovery session, and MUST NOT be
supported on an operational session.
<iSCSI-target-name>
If an iSCSI target name is specified, the session should respond
with addresses for only the named target, if possible. This
value MUST be supported on discovery sessions. A discovery
session MUST be capable of returning addresses for those
targets that would have been returned had value=All had been
designated.
<nothing>
The session should only respond with addresses for the target to
which the session is logged in. This MUST be supported on
operational sessions, and MUST NOT return targets other than
the one to which the session is logged in.
The response to this command is a text response that contains a list
of zero or more targets and, optionally, their addresses. Each
target is returned as a target record. A target record begins with
the TargetName text key, followed by a list of TargetAddress text
keys, and bounded by the end of the text response or the next
TargetName key, which begins a new record. No text keys other than
TargetName and TargetAddress are permitted within a SendTargets
response.
For the format of the TargetName, see Section 12.4 TargetName.
In a discovery session, a target MAY respond to a SendTargets request
with its complete list of targets, or with a list of targets that is
based on the name of the initiator logged in to the session.
A SendTargets response MUST NOT contain target names if there are no
targets for the requesting initiator to access.
Each target record returned includes zero or more TargetAddress
fields.
Each target record starts with one text key of the form:
TargetName=<target-name-goes-here>
Followed by zero or more address keys of the form:
TargetAddress=<hostname-or-ipaddress>[:<tcp-port>],
<portal-group-tag>
The hostname-or-ipaddress contains a domain name, IPv4 address, or
IPv6 address, as specified for the TargetAddress key.
A hostname-or-ipaddress duplicated in TargetAddress responses for a
given node (the port is absent or equal) would probably indicate that
multiple address families are in use at once (IPV6 and IPV4).
Each TargetAddress belongs to a portal group, identified by its
numeric portal group tag (as in Section 12.9 TargetPortalGroupTag).
The iSCSI target name, together with this tag, constitutes the SCSI
port identifier; the tag only needs to be unique within a given
target's name list of addresses.
Multiple-connection sessions can span iSCSI addresses that belong to
the same portal group.
Multiple-connection sessions cannot span iSCSI addresses that belong
to different portal groups.
If a SendTargets response reports an iSCSI address for a target, it
SHOULD also report all other addresses in its portal group in the
same response.
A SendTargets text response can be longer than a single Text Response
PDU, and makes use of the long text responses as specified.
After obtaining a list of targets from the discovery target session,
an iSCSI initiator may initiate new sessions to log in to the
discovered targets for full operation. The initiator MAY keep the
discovery session open, and MAY send subsequent SendTargets commands
to discover new targets.
Examples:
This example is the SendTargets response from a single target that
has no other interface ports.
Initiator sends text request that contains:
SendTargets=All
Target sends a text response that contains:
TargetName=iqn.1993-11.com.example:diskarray.sn.8675309
All the target had to return in the simple case was the target name.
It is assumed by the initiator that the IP address and TCP port for
this target are the same as used on the current connection to the
default iSCSI target.
The next example has two internal iSCSI targets, each accessible via
two different ports with different IP addresses. The following is
the text response:
TargetName=iqn.1993-11.com.example:diskarray.sn.8675309
TargetAddress=10.1.0.45:3000,1 TargetAddress=10.1.1.45:3000,2
TargetName=iqn.1993-11.com.example:diskarray.sn.1234567
TargetAddress=10.1.0.45:3000,1 TargetAddress=10.1.1.45:3000,2
Both targets share both addresses; the multiple addresses are likely
used to provide multi-path support. The initiator may connect to
either target name on either address. Each of the addresses has its
own portal group tag; they do not support spanning
multiple-connection sessions with each other. Keep in mind that the
portal group tags for the two named targets are independent of one
another; portal group "1" on the first target is not necessarily the
same as portal group "1" on the second target.
In the above example, a DNS host name or an IPv6 address could have
been returned instead of an IPv4 address.
The next text response shows a target that supports spanning sessions
across multiple addresses, and further illustrates the use of the
portal group tags:
TargetName=iqn.1993-11.com.example:diskarray.sn.8675309
TargetAddress=10.1.0.45:3000,1 TargetAddress=10.1.1.46:3000,1
TargetAddress=10.1.0.47:3000,2 TargetAddress=10.1.1.48:3000,2
TargetAddress=10.1.1.49:3000,3
In this example, any of the target addresses can be used to reach the
same target. A single-connection session can be established to any
of these TCP addresses. A multiple-connection session could span
addresses .45 and .46 or .47 and .48, but cannot span any other
combination. A TargetAddress with its own tag (.49) cannot be
combined with any other address within the same session.
This SendTargets response does not indicate whether .49 supports
multiple connections per session; it is communicated via the
MaxConnections text key upon login to the target.
Appendix E. Algorithmic Presentation of Error Recovery Classes
This appendix illustrates the error recovery classes using a
pseudo-programming-language. The procedure names are chosen to be
obvious to most implementers. Each of the recovery classes described
has initiator procedures as well as target procedures. These
algorithms focus on outlining the mechanics of error recovery
classes, and do not exhaustively describe all other aspects/cases.
Examples of this approach are:
- Handling for only certain Opcode types is shown.
- Only certain reason codes (e.g., Recovery in Logout command)
are outlined.
- Resultant cases, such as recovery of Synchronization on a
header digest error are considered out-of-scope in these
algorithms. In this particular example, a header digest error
may lead to connection recovery if some type of sync and
steering layer is not implemented.
These algorithms strive to convey the iSCSI error recovery concepts
in the simplest terms, and are not designed to be optimal.
E.1. General Data Structure and Procedure Description
This section defines the procedures and data structures that are
commonly used by all the error recovery algorithms. The structures
may not be the exhaustive representations of what is required for a
typical implementation.
Data structure definitions -
struct TransferContext {
int TargetTransferTag;
int ExpectedDataSN;
};
struct TCB { /* task control block */
Boolean SoFarInOrder;
int ExpectedDataSN; /* used for both R2Ts, and Data */
int MissingDataSNList[MaxMissingDPDU];
Boolean FbitReceived;
Boolean StatusXferd;
Boolean CurrentlyAllegiant;
int ActiveR2Ts;
int Response;
char *Reason;
struct TransferContext
TransferContextList[MaxOutStandingR2T];
int InitiatorTaskTag;
int CmdSN;
int SNACK_Tag;
};
struct Connection {
struct Session SessionReference;
Boolean SoFarInOrder;
int CID;
int State;
int CurrentTimeout;
int ExpectedStatSN;
int MissingStatSNList[MaxMissingSPDU];
Boolean PerformConnectionCleanup;
};
struct Session {
int NumConnections;
int CmdSN;
int Maxconnections;
int ErrorRecoveryLevel;
struct iSCSIEndpoint OtherEndInfo;
struct Connection ConnectionList[MaxSupportedConns];
};
Procedure descriptions -
Receive-a-In-PDU(transport connection, inbound PDU);
check-basic-validity(inbound PDU);
Start-Timer(timeout handler, argument, timeout value);
Build-And-Send-Reject(transport connection, bad PDU, reason code);
E.2. Within-command Error Recovery Algorithms
E.2.1. Procedure Descriptions
Recover-Data-if-Possible(last required DataSN, task control
block);
Build-And-Send-DSnack(task control block);
Build-And-Send-RDSnack(task control block);
Build-And-Send-Abort(task control block);
SCSI-Task-Completion(task control block);
Build-And-Send-A-Data-Burst(transport connection, data-descriptor,
task control block);
Build-And-Send-R2T(transport connection, data-descriptor,
task control block);
Build-And-Send-Status(transport connection, task control block);
Transfer-Context-Timeout-Handler(transfer context);
Notes:
- One procedure used in this section: Handle-Status-SNACK-
request is defined in Within-connection recovery algorithms.
- The Response processing pseudo-code, shown in the target
algorithms, applies to all solicited PDUs that carry StatSN -
SCSI Response, Text Response etc.
E.2.2. Initiator Algorithms
Recover-Data-if-Possible(LastRequiredDataSN, TCB)
{
if (operational ErrorRecoveryLevel > 0) {
if (# of missing PDUs is trackable) {
Note the missing DataSNs in TCB.
if (the task spanned a change in
MaxRecvDataSegmentLength) {
if (TCB.StatusXferd is TRUE)
drop the status PDU;
Build-And-Send-RDSnack(TCB);
} else {
Build-And-Send-DSnack(TCB);
}
} else {
TCB.Reason = "Protocol service CRC error";
}
} else {
TCB.Reason = "Protocol service CRC error";
}
if (TCB.Reason == "Protocol service CRC error") {
Clear the missing PDU list in the TCB.
if (TCB.StatusXferd is not TRUE)
Build-And-Send-Abort(TCB);
}
}
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if ((CurrentPDU.type == Data)
or (CurrentPDU.type = R2T)) {
if (Data-Digest-Bad for Data) {
send-data-SNACK = TRUE;
LastRequiredDataSN = CurrentPDU.DataSN;
} else {
if (TCB.SoFarInOrder = TRUE) {
if (current DataSN is expected) {
Increment TCB.ExpectedDataSN.
} else {
TCB.SoFarInOrder = FALSE;
send-data-SNACK = TRUE;
}
} else {
if (current DataSN was considered missing) {
remove current DataSN from missing PDU list.
} else if (current DataSN is higher than expected)
{
send-data-SNACK = TRUE;
} else {
discard, return;
}
Adjust TCB.ExpectedDataSN if appropriate.
}
LastRequiredDataSN = CurrentPDU.DataSN - 1;
}
if (send-data-SNACK is TRUE and
task is not already considered failed) {
Recover-Data-if-Possible(LastRequiredDataSN, TCB);
}
if (missing data PDU list is empty) {
TCB.SoFarInOrder = TRUE;
}
if (CurrentPDU.type == R2T) {
Increment ActiveR2Ts for this task.
Create a data-descriptor for the data burst.
Build-And-Send-A-Data-Burst(Connection, data-descriptor,
TCB);
}
} else if (CurrentPDU.type == Response) {
if (Data-Digest-Bad) {
send-status-SNACK = TRUE;
} else {
TCB.StatusXferd = TRUE;
Store the status information in TCB.
if (ExpDataSN does not match) {
TCB.SoFarInOrder = FALSE;
Recover-Data-if-Possible(current DataSN, TCB);
}
if (missing data PDU list is empty) {
TCB.SoFarInOrder = TRUE;
}
}
} else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT
SHOWN */
}
if ((TCB.SoFarInOrder == TRUE) and
(TCB.StatusXferd == TRUE)) {
SCSI-Task-Completion(TCB);
}
}
E.2.3. Target Algorithms
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type == Data) {
Retrieve TContext from CurrentPDU.TargetTransferTag;
if (Data-Digest-Bad) {
Build-And-Send-Reject(Connection, CurrentPDU,
Payload-Digest-Error);
Note the missing data PDUs in MissingDataRange[].
send-recovery-R2T = TRUE;
} else {
if (current DataSN is not expected) {
Note the missing data PDUs in MissingDataRange[].
send-recovery-R2T = TRUE;
}
if (CurrentPDU.Fbit == TRUE) {
if (current PDU is solicited) {
Decrement TCB.ActiveR2Ts.
}
if ((current PDU is unsolicited and
data received is less than I/O length and
data received is less than FirstBurstLength)
or (current PDU is solicited and the length of
this burst is less than expected)) {
send-recovery-R2T = TRUE;
Note the missing data in MissingDataRange[].
}
}
}
Increment TContext.ExpectedDataSN.
if (send-recovery-R2T is TRUE and
task is not already considered failed) {
if (operational ErrorRecoveryLevel > 0) {
Increment TCB.ActiveR2Ts.
Create a data-descriptor for the data burst
from MissingDataRange.
Build-And-Send-R2T(Connection, data-descriptor, TCB);
} else {
if (current PDU is the last unsolicited)
TCB.Reason = "Not enough unsolicited data";
else
TCB.Reason = "Protocol service CRC error";
}
}
if (TCB.ActiveR2Ts == 0) {
Build-And-Send-Status(Connection, TCB);
}
} else if (CurrentPDU.type == SNACK) {
snack-failure = FALSE;
if (operational ErrorRecoveryLevel > 0) {
if (CurrentPDU.type == Data/R2T) {
if (the request is satisfiable) {
if (request for Data) {
Create a data-descriptor for the data burst
from BegRun and RunLength.
Build-And-Send-A-Data-Burst(Connection,
data-descriptor, TCB);
} else { /* R2T */
Create a data-descriptor for the data burst
from BegRun and RunLength.
Build-And-Send-R2T(Connection, data-descriptor,
TCB);
}
} else {
snack-failure = TRUE;
}
} else if (CurrentPDU.type == status) {
Handle-Status-SNACK-request(Connection, CurrentPDU);
} else if (CurrentPDU.type == DataACK) {
Consider all data upto CurrentPDU.BegRun as
acknowledged.
Free up the retransmission resources for that data.
} else if (CurrentPDU.type == R-Data SNACK) {
Create a data descriptor for a data burst covering
all unacknowledged data.
Build-And-Send-A-Data-Burst(Connection,
data-descriptor, TCB);
TCB.SNACK_Tag = CurrentPDU.SNACK_Tag;
if (there's no more data to send) {
Build-And-Send-Status(Connection, TCB);
}
}
} else { /* operational ErrorRecoveryLevel = 0 */
snack-failure = TRUE;
}
if (snack-failure == TRUE) {
Build-And-Send-Reject(Connection, CurrentPDU,
SNACK-Reject);
if (TCB.StatusXferd != TRUE) {
TCB.Reason = "SNACK Rejected";
Build-And-Send-Status(Connection, TCB);
}
}
} else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT SHOWN */
}
}
Transfer-Context-Timeout-Handler(TContext)
{
Retrieve TCB and Connection from TContext.
Decrement TCB.ActiveR2Ts.
if (operational ErrorRecoveryLevel > 0 and
task is not already considered failed) {
Note the missing data PDUs in MissingDataRange[].
Create a data-descriptor for the data burst
from MissingDataRange[].
Build-And-Send-R2T(Connection, data-descriptor, TCB);
} else {
TCB.Reason = "Protocol service CRC error";
if (TCB.ActiveR2Ts = 0) {
Build-And-Send-Status(Connection, TCB);
}
}
}
E.3. Within-connection Recovery Algorithms
E.3.1. Procedure Descriptions
Procedure descriptions:
Recover-Status-if-Possible(transport connection,
currently received PDU);
Evaluate-a-StatSN(transport connection, currently received PDU);
Retransmit-Command-if-Possible(transport connection, CmdSN);
Build-And-Send-SSnack(transport connection);
Build-And-Send-Command(transport connection, task control block);
Command-Acknowledge-Timeout-Handler(task control block);
Status-Expect-Timeout-Handler(transport connection);
Build-And-Send-Nop-Out(transport connection);
Handle-Status-SNACK-request(transport connection, status SNACK
PDU);
Retransmit-Status-Burst(status SNACK, task control block);
Is-Acknowledged(beginning StatSN, run length);
Implementation-specific tunables:
InitiatorProactiveSNACKEnabled
Notes:
- The initiator algorithms only deal with unsolicited Nop-In PDUs
for generating status SNACKs. A solicited Nop-In PDU has an
assigned StatSN, which, when out of order, could trigger the
out of order StatSN handling in Within-command algorithms,
again leading to Recover-Status-if-Possible.
- The pseudo-code shown may result in the retransmission of
unacknowledged commands in more cases than necessary. This
will not, however, affect the correctness of the operation
because the target is required to discard the duplicate CmdSNs.
- The procedure Build-And-Send-Async is defined in the Connection
recovery algorithms.
- The procedure Status-Expect-Timeout-Handler describes how
initiators may proactively attempt to retrieve the Status if
they so choose. This procedure is assumed to be triggered much
before the standard ULP timeout.
E.3.2. Initiator Algorithms
Recover-Status-if-Possible(Connection, CurrentPDU)
{
if ((Connection.state == LOGGED_IN) and
connection is not already considered failed) {
if (operational ErrorRecoveryLevel > 0) {
if (# of missing PDUs is trackable) {
Note the missing StatSNs in Connection
that were not already requested with SNACK;
Build-And-Send-SSnack(Connection);
} else {
Connection.PerformConnectionCleanup = TRUE;
}
} else {
Connection.PerformConnectionCleanup = TRUE;
}
if (Connection.PerformConnectionCleanup == TRUE) {
Start-Timer(Connection-Cleanup-Handler, Connection, 0);
}
}
}
Retransmit-Command-if-Possible(Connection, CmdSN)
{
if (operational ErrorRecoveryLevel > 0) {
Retrieve the InitiatorTaskTag, and thus TCB for the CmdSN.
Build-And-Send-Command(Connection, TCB);
}
}
Evaluate-a-StatSN(Connection, CurrentPDU)
{
send-status-SNACK = FALSE;
if (Connection.SoFarInOrder == TRUE) {
if (current StatSN is the expected) {
Increment Connection.ExpectedStatSN.
} else {
Connection.SoFarInOrder = FALSE;
send-status-SNACK = TRUE;
}
} else {
if (current StatSN was considered missing) {
remove current StatSN from the missing list.
} else {
if (current StatSN is higher than expected){
send-status-SNACK = TRUE;
} else {
send-status-SNACK = FALSE;
discard the PDU;
}
}
Adjust Connection.ExpectedStatSN if appropriate.
if (missing StatSN list is empty) {
Connection.SoFarInOrder = TRUE;
}
}
return send-status-SNACK;
}
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type == Nop-In) {
if (the PDU is unsolicited) {
if (current StatSN is not expected) {
Recover-Status-if-Possible(Connection,
CurrentPDU);
}
if (current ExpCmdSN is not Session.CmdSN) {
Retransmit-Command-if-Possible(Connection,
CurrentPDU.ExpCmdSN);
}
}
} else if (CurrentPDU.type == Reject) {
if (it is a data digest error on immediate data) {
Retransmit-Command-if-Possible(Connection,
CurrentPDU.BadPDUHeader.CmdSN);
}
} else if (CurrentPDU.type == Response) {
send-status-SNACK = Evaluate-a-StatSN(Connection,
CurrentPDU);
if (send-status-SNACK == TRUE)
Recover-Status-if-Possible(Connection, CurrentPDU);
} else { /* REST UNRELATED TO WITHIN-CONNECTION-RECOVERY,
* NOT SHOWN */
}
}
Command-Acknowledge-Timeout-Handler(TCB)
{
Retrieve the Connection for TCB.
Retransmit-Command-if-Possible(Connection, TCB.CmdSN);
}
Status-Expect-Timeout-Handler(Connection)
{
if (operational ErrorRecoveryLevel > 0) {
Build-And-Send-Nop-Out(Connection);
} else if (InitiatorProactiveSNACKEnabled){
if ((Connection.state == LOGGED_IN) and
connection is not already considered failed) {
Build-And-Send-SSnack(Connection);
}
}
}
E.3.3. Target Algorithms
Handle-Status-SNACK-request(Connection, CurrentPDU)
{
if (operational ErrorRecoveryLevel > 0) {
if (request for an acknowledged run) {
Build-And-Send-Reject(Connection, CurrentPDU,
Protocol-Error);
} else if (request for an untransmitted run) {
discard, return;
} else {
Retransmit-Status-Burst(CurrentPDU, TCB);
} else {
Build-And-Send-Async(Connection, DroppedConnection,
DefaultTime2Wait,
DefaultTime2Retain);
}
}
E.4. Connection Recovery Algorithms
E.4.1. Procedure Descriptions
Build-And-Send-Async(transport connection, reason code,
minimum time, maximum time);
Pick-A-Logged-In-Connection(session);
Build-And-Send-Logout(transport connection, logout connection
identifier, reason code);
PerformImplicitLogout(transport connection, logout connection
identifier, target information);
PerformLogin(transport connection, target information);
CreateNewTransportConnection(target information);
Build-And-Send-Command(transport connection, task control block);
Connection-Cleanup-Handler(transport connection);
Connection-Resource-Timeout-Handler(transport connection);
Quiesce-And-Prepare-for-New-Allegiance(session, task control
block);
Build-And-Send-Logout-Response(transport connection,
CID of connection in recovery, reason
code);
Build-And-Send-TaskMgmt-Response(transport connection,
task mgmt command PDU, response code);
Establish-New-Allegiance(task control block, transport
connection);
Schedule-Command-To-Continue(task control block);
Notes:
- Transport exception conditions, such as unexpected connection
termination, connection reset, and hung connection while the
connection is in the full-feature phase, are all assumed to be
asynchronously signaled to the iSCSI layer using the
Transport_Exception_Handler procedure.
E.4.2. Initiator Algorithms
Receive-a-In-PDU(Connection, CurrentPDU) {
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB from CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type == Async) {
if (CurrentPDU.AsyncEvent == ConnectionDropped) {
Retrieve the AffectedConnection for
CurrentPDU.Parameter1.
AffectedConnection.CurrentTimeout =
CurrentPDU.Parameter3;
AffectedConnection.State = CLEANUP_WAIT;
Start-Timer(Connection-Cleanup-Handler,
AffectedConnection,
CurrentPDU.Parameter2);
} else if (CurrentPDU.AsyncEvent == LogoutRequest)) {
AffectedConnection = Connection;
AffectedConnection.State = LOGOUT_REQUESTED;
AffectedConnection.PerformConnectionCleanup = TRUE;
AffectedConnection.CurrentTimeout =
CurrentPDU.Parameter3;
Start-Timer(Connection-Cleanup-Handler,
AffectedConnection, 0);
} else if (CurrentPDU.AsyncEvent == SessionDropped)) {
for (each Connection) {
Connection.State = CLEANUP_WAIT;
Connection.CurrentTimeout = CurrentPDU.Parameter3;
Start-Timer(Connection-Cleanup-Handler,
Connection, CurrentPDU.Parameter2);
}
Session.state = FAILED;
}
} else if (CurrentPDU.type == LogoutResponse) {
Retrieve the CleanupConnection for CurrentPDU.CID.
if (CurrentPDU.Response = failure) {
CleanupConnection.State = CLEANUP_WAIT;
} else {
CleanupConnection.State = FREE;
}
} else if (CurrentPDU.type == LoginResponse) {
if (this is a response to an implicit Logout) {
Retrieve the CleanupConnection.
if (successful) {
CleanupConnection.State = FREE;
Connection.State = LOGGED_IN;
} else {
CleanupConnection.State = CLEANUP_WAIT;
DestroyTransportConnection(Connection);
}
}
} else { /* REST UNRELATED TO CONNECTION-RECOVERY,
* NOT SHOWN */
}
if (CleanupConnection.State == FREE) {
for (each command that was active on CleanupConnection) {
/* Establish new connection allegiance */
NewConnection = Pick-A-Logged-In-Connection(Session);
Build-And-Send-Command(NewConnection, TCB);
}
} }
Connection-Cleanup-Handler(Connection) {
Retrieve Session from Connection.
if (Connection can still exchange iSCSI PDUs) {
NewConnection = Connection;
} else {
Start-Timer(Connection-Resource-Timeout-Handler,
Connection, Connection.CurrentTimeout);
if (there are other logged-in connections) {
NewConnection = Pick-A-Logged-In-
Connection(Session);
} else {
NewConnection =
CreateTransportConnection(Session.OtherEndInfo);
Initiate an implicit Logout on NewConnection for
Connection.CID.
return;
}
}
Build-And-Send-Logout(NewConnection, Connection.CID,
RecoveryRemove); }
Transport_Exception_Handler(Connection) {
Connection.PerformConnectionCleanup = TRUE;
if (the event is an unexpected transport disconnect) {
Connection.State = CLEANUP_WAIT;
Connection.CurrentTimeout = DefaultTime2Retain;
Start-Timer(Connection-Cleanup-Handler, Connection,
DefaultTime2Wait);
} else {
Connection.State = FREE;
} }
E.4.3. Target Algorithms
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
else if (Data-Digest-Bad) {
Build-And-Send-Reject(Connection, CurrentPDU,
Payload-Digest-Error);
discard, return;
}
Retrieve TCB and Session.
if (CurrentPDU.type == Logout) {
if (CurrentPDU.ReasonCode = RecoveryRemove) {
Retrieve the CleanupConnection from CurrentPDU.CID).
for (each command active on CleanupConnection) {
Quiesce-And-Prepare-for-New-Allegiance(Session,
TCB);
TCB.CurrentlyAllegiant = FALSE;
}
Cleanup-Connection-State(CleanupConnection);
if ((quiescing successful) and (cleanup successful)) {
Build-And-Send-Logout-Response(Connection,
CleanupConnection.CID, Success);
} else {
Build-And-Send-Logout-Response(Connection,
CleanupConnection.CID, Failure);
}
}
} else if ((CurrentPDU.type == Login) and
operational ErrorRecoveryLevel == 2) {
Retrieve the CleanupConnection from CurrentPDU.CID).
for (each command active on CleanupConnection) {
Quiesce-And-Prepare-for-New-Allegiance(Session, TCB);
TCB.CurrentlyAllegiant = FALSE;
}
Cleanup-Connection-State(CleanupConnection);
if ((quiescing successful) and (cleanup successful)) {
Continue with the rest of the Login processing;
} else {
Build-And-Send-Login-Response(Connection,
CleanupConnection.CID, Target Error);
}
}
} else if (CurrentPDU.type == TaskManagement) {
if (CurrentPDU.function == "TaskReassign") {
if (Session.ErrorRecoveryLevel < 2) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Allegiance reassignment
not supported");
} else if (task is not found) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Task not in task set");
} else if (task is currently allegiant) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Task still allegiant");
} else {
Establish-New-Allegiance(TCB, Connection);
TCB.CurrentlyAllegiant = TRUE;
Schedule-Command-To-Continue(TCB);
}
}
} else { /* REST UNRELATED TO CONNECTION-RECOVERY,
* NOT SHOWN */
}
}
Transport_Exception_Handler(Connection)
{
Connection.PerformConnectionCleanup = TRUE;
if (the event is an unexpected transport disconnect) {
Connection.State = CLEANUP_WAIT;
Start-Timer(Connection-Resource-Timeout-Handler,
Connection,
(DefaultTime2Wait+DefaultTime2Retain));
if (this Session has full-feature phase connections
left)
{
DifferentConnection =
Pick-A-Logged-In-Connection(Session);
Build-And-Send-Async(DifferentConnection,
DroppedConnection, DefaultTime2Wait,
DefaultTime2Retain);
}
} else {
Connection.State = FREE;
}
}
Appendix F. Clearing Effects of Various Events on Targets
F.1. Clearing Effects on iSCSI Objects
The following tables describe the target behavior on receiving the
events specified in the rows of the table. The second table is an
extension of the first table and defines clearing actions for more
objects on the same events. The legend is:
Y = Yes (cleared/discarded/reset on the event specified in the
row). Unless otherwise noted, the clearing action is only
applicable for the issuing initiator port.
N = No (not affected on the event specified in the row, i.e.,
stays at previous value).
NA = Not Applicable or Not Defined.
+-----+-----+-----+-----+-----+
|IT(1)|IC(2)|CT(5)|ST(6)|PP(7)|
+---------------------+-----+-----+-----+-----+-----+
|connection failure(8)|Y |Y |N |N |Y |
+---------------------+-----+-----+-----+-----+-----+
|connection state |NA |NA |Y |N |NA |
|timeout (9) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session timeout/ |Y |Y |Y |Y |Y(14)|
|closure/reinstatement| | | | | |
|(10) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session continuation |NA |NA |N(11)|N |NA |
|(12) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|successful connection|Y |Y |Y |N |Y(13)|
|close logout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session failure (18) |Y |Y |N |N |Y |
+---------------------+-----+-----+-----+-----+-----+
|successful recovery |Y |Y |N |N |Y(13)|
|Logout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|failed Logout |Y |Y |N |N |Y |
+---------------------+-----+-----+-----+-----+-----+
|connection Login |NA |NA |NA |Y(15)|NA |
|(leading) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|connection Login |NA |NA |N(11)|N |Y |
|(non-leading) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|target cold reset(16)|Y |Y |Y |Y |Y |
+---------------------+-----+-----+-----+-----+-----+
|target warm reset(16)|Y |Y |Y |Y |Y |
+---------------------+-----+-----+-----+-----+-----+
|LU reset(19) |Y |Y |Y |Y |Y |
+---------------------+-----+-----+-----+-----+-----+
|powercycle(16) |Y |Y |Y |Y |Y |
+---------------------+-----+-----+-----+-----+-----+
1. Incomplete TTTs - Target Transfer Tags on which the target is
still expecting PDUs to be received. Examples include TTTs received
via R2T, NOP-IN, etc.
2. Immediate Commands - immediate commands, but waiting for
execution on a target. For example, Abort Task Set.
5. Connection Tasks - tasks that are active on the iSCSI connection
in question.
6. Session Tasks - tasks that are active on the entire iSCSI
session. A union of "connection tasks" on all participating
connections.
7. Partial PDUs (if any) - PDUs that are partially sent and waiting
for transport window credit to complete the transmission.
8. Connection failure is a connection exception condition - one of
the transport connections shutdown, transport connections reset, or
transport connections timed out, which abruptly terminated the iSCSI
full-feature phase connection. A connection failure always takes the
connection state machine to the CLEANUP_WAIT state.
9. Connection state timeout happens if a connection spends more time
that agreed upon during Login negotiation in the CLEANUP_WAIT state,
and this takes the connection to the FREE state (M1 transition in
connection cleanup state diagram).
10. These are defined in Section 5.3.5 Session Reinstatement,
Closure, and Timeout.
11. This clearing effect is "Y" only if it is a connection
reinstatement and the operational ErrorRecoveryLevel is less than 2.
12. Session continuation is defined in Section 5.3.6 Session
Continuation and Failure.
13. This clearing effect is only valid if the connection is being
logged out on a different connection and when the connection being
logged out on the target may have some partial PDUs pending to be
sent. In all other cases, the effect is "NA".
14. This clearing effect is only valid for a "close the session"
logout in a multi-connection session. In all other cases, the effect
is "NA".
15. Only applicable if this leading connection login is a session
reinstatement. If this is not the case, it is "NA".
16. This operation affects all logged-in initiators.
18. Session failure is defined in Section 5.3.6 Session Continuation
and Failure.
19. This operation affects all logged-in initiators and the clearing
effects are only applicable to the LU being reset.
+-----+-----+-----+-----+-----+
|DC(1)|DD(2)|SS(3)|CS(4)|DS(5)|
+---------------------+-----+-----+-----+-----+-----+
|connection failure |N |Y |N |N |N |
+---------------------+-----+-----+-----+-----+-----+
|connection state |Y |NA |Y |N |NA |
|timeout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session timeout/ |Y |Y |Y(7) |Y |NA |
|closure/reinstatement| | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session continuation |N(11)|NA*12|NA |N |NA*13|
+---------------------+-----+-----+-----+-----+-----+
|successful connection|Y |Y |Y |N |NA |
|close Logout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|session failure |N |Y |N |N |N |
+---------------------+-----+-----+-----+-----+-----+
|successful recovery |Y |Y |Y |N |N |
|Logout | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|failed Logout |N |Y(9) |N |N |N |
+---------------------+-----+-----+-----+-----+-----+
|connection Login |NA |NA |N(8) |N(8) |NA |
|(leading | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|connection Login |N(11)|NA*12|N(8) |N |NA*13|
|(non-leading) | | | | | |
+---------------------+-----+-----+-----+-----+-----+
|target cold reset |Y |Y |Y |Y(10)|NA |
+---------------------+-----+-----+-----+-----+-----+
|target warm reset |Y |Y |N |N |NA |
+---------------------+-----+-----+-----+-----+-----+
|LU reset |N |Y |N |N |N |
+---------------------+-----+-----+-----+-----+-----+
|powercycle |Y |Y |Y |Y(10)|NA |
+---------------------+-----+-----+-----+-----+-----+
1. Discontiguous Commands - commands allegiant to the connection in
question and waiting to be reordered in the iSCSI layer. All "Y"s in
this column assume that the task causing the event (if indeed the
event is the result of a task) is issued as an immediate command,
because the discontiguities can be ahead of the task.
2. Discontiguous Data - data PDUs received for the task in question
and waiting to be reordered due to prior discontiguities in DataSN.
3. StatSN
4. CmdSN
5. DataSN
7. It clears the StatSN on all the connections.
8. This sequence number is instantiated on this event.
9. A logout failure drives the connection state machine to the
CLEANUP_WAIT state, similar to the connection failure event. Hence,
it has a similar effect on this and several other protocol aspects.
10. This is cleared by virtue of the fact that all sessions with all
initiators are terminated.
11. This clearing effect is "Y" if it is a connection reinstatement.
12. This clearing effect is "Y" only if it is a connection
reinstatement and the operational ErrorRecoveryLevel is 2.
13. This clearing effect is "N" only if it is a connection
reinstatement and the operational ErrorRecoveryLevel is 2.
F.2. Clearing Effects on SCSI Objects
The only iSCSI protocol action that can effect clearing actions on
SCSI objects is the "I_T nexus loss" notification (Section 4.3.5.1
Loss of Nexus notification). [SPC3] describes the clearing effects
of this notification on a variety of SCSI attributes. In addition,
SCSI standards documents (such as [SAM2] and [SBC]) define additional
clearing actions that may take place for several SCSI objects on SCSI
events such as LU resets and power-on resets.
Since iSCSI defines a target cold reset as a protocol-equivalent to a
target power-cycle, the iSCSI target cold reset must also be
considered as the power-on reset event in interpreting the actions
defined in the SCSI standards.
When the iSCSI session is reconstructed (between the same SCSI ports
with the same nexus identifier) reestablishing the same I_T nexus,
all SCSI objects that are defined to not clear on the "I_T nexus
loss" notification event, such as persistent reservations, are
automatically associated to this new session.
Acknowledgements
This protocol was developed by a design team that, in addition to the
authors, included Daniel Smith, Ofer Biran, Jim Hafner and John
Hufferd (IBM), Mark Bakke (Cisco), Randy Haagens (HP), Matt Wakeley
(Agilent, now Sierra Logic), Luciano Dalle Ore (Quantum), and Paul
Von Stamwitz (Adaptec, now TrueSAN Networks).
Furthermore, a large group of people contributed to this work through
their review, comments, and valuable insights. We are grateful to
all of them. We especially thank those people who found the time and
patience to take part in our weekly phone conferences and
intermediate meetings in Almaden and Haifa, which helped shape this
document: Prasenjit Sarkar, Meir Toledano, John Dowdy, Steve Legg,
Alain Azagury (IBM), Dave Nagle (CMU), David Black (EMC), John Matze
(Veritas - now Okapi Software), Steve DeGroote, Mark Schrandt
(Cisco), Gabi Hecht (Gadzoox), Robert Snively and Brian Forbes
(Brocade), Nelson Nachum (StorAge), and Uri Elzur (Broadcom). Many
others helped edit and improve this document within the IPS working
group. We are especially grateful to David Robinson and Raghavendra
Rao (Sun), Charles Monia, Joshua Tseng (Nishan), Somesh Gupta
(Silverback), Michael Krause, Pierre Labat, Santosh Rao, Matthew
Burbridge, Bob Barry, Robert Elliott, Nick Martin (HP), Stephen
Bailey (Sandburst), Steve Senum, Ayman Ghanem, Dave Peterson (Cisco),
Barry Reinhold (Trebia Networks), Bob Russell (UNH), Eddy Quicksall
(iVivity, Inc.), Bill Lynn and Michael Fischer (Adaptec), Vince
Cavanna, Pat Thaler (Agilent), Jonathan Stone (Stanford), Luben
Tuikov (Splentec), Paul Koning (EqualLogic), Michael Krueger
(Windriver), Martins Krikis (Intel), Doug Otis (Sanlight), John
Marberg (IBM), Robert Griswold and Bill Moody (Crossroads), Bill
Studenmund (Wasabi Systems), Elizabeth Rodriguez (Brocade) and Yaron
Klein (Sanrad). The recovery chapter was enhanced with the help of
Stephen Bailey (Sandburst), Somesh Gupta (Silverback), and Venkat
Rangan (Rhapsody Networks). Eddy Quicksall contributed some examples
and began the Definitions section. Michael Fischer and Bob Barry
started the Acronyms section. Last, but not least, we thank Ralph
Weber for keeping us in line with T10 (SCSI) standardization.
We would like to thank Steve Hetzler for his unwavering support and
for coming up with such a good name for the protocol, and Micky
Rodeh, Jai Menon, Clod Barrera, and Andy Bechtolsheim for helping
make this work happen.
In addition to this document, we recommend you acquaint yourself with
the following in order to get a full understanding of the iSCSI
specification: "iSCSI Naming & Discovery"[RFC3721], "Bootstrapping
Clients using the iSCSI Protocol" [BOOT], "Securing Block Storage
Protocols over IP" [RFC3723] documents, "iSCSI Requirements and
Design Considerations" [RFC3347] and "SCSI Command Ordering
Considerations with iSCSI" [CORD].
The "iSCSI Naming & Discovery" document is authored by:
Mark Bakke (Cisco), Jim Hafner, John Hufferd, Kaladhar Voruganti
(IBM), and Marjorie Krueger (HP).
The "Bootstrapping Clients using the iSCSI Protocol" document is
authored by:
Prasenjit Sarkar (IBM), Duncan Missimer (HP), and Costa
Sapuntzakis (Cisco).
The "Securing Block Storage Protocols over IP" document is authored
by:
Bernard Aboba (Microsoft), Joshua Tseng (Nishan), Jesse Walker
(Intel), Venkat Rangan (Rhapsody Networks), and Franco
Travostino (Nortel Networks).
The "iSCSI Requirements and Design Considerations" document is
authored by:
Marjorie Krueger, Randy Haagens (HP), Costa Sapuntzakis, and Mark
Bakke (Cisco).
The "SCSI Command Ordering Considerations with iSCSI" document is
authored by:
Mallikarjun Chadalapaka, Rob Elliot (HP)
We are grateful to all of them for their good work and for helping us
correlate this document with the ones they produced.
Authors' Addresses
Julian Satran
IBM Research Laboratory in Haifa
Haifa University Campus - Mount Carmel
Haifa 31905, Israel
Phone +972.4.829.6264
EMail: Julian_Satran@il.ibm.com
Kalman Meth
IBM Research Laboratory in Haifa
Haifa University Campus - Mount Carmel
Haifa 31905, Israel
Phone +972.4.829.6341
EMail: meth@il.ibm.com
Costa Sapuntzakis
Stanford University
353 Serra Mall Dr #407
Stanford, CA 94305
Phone: +1.650.723.2458
EMail: csapuntz@alum.mit.edu
Efri Zeidner
XIV Ltd.
1 Azrieli Center,
Tel-Aviv 67021, Israel
Phone: +972.3.607.4722
EMail: efri@xiv.co.il
Mallikarjun Chadalapaka
Hewlett-Packard Company
8000 Foothills Blvd.
Roseville, CA 95747-5668, USA
Phone: +1.916.785.5621
EMail: cbm@rose.hp.com
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