| Rfc | 3584 |
|---|
| Title | Coexistence between Version 1, Version 2, and Version 3 of the
Internet-standard Network Management Framework |
|---|
| Author | R. Frye, D. Levi, S.
Routhier, B. Wijnen |
|---|
| Date | August 2003 |
|---|
| Format: | TXT, HTML |
|---|
| Obsoletes | RFC2576 |
|---|
| Also | BCP0074 |
|---|
| Status: | BEST CURRENT PRACTICE |
|---|
|
Network Working Group R. Frye
Request for Comments: 3584 Vibrant Solutions
BCP: 74 D. Levi
Obsoletes: 2576 Nortel Networks
Category: Best Current Practice S. Routhier
Wind River Systems, Inc.
B. Wijnen
Lucent Technologies
August 2003
Coexistence between Version 1, Version 2, and Version 3
of the Internet-standard Network Management Framework
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The purpose of this document is to describe coexistence between
version 3 of the Internet-standard Network Management Framework,
(SNMPv3), version 2 of the Internet-standard Network Management
Framework (SNMPv2), and the original Internet-standard Network
Management Framework (SNMPv1). This document also describes how to
convert MIB modules from SMIv1 format to SMIv2 format. This document
obsoletes RFC 2576.
Table Of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. SNMPv1 . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. SNMPv2 . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. SNMPv3 . . . . . . . . . . . . . . . . . . . . . . . . 5
2. SMI and Management Information Mappings. . . . . . . . . . . 5
2.1. MIB Modules. . . . . . . . . . . . . . . . . . . . . . 6
2.1.1. Object Definitions . . . . . . . . . . . . . . 6
2.1.2. Trap and Notification Definitions . . . . . . 8
2.2. Compliance Statements. . . . . . . . . . . . . . . . . 9
2.3. Capabilities Statements. . . . . . . . . . . . . . . . 9
3. Translating Notification Parameters. . . . . . . . . . . . . 10
3.1. Translating SNMPv1 Notification Parameters to
SNMPv2 Notification Parameters . . . . . . . . . . . . 11
3.2. Translating SNMPv2 Notification Parameters to
SNMPv1 Notification Parameters . . . . . . . . . . . . 12
4. Approaches to Coexistence in a Multi-lingual Network . . . . 14
4.1. SNMPv1 and SNMPv2 Access to MIB Data . . . . . . . . . 14
4.2. Multi-lingual implementations. . . . . . . . . . . . . 15
4.2.1. Command Generator. . . . . . . . . . . . . . . 15
4.2.2. Command Responder. . . . . . . . . . . . . . . 16
4.2.2.1. Handling Counter64 . . . . . . . . . 16
4.2.2.2. Mapping SNMPv2 Exceptions. . . . . . 17
4.2.2.2.1. Mapping noSuchObject
and noSuchInstance. . . . 18
4.2.2.2.2. Mapping endOfMibView. . . 18
4.2.2.3. Processing An SNMPv1 GetReques . . . 18
4.2.2.4. Processing An SNMPv1 GetNextRequest. 19
4.2.2.5. Processing An SNMPv1 SetRequest. . . 20
4.2.3. Notification Originator. . . . . . . . . . . . 21
4.2.4. Notification Receiver. . . . . . . . . . . . . 21
4.3. Proxy Implementations. . . . . . . . . . . . . . . . . 22
4.3.1. Upstream Version Greater Than Downstream
Version. . . . . . . . . . . . . . . . . . . . 22
4.3.2. Upstream Version Less Than Downstream Version. 23
4.4. Error Status Mappings. . . . . . . . . . . . . . . . . 25
5. Message Processing Models and Security Models. . . . . . . . 26
5.1. Mappings . . . . . . . . . . . . . . . . . . . . . . . 26
5.2. The SNMPv1 MP Model and SNMPv1 Community-based
Security Model . . . . . . . . . . . . . . . . . . . . 26
5.2.1. Processing An Incoming Request . . . . . . . . 27
5.2.2. Generating An Outgoing Response. . . . . . . . 29
5.2.3. Generating An Outgoing Notification. . . . . . 29
5.2.4. Proxy Forwarding Of Requests . . . . . . . . . 30
5.3. The SNMP Community MIB Module. . . . . . . . . . . . . 30
6. Intellectual Property Statement. . . . . . . . . . . . . . . 42
7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . 43
8. Security Considerations. . . . . . . . . . . . . . . . . . . 43
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.1. Normative References . . . . . . . . . . . . . . . . . 44
9.2. Informative References . . . . . . . . . . . . . . . . 46
Appendix A. Change Log. . . . . . . . . . . . . . . . . . . . . 47
A.1. Changes From RFC 2576 . . . . . . . . . . . . . . . . . 47
A.2. Changes Between RFC 1908 and RFC 2576 . . . . . . . . . 49
Editors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 51
1. Overview
The purpose of this document is to describe coexistence between
version 3 of the Internet-standard Network Management Framework,
termed the SNMP version 3 framework (SNMPv3), version 2 of the
Internet-standard Network Management Framework, termed the SNMP
version 2 framework (SNMPv2), and the original Internet-standard
Network Management Framework (SNMPv1).
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 RFC 2119 [RFC2119].
There are four general aspects of coexistence described in this
document. Each of these is described in a separate section:
- Conversion of MIB documents between SMIv1 and SMIv2 formats is
documented in section 2.
- Mapping of notification parameters is documented in section 3.
- Approaches to coexistence between entities which support the
various versions of SNMP in a multi-lingual network is documented
in section 4. This section addresses the processing of protocol
operations in multi-lingual implementations, as well as behaviour
of proxy implementations.
- The SNMPv1 Message Processing Model and Community-Based Security
Model, which provides mechanisms for adapting SNMPv1 into the
View-Based Access Control Model (VACM) [20], is documented in
section 5 (this section also addresses the SNMPv2c Message
Processing Model and Community-Based Security Model).
1.1. SNMPv1
SNMPv1 is defined by these documents:
- STD 15, RFC 1157 [RFC1157] which defines the Simple Network
Management Protocol (SNMPv1), the protocol used for network access
to managed objects.
- STD 16, RFC 1155 [RFC1155] which defines the Structure of
Management Information (SMIv1), the mechanisms used for describing
and naming objects for the purpose of management.
- STD 16, RFC 1212 [RFC1212] which defines a more concise
description mechanism, which is wholly consistent with the SMIv1.
- RFC 1215 [RFC1215] which defines a convention for defining Traps
for use with the SMIv1.
Note that throughout this document, the term 'SMIv1' is used. This
term generally refers to the information presented in RFC 1155, RFC
1212, and RFC 1215.
1.2. SNMPv2
SNMPv2 is defined by these documents:
- STD 58, RFC 2578 which defines Version 2 of the Structure of
Management Information (SMIv2) [RFC2578].
- STD 58, RFC 2579 which defines common MIB "Textual Conventions"
[RFC2579].
- STD 58, RFC 2580 which defines Conformance Statements and
requirements for defining agent and manager capabilities
[RFC2580].
- STD 62, RFC 3416 which defines the Protocol Operations used in
processing [RFC3416].
- STD 62, RFC 3417 which defines the Transport Mappings used "on the
wire" [RFC3417].
- STD 62, RFC 3418 which defines the basic Management Information
Base for monitoring and controlling some basic common functions of
SNMP entities [RFC3418].
Note that SMIv2 as used throughout this document refers to the first
three documents listed above (RFCs 2578, 2579, and 2580).
The following document augments the definition of SNMPv2:
- RFC 1901 [RFC1901] is an Experimental definition for using SNMPv2
PDUs within a community-based message wrapper. This is referred
to throughout this document as SNMPv2c.
1.3. SNMPv3
SNMPv3 is defined by these documents:
- STD 62, RFC 3411 which defines an Architecture for Describing SNMP
Management Frameworks [RFC3411].
- STD 62, RFC 3412 which defines Message Processing and Dispatching
[RFC3412].
- STD 62, RFC 3413 which defines various SNMP Applications
[RFC3413].
- STD 62, RFC 3414 which defines the User-based Security Model
(USM), providing for both Authenticated and Private (encrypted)
SNMP messages [RFC3414].
- STD 62, RFC 3415 which defines the View-based Access Control Model
(VACM), providing the ability to limit access to different MIB
objects on a per-user basis [RFC3415].
SNMPv3 also uses the SNMPv2 definitions of RFCs 3416 through 3418 and
the SMIv2 definitions of 2578 through 2580 described above. Note
that text throughout this document that refers to SNMPv2 PDU types
and protocol operations applies to both SNMPv2c and SNMPv3.
2. SMI and Management Information Mappings
The SMIv2 approach towards describing collections of managed objects
is nearly a proper superset of the approach defined in the SMIv1.
For example, both approaches use an adapted subset of ASN.1 [ASN1] as
the basis for a formal descriptive notation. Indeed, one might note
that the SMIv2 approach largely codifies the existing practice for
defining MIB modules, based on extensive experience with the SMIv1.
The following sections consider the three areas: MIB modules,
compliance statements, and capabilities statements.
2.1. MIB Modules
MIB modules defined using the SMIv1 may continue to be used with
protocol versions which use SNMPv2 PDUs. However, for SMIv1 MIB
modules to conform to the SMIv2, the following changes SHALL be made:
2.1.1. Object Definitions
In general, conversion of a MIB module does not require the
deprecation of the objects contained therein. If the definition of
an object is truly inadequate for its intended purpose, the object
SHALL be deprecated or obsoleted, otherwise deprecation is not
required.
(1) The IMPORTS statement MUST reference SNMPv2-SMI, instead of
RFC1155-SMI and RFC-1212.
(2) The MODULE-IDENTITY macro MUST be invoked immediately after any
IMPORTs statement.
(3) For any object with a SYNTAX clause value of Counter, the object
MUST have the value of its SYNTAX clause changed to Counter32.
(4) For any object with a SYNTAX clause value of Gauge, the object
MUST have the value of its SYNTAX clause changed to Gauge32, or
Unsigned32 where appropriate.
(5) For all objects, the ACCESS clause MUST be replaced by a MAX-
ACCESS clause. The value of the MAX-ACCESS clause SHALL be the
same as that of the ACCESS clause unless some other value makes
"protocol sense" as the maximal level of access for the object.
In particular, object types for which instances can be
explicitly created by a protocol set operation, SHALL have a
MAX-ACCESS clause of "read-create". If the value of the ACCESS
clause is "write-only", then the value of the MAX-ACCESS clause
MUST be "read-write", and the DESCRIPTION clause SHALL note that
reading this object will result in implementation-specific
results. Note that in SMIv1, the ACCESS clause specifies the
minimal required access, while in SMIv2, the MAX-ACCESS clause
specifies the maximum allowed access. This should be considered
when converting an ACCESS clause to a MAX-ACCESS clause.
(6) For all objects, if the value of the STATUS clause is
"mandatory" or "optional", the value MUST be replaced with
"current", "deprecated", or "obsolete" depending on the current
usage of such objects.
(7) For any object not containing a DESCRIPTION clause, the object
MUST have a DESCRIPTION clause defined.
(8) For any object corresponding to a conceptual row which does not
have an INDEX clause, the object MUST have either an INDEX
clause or an AUGMENTS clause defined.
(9) If any INDEX clause contains a reference to an object with a
syntax of NetworkAddress, then a new object MUST be created and
placed in this INDEX clause immediately preceding the object
whose syntax is NetworkAddress. This new object MUST have a
syntax of INTEGER, it MUST be not-accessible, and its value MUST
always be 1. The effect of this, and the preceding bullet, is
to allow one to convert a MIB module in SMIv1 format to one in
SMIv2 format, and then use it with the SNMPv1 protocol with no
impact to existing SNMPv1 agents and managers.
(10) For any object with a SYNTAX of NetworkAddress, the SYNTAX MUST
be changed to IpAddress. Note that the use of NetworkAddress in
new MIB documents is strongly discouraged (in fact, new MIB
documents should be written using SMIv2, which does not define
NetworkAddress).
(11) For any object containing a DEFVAL clause with an OBJECT
IDENTIFIER value which is expressed as a collection of sub-
identifiers, the value MUST be changed to reference a single
ASN.1 identifier. This may require defining a series of new
administrative assignments (OBJECT IDENTIFIERS) in order to
define the single ASN.1 identifier.
(12) One or more OBJECT-GROUPS MUST be defined, and related objects
MUST be collected into appropriate groups. Note that SMIv2
requires all OBJECT-TYPEs to be a member of at least one
OBJECT-GROUP.
(13) For any non-columnar object that is instanced as if it were
immediately subordinate to a conceptual row, the value of the
STATUS clause of that object MUST be changed to "obsolete".
(14) For any conceptual row object that is not immediately
subordinate to a conceptual table, the value of the STATUS
clause of that object (and all subordinate objects) MUST be
changed to "obsolete".
Other changes are desirable, but not necessary:
(1) Creation and deletion of conceptual rows is inconsistent using
the SMIv1. The SMIv2 corrects this. As such, if the MIB module
undergoes review early in its lifetime, and it contains
conceptual tables which allow creation and deletion of
conceptual rows, then the objects relating to those tables MAY
be deprecated and replaced with objects defined using the new
approach. The approach based on SMIv2 can be found in section 7
of RFC 2578 [RFC2578], and the RowStatus and StorageType
TEXTUAL-CONVENTIONs are described in section 2 of RFC 2579
[RFC2579].
(2) For any object with an integer-valued SYNTAX clause, in which
the corresponding INTEGER does not have a range restriction
(i.e., the INTEGER has neither a defined set of named-number
enumerations nor an assignment of lower- and upper-bounds on its
value), the object SHOULD have the value of its SYNTAX clause
changed to Integer32, or have an appropriate range specified.
(3) For any object with a string-valued SYNTAX clause, in which the
corresponding OCTET STRING does not have a size restriction
(i.e., the OCTET STRING has no assignment of lower- and upper-
bounds on its length), the bounds for the size of the object
SHOULD be defined.
(4) All textual conventions informally defined in the MIB module
SHOULD be redefined using the TEXTUAL-CONVENTION macro. Such a
change would not necessitate deprecating objects previously
defined using an informal textual convention.
(5) For any object which represents a measurement in some kind of
units, a UNITS clause SHOULD be added to the definition of that
object.
(6) For any conceptual row which is an extension of another
conceptual row, i.e., for which subordinate columnar objects
both exist and are identified via the same semantics as the
other conceptual row, an AUGMENTS clause SHOULD be used in place
of the INDEX clause for the object corresponding to the
conceptual row which is an extension.
2.1.2. Trap and Notification Definitions
If a MIB module is changed to conform to the SMIv2, then each
occurrence of the TRAP-TYPE macro MUST be changed to a corresponding
invocation of the NOTIFICATION-TYPE macro:
(1) The IMPORTS statement MUST NOT reference RFC-1215 [RFC1215], and
MUST reference SNMPv2-SMI instead.
(2) The ENTERPRISE clause MUST be removed.
(3) The VARIABLES clause MUST be renamed to the OBJECTS clause.
(4) A STATUS clause MUST be added, with an appropriate value.
Normally the value should be 'current', although 'deprecated' or
'obsolete' may be used as needed.
(5) The value of an invocation of the NOTIFICATION-TYPE macro is an
OBJECT IDENTIFIER, not an INTEGER, and MUST be changed
accordingly. Specifically, if the value of the ENTERPRISE
clause is not 'snmp' then the value of the invocation SHALL be
the value of the ENTERPRISE clause extended with two sub-
identifiers, the first of which has the value 0, and the second
has the value of the invocation of the TRAP-TYPE. If the value
of the ENTERPRISE clause is 'snmp', then the value of the
invocation of the NOTIFICATION-TYPE macro SHALL be mapped in the
same manner as described in section 3.1 in this document.
(6) A DESCRIPTION clause MUST be added, if not already present.
(7) One or more NOTIFICATION-GROUPs MUST be defined, and related
notifications MUST be collected into those groups. Note that
SMIv2 requires that all NOTIFICATION-TYPEs be a member of at
least one NOTIFICATION-GROUP.
2.2. Compliance Statements
For those information modules which are "standards track", a
corresponding invocation of the MODULE-COMPLIANCE macro and related
OBJECT-GROUP and/or NOTIFICATION-GROUP macros MUST be included within
the information module (or in a companion information module), and
any commentary text in the information module which relates to
compliance SHOULD be removed. Typically this editing can occur when
the information module undergoes review.
Note that a MODULE-COMPLIANCE statement is not required for a MIB
document that is not on the standards track (for example, an
enterprise MIB), though it may be useful in some circumstances to
define a MODULE-COMPLIANCE statement for such a MIB document.
2.3. Capabilities Statements
RFC 1303 [RFC1303] uses the MODULE-CONFORMANCE macro to describe an
agent's capabilities with respect to one or more MIB modules.
Converting such a description for use with the SMIv2 requires these
changes:
(1) The macro name AGENT-CAPABILITIES MUST be used instead of
MODULE-CONFORMANCE.
(2) The STATUS clause MUST be added, with a value of 'current'.
(3) All occurrences of the CREATION-REQUIRES clause MUST either be
omitted if appropriate, or be changed such that the semantics
are consistent with RFC 2580 [RFC2580].
In order to ease coexistence, object groups defined in an SMIv1
compliant MIB module may be referenced by the INCLUDES clause of an
invocation of the AGENT-CAPABILITIES macro: upon encountering a
reference to an OBJECT IDENTIFIER subtree defined in an SMIv1 MIB
module, all leaf objects which are subordinate to the subtree and
have a STATUS clause value of mandatory are deemed to be INCLUDEd.
(Note that this method is ambiguous when different revisions of an
SMIv1 MIB have different sets of mandatory objects under the same
subtree; in such cases, the only solution is to rewrite the MIB using
the SMIv2 in order to define the object groups unambiguously.)
3. Translating Notification Parameters
This section describes how parameters used for generating
notifications are translated between the format used for SNMPv1
notification protocol operations and the format used for SNMPv2
notification protocol operations. The parameters used to generate a
notification are called 'notification parameters'. The format of
parameters used for SNMPv1 notification protocol operations is
referred to in this document as 'SNMPv1 notification parameters'.
The format of parameters used for SNMPv2 notification protocol
operations is referred to in this document as 'SNMPv2 notification
parameters'.
The situations where notification parameters MUST be translated are:
- When an entity generates a set of notification parameters in a
particular format, and the configuration of the entity indicates
that the notification must be sent using an SNMP message version
that requires the other format for notification parameters.
- When a proxy receives a notification that was sent using an SNMP
message version that requires one format of notification
parameters, and must forward the notification using an SNMP
message version that requires the other format of notification
parameters.
In addition, it MAY be desirable to translate notification parameters
in a notification receiver application in order to present
notifications to the end user in a consistent format.
Note that for the purposes of this section, the set of notification
parameters is independent of whether the notification is to be sent
as a trap or an inform.
SNMPv1 notification parameters consist of:
- An enterprise parameter (OBJECT IDENTIFIER).
- An agent-addr parameter (NetworkAddress).
- A generic-trap parameter (INTEGER).
- A specific-trap parameter (INTEGER).
- A time-stamp parameter (TimeTicks).
- A list of variable-bindings (VarBindList).
SNMPv2 notification parameters consist of:
- A sysUpTime parameter (TimeTicks). This appears in the first
variable-binding in an SNMPv2-Trap-PDU or InformRequest-PDU.
- An snmpTrapOID parameter (OBJECT IDENTIFIER). This appears in the
second variable-binding in an SNMPv2-Trap-PDU or InformRequest-
PDU, and is equal to the value portion of that variable-binding
(not the name portion, as both the name and value are OBJECT
IDENTIFIERs).
- A list of variable-bindings (VarBindList). This refers to all but
the first two variable-bindings in an SNMPv2-Trap-PDU or
InformRequest-PDU.
3.1. Translating SNMPv1 Notification Parameters to SNMPv2 Notification
Parameters
The following procedure describes how to translate SNMPv1
notification parameters into SNMPv2 notification parameters:
(1) The SNMPv2 sysUpTime parameter SHALL be taken directly from the
SNMPv1 time-stamp parameter.
(2) If the SNMPv1 generic-trap parameter is 'enterpriseSpecific(6)',
the SNMPv2 snmpTrapOID parameter SHALL be the concatenation of
the SNMPv1 enterprise parameter and two additional sub-
identifiers, '0', and the SNMPv1 specific-trap parameter.
(3) If the SNMPv1 generic-trap parameter is not
'enterpriseSpecific(6)', the SNMPv2 snmpTrapOID parameter SHALL
be the corresponding trap as defined in section 2 of RFC 3418
[RFC3418]:
generic-trap
parameter snmpTrapOID.0
============ =============
0 1.3.6.1.6.3.1.1.5.1 (coldStart)
1 1.3.6.1.6.3.1.1.5.2 (warmStart)
2 1.3.6.1.6.3.1.1.5.3 (linkDown)
3 1.3.6.1.6.3.1.1.5.4 (linkUp)
4 1.3.6.1.6.3.1.1.5.5 (authenticationFailure)
5 1.3.6.1.6.3.1.1.5.6 (egpNeighborLoss)
(4) The SNMPv2 variable-bindings SHALL be the SNMPv1 variable-
bindings. In addition, if the translation is being performed by
a proxy in order to forward a received trap, three additional
variable-bindings will be appended, if these three additional
variable-bindings do not already exist in the SNMPv1 variable-
bindings. The name portion of the first additional variable
binding SHALL contain snmpTrapAddress.0, and the value SHALL
contain the SNMPv1 agent-addr parameter. The name portion of
the second additional variable binding SHALL contain
snmpTrapCommunity.0, and the value SHALL contain the value of
the community-string field from the received SNMPv1 message
which contained the SNMPv1 Trap-PDU. The name portion of the
third additional variable binding SHALL contain
snmpTrapEnterprise.0 [RFC3418], and the value SHALL be the
SNMPv1 enterprise parameter.
3.2. Translating SNMPv2 Notification Parameters to SNMPv1 Notification
Parameters
The following procedure describes how to translate SNMPv2
notification parameters into SNMPv1 notification parameters:
(1) The SNMPv1 enterprise parameter SHALL be determined as follows:
- If the SNMPv2 snmpTrapOID parameter is one of the standard
traps as defined in RFC 3418 [RFC3418], then the SNMPv1
enterprise parameter SHALL be set to the value of the
variable-binding in the SNMPv2 variable-bindings whose name is
snmpTrapEnterprise.0 if that variable-binding exists. If it
does not exist, the SNMPv1 enterprise parameter SHALL be set
to the value 'snmpTraps' as defined in RFC 3418 [RFC3418].
- If the SNMPv2 snmpTrapOID parameter is not one of the standard
traps as defined in RFC 3418 [RFC3418], then the SNMPv1
enterprise parameter SHALL be determined from the SNMPv2
snmpTrapOID parameter as follows:
- If the next-to-last sub-identifier of the snmpTrapOID value
is zero, then the SNMPv1 enterprise SHALL be the SNMPv2
snmpTrapOID value with the last 2 sub-identifiers removed,
otherwise
- If the next-to-last sub-identifier of the snmpTrapOID value
is non-zero, then the SNMPv1 enterprise SHALL be the SNMPv2
snmpTrapOID value with the last sub-identifier removed.
(2) The SNMPv1 agent-addr parameter SHALL be determined based on the
situation in which the translation occurs.
- If the translation occurs within a notification originator
application, and the notification is to be sent over IP, the
SNMPv1 agent-addr parameter SHALL be set to the IP address of
the SNMP entity in which the notification originator resides.
If the notification is to be sent over some other transport,
the SNMPv1 agent-addr parameter SHALL be set to 0.0.0.0.
- If the translation occurs within a proxy application, the
proxy must attempt to extract the original source of the
notification from the variable-bindings. If the SNMPv2
variable-bindings contains a variable binding whose name is
snmpTrapAddress.0, the agent-addr parameter SHALL be set to
the value of that variable binding. Otherwise, the SNMPv1
agent-addr parameter SHALL be set to 0.0.0.0.
(3) If the SNMPv2 snmpTrapOID parameter is one of the standard traps
as defined in RFC 3418 [RFC3418], the SNMPv1 generic-trap
parameter SHALL be set as follows:
snmpTrapOID.0 parameter generic-trap
=============================== ============
1.3.6.1.6.3.1.1.5.1 (coldStart) 0
1.3.6.1.6.3.1.1.5.2 (warmStart) 1
1.3.6.1.6.3.1.1.5.3 (linkDown) 2
1.3.6.1.6.3.1.1.5.4 (linkUp) 3
1.3.6.1.6.3.1.1.5.5 (authenticationFailure) 4
1.3.6.1.6.3.1.1.5.6 (egpNeighborLoss) 5
Otherwise, the SNMPv1 generic-trap parameter SHALL be set to 6.
(4) If the SNMPv2 snmpTrapOID parameter is one of the standard traps
as defined in RFC 3418 [RFC3418], the SNMPv1 specific-trap
parameter SHALL be set to zero. Otherwise, the SNMPv1
specific-trap parameter SHALL be set to the last sub-identifier
of the SNMPv2 snmpTrapOID parameter.
(5) The SNMPv1 time-stamp parameter SHALL be taken directly from the
SNMPv2 sysUpTime parameter.
(6) The SNMPv1 variable-bindings SHALL be the SNMPv2 variable-
bindings (and note that the SNMPv2 variable-bindings do not
include the variable-bindings containing sysUpTime.0,
snmpTrapOID.0). Note, however, that if the SNMPv2 variable-
bindings contain any objects whose type is Counter64, the
translation to SNMPv1 notification parameters cannot be
performed. In this case, the notification cannot be encoded in
an SNMPv1 packet (and so the notification cannot be sent using
SNMPv1, see section 4.2.3 and section 4.3).
4. Approaches to Coexistence in a Multi-lingual Network
There are two basic approaches to coexistence in a multi-lingual
network, multi-lingual implementations and proxy implementations.
Multi-lingual implementations allow elements in a network to
communicate with each other using an SNMP version which both elements
support. This allows a multi-lingual implementation to communicate
with any mono-lingual implementation, regardless of the SNMP version
supported by the mono-lingual implementation.
Proxy implementations provide a mechanism for translating between
SNMP versions using a third party network element. This allows
network elements which support only a single, but different, SNMP
version to communicate with each other. Proxy implementations are
also useful for securing communications over an insecure link between
two locally secure networks.
4.1. SNMPv1 and SNMPv2 Access to MIB Data
Throughout section 4., this document refers to 'SNMPv1 Access to MIB
Data' and 'SNMPv2 Access to MIB Data'. These terms refer to the part
of an SNMP agent which actually accesses instances of MIB objects,
and which actually initiates generation of notifications.
Differences between the two types of access to MIB data are:
- Error-status values generated.
- Generation of exception codes.
- Use of the Counter64 data type.
- The format of parameters provided when a notification is
generated.
SNMPv1 access to MIB data may generate SNMPv1 error-status values,
will never generate exception codes nor use the Counter64 data type,
and will provide SNMPv1 format parameters for generating
notifications. Note also that SNMPv1 access to MIB data will
actually never generate a readOnly error (a noSuchName error would
always occur in the situation where one would expect a readOnly
error).
SNMPv2 access to MIB data may generate SNMPv2 error-status values,
may generate exception codes, may use the Counter64 data type, and
will provide SNMPv2 format parameters for generating notifications.
Note that SNMPv2 access to MIB data will never generate readOnly,
noSuchName, or badValue errors.
Note that a particular multi-lingual implementation may choose to
implement all access to MIB data as SNMPv2 access to MIB data, and
perform the translations described herein for SNMPv1-based
transactions.
Further, note that there is no mention of 'SNMPv3 access to MIB data'
in this document, as SNMPv3 uses SNMPv2 PDU types and protocol
operations.
4.2. Multi-lingual implementations
This approach requires an entity to support multiple SNMP message
versions. Typically this means supporting SNMPv1, SNMPv2c, and
SNMPv3 message versions. The behaviour of various types of SNMP
applications which support multiple message versions is described in
the following sections. This approach allows entities which support
multiple SNMP message versions to coexist with and communicate with
entities which support only a single SNMP message version.
4.2.1. Command Generator
A command generator must select an appropriate message version when
sending requests to another entity. One way to achieve this is to
consult a local database to select the appropriate message version.
In addition, a command generator MUST 'downgrade' GetBulk requests to
GetNext requests when selecting SNMPv1 as the message version for an
outgoing request. This is done by simply changing the operation type
to GetNext, ignoring any non-repeaters and max-repetitions values,
and setting error-status and error-index to zero.
4.2.2. Command Responder
A command responder must be able to deal with both SNMPv1 and SNMPv2
access to MIB data. There are three aspects to dealing with this. A
command responder must:
- Deal correctly with SNMPv2 access to MIB data that returns a
Counter64 value while processing an SNMPv1 message,
- Deal correctly with SNMPv2 access to MIB data that returns one of
the three exception values while processing an SNMPv1 message, and
- Map SNMPv2 error codes returned from SNMPv2 access to MIB data
into SNMPv1 error codes when processing an SNMPv1 message.
Note that SNMPv1 error codes SHOULD NOT be used without any change
when processing SNMPv2c or SNMPv3 messages, except in the case of
proxy forwarding. Also, SNMPv1 access to MIB data SHOULD NOT be used
when processing SNMPv2c or SNMPv3 messages. In the case of proxy
forwarding, for backwards compatibility, SNMPv1 error codes may be
used without any change in a forwarded SNMPv2c or SNMPv3 message.
The following sections describe the behaviour of a command responder
application which supports multiple SNMP message versions, and which
uses SNMPv2 access to MIB data when processing an SNMPv1 message.
4.2.2.1. Handling Counter64
The SMIv2 [RFC2578] defines one new syntax that is incompatible with
SMIv1. This syntax is Counter64. All other syntaxes defined by
SMIv2 are compatible with SMIv1.
The impact on multi-lingual command responders is that they MUST NOT
ever return a variable binding containing a Counter64 value in a
response to a request that was received using the SNMPv1 message
version.
Multi-lingual command responders SHALL take the approach that object
instances whose type is Counter64 are implicitly excluded from view
when processing an SNMPv1 message. So:
- On receipt of an SNMPv1 GetRequest-PDU containing a variable
binding whose name field points to an object instance of type
Counter64, a GetResponsePDU SHALL be returned, with an error-
status of noSuchName and the error-index set to the variable
binding that caused this error.
- On an SNMPv1 GetNextRequest-PDU, any object instance which
contains a syntax of Counter64 SHALL be skipped, and the next
accessible object instance that does not have the syntax of
Counter64 SHALL be retrieved. If no such object instance exists,
then an error-status of noSuchName SHALL be returned, and the
error-index SHALL be set to the variable binding that caused this
error.
- Any SNMPv1 request which contains a variable binding with a
Counter64 value is ill-formed, so the foregoing rules do not
apply. If that error is detected, a response SHALL NOT be
returned, since it would contain a copy of the ill-formed variable
binding. Instead, the offending PDU SHALL be discarded and the
counter snmpInASNParseErrs SHALL be incremented.
4.2.2.2. Mapping SNMPv2 Exceptions
SNMPv2 provides a feature called exceptions, which allow an SNMPv2
Response PDU to return as much management information as possible,
even when an error occurs. However, SNMPv1 does not support
exceptions, and so an SNMPv1 Response PDU cannot return any
management information, and can only return an error-status and an
error-index value.
When an SNMPv1 request is received, a command responder MUST check
any variable bindings returned using SNMPv2 access to MIB data for
exception values, and convert these exception values into SNMPv1
error codes.
The type of exception that can be returned when accessing MIB data
and the action taken depends on the type of SNMP request.
- For a GetRequest, a noSuchObject or noSuchInstance exception may
be returned.
- For a GetNextRequest, an endOfMibView exception may be returned.
- No exceptions will be returned for a SetRequest, and a
GetBulkRequest should only be received in an SNMPv2c or SNMPv3
message, so these request types may be ignored when mapping
exceptions.
Note that when a response contains multiple exceptions, it is an
implementation choice as to which variable binding the error-index
should reference.
4.2.2.2.1. Mapping noSuchObject and noSuchInstance
A noSuchObject or noSuchInstance exception generated by an SNMPv2
access to MIB data indicates that the requested object instance can
not be returned. The SNMPv1 error code for this condition is
noSuchName, and so the error-status field of the response PDU SHALL
be set to noSuchName. Also, the error-index field SHALL be set to
the index of the variable binding for which an exception occurred (if
there is more than one then it is an implementation decision as to
which is used), and the variable binding list from the original
request SHALL be returned with the response PDU.
4.2.2.2.2. Mapping endOfMibView
When an SNMPv2 access to MIB data returns a variable binding
containing an endOfMibView exception, it indicates that there are no
object instances available which lexicographically follow the object
in the request. In an SNMPv1 agent, this condition normally results
in a noSuchName error, and so the error-status field of the response
PDU SHALL be set to noSuchName. Also, the error-index field SHALL be
set to the index of the variable binding for which an exception
occurred (if there is more than one then it is an implementation
decision as to which is used), and the variable binding list from the
original request SHALL be returned with the response PDU.
4.2.2.3. Processing An SNMPv1 GetRequest
When processing an SNMPv1 GetRequest, the following procedures MUST
be followed when using an SNMPv2 access to MIB data.
When such an access to MIB data returns response data using SNMPv2
syntax and error-status values, then:
(1) If the error-status is anything other than noError,
- The error status SHALL be translated to an SNMPv1 error-
status using the table in section 4.4, "Error Status
Mappings".
- The error-index SHALL be set to the position (in the
original request) of the variable binding that caused the
error-status.
- The variable binding list of the response PDU SHALL be made
exactly the same as the variable binding list that was
received in the original request.
(2) If the error-status is noError, the variable bindings SHALL be
checked for any SNMPv2 exception (noSuchObject or
noSuchInstance) or an SNMPv2 syntax that is unknown to SNMPv1
(Counter64). If there are any such variable bindings, one of
those variable bindings SHALL be selected (it is an
implementation choice as to which is selected), and:
- The error-status SHALL be set to noSuchName,
- The error-index SHALL be set to the position (in the
variable binding list of the original request) of the
selected variable binding, and
- The variable binding list of the response PDU SHALL be
exactly the same as the variable binding list that was
received in the original request.
(3) If there are no such variable bindings, then:
- The error-status SHALL be set to noError,
- The error-index SHALL be set to zero, and
- The variable binding list of the response SHALL be composed
from the data as it is returned by the access to MIB data.
4.2.2.4. Processing An SNMPv1 GetNextRequest
When processing an SNMPv1 GetNextRequest, the following procedures
MUST be followed when SNMPv2 access to MIB data is used as part of
processing the request. There may be repetitive accesses to MIB data
to try to find the first object which lexicographically follows each
of the objects in the request. This is implementation specific.
These procedures are followed only for data returned when using
SNMPv2 access to MIB data. Data returned using SNMPv1 access to MIB
data may be treated in the normal manner for an SNMPv1 request.
First, if the access to MIB data returns an error-status of anything
other than noError:
(1) The error status SHALL be translated to an SNMPv1 error-status
using the table in section 4.4, "Error Status Mappings".
(2) The error-index SHALL be set to the position (in the original
request) of the variable binding that caused the error-status.
(3) The variable binding list of the response PDU SHALL be exactly
the same as the variable binding list that was received in the
original request.
Otherwise, if the access to MIB data returns an error-status of
noError:
(1) Any variable bindings containing an SNMPv2 syntax of Counter64
SHALL be considered to be not in view, and MIB data SHALL be
accessed as many times as is required until either a value other
than Counter64 is returned, or an error or endOfMibView
exception occurs.
(2) If there is any variable binding that contains an SNMPv2
exception endOfMibView (if there is more than one then it is an
implementation decision as to which is chosen):
- The error-status SHALL be set to noSuchName,
- The error-index SHALL be set to the position (in the
variable binding list of the original request) of the
variable binding that returned such an SNMPv2 exception, and
- The variable binding list of the response PDU SHALL be
exactly the same as the variable binding list that was
received in the original request.
(3) If there are no such variable bindings, then:
- The error-status SHALL be set to noError,
- The error-index SHALL be set to zero, and
- The variable binding list of the response SHALL be composed
from the data as it is returned by the access to MIB data.
4.2.2.5. Processing An SNMPv1 SetRequest
When processing an SNMPv1 SetRequest, the following procedures MUST
be followed when using SNMPv2 access to MIB data.
When such MIB access returns response data using SNMPv2 syntax and
error-status values, and the error-status is anything other than
noError, then:
- The error status SHALL be translated to an SNMPv1 error-status
using the table in section 4.4, "Error Status Mappings".
- The error-index SHALL be set to the position (in the original
request) of the variable binding that caused the error-status.
- The variable binding list of the response PDU SHALL be made
exactly the same as the variable binding list that was received in
the original request.
4.2.3. Notification Originator
A notification originator must be able to translate between SNMPv1
notification parameters and SNMPv2 notification parameters in order
to send a notification using a particular SNMP message version. If a
notification is generated using SNMPv1 notification parameters, and
configuration information specifies that notifications be sent using
SNMPv2c or SNMPv3, the notification parameters must be translated to
SNMPv2 notification parameters. Likewise, if a notification is
generated using SNMPv2 notification parameters, and configuration
information specifies that notifications be sent using SNMPv1, the
notification parameters must be translated to SNMPv1 notification
parameters. In this case, if the notification cannot be translated
(due to the presence of a Counter64 type), it will not be sent using
SNMPv1.
When a notification originator generates a notification, using
parameters obtained from the SNMP-TARGET-MIB and SNMP-NOTIFICATION-
MIB, if the SNMP version used to generate the notification is SNMPv1,
the PDU type used will always be a TrapPDU, regardless of whether the
value of snmpNotifyType is trap(1) or inform(2).
Note also that access control and notification filtering are
performed in the usual manner for notifications, regardless of the
SNMP message version to be used when sending a notification. The
parameters for performing access control are found in the usual
manner (i.e., from inspecting the SNMP-TARGET-MIB and SNMP-
NOTIFICATION-MIB). In particular, when generating an SNMPv1 Trap, in
order to perform the access check specified in [RFC3413], section
3.3, bullet (3), the notification originator may need to generate a
value for snmpTrapOID.0 as described in section 3.1, bullets (2) and
(3) of this document. If the SNMPv1 notification parameters being
used were previously translated from a set of SNMPv2 notification
parameters, this value may already be known, in which case it need
not be generated.
4.2.4. Notification Receiver
There are no special requirements of a notification receiver.
However, an implementation may find it useful to allow a higher level
application to request whether notifications should be delivered to a
higher level application using SNMPv1 notification parameter or
SNMPv2 notification parameters. The notification receiver would then
translate notification parameters when required in order to present a
notification using the desired set of parameters.
4.3. Proxy Implementations
A proxy implementation may be used to enable communication between
entities which support different SNMP message versions. This is
accomplished in a proxy forwarder application by performing
translations on PDUs. These translations depend on the PDU type, the
SNMP version of the packet containing a received PDU, and the SNMP
version to be used to forward a received PDU. The following sections
describe these translations. In all cases other than those described
below, the proxy SHALL forward a received PDU without change, subject
to size constraints as defined in section 5.3 (Community MIB) of this
document. Note that in the following sections, the 'Upstream
Version' refers to the version used between the command generator or
notification receiver and the proxy, and the 'Downstream Version'
refers to the version used between the proxy and the command
responder or notification originator, regardless of the PDU type or
direction.
4.3.1. Upstream Version Greater Than Downstream Version
- If a GetBulkRequest-PDU is received and must be forwarded using
the SNMPv1 message version, the proxy forwarder SHALL act as if
the non-repeaters and max-repetitions fields were both set to 0,
and SHALL set the tag of the PDU to GetNextRequest-PDU.
- If a GetResponse-PDU is received whose error-status field has a
value of 'tooBig', and the message will be forwarded using the
SNMPv2c or SNMPv3 message version, and the original request
received by the proxy was not a GetBulkRequest-PDU, the proxy
forwarder SHALL remove the contents of the variable-bindings field
and ensure that the error-index field is set to 0 before
forwarding the response.
- If a GetResponse-PDU is received whose error-status field has a
value of 'tooBig', and the message will be forwarded using the
SNMPv2c or SNMPv3 message version, and the original request
received by the proxy was a GetBulkRequest-PDU, the proxy
forwarder SHALL re-send the forwarded request (which would have
been altered to be a GetNextRequest-PDU) with all but the first
variable-binding removed. The proxy forwarder SHALL only re-send
such a request a single time. If the resulting GetResponse-PDU
also contains an error-status field with a value of 'tooBig', then
the proxy forwarder SHALL remove the contents of the variable-
bindings field, and change the error-status field to 'noError',
and ensure that the error-index field is set to 0 before
forwarding the response. Note that if the original request only
contained a single variable-binding, the proxy may skip re-sending
the request and simply remove the variable-bindings and change the
error-status to 'noError'. Further note that, while it might have
been possible to fit more variable bindings if the proxy only re-
sent the request multiple times, and stripped only a single
variable binding from the request at a time, this is deemed too
expensive. The approach described here preserves the behaviour of
a GetBulkRequest as closely as possible, without incurring the
cost of re-sending the request multiple times.
- If a Trap-PDU is received, and will be forwarded using the SNMPv2c
or SNMPv3 message version, the proxy SHALL apply the translation
rules described in section 3, and SHALL forward the notification
as an SNMPv2-Trap-PDU.
Note that when an SNMPv1 agent generates a message containing a
Trap-PDU which is subsequently forwarded by one or more proxy
forwarders using SNMP versions other than SNMPv1, the community
string and agent-addr fields from the original message generated
by the SNMPv1 agent will be preserved through the use of the
snmpTrapAddress and snmpTrapCommunity objects.
4.3.2. Upstream Version Less Than Downstream Version
- If a GetResponse-PDU is received in response to a GetRequest-PDU
(previously generated by the proxy) which contains variable-
bindings of type Counter64 or which contain an SNMPv2 exception
code, and the message would be forwarded using the SNMPv1 message
version, the proxy MUST generate an alternate response PDU
consisting of the request-id and variable bindings from the
original SNMPv1 request, containing a noSuchName error-status
value, and containing an error-index value indicating the position
of the variable-binding containing the Counter64 type or exception
code.
- If a GetResponse-PDU is received in response to a GetNextRequest-
PDU (previously generated by the proxy) which contains variable-
bindings that contain an SNMPv2 exception code, and the message
would be forwarded using the SNMPv1 message version, the proxy
MUST generate an alternate response PDU consisting of the
request-id and variable bindings from the original SNMPv1 request,
containing a noSuchName error-status value, and containing an
error-index value indicating the position of the variable-binding
containing the exception code.
- If a GetResponse-PDU is received in response to a GetNextRequest-
PDU (previously generated by the proxy) which contains variable-
bindings of type Counter64, the proxy MUST re-send the entire
GetNextRequest-PDU, with the following modifications. For any
variable bindings in the received GetResponse which contained
Counter64 types, the proxy substitutes the object names of these
variable bindings for the corresponding object names in the
previously-sent GetNextRequest. The proxy MUST repeat this
process until no Counter64 objects are returned. Note that an
implementation may attempt to optimize this process of skipping
Counter64 objects. One approach to such an optimization would be
to replace the last sub-identifier of the object names of varbinds
containing a Counter64 type with 65535 if that sub-identifier is
less than 65535, or with 4294967295 if that sub-identifier is
greater than 65535. This approach should skip multiple instances
of the same Counter64 object, while maintaining compatibility with
some broken agent implementations (which only use 16-bit integers
for sub-identifiers).
Deployment Hint: The process of repeated GetNext requests used by
a proxy when Counter64 types are returned can be expensive. When
deploying a proxy, this can be avoided by configuring the target
agents to which the proxy forwards requests in a manner such that
any objects of type Counter64 are in fact not-in-view for the
principal that the proxy is using when communicating with these
agents. However, when using such a configuration, one should be
careful to use a different principal for communicating with the
target agent when an incoming SNMPv2c or SNMPv3 request is
received, to ensure that objects of type Counter64 are properly
returned.
- If a GetResponse-PDU is received which contains an SNMPv2 error-
status value of wrongValue, wrongEncoding, wrongType, wrongLength,
inconsistentValue, noAccess, notWritable, noCreation,
inconsistentName, resourceUnavailable, commitFailed, undoFailed,
or authorizationError, and the message would be forwarded using
the SNMPv1 message version, the error-status value is modified
using the mappings in section 4.4.
- If an SNMPv2-Trap-PDU is received, and will be forwarded using the
SNMPv1 message version, the proxy SHALL apply the translation
rules described in section 3, and SHALL forward the notification
as a Trap-PDU. Note that if the translation fails due to the
existence of a Counter64 data-type in the received SNMPv2-Trap-
PDU, the trap cannot be forwarded using SNMPv1.
- If an InformRequest-PDU is received, any configuration information
indicating that it would be forwarded using the SNMPv1 message
version SHALL be ignored. An InformRequest-PDU can only be
forwarded using the SNMPv2c or SNMPv3 message version. The
InformRequest-PDU may still be forwarded if there is other
configuration information indicating that it should be forwarded
using SNMPv2c or SNMPv3.
4.4. Error Status Mappings
The following tables shows the mappings of SNMPv1 error-status values
into SNMPv2 error-status values, and the mappings of SNMPv2 error-
status values into SNMPv1 error-status values.
SNMPv1 error-status SNMPv2 error-status
=================== ===================
noError noError
tooBig tooBig
noSuchName noSuchName
badValue badValue
genErr genErr
SNMPv2 error-status SNMPv1 error-status
=================== ===================
noError noError
tooBig tooBig
genErr genErr
wrongValue badValue
wrongEncoding badValue
wrongType badValue
wrongLength badValue
inconsistentValue badValue
noAccess noSuchName
notWritable noSuchName
noCreation noSuchName
inconsistentName noSuchName
resourceUnavailable genErr
commitFailed genErr
undoFailed genErr
authorizationError noSuchName
Whenever the SNMPv2 error-status value of authorizationError is
translated to an SNMPv1 error-status value of noSuchName, the value
of snmpInBadCommunityUses MUST be incremented.
5. Message Processing Models and Security Models
In order to adapt SNMPv1 (and SNMPv2c) into the SNMP architecture,
the following Message Processing (MP) models are defined in this
document:
- The SNMPv1 Message Processing Model
- The SNMPv1 Community-Based Security Model
- The SNMPv2c Message Processing Model
- The SNMPv2c Community-Based Security Model
In most respects, the SNMPv1 Message Processing Model and the SNMPv2c
Message Processing Model are identical, and so these are not
discussed independently in this document. Differences between the
two models are described as required.
Similarly, the SNMPv1 Community-Based Security Model and the SNMPv2c
Community-Based Security Model are nearly identical, and so are not
discussed independently. Differences between these two models are
also described as required.
5.1. Mappings
The SNMPv1 (and SNMPv2c) Message Processing Model and Security Model
require mappings between parameters used in SNMPv1 (and SNMPv2c)
messages, and the version independent parameters used in the SNMP
architecture [RFC3411]. The parameters which MUST be mapped consist
of the SNMPv1 (and SNMPv2c) community name, and the SNMP securityName
and contextEngineID/contextName pair. A MIB module (the SNMP-
COMMUNITY-MIB) is provided in this document in order to perform these
mappings. This MIB provides mappings in both directions, that is, a
community name may be mapped to a securityName, contextEngineID, and
contextName, or the combination of securityName, contextEngineID, and
contextName may be mapped to a community name.
5.2. The SNMPv1 MP Model and SNMPv1 Community-based Security Model
The SNMPv1 Message Processing Model handles processing of SNMPv1
messages. The processing of messages is handled generally in the
same manner as described in RFC 1157 [RFC1157], with differences and
clarifications as described in the following sections. The
SnmpMessageProcessingModel value for SNMPv1 is 0 (the value for
SNMPv2c is 1).
5.2.1. Processing An Incoming Request
In RFC 1157 [RFC1157], section 4.1, item (3) for an entity which
receives a message, states that various parameters are passed to the
"desired authentication scheme". The desired authentication scheme
in this case is the SNMPv1 Community-Based Security Model, which will
be called using the processIncomingMsg ASI. The parameters passed to
this ASI are:
- The messageProcessingModel, which will be 0 (or 1 for SNMPv2c).
- The maxMessageSize, which should be the maximum size of a message
that the receiving entity can generate (since there is no such
value in the received message).
- The securityParameters, which consist of the community string and
the message's source and destination transport domains and
addresses.
- The securityModel, which will be 1 (or 2 for SNMPv2c).
- The securityLevel, which will be noAuthNoPriv.
- The wholeMsg and wholeMsgLength.
The Community-Based Security Model will attempt to select a row in
the snmpCommunityTable. This is done by performing a search through
the snmpCommunityTable in lexicographic order. The first entry for
which the following matching criteria are satisfied will be selected:
- The community string is equal to the snmpCommunityName value.
- If the snmpCommunityTransportTag is an empty string, it is ignored
for the purpose of matching. If the snmpCommunityTransportTag is
not an empty string, the transportDomain and transportAddress from
which the message was received must match one of the entries in
the snmpTargetAddrTable selected by the snmpCommunityTransportTag
value. The snmpTargetAddrTMask object is used as described in
section 5.3 when checking whether the transportDomain and
transportAddress matches a entry in the snmpTargetAddrTable.
If no such entry can be found, an authentication failure occurs as
described in RFC 1157 [RFC1157], and the snmpInBadCommunityNames
counter is incremented.
The parameters returned from the Community-Based Security Model are:
- The securityEngineID, which will always be the local value of
snmpEngineID.0.
- The securityName, which will be the value of
snmpCommunitySecurityName from the selected row in the
snmpCommunityTable.
- The scopedPDU. Note that this parameter will actually consist of
three values, the contextSnmpEngineID (which will be the value of
snmpCommunityContextEngineID from the selected entry in the
snmpCommunityTable), the contextName (which will be the value of
snmpCommunityContextName from the selected entry in the
snmpCommunityTable), and the PDU. These must be separate values,
since the first two do not actually appear in the message.
- The maxSizeResponseScopedPDU, which will be derived using the
minimum of the maxMessageSize above, and the value of
snmpTargetAddrMMS of the selected row in the snmpTargetAddrTable.
If no such entry was selected, then this value will be derived
from the maxMessageSize only.
- The securityStateReference, which MUST contain the community
string from the original request.
The appropriate SNMP application will then be called (depending on
the value of the contextEngineID and the request type in the PDU)
using the processPdu ASI. The parameters passed to this ASI are:
- The messageProcessingModel, which will be 0 (or 1 for SNMPv2c).
- The securityModel, which will be 1 (or 2 for SNMPv2c).
- The securityName, which was returned from the call to
processIncomingMsg.
- The securityLevel, which is noAuthNoPriv.
- The contextEngineID, which was returned as part of the ScopedPDU
from the call to processIncomingMsg.
- The contextName, which was returned as part of the ScopedPDU from
the call to processIncomingMsg.
- The pduVersion, which should indicate an SNMPv1 version PDU (if
the message version was SNMPv2c, this would be an SNMPv2 version
PDU).
- The PDU, which was returned as part of the ScopedPDU from the call
to processIncomingMsg.
- The maxSizeResponseScopedPDU which was returned from the call to
processIncomingMsg.
- The stateReference which was returned from the call to
processIncomingMsg.
The SNMP application should process the request as described
previously in this document. Note that access control is applied by
an SNMPv3 command responder application as usual. The parameters as
passed to the processPdu ASI will be used in calls to the
isAccessAllowed ASI.
5.2.2. Generating An Outgoing Response
There is no special processing required for generating an outgoing
response. However, the community string used in an outgoing response
must be the same as the community string from the original request.
The original community string MUST be present in the
securityStateReference information of the original request.
5.2.3. Generating An Outgoing Notification
In a multi-lingual SNMP entity, the parameters used for generating
notifications will be obtained by examining the SNMP-TARGET-MIB and
SNMP-NOTIFICATION-MIB. These parameters will be passed to the SNMPv1
Message Processing Model using the sendPdu ASI. The SNMPv1 Message
Processing Model will attempt to locate an appropriate community
string in the snmpCommunityTable based on the parameters passed to
the sendPdu ASI. This is done by performing a search through the
snmpCommunityTable in lexicographic order. The first entry for which
the following matching criteria are satisfied will be selected:
- The securityName must be equal to the snmpCommunitySecurityName
value.
- The contextEngineID must be equal to the
snmpCommunityContextEngineID value.
- The contextName must be equal to the snmpCommunityContextName
value.
- If the snmpCommunityTransportTag is an empty string, it is ignored
for the purpose of matching. If the snmpCommunityTransportTag is
not an empty string, the transportDomain and transportAddress must
match one of the entries in the snmpTargetAddrTable selected by
the snmpCommunityTransportTag value.
If no such entry can be found, the notification is not sent.
Otherwise, the community string used in the outgoing notification
will be the value of the snmpCommunityName column of the selected
row.
5.2.4. Proxy Forwarding Of Requests
In a proxy forwarding application, when a received request is to be
forwarded using the SNMPv1 Message Processing Model, the parameters
used for forwarding will be obtained by examining the SNMP-PROXY-MIB
and the SNMP-TARGET-MIB. These parameters will be passed to the
SNMPv1 Message Processing Model using the sendPdu ASI. The SNMPv1
Message Processing Model will attempt to locate an appropriate
community string in the snmpCommunityTable based on the parameters
passed to the sendPdu ASI. This is done by performing a search
through the snmpCommunityTable in lexicographic order. The first
entry for which the following matching criteria are satisfied will be
selected:
- The securityName must be equal to the snmpCommunitySecurityName
value.
- The contextEngineID must be equal to the
snmpCommunityContextEngineID value.
- The contextName must be equal to the snmpCommunityContextName
value.
If no such entry can be found, the proxy forwarding application
should follow the procedure described in RFC 3413 [RFC3413], section
3.5.1.1, item (2). This procedure states that the snmpProxyDrops
counter [RFC3418] is incremented, and that a Response-PDU is
generated by calling the Dispatcher using the returnResponsePdu
abstract service interface.
5.3. The SNMP Community MIB Module
The SNMP-COMMUNITY-MIB contains objects for mapping between community
strings and version-independent SNMP message parameters. In
addition, this MIB provides a mechanism for performing source address
validation on incoming requests, and for selecting community strings
based on target addresses for outgoing notifications. These two
features are accomplished by providing a tag in the
snmpCommunityTable which selects sets of entries in the
snmpTargetAddrTable [RFC3413]. In addition, the SNMP-COMMUNITY-MIB
augments the snmpTargetAddrTable with a transport address mask value
and a maximum message size value. These values are used only where
explicitly stated. In cases where the snmpTargetAddrTable is used
without mention of these augmenting values, the augmenting values
should be ignored.
The mask value, snmpTargetAddrTMask, allows selected entries in the
snmpTargetAddrTable to specify multiple addresses (rather than just a
single address per entry). This would typically be used to specify a
subnet in an snmpTargetAddrTable rather than just a single address.
The mask value is used to select which bits of a transport address
must match bits of the corresponding instance of
snmpTargetAddrTAddress, in order for the transport address to match a
particular entry in the snmpTargetAddrTable. The value of an
instance of snmpTargetAddrTMask must always be an OCTET STRING whose
length is either zero or the same as that of the corresponding
instance of snmpTargetAddrTAddress.
Note that the snmpTargetAddrTMask object is only used where
explicitly stated. In particular, it is not used when generating
notifications (i.e., when generating notifications, entries in the
snmpTargetAddrTable only specify individual addresses). If use of
the snmpTargetAddrTMask object is not mentioned in text describing
matching addresses in the snmpTargetAddrTable, then its value MUST be
ignored.
When checking whether a transport address matches an entry in the
snmpTargetAddrTable, if the value of snmpTargetAddrTMask is a zero-
length OCTET STRING, the mask value is ignored, and the value of
snmpTargetAddrTAddress must exactly match a transport address.
Otherwise, each bit of each octet in the snmpTargetAddrTMask value
corresponds to the same bit of the same octet in the
snmpTargetAddrTAddress value. For bits that are set in the
snmpTargetAddrTMask value (i.e., bits equal to 1), the corresponding
bits in the snmpTargetAddrTAddress value must match the bits in a
transport address. If all such bits match, the transport address is
matched by that snmpTargetAddrTable entry. Otherwise, the transport
address is not matched.
The maximum message size value, snmpTargetAddrMMS, is used to
determine the maximum message size acceptable to another SNMP entity
when the value cannot be determined from the protocol.
SNMP-COMMUNITY-MIB DEFINITIONS ::= BEGIN
IMPORTS
IpAddress,
MODULE-IDENTITY,
OBJECT-TYPE,
Integer32,
snmpModules
FROM SNMPv2-SMI
RowStatus,
StorageType
FROM SNMPv2-TC
SnmpAdminString,
SnmpEngineID
FROM SNMP-FRAMEWORK-MIB
SnmpTagValue,
snmpTargetAddrEntry
FROM SNMP-TARGET-MIB
MODULE-COMPLIANCE,
OBJECT-GROUP
FROM SNMPv2-CONF;
snmpCommunityMIB MODULE-IDENTITY
LAST-UPDATED "200308060000Z" -- 06 Aug 2003, midnight
ORGANIZATION "SNMPv3 Working Group"
CONTACT-INFO "WG-email: snmpv3@lists.tislabs.com
Subscribe: majordomo@lists.tislabs.com
In msg body: subscribe snmpv3
Co-Chair: Russ Mundy
SPARTA, Inc
Postal: 7075 Samuel Morse Drive
Columbia, MD 21045
USA
EMail: mundy@tislabs.com
Phone: +1 410-872-1515
Co-Chair: David Harrington
Enterasys Networks
Postal: 35 Industrial Way
P. O. Box 5005
Rochester, New Hampshire 03866-5005
USA
EMail: dbh@enterasys.com
Phone: +1 603-337-2614
Co-editor: Rob Frye
Vibrant Solutions
Postal: 2711 Prosperity Ave
Fairfax, Virginia 22031
USA
E-mail: rfrye@vibrant-1.com
Phone: +1-703-270-2000
Co-editor: David B. Levi
Nortel Networks
Postal: 3505 Kesterwood Drive
Knoxville, Tennessee 37918
E-mail: dlevi@nortelnetworks.com
Phone: +1 865 686 0432
Co-editor: Shawn A. Routhier
Wind River Systems, Inc.
Postal: 500 Wind River Way
Alameda, CA 94501
E-mail: sar@epilogue.com
Phone: +1 510 749 2095
Co-editor: Bert Wijnen
Lucent Technologies
Postal: Schagen 33
3461 GL Linschoten
Netherlands
Email: bwijnen@lucent.com
Phone: +31-348-407-775
"
DESCRIPTION
"This MIB module defines objects to help support
coexistence between SNMPv1, SNMPv2c, and SNMPv3.
Copyright (C) The Internet Society (2003) This
version of this MIB module is part of RFC 3584;
see the RFC itself for full legal notices."
REVISION "200308060000Z" -- 06 Aug 2003
DESCRIPTION
"Updated the LAST-UPDATED, CONTACT-INFO, and REVISION
clauses and added a copyright notice to the
DESCRIPTION clause of the MIB module's
MODULE-IDENTITY invocation.
Updated the description of snmpCommunityTransportTag
to make it consistent with the rest of the document.
Updated the description of `snmpTargetAddrMMS' to
clarify that a value of 0 means that the maximum
message size is unknown.
Changed the name of 'snmpCommunityGroup' to
snmpCommunityTableGroup to avoid a name conflict
with the SNMPv2-MIB.
Updated DESCRIPTION of snmpCommunityName.
Updated DESCRIPTION of snmpTrapCommunity.
Added snmpCommunityMIBFullCompliance.
This version published as RFC 3584."
REVISION "200003060000Z" -- 6 Mar 2000
DESCRIPTION "This version published as RFC 2576."
::= { snmpModules 18 }
-- Administrative assignments ************************************
snmpCommunityMIBObjects
OBJECT IDENTIFIER ::= { snmpCommunityMIB 1 }
snmpCommunityMIBConformance
OBJECT IDENTIFIER ::= { snmpCommunityMIB 2 }
--
-- The snmpCommunityTable contains a database of community
-- strings. This table provides mappings between community
-- strings, and the parameters required for View-based Access
-- Control.
--
snmpCommunityTable OBJECT-TYPE
SYNTAX SEQUENCE OF SnmpCommunityEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The table of community strings configured in the SNMP
engine's Local Configuration Datastore (LCD)."
::= { snmpCommunityMIBObjects 1 }
snmpCommunityEntry OBJECT-TYPE
SYNTAX SnmpCommunityEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Information about a particular community string."
INDEX { IMPLIED snmpCommunityIndex }
::= { snmpCommunityTable 1 }
SnmpCommunityEntry ::= SEQUENCE {
snmpCommunityIndex SnmpAdminString,
snmpCommunityName OCTET STRING,
snmpCommunitySecurityName SnmpAdminString,
snmpCommunityContextEngineID SnmpEngineID,
snmpCommunityContextName SnmpAdminString,
snmpCommunityTransportTag SnmpTagValue,
snmpCommunityStorageType StorageType,
snmpCommunityStatus RowStatus
}
snmpCommunityIndex OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The unique index value of a row in this table."
::= { snmpCommunityEntry 1 }
snmpCommunityName OBJECT-TYPE
SYNTAX OCTET STRING
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The community string for which a row in this table
represents a configuration. There is no SIZE constraint
specified for this object because RFC 1157 does not
impose any explicit limitation on the length of community
strings (their size is constrained indirectly by the
SNMP message size)."
::= { snmpCommunityEntry 2 }
snmpCommunitySecurityName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A human readable string representing the corresponding
value of snmpCommunityName in a Security Model
independent format."
::= { snmpCommunityEntry 3 }
snmpCommunityContextEngineID OBJECT-TYPE
SYNTAX SnmpEngineID
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The contextEngineID indicating the location of the
context in which management information is accessed
when using the community string specified by the
corresponding instance of snmpCommunityName.
The default value is the snmpEngineID of the entity in
which this object is instantiated."
::= { snmpCommunityEntry 4 }
snmpCommunityContextName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The context in which management information is accessed
when using the community string specified by the
corresponding instance of snmpCommunityName."
DEFVAL { ''H } -- the empty string
::= { snmpCommunityEntry 5 }
snmpCommunityTransportTag OBJECT-TYPE
SYNTAX SnmpTagValue
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"This object specifies a set of transport endpoints
which are used in two ways:
- to specify the transport endpoints from which an
SNMP entity will accept management requests, and
- to specify the transport endpoints to which a
notification may be sent using the community
string matching the corresponding instance of
snmpCommunityName.
In either case, if the value of this object has
zero-length, transport endpoints are not checked when
either authenticating messages containing this community
string, nor when generating notifications.
The transports identified by this object are specified
in the snmpTargetAddrTable. Entries in that table
whose snmpTargetAddrTagList contains this tag value
are identified.
If a management request containing a community string
that matches the corresponding instance of
snmpCommunityName is received on a transport endpoint
other than the transport endpoints identified by this
object the request is deemed unauthentic.
When a notification is to be sent using an entry in
this table, if the destination transport endpoint of
the notification does not match one of the transport
endpoints selected by this object, the notification
is not sent."
DEFVAL { ''H } -- the empty string
::= { snmpCommunityEntry 6 }
snmpCommunityStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row in the
snmpCommunityTable. Conceptual rows having the value
'permanent' need not allow write-access to any
columnar object in the row."
::= { snmpCommunityEntry 7 }
snmpCommunityStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row in the
snmpCommunityTable.
An entry in this table is not qualified for activation
until instances of all corresponding columns have been
initialized, either through default values, or through
Set operations. The snmpCommunityName and
snmpCommunitySecurityName objects must be explicitly set.
There is no restriction on setting columns in this table
when the value of snmpCommunityStatus is active(1)."
::= { snmpCommunityEntry 8 }
--
-- The snmpTargetAddrExtTable
--
snmpTargetAddrExtTable OBJECT-TYPE
SYNTAX SEQUENCE OF SnmpTargetAddrExtEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The table of mask and maximum message size (mms) values
associated with the snmpTargetAddrTable.
The snmpTargetAddrExtTable augments the
snmpTargetAddrTable with a transport address mask value
and a maximum message size value. The transport address
mask allows entries in the snmpTargetAddrTable to define
a set of addresses instead of just a single address.
The maximum message size value allows the maximum
message size of another SNMP entity to be configured for
use in SNMPv1 (and SNMPv2c) transactions, where the
message format does not specify a maximum message size."
::= { snmpCommunityMIBObjects 2 }
snmpTargetAddrExtEntry OBJECT-TYPE
SYNTAX SnmpTargetAddrExtEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Information about a particular mask and mms value."
AUGMENTS { snmpTargetAddrEntry }
::= { snmpTargetAddrExtTable 1 }
SnmpTargetAddrExtEntry ::= SEQUENCE {
snmpTargetAddrTMask OCTET STRING,
snmpTargetAddrMMS Integer32
}
snmpTargetAddrTMask OBJECT-TYPE
SYNTAX OCTET STRING (SIZE (0..255))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The mask value associated with an entry in the
snmpTargetAddrTable. The value of this object must
have the same length as the corresponding instance of
snmpTargetAddrTAddress, or must have length 0. An
attempt to set it to any other value will result in
an inconsistentValue error.
The value of this object allows an entry in the
snmpTargetAddrTable to specify multiple addresses.
The mask value is used to select which bits of
a transport address must match bits of the corresponding
instance of snmpTargetAddrTAddress, in order for the
transport address to match a particular entry in the
snmpTargetAddrTable. Bits which are 1 in the mask
value indicate bits in the transport address which
must match bits in the snmpTargetAddrTAddress value.
Bits which are 0 in the mask indicate bits in the
transport address which need not match. If the
length of the mask is 0, the mask should be treated
as if all its bits were 1 and its length were equal
to the length of the corresponding value of
snmpTargetAddrTable.
This object may not be modified while the value of the
corresponding instance of snmpTargetAddrRowStatus is
active(1). An attempt to set this object in this case
will result in an inconsistentValue error."
DEFVAL { ''H }
::= { snmpTargetAddrExtEntry 1 }
snmpTargetAddrMMS OBJECT-TYPE
SYNTAX Integer32 (0|484..2147483647)
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The maximum message size value associated with an entry
in the snmpTargetAddrTable. Note that a value of 0 means
that the maximum message size is unknown."
DEFVAL { 484 }
::= { snmpTargetAddrExtEntry 2 }
--
-- The snmpTrapAddress and snmpTrapCommunity objects are included
-- in notifications that are forwarded by a proxy, which were
-- originally received as SNMPv1 Trap messages.
--
snmpTrapAddress OBJECT-TYPE
SYNTAX IpAddress
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"The value of the agent-addr field of a Trap PDU which
is forwarded by a proxy forwarder application using
an SNMP version other than SNMPv1. The value of this
object SHOULD contain the value of the agent-addr field
from the original Trap PDU as generated by an SNMPv1
agent."
::= { snmpCommunityMIBObjects 3 }
snmpTrapCommunity OBJECT-TYPE
SYNTAX OCTET STRING
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"The value of the community string field of an SNMPv1
message containing a Trap PDU which is forwarded by a
a proxy forwarder application using an SNMP version
other than SNMPv1. The value of this object SHOULD
contain the value of the community string field from
the original SNMPv1 message containing a Trap PDU as
generated by an SNMPv1 agent. There is no SIZE
constraint specified for this object because RFC 1157
does not impose any explicit limitation on the length
of community strings (their size is constrained
indirectly by the SNMP message size)."
::= { snmpCommunityMIBObjects 4 }
-- Conformance Information **************************************
snmpCommunityMIBCompliances OBJECT IDENTIFIER
::= { snmpCommunityMIBConformance 1 }
snmpCommunityMIBGroups OBJECT IDENTIFIER
::= { snmpCommunityMIBConformance 2 }
-- Compliance statements
snmpCommunityMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines which
implement the SNMP-COMMUNITY-MIB."
MODULE -- this module
MANDATORY-GROUPS { snmpCommunityTableGroup }
OBJECT snmpCommunityName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunitySecurityName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityContextEngineID
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityContextName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityTransportTag
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityStorageType
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityStatus
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
::= { snmpCommunityMIBCompliances 1 }
snmpProxyTrapForwardCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines which
contain a proxy forwarding application which is
capable of forwarding SNMPv1 traps using SNMPv2c
or SNMPv3."
MODULE -- this module
MANDATORY-GROUPS { snmpProxyTrapForwardGroup }
::= { snmpCommunityMIBCompliances 2 }
snmpCommunityMIBFullCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines which
implement the SNMP-COMMUNITY-MIB with full read-create
access."
MODULE -- this module
MANDATORY-GROUPS { snmpCommunityTableGroup }
::= { snmpCommunityMIBCompliances 3 }
snmpCommunityTableGroup OBJECT-GROUP
OBJECTS {
snmpCommunityName,
snmpCommunitySecurityName,
snmpCommunityContextEngineID,
snmpCommunityContextName,
snmpCommunityTransportTag,
snmpCommunityStorageType,
snmpCommunityStatus,
snmpTargetAddrTMask,
snmpTargetAddrMMS
}
STATUS current
DESCRIPTION
"A collection of objects providing for configuration
of community strings for SNMPv1 (and SNMPv2c) usage."
::= { snmpCommunityMIBGroups 1 }
snmpProxyTrapForwardGroup OBJECT-GROUP
OBJECTS {
snmpTrapAddress,
snmpTrapCommunity
}
STATUS current
DESCRIPTION
"Objects which are used by proxy forwarding applications
when translating traps between SNMP versions. These are
used to preserve SNMPv1-specific information when
translating to SNMPv2c or SNMPv3."
::= { snmpCommunityMIBGroups 3 }
END
6. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
7. Acknowledgments
This document is the result of the efforts of the SNMPv3 Working
Group. The design of the SNMP-COMMUNITY-MIB incorporates work done
by the authors of SNMPv2*:
Jeff Case (SNMP Research, Inc.)
David Harrington (Enterasys Networks)
David Levi (Nortel Networks)
Brian O'Keefe (Hewlett Packard)
Jon Saperia (IronBridge Networks, Inc.)
Steve Waldbusser (International Network Services)
8. Security Considerations
Although SNMPv1 and SNMPv2 do not provide any security, allowing
community names to be mapped into securityName/contextName provides
the ability to use view-based access control to limit the access of
unsecured SNMPv1 and SNMPv2 operations. In fact, it is important for
network administrators to make use of this capability in order to
avoid unauthorized access to MIB data that would otherwise be secure.
When a proxy implementation translates messages between SNMPv1 (or
SNMPv2c) and SNMPv3, there may be a loss of security. For example,
an SNMPv3 message received using authentication and privacy which is
subsequently forwarded using SNMPv1 will lose the security benefits
of using authentication and privacy (also known as confidentiality).
Careful configuration of proxies is required to address such
situations. One approach to deal with such situations might be to
use an encrypted tunnel.
There are a number of management objects defined in this MIB module
with a MAX-ACCESS clause of read-write and/or read-create. Such
objects may be considered sensitive or vulnerable in some network
environments. The support for SET operations in a non-secure
environment without proper protection can have a negative effect on
network operations. These are the tables and objects and their
sensitivity/vulnerability:
- The snmpCommunityTable allows creation and deletion of community
strings, which is potentially a serious security hole. Access to
this table should be greatly restricted, preferably by only
allowing write access using SNMPv3 VACM and USM, with
authentication and privacy.
- The snmpTargetAddrExtTable contains write-able objects which may
also be considered sensitive, and so access to it should be
restricted as well.
Some of the readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or
vulnerable in some network environments. It is thus important to
control even GET and/or NOTIFY access to these objects and possibly
to even encrypt the values of these objects when sending them over
the network via SNMP. These are the tables and objects and their
sensitivity/vulnerability:
- The snmpCommunityTable has the potential to expose community
strings which provide access to more information than that which
is available using the usual 'public' community string. For this
reason, a security administrator may wish to limit accessibility
to objects in the snmpCommunityTable, and in particular, to make
it inaccessible when using the 'public' community string.
SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example by using IPSec),
even then, there is no control as to who on the secure network is
allowed to access and GET/SET (read/change/create/delete) the objects
in this MIB module.
It is RECOMMENDED that implementers consider the security features as
provided by the SNMPv3 framework (see [RFC3410], section 8),
including full support for the SNMPv3 cryptographic mechanisms (for
authentication and privacy).
Further, deployment of SNMP versions prior to SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to
enable cryptographic security. It is then a customer/operator
responsibility to ensure that the SNMP entity giving access to an
instance of this MIB module is properly configured to give access to
the objects only to those principals (users) that have legitimate
rights to indeed GET or SET (change/create/delete) them.
9. References
9.1. Normative References
[RFC1155] Rose, M. and K. McCloghrie, "Structure and Identification
of Management Information for TCP/IP-based internets",
STD 16, RFC 1155, May 1990.
[RFC1157] Case, J., Fedor, M., Schoffstall, M. and C. Davin,
"Simple Network Management Protocol (SNMP)", STD 15, RFC
1157, May 1990.
[RFC1212] Rose, M. and K. McCloghrie, Eds., "Concise MIB
Definitions", STD 16, RFC 1212, March 1991.
[RFC1215] Rose, M., "A Convention for Defining Traps for use with
the SNMP", RFC 1215, March 1991.
[RFC1303] McCloghrie, K. and M. Rose, "A Convention for Describing
SNMP-based Agents", RFC 1303, February 1992.
[RFC1901] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Introduction to Community-based SNMPv2", RFC 1901,
January 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2578] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Structure of Management Information Version 2 (SMIv2)",
RFC 2578, STD 58, April 1999.
[RFC2579] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Textual Conventions for SMIv2", STD 58, RFC 2579, April
1999.
[RFC2580] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580,
April 1999.
[RFC3411] Harrington, D., Presuhn, R. and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
December 2002.
[RFC3412] Case, J., Harrington, D., Presuhn, R. and B. Wijnen,
"Message Processing and Dispatching for the Simple
Network Management Protocol (SNMP)", STD 62, RFC 3412,
December 2002.
[RFC3413] Levi, D., Meyer, P. and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62, RFC
3413, December 2002.
[RFC3414] Blumenthal, U. and B. Wijnen, "The User-Based Security
Model (USM) for Version 3 of the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3414, December
2002.
[RFC3415] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3415, December
2002.
[RFC3416] Presuhn, R., Ed., "Version 2 of the Protocol Operations
for the Simple Network Management Protocol (SNMPv2)", STD
62, RFC 3416, December 2002.
[RFC3417] Presuhn, R., Ed., "Transport Mappings for Version 2 of
the Simple Network Management Protocol (SNMPv2)", STD 62,
RFC 3417, December 2002.
[RFC3418] Presuhn, R., Ed., "Management Information Base (MIB) for
Version 2 of the Simple Network Management Protocol
(SNMP)", STD 62, RFC 3418, December 2002.
[ASN1] Information processing systems - Open Systems
Interconnection - Specification of Abstract Syntax
Notation One (ASN.1), International Organization for
Standardization. International Standard 8824, (December,
1987).
9.2. Informative References
[RFC1908] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Coexistence between Version 1 and Version 2 of the
Internet-standard Network Management Framework", RFC
1908, January 1996.
[RFC2089] Levi, D. and B. Wijnen, "Mapping SNMPv2 onto SNMPv1
within a bilingual SNMP agent", RFC 2089, January 1997.
[RFC2576] Frye, R., Levi, D., Routhier, S. and B. Wijnen,
"Coexistence between Version 1, Version 2, and Version 3
of the Internet-standard Network Management Framework",
RFC 2576, March 2000.
[RFC3410] Case, J., Mundy, R., Partain, D. and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
Appendix A. Change Log
A.1. Changes From RFC 2576
Section numbers below refer to the old section numbers from RFC 2576.
Some section numbers have changed since RFC 2576.
- Added text to abstract about conversion of MIBs from SMIv1 to
SMIv2.
- Added note at end of section 1.3 that all discussion of SNMPv2 PDU
types and protocol operations applies to both SNMPv2c and SNMPv3.
- Added text at end of section 1.4 to clarify that there is no such
thing as 'SNMPv3 access to MIB data', as SNMPv3 just uses SNMPv2
PDU types and protocol operations.
- Moved section 1.4 to the beginning of section 4.
- Changed "MUST" to "SHOULD" in item (3) of the first list in
Section 2.1.1 to since unconstrained INTEGER is not actually
illegal in SMIv2.
- Changed "SHOULD" to "MUST" in item (13) of the first list in
Section 2.1.1 to clarify that collecting related objects into
groups is required when translating a MIB module from SMIv1 to
SMIv2.
- Re-organized bullets in section 2.1.1 to improve clarity.
- Changed "SHOULD" to "MUST" in items (1) and (2) of Section 2.3
since those updates are indeed required when translating a
capabilities statement from the language defined by RFC 1303 into
SMIv2.
- In the second bullet of the last part of Section 3 listing the
SNMPv2 notification parameters, clarified that the snmpTrapOID
parameter refers to the value portion (not the name portion) of
the second variable-binding, and changed the wording in the text
under bullet (1) of Section 3.2 from "the snmpTrapOID" to "the
snmpTrapOID value" to emphasize this point.
- In bullet (6) of Section 3.2 emphasized that the SNMPv2 variable-
bindings do not include sysUpTime.0 an snmpTrapOID.0.
- In Section 4.2 clarified that the 'Upstream Version' refers to the
version used between the command generator or notification
receiver and the proxy, and the 'Downstream Version' refers to the
version used between the proxy and the command responder or
notification originator. RFC 2576 neglected to mention the
notification receiver and notification originator.
- In Section 4.1.2 added text noting that SNMPv1 access to MIB data
SHOULD NOT be used when processing SNMPv2c or SNMPv3 messages and
re-worded final paragraph to note that the sub-sections that
follow are concerned solely with command responders that use
SNMPv2 access to MIB data while processing an SNMPv1 request.
- Re-worded first bullet, section 4.2.1, to make it more readable.
- In Section 4.2.1 clarified that the error-index field must be set
to zero in a translated GetResponse-PDU with an error-status of
'tooBig' and made explicit the rationale for retrying a
GetBulkRequest-PDU only once.
- Added text to the Deployment Hint in Section 4.2.2 to clarify that
different principals should be used for SNMPv1 requests and
SNMPv2/v3c requests if for SNMPv1 requests a principal for which
Counter64 objects are not-in-view is used.
- In Section 5.2.1 clarified that the securityName value and the
scopedPDU's contextSnmpEngineID and contextName values come from
the selected entry in the snmpCommunityTable. Also clarified how
maxSizeResponseScopedPDU is determined and that
securityStateReference must contain the community string of the
original request.
- Added Section 5.2.4 on Proxy Forwarding Of Requests.
- In Section 5.3 clarified that snmpTargetAddrTMask is to be ignored
whenever its use is not explicitly called for.
- Updated the LAST-UPDATED, CONTACT-INFO, and REVISION clauses and
added a copyright notice to the DESCRIPTION clause of the MIB
module's MODULE-IDENTITY invocation.
- Added text to DESCRIPTION of snmpCommunityName and
snmpTrapCommunity to clarify why the object has no size
restriction.
- Updated the description of snmpCommunityTransportTag to make it
consistent with the rest of the document.
- Updated the description of 'snmpTargetAddrMMS' to clarify that a
value of 0 means that the maximum message size is unknown.
- Changed the name of 'snmpCommunityGroup' to
'snmpCommunityTableGroup' in order to resolve a name conflict with
the SNMPv2-MIB.
- Added compliance statement to SNMP-COMMUNITY-MIB for full read-
create compliance.
- Divided references into Normative References and Informative
Reference and updated them to point to current documents.
- Inserted current year into all copyright notices.
- Corrected various typographical and grammatical errors.
A.2. Changes Between RFC 1908 and RFC 2576
- Editorial changes to comply with current RFC requirements.
- Added/updated copyright statements.
- Added Intellectual Property section.
- Replaced old introduction with complete new introduction/overview.
- Added content for the Security Considerations Section.
- Updated References to current documents.
- Updated text to use current SNMP terminology.
- Added coexistence for/with SNMPv3.
- Added description for SNMPv1 and SNMPv2c Message Processing Models
and SNMPv1 and SNMPv2c Community-based Security Models.
- Added snmpCommunityMIB so that SNMPv1 and SNMPv2 community strings
can be mapped into the SNMP Version Independent parameters which
can then be used for access control using the standard SNMPv3
View-based Access Control Model and the snmpVacmMIB.
- Added two MIB objects such that when an SNMPv1 notification (trap)
must be converted into an SNMPv2 notification we add those two
objects in order to preserve information about the address and
community of the originating SNMPv1 agent.
- Included (and extended) from RFC 2089 the SNMPv2 to SNMPv1 mapping
within a multi-lingual SNMP Engine.
- Use keywords from RFC 2119 to describe requirements for
compliance.
- Changed/added some rules for converting a MIB module from SMIv1 to
SMIv2.
- Extended and improved the description of Proxy Forwarder behaviour
when multiple SNMP versions are involved.
Editors' Addresses
Rob Frye
Vibrant Solutions
2711 Prosperity Ave
Fairfax, Virginia 22031
U.S.A.
Phone: +1 703 270 2000
EMail: rfrye@vibrant-1.com
David B. Levi
Nortel Networks
3505 Kesterwood Drive
Knoxville, TN 37918
U.S.A.
Phone: +1 865 686 0432
EMail: dlevi@nortelnetworks.com
Shawn A. Routhier
Wind River Systems, Inc.
500 Wind River Way
Alameda, CA 94501
U.S.A.
Phone: + 1 510 749 2095
EMail: sar@epilogue.com
Bert Wijnen
Lucent Technologies
Schagen 33
3461 GL Linschoten
Netherlands
Phone: +31 348 407 775
EMail: bwijnen@lucent.com
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