| Rfc | 5607 |
|---|
| Title | Remote Authentication Dial-In User Service (RADIUS) Authorization
for Network Access Server (NAS) Management |
|---|
| Author | D. Nelson, G. Weber |
|---|
| Date | July 2009 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | PROPOSED STANDARD |
|---|
|
Network Working Group D. Nelson
Request for Comments: 5607 Elbrys Networks, Inc.
Category: Standards Track G. Weber
Individual Contributor
July 2009
Remote Authentication Dial-In User Service (RADIUS) Authorization for
Network Access Server (NAS) Management
Abstract
This document specifies Remote Authentication Dial-In User Service
(RADIUS) attributes for authorizing management access to a Network
Access Server (NAS). Both local and remote management are supported,
with granular access rights and management privileges. Specific
provisions are made for remote management via Framed Management
protocols and for management access over a secure transport protocol.
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Domain of Applicability . . . . . . . . . . . . . . . . . . . 5
5. New Values for Existing RADIUS Attributes . . . . . . . . . . 6
5.1. Service-Type . . . . . . . . . . . . . . . . . . . . . . .6
6. New RADIUS Attributes . . . . . . . . . . . . . . . . . . . . 6
6.1. Framed-Management-Protocol . . . . . . . . . . . . . . . . 6
6.2. Management-Transport-Protection . . . . . . . . . . . . . 9
6.3. Management-Policy-Id . . . . . . . . . . . . . . . . . . . 11
6.4. Management-Privilege-Level . . . . . . . . . . . . . . . . 13
7. Use with Dynamic Authorization . . . . . . . . . . . . . . . . 15
8. Examples of Attribute Groupings . . . . . . . . . . . . . . . 15
9. Diameter Translation Considerations . . . . . . . . . . . . . 17
10. Table of Attributes . . . . . . . . . . . . . . . . . . . . . 18
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
12. Security Considerations . . . . . . . . . . . . . . . . . . . 20
12.1. General Considerations . . . . . . . . . . . . . . . . . . 20
12.2. RADIUS Proxy Operation Considerations . . . . . . . . . . 22
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
14.1. Normative References . . . . . . . . . . . . . . . . . . . 23
14.2. Informative References . . . . . . . . . . . . . . . . . . 23
1. Introduction
RFC 2865 [RFC2865] defines the NAS-Prompt (7) and Administrative (6)
values of the Service-Type (6) Attribute. Both of these values
provide access to the interactive, text-based Command Line Interface
(CLI) of the NAS, and were originally developed to control access to
the physical console port of the NAS, most often a serial port.
Remote access to the CLI of the NAS has been available in NAS
implementations for many years, using protocols such as Telnet,
Rlogin, and the remote terminal service of the Secure SHell (SSH).
In order to distinguish local, physical, console access from remote
access, the NAS-Port-Type (61) Attribute is generally included in
Access-Request and Access-Accept messages, along with the Service-
Type (6) Attribute, to indicate the form of access. A NAS-Port-Type
(61) Attribute with a value of Async (0) is used to signify a local
serial port connection, while a value of Virtual (5) is used to
signify a remote connection, via a remote terminal protocol. This
usage provides no selectivity among the various available remote
terminal protocols (e.g., Telnet, Rlogin, SSH, etc.).
Today, it is common for network devices to support more than the two
privilege levels for management access provided by the Service-Type
(6) Attribute with values of NAS-Prompt (7) (non-privileged) and
Administrative (6) (privileged). Also, other management mechanisms
may be used, such as Web-based management, the Simple Network
Management Protocol (SNMP), and the Network Configuration Protocol
(NETCONF). To provide support for these additional features, this
specification defines attributes for Framed Management protocols,
management protocol security, and management access privilege levels.
Remote management via the command line is carried over protocols such
as Telnet, Rlogin, and the remote terminal service of SSH. Since
these protocols are primarily for the delivery of terminal or
terminal emulation services, the term "Framed Management" is used to
describe management protocols supporting techniques other than the
command line. Typically, these mechanisms format management
information in a binary or textual encoding such as HTML, XML, or
ASN.1/BER. Examples include Web-based management (HTML over HTTP or
HTTPS), NETCONF (XML over SSH or BEEP or SOAP), and SNMP (SMI over
ASN.1/BER). Command line interface, menu interface, or other text-
based (e.g., ASCII or UTF-8) terminal emulation services are not
considered to be Framed Management protocols.
2. Terminology
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].
This document uses terminology from RFC 2865 [RFC2865], RFC 2866
[RFC2866], and RFC 5176 [RFC5176].
The term "integrity protection", as used in this document, is *not*
the same as "authentication", as used in SNMP. Integrity protection
requires the sharing of cryptographic keys, but it does not require
authenticated principals. Integrity protection could be used, for
example, with anonymous Diffie-Hellman key agreement. In SNMP, the
proof of identity of the principals (authentication) is conflated
with tamper-resistance of the protected messages (integrity). In
this document, we assume that integrity protection and authentication
are separate concerns. Authentication is part of the base RADIUS
protocol.
SNMP uses the terms "auth" and "noAuth", as well as "priv" and
"noPriv". There is no analog to auth or noAuth in this document. In
this document, we are assuming that authentication always occurs when
it is required, i.e., as a prerequisite to provisioning of access via
an Access-Accept packet.
3. Overview
To support the authorization and provisioning of Framed Management
access to managed entities, this document introduces a new value for
the Service-Type (6) Attribute [RFC2865] and one new attribute. The
new value for the Service-Type (6) Attribute is Framed-Management
(18), used for remote device management via a Framed Management
protocol. The new attribute is Framed-Management-Protocol (133), the
value of which specifies a particular protocol for use in the remote
management session.
Two new attributes are introduced in this document in support of
granular management access rights or command privilege levels. The
Management-Policy-Id (135) Attribute provides a text string
specifying a policy name of local scope, that is assumed to have been
pre-provisioned on the NAS. This use of an attribute to specify use
of a pre-provisioned policy is similar to the Filter-Id (11)
Attribute defined in [RFC2865] Section 5.11.
The local application of the Management-Policy-Id (135) Attribute
within the managed entity may take the form of (a) one of an
enumeration of command privilege levels, (b) a mapping into an SNMP
Access Control Model, such as the View-Based Access Control Model
(VACM) [RFC3415], or (c) some other set of management access policy
rules that is mutually understood by the managed entity and the
remote management application. Examples are given in Section 8.
The Management-Privilege-Level (136) Attribute contains an integer-
valued management privilege level indication. This attribute serves
to modify or augment the management permissions provided by the NAS-
Prompt (7) value of the Service-Type (6) Attribute, and thus applies
to CLI management.
To enable management security requirements to be specified, the
Management-Transport-Protection (134) Attribute is introduced. The
value of this attribute indicates the minimum level of secure
transport protocol protection required for the provisioning of NAS-
Prompt (7), Administrative (6), or Framed-Management (18) service.
4. Domain of Applicability
Most of the RADIUS attributes defined in this document have broad
applicability for provisioning local and remote management access to
NAS devices. However, those attributes that provision remote access
over Framed Management protocols and over secure transports have
special considerations. This document does not specify the details
of the integration of these protocols with a RADIUS client in the NAS
implementation. However, there are functional requirements for
correct application of Framed Management protocols and/or secure
transport protocols that will limit the selection of such protocols
that can be considered for use with RADIUS. Since the RADIUS user
credentials are typically obtained by the RADIUS client from the
secure transport protocol server or the Framed Management protocol
server, the protocol, and its implementation in the NAS, MUST support
forms of credentials that are compatible with the authentication
methods supported by RADIUS.
RADIUS currently supports the following user authentication methods,
although others may be added in the future:
o Password - RFC 2865
o CHAP (Challenge Handshake Authentication Protocol) - RFC 2865
o ARAP (Apple Remote Access Protocol) - RFC 2869
o EAP (Extensible Authentication Protocol) - RFC 2869, RFC 3579
o HTTP Digest - RFC 5090
The remote management protocols selected for use with the RADIUS
remote NAS management sessions, for example, those described in
Section 6.1, and the secure transport protocols selected to meet the
protection requirements, as described in Section 6.2, obviously need
to support user authentication methods that are compatible with those
that exist in RADIUS. The RADIUS authentication methods most likely
usable with these protocols are Password, CHAP, and possibly HTTP
Digest, with Password being the distinct common denominator. There
are many secure transports that support other, more robust,
authentication mechanisms, such as public key. RADIUS has no support
for public key authentication, except within the context of an EAP
Method. The applicability statement for EAP indicates that it is not
intended for use as an application-layer authentication mechanism, so
its use with the mechanisms described in this document is NOT
RECOMMENDED. In some cases, Password may be the only compatible
RADIUS authentication method available.
5. New Values for Existing RADIUS Attributes
5.1. Service-Type
The Service-Type (6) Attribute is defined in Section 5.6 of RFC 2865
[RFC2865]. This document defines a new value of the Service-Type
Attribute, as follows:
18 Framed-Management
The semantics of the Framed-Management service are as follows:
Framed-Management A Framed Management protocol session should
be started on the NAS.
6. New RADIUS Attributes
This document defines four new RADIUS attributes related to
management authorization.
6.1. Framed-Management-Protocol
The Framed-Management-Protocol (133) Attribute indicates the
application-layer management protocol to be used for Framed
Management access. It MAY be used in both Access-Request and Access-
Accept packets. This attribute is used in conjunction with a
Service-Type (6) Attribute with the value of Framed-Management (18).
It is RECOMMENDED that the NAS include an appropriately valued
Framed-Management-Protocol (133) Attribute in an Access-Request
packet, indicating the type of management access being requested. It
is further RECOMMENDED that the NAS include a Service-Type (6)
Attribute with the value Framed-Management (18) in the same Access-
Request packet. The RADIUS server MAY use these attributes as a hint
in making its authorization decision.
The RADIUS server MAY include a Framed-Management-Protocol (133)
Attribute in an Access-Accept packet that also includes a Service-
Type (6) Attribute with a value of Framed-Management (18), when the
RADIUS server chooses to enforce a management access policy for the
authenticated user that dictates one form of management access in
preference to others.
When a NAS receives a Framed-Management-Protocol (133) Attribute in
an Access-Accept packet, it MUST deliver that specified form of
management access or disconnect the session. If the NAS does not
support the provisioned management application-layer protocol, or the
management access protocol requested by the user does not match that
of the Framed-Management-Protocol (133) Attribute in the Access-
Accept packet, the NAS MUST treat the Access-Accept packet as if it
had been an Access-Reject.
A summary of the Framed-Management-Protocol (133) Attribute format is
shown below. The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
133 for Framed-Management-Protocol.
Length
6
Value
The Value field is a four-octet enumerated value.
1 SNMP
2 Web-based
3 NETCONF
4 FTP
5 TFTP
6 SFTP
7 RCP
8 SCP
All other values are reserved for IANA allocation subject to the
provisions of Section 11.
The acronyms used in the above table expand as follows:
o SNMP: Simple Network Management Protocol [RFC3411], [RFC3412],
[RFC3413], [RFC3414], [RFC3415], [RFC3416], [RFC3417], [RFC3418].
o Web-based: Use of an embedded web server in the NAS for management
via a generic web browser client. The interface presented to the
administrator may be graphical, tabular, or textual. The protocol
is HTML over HTTP. The protocol may optionally be HTML over
HTTPS, i.e., using HTTP over TLS [HTML] [RFC2616].
o NETCONF: Management via the NETCONF protocol using XML over
supported transports (e.g., SSH, BEEP, SOAP). As secure transport
profiles are defined for NETCONF, the list of transport options
may expand [RFC4741], [RFC4742], [RFC4743], [RFC4744].
o FTP: File Transfer Protocol, used to transfer configuration files
to and from the NAS [RFC0959].
o TFTP: Trivial File Transfer Protocol, used to transfer
configuration files to and from the NAS [RFC1350].
o SFTP: SSH File Transfer Protocol, used to securely transfer
configuration files to and from the NAS. SFTP uses the services
of SSH [SFTP]. See also Section 3.7, "SSH and File Transfers" of
[SSH]. Additional information on the "sftp" program may typically
be found in the online documentation ("man" pages) of Unix
systems.
o RCP: Remote CoPy file copy utility (Unix-based), used to transfer
configuration files to and from the NAS. See Section 3.7, "SSH
and File Transfers", of [SSH]. Additional information on the
"rcp" program may typically be found in the online documentation
("man" pages) of Unix systems.
o SCP: Secure CoPy file copy utility (Unix-based), used to transfer
configuration files to and from the NAS. The "scp" program is a
simple wrapper around SSH. It's basically a patched BSD Unix
"rcp", which uses ssh to do the data transfer (instead of using
"rcmd"). See Section 3.7, "SSH and File Transfers", of [SSH].
Additional information on the "scp" program may typically be found
in the online documentation ("man" pages) of Unix systems.
6.2. Management-Transport-Protection
The Management-Transport-Protection (134) Attribute specifies the
minimum level of protection that is required for a protected
transport used with the Framed or non-Framed Management access
session. The protected transport used by the NAS MAY provide a
greater level of protection, but MUST NOT provide a lower level of
protection.
When a secure form of non-Framed Management access is specified, it
means that the remote terminal session is encapsulated in some form
of protected transport, or tunnel. It may also mean that an explicit
secure mode of operation is required, when the Framed Management
protocol contains an intrinsic secure mode of operation. The
Management-Transport-Protection (134) Attribute does not apply to CLI
access via a local serial port, or other non-remote connection.
When a secure form of Framed Management access is specified, it means
that the application-layer management protocol is encapsulated in
some form of protected transport, or tunnel. It may also mean that
an explicit secure mode of operation is required, when the Framed
Management protocol contains an intrinsic secure mode of operation.
A value of "No Protection (1)" indicates that a secure transport
protocol is not required, and that the NAS SHOULD accept a connection
over any transport associated with the application-layer management
protocol. The definitions of management application to transport
bindings are defined in the relevant documents that specify those
management application protocols. The same "No Protection" semantics
are conveyed by omitting this attribute from an Access-Accept packet.
Specific protected transport protocols, cipher suites, key agreement
methods, or authentication methods are not specified by this
attribute. Such provisioning is beyond the scope of this document.
It is RECOMMENDED that the NAS include an appropriately valued
Management-Transport-Protection (134) Attribute in an Access-Request
packet, indicating the level of transport protection for the
management access being requested, when that information is available
to the RADIUS client. The RADIUS server MAY use this attribute as a
hint in making its authorization decision.
The RADIUS server MAY include a Management-Transport-Protection (134)
Attribute in an Access-Accept packet that also includes a Service-
Type (6) Attribute with a value of Framed-Management (18), when the
RADIUS server chooses to enforce a management access security policy
for the authenticated user that dictates a minimum level of transport
security.
When a NAS receives a Management-Transport-Protection (134) Attribute
in an Access-Accept packet, it MUST deliver the management access
over a transport with equal or better protection characteristics or
disconnect the session. If the NAS does not support protected
management transport protocols, or the level of protection available
does not match that of the Management-Transport-Protection (134)
Attribute in the Access-Accept packet, the NAS MUST treat the
response packet as if it had been an Access-Reject.
A summary of the Management-Transport-Protection (134) Attribute
format is shown below. The fields are transmitted from left to
right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
134 for Management-Transport-Protection.
Length
6
Value
The Value field is a four-octet enumerated value.
1 No-Protection
2 Integrity-Protection
3 Integrity-Confidentiality-Protection
All other values are reserved for IANA allocation subject to the
provisions of Section 11.
The names used in the above table are elaborated as follows:
o No-Protection: No transport protection is required. Accept
connections via any supported transport.
o Integrity-Protection: The management transport MUST provide
Integrity Protection, i.e., protection from unauthorized
modification, using a cryptographic checksum.
o Integrity-Confidentiality-Protection: The management transport
MUST provide both Integrity Protection and Confidentiality
Protection, i.e., protection from unauthorized modification, using
a cryptographic checksum, and protection from unauthorized
disclosure, using encryption.
The configuration or negotiation of acceptable algorithms, modes, and
credentials for the cryptographic protection mechanisms used in
implementing protected management transports is outside the scope of
this document. Many such mechanisms have standardized methods of
configuration and key management.
6.3. Management-Policy-Id
The Management-Policy-Id (135) Attribute indicates the name of the
management access policy for this user. Zero or one Management-
Policy-Id (135) Attributes MAY be sent in an Access-Accept packet.
Identifying a policy by name allows the policy to be used on
different NASes without regard to implementation details.
Multiple forms of management access rules may be expressed by the
underlying named policy, the definition of which is beyond the scope
of this document. The management access policy MAY be applied
contextually, based on the nature of the management access method.
For example, some named policies may only be valid for application to
NAS-Prompt (7) services and some other policies may only be valid for
SNMP.
The management access policy named in this attribute, received in an
Access-Accept packet, MUST be applied to the session authorized by
the Access-Accept. If the NAS supports this attribute, but the
policy name is unknown, or if the RADIUS client is able to determine
that the policy rules are incorrectly formatted, the NAS MUST treat
the Access-Accept packet as if it had been an Access-Reject.
No precedence relationship is defined for multiple occurrences of the
Management-Policy-Id (135) Attribute. NAS behavior in such cases is
undefined. Therefore, two or more occurrences of this attribute
SHOULD NOT be included in an Access-Accept or CoA-Request (Change-of-
Authorization). In the absence of further specification defining
some sort of precedence relationship, it is not possible to guarantee
multi-vendor interoperability when using multiple instances of this
attribute in a single Access-Accept or CoA-Request packet.
The content of the Management-Policy-Id (135) Attribute is expected
to be the name of a management access policy of local significance to
the NAS, within a namespace of significance to the NAS. In this
regard, the behavior is similar to that for the Filter-Id (11)
Attribute. The policy names and rules are committed to the local
configuration data-store of the NAS, and are provisioned by means
beyond the scope of this document, such as via SNMP, NETCONF, or CLI.
The namespace used in the Management-Policy-Id (135) Attribute is
simple and monolithic. There is no explicit or implicit structure or
hierarchy. For example, in the text string "example.com", the "."
(period or dot) is just another character. It is expected that text
string matching will be performed without parsing the text string
into any sub-fields.
Overloading or subdividing this simple name with multi-part
specifiers (e.g., Access=remote, Level=7) is likely to lead to poor
multi-vendor interoperability and SHOULD NOT be utilized. If a
simple, unstructured policy name is not sufficient, it is RECOMMENDED
that a Vendor Specific (26) Attribute be used instead, rather than
overloading the semantics of Management-Policy-Id.
A summary of the Management-Policy-Id (135) Attribute format is shown
below. The fields are transmitted from left to right.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | Text ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type
135 for Management-Policy-Id.
Length
>= 3
Text
The Text field is one or more octets, and its contents are
implementation dependent. It is intended to be human
readable and the contents MUST NOT be parsed by the receiver;
the contents can only be used to look up locally defined
policies. It is RECOMMENDED that the message contain UTF-8
encoded 10646 [RFC3629] characters.
6.4. Management-Privilege-Level
The Management-Privilege-Level (136) Attribute indicates the integer-
valued privilege level to be assigned for management access for the
authenticated user. Many NASes provide the notion of differentiated
management privilege levels denoted by an integer value. The
specific access rights conferred by each value are implementation
dependent. It MAY be used in both Access-Request and Access-Accept
packets.
The mapping of integer values for this attribute to specific
collections of management access rights or permissions on the NAS is
vendor and implementation specific. Such mapping is often a user-
configurable feature. It's RECOMMENDED that greater numeric values
imply greater privilege. However, it would be a mistake to assume
that this recommendation always holds.
The management access level indicated in this attribute, received in
an Access-Accept packet, MUST be applied to the session authorized by
the Access-Accept. If the NAS supports this attribute, but the
privilege level is unknown, the NAS MUST treat the Access-Accept
packet as if it had been an Access-Reject.
A summary of the Management-Privilege-Level (136) Attribute format is
show below. The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
136 for Management-Privilege-Level.
Length
6
Value
The Value field is a four-octet Integer, denoting a management
privilege level.
It is RECOMMENDED to limit use of the Management-Privilege-Level
(136) Attribute to sessions where the Service-Type (6) Attribute has
a value of NAS-Prompt (7) (not Administrative). Typically, NASes
treat NAS-Prompt as the minimal privilege CLI service and
Administrative as full privilege. Using the Management-Privilege-
Level (136) Attribute with a Service-Type (6) Attribute having a
value of NAS-Prompt (7) will have the effect of increasing the
minimum privilege level. Conversely, it is NOT RECOMMENDED to use
this attribute with a Service-Type (6) Attribute with a value of
Administrative (6), which may require decreasing the maximum
privilege level.
It is NOT RECOMMENDED to use the Management-Privilege-Level (136)
Attribute in combination with a Management-Policy-Id (135) Attribute
or for management access methods other than interactive CLI. The
behavior resulting from such an overlay of management access control
provisioning is not defined by this document, and in the absence of
further specification, is likely to lead to unexpected behaviors,
especially in multi-vendor environments.
7. Use with Dynamic Authorization
It is entirely OPTIONAL for the NAS management authorization
attributes specified in this document to be used in conjunction with
Dynamic Authorization extensions to RADIUS [RFC5176]. When such
usage occurs, those attributes MAY be used as listed in the Table of
Attributes in Section 10.
Some guidance on how to identify existing management sessions on a
NAS for the purposes of Dynamic Authorization is useful. The primary
session identifiers SHOULD be User-Name (1) and Service-Type (6). To
accommodate instances when that information alone does not uniquely
identify a session, a NAS supporting Dynamic Authorization SHOULD
maintain one or more internal session identifiers that can be
represented as RADIUS attributes. Examples of such attributes
include Acct-Session-Id (44), Acct-Multi-Session-Id (50), NAS-Port
(5), or NAS-Port-Id (87). In the case of a remote management
session, common identifier values might include things such as the
remote IP address and remote TCP port number, or the file descriptor
value for use with the open socket. Any such identifier is obviously
transient in nature, and implementations SHOULD take care to avoid
and/or properly handle duplicate or stale values.
In order for the session identification attributes to be available to
the Dynamic Authorization Client, a NAS supporting Dynamic
Authorization for management sessions SHOULD include those session
identification attributes in the Access-Request message for each such
session. Additional discussion of session identification attribute
usage may be found in Section 3 of [RFC5176].
8. Examples of Attribute Groupings
1. Unprotected CLI access, via the local console, to the "super-
user" access level:
* Service-Type (6) = Administrative (6)
* NAS-Port-Type (61) = Async (0)
* Management-Transport-Protection (134) = No-Protection (1)
2. Unprotected CLI access, via a remote console, to the "super-user"
access level:
* Service-Type (6) = Administrative (6)
* NAS-Port-Type (61) = Virtual (5)
* Management-Transport-Protection (134) = No-Protection (1)
3. CLI access, via a fully protected secure remote terminal service
to the non-privileged user access level:
* Service-Type (6) = NAS-Prompt (7)
* NAS-Port-Type (61) = Virtual (5)
* Management-Transport-Protection (134) = Integrity-
Confidentiality-Protection (3)
4. CLI access, via a fully protected secure remote terminal service,
to a custom management access level, defined by a policy:
* Service-Type (6) = NAS-Prompt (7)
* NAS-Port-Type (61) = Virtual (5)
* Management-Transport-Protection (134) = Integrity-
Confidentiality-Protection (3)
* Management-Policy-Id (135) = "Network Administrator"
5. CLI access, via a fully protected secure remote terminal service,
with a management privilege level of 15:
* Service-Type (6) = NAS-Prompt (7)
* NAS-Port-Type (61) = Virtual (5)
* Management-Transport-Protection (134) = Integrity-
Confidentiality-Protection (3)
* Management-Privilege-Level (136) = 15
6. SNMP access, using an Access Control Model specifier, such as a
custom VACM View, defined by a policy:
* Service-Type (6) = Framed-Management (18)
* NAS-Port-Type (61) = Virtual (5)
* Framed-Management-Protocol (133) = SNMP (1)
* Management-Policy-Id (135) = "SNMP Network Administrator View"
There is currently no standardized way of implementing this
management policy mapping within SNMP. Such mechanisms are the
topic of current research.
7. SNMP fully protected access:
* Service-Type (6) = Framed-Management (18)
* NAS-Port-Type (61) = Virtual (5)
* Framed-Management-Protocol (133) = SNMP (1)
* Management-Transport-Protection (134) = Integrity-
Confidentiality-Protection (3)
8. Web (HTTP/HTML) access:
* Service-Type (6) = Framed-Management (18)
* NAS-Port-Type (61) = Virtual (5)
* Framed-Management-Protocol (133) = Web-based (2)
9. Secure web access, using a custom management access level,
defined by a policy:
* Service-Type (6) = Framed-Management (18)
* NAS-Port-Type (61) = Virtual (5)
* Framed-Management-Protocol (133) = Web-based (2)
* Management-Transport-Protection (134) = Integrity-
Confidentiality-Protection (3)
* Management-Policy-Id (135) = "Read-only web access"
9. Diameter Translation Considerations
When used in Diameter, the attributes defined in this specification
can be used as Diameter attribute-value pairs (AVPs) from the Code
space 1-255 (RADIUS attribute compatibility space). No additional
Diameter Code values are therefore allocated. The data types and
flag rules for the attributes are as follows:
+---------------------+
| AVP Flag rules |
|----+-----+----+-----|----+
| | SHOULD MUST| |
Attribute Name Value Type |MUST| MAY | NOT| NOT|Encr|
---------------------------------|----+-----+----+-----|----|
Service-Type | | | | | |
Enumerated | M | P | | V | Y |
Framed-Management-Protocol | | | | | |
Enumerated | M | P | | V | Y |
Management-Transport-Protection | | | | | |
Enumerated | M | P | | V | Y |
Management-Policy-Id | | | | | |
UTF8String | M | P | | V | Y |
Management-Privilege-Level | | | | | |
Integer | M | P | | V | Y |
---------------------------------|----+-----+----+-----|----|
The attributes in this specification have no special translation
requirements for Diameter to RADIUS or RADIUS to Diameter gateways;
they are copied as is, except for changes relating to headers,
alignment, and padding. See also [RFC3588], Section 4.1, and
[RFC4005], Section 9.
What this specification says about the applicability of the
attributes for RADIUS Access-Request packets applies in Diameter to
AA-Request [RFC4005].
What is said about Access-Accept applies in Diameter to AA-Answer
messages that indicate success.
10. Table of Attributes
The following table provides a guide to which attributes may be found
in which kinds of packets, and in what quantity.
Access Messages
Request Accept Reject Challenge # Attribute
---------------------------------------------------------------------
0-1 0-1 0 0 133 Framed-Management-Protocol
0-1 0-1 0 0 134 Management-Transport-Protection
0 0-1 0 0 135 Management-Policy-Id
0 0-1 0 0 136 Management-Privilege-Level
Accounting Messages
Request Response # Attribute
---------------------------------------------------------------------
0-1 0 133 Framed-Management-Protocol
0-1 0 134 Management-Transport-Protection
0-1 0 135 Management-Policy-Id
0-1 0 136 Management-Privilege-Level
Change-of-Authorization Messages
Request ACK NAK # Attribute
--------------------------------------------------------------------
0 0 0 133 Framed-Management-Protocol
0 0 0 134 Management-Transport-Protection
0-1 0 0 135 Management-Policy-Id (Note 1)
0-1 0 0 136 Management-Privilege-Level (Note 1)
Disconnect Messages
Request ACK NAK # Attribute
---------------------------------------------------------------------
0 0 0 133 Framed-Management-Protocol
0 0 0 134 Management-Transport-Protection
0 0 0 135 Management-Policy-Id
0 0 0 136 Management-Privilege-Level
(Note 1) When included within a CoA-Request, these attributes
represent an authorization change request. When one of these
attributes is omitted from a CoA-Request, the NAS assumes that the
attribute value is to remain unchanged. Attributes included in a
CoA-Request replace all existing values of the same attribute(s).
The following table defines the meaning of the above table entries.
0 This attribute MUST NOT be present in a packet.
0+ Zero or more instances of this attribute MAY be present in
a packet.
0-1 Zero or one instance of this attribute MAY be present in
a packet.
1 Exactly one instance of this attribute MUST be present in
a packet.
11. IANA Considerations
The following numbers have been assigned in the RADIUS Attribute
Types registry.
o New enumerated value for the existing Service-Type Attribute:
* Framed-Management (18)
o New RADIUS Attribute Types:
* Framed-Management-Protocol (133)
* Management-Transport-Protection (134)
* Management-Policy-Id (135)
* Management-Privilege-Level (136)
The enumerated values of the newly assigned RADIUS Attribute Types as
defined in this document were assigned at the same time as the new
Attribute Types.
For the Framed-Management-Protocol Attribute:
1 SNMP
2 Web-based
3 NETCONF
4 FTP
5 TFTP
6 SFTP
7 RCP
8 SCP
For the Management-Transport-Protection Attribute:
1 No-Protection
2 Integrity-Protection
3 Integrity-Confidentiality-Protection
Assignments of additional enumerated values for the RADIUS attributes
defined in this document are to be processed as described in
[RFC3575], subject to the additional requirement of a published
specification.
12. Security Considerations
12.1. General Considerations
This specification describes the use of RADIUS and Diameter for
purposes of authentication, authorization, and accounting for
management access to devices within networks. RADIUS threats and
security issues for this application are described in [RFC3579] and
[RFC3580]; security issues encountered in roaming are described in
[RFC2607]. For Diameter, the security issues relating to this
application are described in [RFC4005] and [RFC4072].
This document specifies new attributes that can be included in
existing RADIUS packets, which may be protected as described in
[RFC3579] and [RFC5176]. In Diameter, the attributes are protected
as specified in [RFC3588]. See those documents for a more detailed
description.
The security mechanisms supported in RADIUS and Diameter are focused
on preventing an attacker from spoofing packets or modifying packets
in transit. They do not prevent an authorized RADIUS/Diameter server
or proxy from inserting attributes with malicious intent.
A legacy NAS may not recognize the attributes in this document that
supplement the provisioning of CLI management access. If the value
of the Service-Type Attribute is NAS-Prompt or Administrative, the
legacy NAS may silently discard such attributes, while permitting the
user to access the CLI management interface(s) of the NAS. This can
lead to users improperly receiving authorized management access to
the NAS, or access with greater levels of access rights than were
intended. RADIUS servers SHOULD attempt to ascertain whether or not
the NAS supports these attributes before sending them in an Access-
Accept message that provisions CLI access.
It is possible that certain NAS implementations may not be able to
determine the protection properties of the underlying transport
protocol as specified by the Management-Transport-Protection
Attribute. This may be a limitation of the standard application
programming interface of the underlying transport implementation or
of the integration of the transport into the NAS implementation. In
either event, NASes conforming to this specification, which cannot
determine the protection state of the remote management connection,
MUST treat an Access-Accept message containing a Management-
Transport-Protection Attribute containing a value other than No-
Protection (1) as if it were an Access-Reject message, unless
specifically overridden by local policy configuration.
Use of the No-Protection (1) option for the Management-Transport-
Protection (134) Attribute is NOT RECOMMENDED in any deployment where
secure management or configuration is required.
12.2. RADIUS Proxy Operation Considerations
The device management access authorization attributes presented in
this document present certain considerations when used in RADIUS
proxy environments. These considerations are not different from
those that exist in RFC 2865 [RFC2865] with respect to the Service-
Type Attribute values of Administrative and NAS-Prompt.
Most RADIUS proxy environments are also multi-party environments. In
multi-party proxy environments it is important to distinguish which
entities have the authority to provision management access to the
edge devices, i.e., NASes, and which entities only have authority to
provision network access services of various sorts.
It may be important that operators of the NAS are able to ensure that
access to the CLI, or other management interfaces of the NAS, is only
provisioned to their own employees or contractors. One way for the
NAS to enforce this requirement is to use only local, non-proxy
RADIUS servers for management access requests. Proxy RADIUS servers
could be used for non-management access requests, based on local
policy. This "bifurcation" of RADIUS authentication and
authorization is a simple case of separate administrative realms.
The NAS may be designed so as to maintain separate lists of RADIUS
servers for management AAA use and for non-management AAA use.
An alternate method of enforcing this requirement would be for the
first-hop RADIUS proxy server, operated by the owner of the NAS, to
filter out any RADIUS attributes that provision management access
rights that originate from "up-stream" proxy servers not operated by
the NAS owner. Access-Accept messages that provision such locally
unauthorized management access MAY be treated as if they were an
Access-Reject by the first-hop proxy server.
An additional exposure present in proxy deployments is that sensitive
user credentials, e.g., passwords, are likely to be available in
cleartext form at each of the proxy servers. Encrypted or hashed
credentials are not subject to this risk, but password authentication
is a very commonly used mechanism for management access
authentication, and in RADIUS passwords are only protected on a hop-
by-hop basis. Malicious proxy servers could misuse this sensitive
information.
These issues are not of concern when all the RADIUS servers, local
and proxy, used by the NAS are under the sole administrative control
of the NAS owner.
13. Acknowledgments
Many thanks to all reviewers, including Bernard Aboba, Alan DeKok,
David Harrington, Mauricio Sanchez, Juergen Schoenwaelder, Hannes
Tschofenig, Barney Wolff, and Glen Zorn.
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
14.2. Informative References
[HTML] Raggett, D., Le Hors, A., and I. Jacobs, "The HTML 4.01
Specification, W3C", December 1999.
[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[RFC1350] Sollins, K., "The TFTP Protocol (Revision 2)", STD 33,
RFC 1350, July 1992.
[RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
Implementation in Roaming", RFC 2607, June 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[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, "User-based Security Model
(USM) for version 3 of the Simple Network Management
Protocol (SNMPv3)", 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., "Version 2 of the Protocol Operations for the
Simple Network Management Protocol (SNMP)", STD 62,
RFC 3416, December 2002.
[RFC3417] Presuhn, R., "Transport Mappings for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3417,
December 2002.
[RFC3418] Presuhn, R., "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62,
RFC 3418, December 2002.
[RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote
Authentication Dial In User Service)", RFC 3575,
July 2003.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,
"IEEE 802.1X Remote Authentication Dial In User Service
(RADIUS) Usage Guidelines", RFC 3580, September 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
"Diameter Network Access Server Application", RFC 4005,
August 2005.
[RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", RFC 4072,
August 2005.
[RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[RFC4742] Wasserman, M. and T. Goddard, "Using the NETCONF
Configuration Protocol over Secure SHell (SSH)", RFC 4742,
December 2006.
[RFC4743] Goddard, T., "Using NETCONF over the Simple Object Access
Protocol (SOAP)", RFC 4743, December 2006.
[RFC4744] Lear, E. and K. Crozier, "Using the NETCONF Protocol over
the Blocks Extensible Exchange Protocol (BEEP)", RFC 4744,
December 2006.
[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 5176,
January 2008.
[SFTP] Galbraith, J. and O. Saarenmaa, "SSH File Transfer
Protocol", Work in Progress, July 2006.
[SSH] Barrett, D., Silverman, R., and R. Byrnes, "SSH, the
Secure Shell: The Definitive Guide, Second Edition,
O'Reilly and Associates", May 2005.
Authors' Addresses
David B. Nelson
Elbrys Networks, Inc.
282 Corporate Drive
Portsmouth, NH 03801
USA
EMail: dnelson@elbrysnetworks.com
Greg Weber
Individual Contributor
Knoxville, TN 37932
USA
EMail: gdweber@gmail.com