Difference between revisions of "RFC6065"
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received public review and has been approved for publication by the | received public review and has been approved for publication by the | ||
Internet Engineering Steering Group (IESG). Further information on | Internet Engineering Steering Group (IESG). Further information on | ||
− | Internet Standards is available in Section 2 of RFC 5741. | + | Internet Standards is available in Section 2 of [[RFC5741|RFC 5741]]. |
Information about the current status of this document, any errata, | Information about the current status of this document, any errata, | ||
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document authors. All rights reserved. | document authors. All rights reserved. | ||
− | This document is subject to BCP 78 and the IETF Trust's Legal | + | This document is subject to [[BCP78|BCP 78]] and the IETF Trust's Legal |
Provisions Relating to IETF Documents | Provisions Relating to IETF Documents | ||
(http://trustee.ietf.org/license-info) in effect on the date of | (http://trustee.ietf.org/license-info) in effect on the date of | ||
Line 59: | Line 59: | ||
This memo specifies a way to dynamically provision selected View- | This memo specifies a way to dynamically provision selected View- | ||
− | based Access Control Model (VACM) | + | based Access Control Model (VACM) [[RFC3415]] Management Information |
Base (MIB) objects, based on information received from an | Base (MIB) objects, based on information received from an | ||
Authentication, Authorization, and Accounting (AAA) service, such as | Authentication, Authorization, and Accounting (AAA) service, such as | ||
− | RADIUS | + | RADIUS [[RFC2865]] and [[RFC5607]]. It reduces the need for security |
administrators to manually update VACM configurations due to user | administrators to manually update VACM configurations due to user | ||
churn, allowing a centralized AAA service to provide the information | churn, allowing a centralized AAA service to provide the information | ||
Line 76: | Line 76: | ||
corresponding updates to VACM MIB data. | corresponding updates to VACM MIB data. | ||
− | The reader is expected to be familiar with | + | The reader is expected to be familiar with [[RFC3415]], [[RFC5607]], |
− | + | [[RFC5608]], and their supporting specifications. | |
== The Internet-Standard Management Framework == | == The Internet-Standard Management Framework == | ||
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For a detailed overview of the documents that describe the current | For a detailed overview of the documents that describe the current | ||
Internet-Standard Management Framework, please refer to section 7 of | Internet-Standard Management Framework, please refer to section 7 of | ||
− | RFC 3410 | + | [[RFC3410|RFC 3410]] [[RFC3410]]. |
Managed objects are accessed via a virtual information store, termed | Managed objects are accessed via a virtual information store, termed | ||
Line 90: | Line 90: | ||
Objects in the MIB are defined using the mechanisms defined in the | Objects in the MIB are defined using the mechanisms defined in the | ||
Structure of Management Information (SMI). This memo specifies a MIB | Structure of Management Information (SMI). This memo specifies a MIB | ||
− | module that is compliant to the SMIv2, which is described in STD 58, | + | module that is compliant to the SMIv2, which is described in [[STD58|STD 58]], |
− | RFC 2578 | + | [[RFC2578|RFC 2578]] [[RFC2578]], [[STD58|STD 58]], [[RFC2579|RFC 2579]] [[RFC2579]] and [[STD58|STD 58]], [[RFC2580|RFC 2580]] |
− | + | [[RFC2580]]. | |
== Conventions == | == Conventions == | ||
Line 99: | Line 99: | ||
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and | "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and | ||
"OPTIONAL" in this document are to be interpreted as described in RFC | "OPTIONAL" in this document are to be interpreted as described in RFC | ||
− | 2119 | + | 2119 [[RFC2119]]. |
== Overview == | == Overview == | ||
Line 107: | Line 107: | ||
There are two use cases for AAA support of management access via | There are two use cases for AAA support of management access via | ||
SNMP. These are (a) service authorization and (b) access control | SNMP. These are (a) service authorization and (b) access control | ||
− | authorization. The former is discussed in detail in | + | authorization. The former is discussed in detail in [[RFC5608]]. The |
latter is the subject of this memo. | latter is the subject of this memo. | ||
Line 130: | Line 130: | ||
already in place in VACM. | already in place in VACM. | ||
− | The SNMP architecture | + | The SNMP architecture [[RFC3411]] maintains strong modularity and |
separation of concerns, separating user identity (authentication) | separation of concerns, separating user identity (authentication) | ||
from user database access rights (authorization). RADIUS, on the | from user database access rights (authorization). RADIUS, on the | ||
Line 136: | Line 136: | ||
authentication. Consequently, the approach here is to leverage | authentication. Consequently, the approach here is to leverage | ||
existing RADIUS usage for identifying a principal, documented in | existing RADIUS usage for identifying a principal, documented in | ||
− | + | [[RFC5608]], along with the RADIUS Management-Policy-Id Attribute | |
− | + | [[RFC5607]]. | |
A unique identifier is needed for each AAA-authorized "session", | A unique identifier is needed for each AAA-authorized "session", | ||
Line 162: | Line 162: | ||
Some of the binding is done via other specifications. A transport | Some of the binding is done via other specifications. A transport | ||
− | model, such as the Secure Shell Transport Model | + | model, such as the Secure Shell Transport Model [[RFC5592]], provides a |
binding between 1 and 2 and 3, providing a securityName. In turn, | binding between 1 and 2 and 3, providing a securityName. In turn, | ||
− | + | [[RFC5607]] provides a binding between (1+2+3) and 4. This document | |
extends that further, to create a binding between (1+2+3+4) and the | extends that further, to create a binding between (1+2+3+4) and the | ||
local (VACM MIB) definition of the named policy, called a group in | local (VACM MIB) definition of the named policy, called a group in | ||
Line 172: | Line 172: | ||
Though this memo was motivated to support the use of specific | Though this memo was motivated to support the use of specific | ||
− | Transport Models, such as the Secure Shell Transport Model | + | Transport Models, such as the Secure Shell Transport Model [[RFC5592]], |
it MAY be used with other implementation environments satisfying | it MAY be used with other implementation environments satisfying | ||
these requirements: | these requirements: | ||
Line 182: | Line 182: | ||
authenticated principal in a particular role, based on information | authenticated principal in a particular role, based on information | ||
provided by the AAA service. The principal will be identified | provided by the AAA service. The principal will be identified | ||
− | using an SNMP securityName | + | using an SNMP securityName [[RFC3411]]. The role will be identified |
by the name of the corresponding VACM group. | by the name of the corresponding VACM group. | ||
Line 194: | Line 194: | ||
o the service provides information semantically equivalent to the | o the service provides information semantically equivalent to the | ||
− | RADIUS Management-Policy-Id Attribute | + | RADIUS Management-Policy-Id Attribute [[RFC5607]], which corresponds |
to the name of a VACM group; | to the name of a VACM group; | ||
o the service provides an authenticated principal identifier (e.g., | o the service provides an authenticated principal identifier (e.g., | ||
− | the RADIUS User-Name Attribute | + | the RADIUS User-Name Attribute [[RFC2865]]) that can be transformed |
to an equivalent principal identifier in the form of a | to an equivalent principal identifier in the form of a | ||
− | securityName | + | securityName [[RFC3411]]. |
== Structure of the MIB Module == | == Structure of the MIB Module == | ||
Line 206: | Line 206: | ||
=== Textual Conventions === | === Textual Conventions === | ||
− | This MIB module makes use of the SnmpAdminString | + | This MIB module makes use of the SnmpAdminString [[RFC3411]] and |
− | SnmpSecurityModel | + | SnmpSecurityModel [[RFC3411]] textual conventions. |
=== The Table Structure === | === The Table Structure === | ||
Line 221: | Line 221: | ||
This MIB module has a close operational relationship with the SNMP- | This MIB module has a close operational relationship with the SNMP- | ||
VIEW-BASED-ACM-MIB (more commonly known as the "VACM MIB") from | VIEW-BASED-ACM-MIB (more commonly known as the "VACM MIB") from | ||
− | + | [[RFC3415]]. It also relies on IMPORTS from several other modules. | |
=== Relationship to the VACM MIB === | === Relationship to the VACM MIB === | ||
Line 234: | Line 234: | ||
=== MIB modules Required for IMPORTS === | === MIB modules Required for IMPORTS === | ||
− | This MIB module employs definitions from | + | This MIB module employs definitions from [[RFC2578]], [[RFC2579]], and |
− | + | [[RFC3411]]. | |
=== Documents Required for REFERENCE Clauses === | === Documents Required for REFERENCE Clauses === | ||
This MIB module contains REFERENCE clauses making reference to | This MIB module contains REFERENCE clauses making reference to | ||
− | + | [[RFC2865]], [[RFC3411]], and [[RFC5590]]. | |
== Elements of Procedure == | == Elements of Procedure == | ||
Line 260: | Line 260: | ||
=== Sequencing Requirements === | === Sequencing Requirements === | ||
− | These procedures assume that a transport model, such as | + | These procedures assume that a transport model, such as [[RFC5592]], |
coordinates session establishment with AAA authentication and | coordinates session establishment with AAA authentication and | ||
authorization. They rely on the receipt by the AAA client of the | authorization. They rely on the receipt by the AAA client of the | ||
− | RADIUS Management-Policy-Id | + | RADIUS Management-Policy-Id [[RFC5607]] Attribute (or its equivalent) |
from the RADIUS Access-Accept message (or equivalent). They also | from the RADIUS Access-Accept message (or equivalent). They also | ||
− | assume that the User-Name | + | assume that the User-Name [[RFC2865]] from the RADIUS Access-Request |
− | message (or equivalent) corresponds to a securityName | + | message (or equivalent) corresponds to a securityName [[RFC3411]]. |
To ensure correct processing of SNMP PDUs, the handling of the | To ensure correct processing of SNMP PDUs, the handling of the | ||
indication of the establishment of a session in accordance with the | indication of the establishment of a session in accordance with the | ||
elements of procedure below MUST be completed before the | elements of procedure below MUST be completed before the | ||
− | isAccessAllowed() Abstract Service Interface | + | isAccessAllowed() Abstract Service Interface [[RFC3415]] is invoked for |
any SNMP PDUs from that session. | any SNMP PDUs from that session. | ||
If a session termination indication occurs before all invocations of | If a session termination indication occurs before all invocations of | ||
− | the isAccessAllowed() Abstract Service Interface | + | the isAccessAllowed() Abstract Service Interface [[RFC3415]] have |
completed for all SNMP PDUs from that session, those remaining | completed for all SNMP PDUs from that session, those remaining | ||
invocations MAY result in denial of access. | invocations MAY result in denial of access. | ||
Line 286: | Line 286: | ||
establishment indication: | establishment indication: | ||
− | o the SnmpSecurityModel | + | o the SnmpSecurityModel [[RFC3411]] needed as an index into the |
vacmSecurityToGroupTable; | vacmSecurityToGroupTable; | ||
Line 319: | Line 319: | ||
o vacmAaaSecurityName = RADIUS User-Name Attribute or equivalent, | o vacmAaaSecurityName = RADIUS User-Name Attribute or equivalent, | ||
the securityName that will be used in invocations of the | the securityName that will be used in invocations of the | ||
− | isAccessAllowed() Abstract Service Interface | + | isAccessAllowed() Abstract Service Interface [[RFC3415]]; |
o vacmAaaSessionID = session identifier, unique across all open | o vacmAaaSessionID = session identifier, unique across all open | ||
Line 432: | Line 432: | ||
(http://trustee.ietf.org/license-info). | (http://trustee.ietf.org/license-info). | ||
− | This version of this MIB module is part of RFC 6065; | + | This version of this MIB module is part of [[RFC6065|RFC 6065]]; |
see the RFC itself for full legal notices." | see the RFC itself for full legal notices." | ||
REVISION "201012090000Z" | REVISION "201012090000Z" | ||
− | DESCRIPTION "Initial version, published as RFC 6065." | + | DESCRIPTION "Initial version, published as [[RFC6065|RFC 6065]]." |
::= { mib-2 199 } | ::= { mib-2 199 } | ||
Line 455: | Line 455: | ||
control policy to be used for the corresponding | control policy to be used for the corresponding | ||
principals." | principals." | ||
− | REFERENCE "RFC 3411, Section 3.2.2, defines securityName." | + | REFERENCE "[[RFC3411|RFC 3411]], Section 3.2.2, defines securityName." |
::= { vacmAaaMIBObjects 1 } | ::= { vacmAaaMIBObjects 1 } | ||
Line 479: | Line 479: | ||
or otherwise terminated for any reason, the | or otherwise terminated for any reason, the | ||
corresponding vacmAaaSecurityToGroupEntry is deleted." | corresponding vacmAaaSecurityToGroupEntry is deleted." | ||
− | REFERENCE "RFC 3411, Section 3.2.2, defines securityName." | + | REFERENCE "[[RFC3411|RFC 3411]], Section 3.2.2, defines securityName." |
INDEX { | INDEX { | ||
vacmAaaSecurityModel, | vacmAaaSecurityModel, | ||
Line 513: | Line 513: | ||
environments, this corresponds to the User-Name | environments, this corresponds to the User-Name | ||
Attribute." | Attribute." | ||
− | REFERENCE "RFC 3411, Section 3.2.2, defines securityName, and | + | REFERENCE "[[RFC3411|RFC 3411]], Section 3.2.2, defines securityName, and |
− | RFC 2865, Section 5.1, defines User-Name." | + | [[RFC2865|RFC 2865]], Section 5.1, defines User-Name." |
::= { vacmAaaSecurityToGroupEntry 2 } | ::= { vacmAaaSecurityToGroupEntry 2 } | ||
Line 532: | Line 532: | ||
use that value." | use that value." | ||
REFERENCE "The Abstract Service Interface parameter tmSessionID | REFERENCE "The Abstract Service Interface parameter tmSessionID | ||
− | is defined in RFC 5590, Section 5.2.4." | + | is defined in [[RFC5590|RFC 5590]], Section 5.2.4." |
::= { vacmAaaSecurityToGroupEntry 3 } | ::= { vacmAaaSecurityToGroupEntry 3 } | ||
Line 546: | Line 546: | ||
the value of this object is applied the vacmGroupName | the value of this object is applied the vacmGroupName | ||
in the corresponding vacmSecurityToGroupEntry." | in the corresponding vacmSecurityToGroupEntry." | ||
− | REFERENCE "RFC 3415" | + | REFERENCE "[[RFC3415|RFC 3415]]" |
::= { vacmAaaSecurityToGroupEntry 4 } | ::= { vacmAaaSecurityToGroupEntry 4 } | ||
Line 681: | Line 681: | ||
It is RECOMMENDED that implementers consider the security features as | It is RECOMMENDED that implementers consider the security features as | ||
− | provided by the SNMPv3 framework (see | + | provided by the SNMPv3 framework (see [[RFC3410]], section 8), |
including full support for the SNMPv3 cryptographic mechanisms (for | including full support for the SNMPv3 cryptographic mechanisms (for | ||
authentication and privacy). | authentication and privacy). | ||
Line 753: | Line 753: | ||
12.1. Normative References | 12.1. Normative References | ||
− | + | [[RFC2119]] Bradner, S., "Key words for use in RFCs to Indicate | |
− | Requirement Levels", BCP 14, RFC 2119, March 1997. | + | Requirement Levels", [[BCP14|BCP 14]], [[RFC2119|RFC 2119]], March 1997. |
− | + | [[RFC2578]] McCloghrie, K., Ed., Perkins, D., Ed., and J. | |
Schoenwaelder, Ed., "Structure of Management Information | Schoenwaelder, Ed., "Structure of Management Information | ||
− | Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. | + | Version 2 (SMIv2)", [[STD58|STD 58]], [[RFC2578|RFC 2578]], April 1999. |
− | + | [[RFC2579]] McCloghrie, K., Ed., Perkins, D., Ed., and J. | |
Schoenwaelder, Ed., "Textual Conventions for SMIv2", | Schoenwaelder, Ed., "Textual Conventions for SMIv2", | ||
− | STD 58, RFC 2579, April 1999. | + | [[STD58|STD 58]], [[RFC2579|RFC 2579]], April 1999. |
− | + | [[RFC2580]] McCloghrie, K., Perkins, D., and J. Schoenwaelder, | |
− | "Conformance Statements for SMIv2", STD 58, RFC 2580, | + | "Conformance Statements for SMIv2", [[STD58|STD 58]], [[RFC2580|RFC 2580]], |
April 1999. | April 1999. | ||
− | + | [[RFC2865]] Rigney, C., Willens, S., Rubens, A., and W. Simpson, | |
"Remote Authentication Dial In User Service (RADIUS)", | "Remote Authentication Dial In User Service (RADIUS)", | ||
− | RFC 2865, June 2000. | + | [[RFC2865|RFC 2865]], June 2000. |
− | + | [[RFC3411]] Harrington, D., Presuhn, R., and B. Wijnen, "An | |
Architecture for Describing Simple Network Management | Architecture for Describing Simple Network Management | ||
− | Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, | + | Protocol (SNMP) Management Frameworks", [[STD62|STD 62]], [[RFC3411|RFC 3411]], |
December 2002. | December 2002. | ||
− | + | [[RFC3415]] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based | |
Access Control Model (VACM) for the Simple Network | Access Control Model (VACM) for the Simple Network | ||
− | Management Protocol (SNMP)", STD 62, RFC 3415, | + | Management Protocol (SNMP)", [[STD62|STD 62]], [[RFC3415|RFC 3415]], |
December 2002. | December 2002. | ||
− | + | [[RFC5590]] Harrington, D. and J. Schoenwaelder, "Transport Subsystem | |
for the Simple Network Management Protocol (SNMP)", | for the Simple Network Management Protocol (SNMP)", | ||
− | RFC 5590, June 2009. | + | [[RFC5590|RFC 5590]], June 2009. |
− | + | [[RFC5607]] Nelson, D. and G. Weber, "Remote Authentication Dial-In | |
User Service (RADIUS) Authorization for Network Access | User Service (RADIUS) Authorization for Network Access | ||
− | Server (NAS) Management", RFC 5607, July 2009. | + | Server (NAS) Management", [[RFC5607|RFC 5607]], July 2009. |
− | + | [[RFC5608]] Narayan, K. and D. Nelson, "Remote Authentication Dial-In | |
User Service (RADIUS) Usage for Simple Network Management | User Service (RADIUS) Usage for Simple Network Management | ||
− | Protocol (SNMP) Transport Models", RFC 5608, August 2009. | + | Protocol (SNMP) Transport Models", [[RFC5608|RFC 5608]], August 2009. |
12.2. Informative References | 12.2. Informative References | ||
− | + | [[RFC3410]] Case, J., Mundy, R., Partain, D., and B. Stewart, | |
"Introduction and Applicability Statements for Internet- | "Introduction and Applicability Statements for Internet- | ||
− | Standard Management Framework", RFC 3410, December 2002. | + | Standard Management Framework", [[RFC3410|RFC 3410]], December 2002. |
− | + | [[RFC5592]] Harrington, D., Salowey, J., and W. Hardaker, "Secure | |
Shell Transport Model for the Simple Network Management | Shell Transport Model for the Simple Network Management | ||
− | Protocol (SNMP)", RFC 5592, June 2009. | + | Protocol (SNMP)", [[RFC5592|RFC 5592]], June 2009. |
Authors' Addresses | Authors' Addresses |
Latest revision as of 02:40, 22 October 2020
Internet Engineering Task Force (IETF) K. Narayan Request for Comments: 6065 Cisco Systems, Inc. Category: Standards Track D. Nelson ISSN: 2070-1721 Elbrys Networks, Inc.
R. Presuhn, Ed. December 2010
Using Authentication, Authorization, and Accounting Services to Dynamically Provision View-Based Access Control Model User-to-Group Mappings
Abstract
This memo defines a portion of the Management Information Base (MIB) for use with network management protocols. It describes the use of information provided by Authentication, Authorization, and Accounting (AAA) services, such as the Remote Authentication Dial-In User Service (RADIUS), to dynamically update user-to-group mappings in the View-based Access Control Model (VACM).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6065.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
7.2.2. Creation of Entries in vacmAaaSecurityToGroupTable . . 8 7.2.3. Creation of Entries in vacmSecurityToGroupTable . . . 8
7.3.1. Deletion of Entries from
7.3.2. Deletion of Entries from vacmSecurityToGroupTable . . 10
Contents
- 1 Introduction
- 2 The Internet-Standard Management Framework
- 3 Conventions
- 4 Overview
- 5 Structure of the MIB Module
- 6 Relationship to Other MIB Modules
- 7 Elements of Procedure
- 8 Definitions
- 9 Security Considerations
Introduction
This memo specifies a way to dynamically provision selected View- based Access Control Model (VACM) RFC3415 Management Information Base (MIB) objects, based on information received from an Authentication, Authorization, and Accounting (AAA) service, such as RADIUS RFC2865 and RFC5607. It reduces the need for security administrators to manually update VACM configurations due to user churn, allowing a centralized AAA service to provide the information associating a given user with the access control policy (known as a "group" in VACM) governing that user's access to management information.
This memo requires no changes to the Abstract Service Interface for the Access Control Subsystem, and requires no changes to the Elements of Procedure for VACM. It provides a MIB module that reflects the information provided by the AAA service, along with elements of procedure for maintaining that information and performing corresponding updates to VACM MIB data.
The reader is expected to be familiar with RFC3415, RFC5607, RFC5608, and their supporting specifications.
The Internet-Standard Management Framework
For a detailed overview of the documents that describe the current Internet-Standard Management Framework, please refer to section 7 of RFC 3410 RFC3410.
Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. MIB objects are generally accessed through the Simple Network Management Protocol (SNMP). Objects in the MIB are defined using the mechanisms defined in the Structure of Management Information (SMI). This memo specifies a MIB module that is compliant to the SMIv2, which is described in STD 58, RFC 2578 RFC2578, STD 58, RFC 2579 RFC2579 and STD 58, RFC 2580 RFC2580.
Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 RFC2119.
Overview
Using AAA services with SNMP
There are two use cases for AAA support of management access via SNMP. These are (a) service authorization and (b) access control authorization. The former is discussed in detail in RFC5608. The latter is the subject of this memo.
The use case assumption here is that roles within an organization (which are represented in VACM as groups, which in turn name access control policies) change infrequently, while the users assigned to those roles change much more frequently. This memo describes how the user-to-role (group) mapping can be delegated to the RADIUS server, avoiding the need to re-provision managed devices as users are added, deleted, or assigned new roles in an organization.
This memo assumes that the detailed access control policies are pre- configured in VACM, and does not attempt to address the question of how the policy associated with a given role is put in place.
The only additional information obtained from the AAA service is the mapping of the authenticated user's identifier to a specific role (or "group" in VACM terminology) in the access control policy. Dynamic user authorization for MIB database access control, as defined herein, is limited to mapping the authenticated user to a group, which in turn is mapped to whatever access control policies are already in place in VACM.
The SNMP architecture RFC3411 maintains strong modularity and separation of concerns, separating user identity (authentication) from user database access rights (authorization). RADIUS, on the other hand, allows for no such separation of authorization from authentication. Consequently, the approach here is to leverage existing RADIUS usage for identifying a principal, documented in RFC5608, along with the RADIUS Management-Policy-Id Attribute RFC5607.
A unique identifier is needed for each AAA-authorized "session", corresponding to a communication channel, such as a transport session, for which a principal has been AAA-authenticated and which is authorized to offer SNMP service. How these identifiers are assigned is implementation dependent. When a RADIUS Management- Policy-Id Attribute (or equivalent) is bound to such a session and principal authentication, this binding provides sufficient information to compute dynamic updates to VACM. How this information is communicated within an implementation is implementation dependent; this memo is only concerned with externally observable behavior.
The key concept here is that what we will informally call a "AAA binding" binds:
1. a communications channel
2. an authenticated principal
3. service authorization
4. an access control policy name
Some of the binding is done via other specifications. A transport model, such as the Secure Shell Transport Model RFC5592, provides a binding between 1 and 2 and 3, providing a securityName. In turn, RFC5607 provides a binding between (1+2+3) and 4. This document extends that further, to create a binding between (1+2+3+4) and the local (VACM MIB) definition of the named policy, called a group in VACM.
Applicability
Though this memo was motivated to support the use of specific Transport Models, such as the Secure Shell Transport Model RFC5592, it MAY be used with other implementation environments satisfying these requirements:
o use an AAA service for sign-on service and data access
authorization;
o provide an indication of the start of a session for a particular
authenticated principal in a particular role, based on information provided by the AAA service. The principal will be identified using an SNMP securityName RFC3411. The role will be identified by the name of the corresponding VACM group.
o provide an indication of the end of the need for being able to
make access decisions for a particular authenticated principal, as at the end of a session, whether due to disconnection, termination due to timeout, or any other reason.
Likewise, although this memo specifically refers to RADIUS, it MAY be used with other AAA services satisfying these requirements:
o the service provides information semantically equivalent to the
RADIUS Management-Policy-Id Attribute RFC5607, which corresponds to the name of a VACM group;
o the service provides an authenticated principal identifier (e.g.,
the RADIUS User-Name Attribute RFC2865) that can be transformed to an equivalent principal identifier in the form of a securityName RFC3411.
Structure of the MIB Module
Textual Conventions
This MIB module makes use of the SnmpAdminString RFC3411 and SnmpSecurityModel RFC3411 textual conventions.
The Table Structure
This MIB module defines a single table, the vacmAaaSecurityToGroupTable. This table is indexed by the integer assigned to each security model, the protocol-independent securityName corresponding to a principal, and the unique identifier of a session.
Relationship to Other MIB Modules
This MIB module has a close operational relationship with the SNMP- VIEW-BASED-ACM-MIB (more commonly known as the "VACM MIB") from RFC3415. It also relies on IMPORTS from several other modules.
Relationship to the VACM MIB
Although the MIB module defined here has a close relationship with the VACM MIB's vacmSecurityToGroupTable, it in no way changes the elements of procedure for VACM, nor does it affect any other tables defined in VACM. See the elements of procedure (below) for details of how the contents of the vacmSecurityToGroupTable are affected by this MIB module.
MIB modules Required for IMPORTS
This MIB module employs definitions from RFC2578, RFC2579, and RFC3411.
Documents Required for REFERENCE Clauses
This MIB module contains REFERENCE clauses making reference to RFC2865, RFC3411, and RFC5590.
Elements of Procedure
The following elements of procedure are formulated in terms of two types of events: an indication of the establishment of a session, and an indication that one has ended. These can result in the creation of entries in the vacmAaaSecurityToGroupTable, which can in turn trigger creation, update, or deletion of entries in the vacmSecurityToGroupTable.
There are various possible implementation-dependent error cases not spelled out here, such as running out of memory. By their nature, recovery in such cases will be implementation dependent. Implementors are advised to consider fail-safe strategies, e.g., prematurely terminating access in preference to erroneously perpetuating access.
Sequencing Requirements
These procedures assume that a transport model, such as RFC5592, coordinates session establishment with AAA authentication and authorization. They rely on the receipt by the AAA client of the RADIUS Management-Policy-Id RFC5607 Attribute (or its equivalent) from the RADIUS Access-Accept message (or equivalent). They also assume that the User-Name RFC2865 from the RADIUS Access-Request message (or equivalent) corresponds to a securityName RFC3411.
To ensure correct processing of SNMP PDUs, the handling of the indication of the establishment of a session in accordance with the elements of procedure below MUST be completed before the isAccessAllowed() Abstract Service Interface RFC3415 is invoked for any SNMP PDUs from that session.
If a session termination indication occurs before all invocations of the isAccessAllowed() Abstract Service Interface RFC3415 have completed for all SNMP PDUs from that session, those remaining invocations MAY result in denial of access.
Actions upon Session Establishment Indication
Required Information
Four pieces of information are needed to process the session establishment indication:
o the SnmpSecurityModel RFC3411 needed as an index into the
vacmSecurityToGroupTable;
o the RADIUS User-Name Attribute;
o a session identifier, as a unique, definitive identifier of the
session that the AAA authorization is tied to;
o the RADIUS Management-Policy-Id Attribute.
All four of these pieces of information are REQUIRED. In particular, if either the User-Name or Management-Policy-Id is absent, invalid, or a zero-length string, no further processing of the session establishment indication is undertaken.
As noted in Section 4.2, the above text refers specifically to RADIUS attributes. Other AAA services can be substituted, but the requirements imposed on the User-Name and the Management-Policy-Id- Attribute MUST be satisfied using the equivalent fields for those services.
Creation of Entries in vacmAaaSecurityToGroupTable
Whenever an indication arrives that a new session has been established, determine whether a corresponding entry exists in the vacmAaaSecurityToGroupTable. If one does not, create a new row with the columns populated as follows:
o vacmAaaSecurityModel = value of SnmpSecurityModel corresponding to
the security model in use;
o vacmAaaSecurityName = RADIUS User-Name Attribute or equivalent,
the securityName that will be used in invocations of the isAccessAllowed() Abstract Service Interface RFC3415;
o vacmAaaSessionID = session identifier, unique across all open
sessions of all of this SNMP engine's transport models;
o vacmAaaGroupName = RADIUS Management-Policy-Id Attribute or
equivalent.
Otherwise, if the row already exists, update the vacmAaaGroupName with the RADIUS Management-Policy-Id Attribute or equivalent supplied.
Creation of Entries in vacmSecurityToGroupTable
Whenever an entry is created in the vacmAaaSecurityToGroupTable, the vacmSecurityToGroupTable is examined to determine whether a corresponding entry exists there, using the value of vacmAaaSecurityModel for vacmSecurityModel, and the value of vacmAaaSecurityName for vacmSecurityName. If no corresponding entry exists, create one using the vacmAaaGroupName of the newly created
entry to fill in vacmGroupName, using a value of "volatile" for the row's StorageType, and a value of "active" for its RowStatus.
Update of vacmGroupName
Whenever the value of an instance of vacmAaaGroupName is updated, if a corresponding entry exists in the vacmSecurityToGroupTable, and that entry's StorageType is "volatile" and its RowStatus is "active", update the value of vacmGroupName with the value from vacmAaaGroupName.
If a corresponding entry already exists in the vacmSecurityToGroupTable, and that row's StorageType is anything other than "volatile", or its RowStatus is anything other than "active", then that instance of vacmGroupName MUST NOT be modified.
The operational assumption here is that if the row's StorageType is "volatile", then this entry was probably dynamically created; an entry created by a security administrator would not normally be given a StorageType of "volatile". If the value being provided by RADIUS (or another AAA service) is the same as what is already there, this is a no-op. If the value is different, the new information is understood as a more recent role (group) assignment for the user, which should supersede the one currently held there. The structure of the vacmSecurityToGroupTable makes it impossible for a (vacmSecurityModel, vacmSecurityName) tuple to map to more than one group.
Actions upon Session Termination Indication
Whenever a RADIUS (or other AAA) authenticated session ends for any reason, an indication is provided. This indication MUST provide means of determining the SnmpSecurityModel, and an identifier for the transport session tied to the AAA authorization. The manner in which this occurs is implementation dependent.
Deletion of Entries from vacmAaaSecurityToGroupTable
Entries in the vacmAaaSecurityToGroupTable MUST NOT persist across system reboots.
When a session has been terminated, the vacmAaaSecurityToGroupTable is searched for a corresponding entry. A "matching" entry is any entry for which the SnmpSecurityModel and session ID match the information associated with the session termination indication. Any matching entries are deleted. It is possible that no entries will match; this is not an error, and no special processing is required in this case.
Deletion of Entries from vacmSecurityToGroupTable
Whenever the last remaining row bearing a particular (vacmAaaSecurityModel, vacmAaaSecurityName) pair is deleted from the vacmAaaSecurityToGroupTable, the vacmSecurityToGroupTable is examined for a corresponding row. If one exists, and if its StorageType is "volatile" and its RowStatus is "active", that row MUST be deleted as well. The mechanism to accomplish this task is implementation dependent.
Definitions
SNMP-VACM-AAA-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF MODULE-IDENTITY, OBJECT-TYPE, mib-2, Unsigned32 FROM SNMPv2-SMI SnmpAdminString, SnmpSecurityModel FROM SNMP-FRAMEWORK-MIB;
vacmAaaMIB MODULE-IDENTITY
LAST-UPDATED "201012090000Z" -- 9 December 2010 ORGANIZATION "ISMS Working Group" CONTACT-INFO "WG-email: [email protected]"
DESCRIPTION "The management and local datastore information definitions for the AAA-Enabled View-based Access Control Model for SNMP.
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info).
This version of this MIB module is part of RFC 6065; see the RFC itself for full legal notices."
REVISION "201012090000Z" DESCRIPTION "Initial version, published as RFC 6065."
::= { mib-2 199 }
vacmAaaMIBObjects OBJECT IDENTIFIER ::= { vacmAaaMIB 1 }
vacmAaaMIBConformance OBJECT IDENTIFIER ::= { vacmAaaMIB 2 }
vacmAaaSecurityToGroupTable OBJECT-TYPE
SYNTAX SEQUENCE OF VacmAaaSecurityToGroupEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "This table provides a listing of all currently active sessions for which a mapping of the combination of SnmpSecurityModel and securityName into the name of a VACM group has been provided by an AAA service. The group name (in VACM) in turn identifies an access control policy to be used for the corresponding principals." REFERENCE "RFC 3411, Section 3.2.2, defines securityName." ::= { vacmAaaMIBObjects 1 }
vacmAaaSecurityToGroupEntry OBJECT-TYPE
SYNTAX VacmAaaSecurityToGroupEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "An entry in this table maps the combination of a SnmpSecurityModel and securityName into the name of a VACM group defining the access control policy that is to govern a particular session.
Each entry corresponds to a session.
Entries do not persist across reboots.
An entry is created whenever an indication occurs that a new session has been established that would not have the same index values as an existing entry.
When a session is torn down, disconnected, timed out (e.g., following the RADIUS Session-Timeout Attribute), or otherwise terminated for any reason, the corresponding vacmAaaSecurityToGroupEntry is deleted." REFERENCE "RFC 3411, Section 3.2.2, defines securityName." INDEX { vacmAaaSecurityModel, vacmAaaSecurityName, vacmAaaSessionID } ::= { vacmAaaSecurityToGroupTable 1 }
VacmAaaSecurityToGroupEntry ::= SEQUENCE
{ vacmAaaSecurityModel SnmpSecurityModel, vacmAaaSecurityName SnmpAdminString, vacmAaaSessionID Unsigned32, vacmAaaGroupName SnmpAdminString }
vacmAaaSecurityModel OBJECT-TYPE
SYNTAX SnmpSecurityModel(1..2147483647) MAX-ACCESS not-accessible STATUS current DESCRIPTION "The security model associated with the AAA binding represented by this entry.
This object cannot take the 'any' (0) value." ::= { vacmAaaSecurityToGroupEntry 1 }
vacmAaaSecurityName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32)) MAX-ACCESS not-accessible STATUS current DESCRIPTION "The securityName of the principal associated with the AAA binding represented by this entry. In RADIUS environments, this corresponds to the User-Name Attribute." REFERENCE "RFC 3411, Section 3.2.2, defines securityName, and RFC 2865, Section 5.1, defines User-Name." ::= { vacmAaaSecurityToGroupEntry 2 }
vacmAaaSessionID OBJECT-TYPE
SYNTAX Unsigned32 MAX-ACCESS not-accessible STATUS current DESCRIPTION "An implementation-dependent identifier of the session.
This value MUST be unique among all currently open sessions of all of this SNMP engine's transport models. The value has no particular significance other than to distinguish sessions.
Implementations in which tmSessionID has a compatible syntax and is unique across all transport models MAY use that value." REFERENCE "The Abstract Service Interface parameter tmSessionID is defined in RFC 5590, Section 5.2.4." ::= { vacmAaaSecurityToGroupEntry 3 }
vacmAaaGroupName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32)) MAX-ACCESS read-only STATUS current DESCRIPTION "The name of the group to which this entry is to belong. In RADIUS environments, this comes from the RADIUS Management-Policy-Id Attribute.
When the appropriate conditions are met, the value of this object is applied the vacmGroupName in the corresponding vacmSecurityToGroupEntry." REFERENCE "RFC 3415" ::= { vacmAaaSecurityToGroupEntry 4 }
-- Conformance information ******************************************
vacmAaaMIBCompliances
OBJECT IDENTIFIER ::= {vacmAaaMIBConformance 1}
vacmAaaMIBGroups
OBJECT IDENTIFIER ::= {vacmAaaMIBConformance 2}
-- compliance statements
vacmAaaMIBBasicCompliance MODULE-COMPLIANCE
STATUS current DESCRIPTION "The compliance statement for SNMP engines implementing the AAA-Enabled View-based Access Control Model for SNMP." MODULE -- this module MANDATORY-GROUPS { vacmAaaGroup }
::= { vacmAaaMIBCompliances 1 }
-- units of conformance
vacmAaaGroup OBJECT-GROUP
OBJECTS { vacmAaaGroupName } STATUS current DESCRIPTION "A collection of objects for supporting the use of AAA services to provide user-to-group mappings for VACM." ::= { vacmAaaMIBGroups 1 }
END
Security Considerations
The algorithms in this memo make heuristic use of the StorageType of entries in the vacmSecurityToGroupTable to distinguish those provisioned by a security administrator (which would presumably not be configured as "volatile") from those dynamically generated. In making this distinction, it assumes that those entries explicitly provisioned by a security administrator and given a non-"volatile" status are not to be dynamically overridden. Furthermore, it assumes that any active entries with "volatile" status can be treated as dynamic, and deleted or updated as needed. Users of this memo need to be aware of this operational assumption, which, while reasonable, is not necessarily universally valid. For example, this situation could also occur if the SNMP security administrator had mistakenly created these non-volatile entries in error.
The design of VACM ensures that if an unknown policy (group name) is used in the vacmSecurityToGroupTable, no access is granted. A consequence of this is that no matter what information is provided by the AAA server, no user can gain SNMP access rights not already granted to some group through the VACM configuration.
Principal Identity Naming
In order to ensure that the access control policy ultimately applied as a result of the mechanisms described here is indeed the intended policy for a given principal using a particular security model, care needs to be applied in the mapping of the authenticated user (principal) identity to the securityName used to make the access control decision. Broadly speaking, there are two approaches to ensure consistency of identity:
o Entries for the vacmSecurityToGroupTable corresponding to a given
security model are created only through the operation of the procedures described in this memo. A consequence of this would be that all such entries would have been created using the RADIUS User-Name (or other AAA-authenticated identity) and RADIUS Management-Policy-Id Attribute (or equivalent).
o Administrative policy allows a matching pre-configured entry to
exist in the vacmSecurityToGroupTable, i.e., an entry with the corresponding vacmSecurityModel and with a vacmSecurityName matching the authenticated principal's RADIUS User-Name. In this case, administrative policy also needs to ensure consistency of identity between each authenticated principal's RADIUS User-Name and the administratively configured vacmSecurityName in the vacmSecurityToGroupTable row entries for that particular security model.
In the latter case, inconsistent re-use of the same name for different entities or individuals (principals) can cause the incorrect access control policy to be applied for the authenticated principal, depending on whether the policy that is configured using SNMP or the policy that is applied using the procedures of this memo is the intended policy. This may result in greater or lesser access rights than the administrative policy intended. Inadvertent misidentification in such cases may be undetectable by the SNMP engine or other software elements of the managed entity.
Management Information Considerations
There are no management objects defined in this MIB module that have a MAX-ACCESS clause of read-write and/or read-create. So, if this MIB module is implemented correctly, then there is no risk that an intruder can alter or create any management objects of this MIB module via direct SNMP SET operations.
Some of the readable objects in this MIB module (including some objects with a MAX-ACCESS of not-accessible, whose values are exposed as a result of access to indexed objects) 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:
o vacmAaaSecurityToGroupTable - the entire table is potentially
sensitive, since walking the table will reveal user names, security models in use, session identifiers, and group names;
o vacmAaaSecurityModel - though not-accessible, this is exposed as
an index of vacmAaaGroupName;
o vacmAaaSecurityName - though not-accessible, this is exposed as an
index of vacmAaaGroupName;
o vacmAaaSessionID - though not-accessible, this is exposed as an
index of vacmAaaGroupName;
o vacmAaaGroupName - since this identifies a security policy and
associates it with a particular user, this is potentially sensitive.
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.
10. IANA Considerations
The MIB module in this document uses the following IANA-assigned OBJECT IDENTIFIER value recorded in the SMI Numbers registry:
Descriptor OBJECT IDENTIFIER value ---------- ----------------------- vacmAaaMIB { mib-2 199 }
11. Contributors
The following participants from the ISMS working group contributed to the development of this document:
o Andrew Donati
o David Harrington
o Jeffrey Hutzelman
o Juergen Schoenwaelder
o Tom Petch
o Wes Hardaker
During the IESG review, additional comments were received from:
o Adrian Farrel
o Amanda Baber
o Dan Romescanu
o David Kessens
o Francis Dupont
o Glenn Keeni
o Jari Arkko
o Joel Jaeggli
o Magnus Nystrom
o Mike Heard
o Robert Story
o Russ Housley
o Sean Turner
o Tim Polk
12. References
12.1. Normative References
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
RFC2578 McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
RFC2579 McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "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.
RFC2865 Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC 2865, 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.
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.
RFC5590 Harrington, D. and J. Schoenwaelder, "Transport Subsystem
for the Simple Network Management Protocol (SNMP)", RFC 5590, June 2009.
RFC5607 Nelson, D. and G. Weber, "Remote Authentication Dial-In
User Service (RADIUS) Authorization for Network Access Server (NAS) Management", RFC 5607, July 2009.
RFC5608 Narayan, K. and D. Nelson, "Remote Authentication Dial-In
User Service (RADIUS) Usage for Simple Network Management Protocol (SNMP) Transport Models", RFC 5608, August 2009.
12.2. Informative References
RFC3410 Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet- Standard Management Framework", RFC 3410, December 2002.
RFC5592 Harrington, D., Salowey, J., and W. Hardaker, "Secure
Shell Transport Model for the Simple Network Management Protocol (SNMP)", RFC 5592, June 2009.
Authors' Addresses
Kaushik Narayan Cisco Systems, Inc. 10 West Tasman Drive San Jose, CA 95134 USA
Phone: +1 408-526-8168 EMail: [email protected]
David Nelson Elbrys Networks, Inc. 282 Corporate Drive, Unit #1, Portsmouth, NH 03801 USA
Phone: +1 603-570-2636 EMail: [email protected]
Randy Presuhn (editor) San Jose, CA 95120 USA
EMail: [email protected]