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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
Narayan, et al. Standards Track [Page 1]
RFC 6065 AAA-Enabled VACM December 2010
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Internet-Standard Management Framework . . . . . . . . . . 3
3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Using AAA services with SNMP . . . . . . . . . . . . . . . 4
4.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 5
5. Structure of the MIB Module . . . . . . . . . . . . . . . . . 6
5.1. Textual Conventions . . . . . . . . . . . . . . . . . . . 6
5.2. The Table Structure . . . . . . . . . . . . . . . . . . . 6
6. Relationship to Other MIB Modules . . . . . . . . . . . . . . 6
6.1. Relationship to the VACM MIB . . . . . . . . . . . . . . . 6
6.2. MIB modules Required for IMPORTS . . . . . . . . . . . . . 6
6.3. Documents Required for REFERENCE Clauses . . . . . . . . . 6
7. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 7
7.1. Sequencing Requirements . . . . . . . . . . . . . . . . . 7
7.2. Actions upon Session Establishment Indication . . . . . . 7
7.2.1. Required Information . . . . . . . . . . . . . . . . . 7
7.2.2. Creation of Entries in vacmAaaSecurityToGroupTable . . 8
7.2.3. Creation of Entries in vacmSecurityToGroupTable . . . 8
7.2.4. Update of vacmGroupName . . . . . . . . . . . . . . . 9
7.3. Actions upon Session Termination Indication . . . . . . . 9
7.3.1. Deletion of Entries from
vacmAaaSecurityToGroupTable . . . . . . . . . . . . . 9
7.3.2. Deletion of Entries from vacmSecurityToGroupTable . . 10
8. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9.1. Principal Identity Naming . . . . . . . . . . . . . . . . 14
9.2. Management Information Considerations . . . . . . . . . . 15
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . . 17
12.2. Informative References . . . . . . . . . . . . . . . . . . 18
Narayan, et al. Standards Track [Page 2]
RFC 6065 AAA-Enabled VACM December 2010
1. 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.
2. 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].
3. 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].
Narayan, et al. Standards Track [Page 3]
RFC 6065 AAA-Enabled VACM December 2010
4. Overview
4.1. 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.
Narayan, et al. Standards Track [Page 4]
RFC 6065 AAA-Enabled VACM December 2010
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.
4.2. 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;
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RFC 6065 AAA-Enabled VACM December 2010
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].
5. Structure of the MIB Module
5.1. Textual Conventions
This MIB module makes use of the SnmpAdminString [RFC3411] and
SnmpSecurityModel [RFC3411] textual conventions.
5.2. 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.
6. 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.
6.1. 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.
6.2. MIB modules Required for IMPORTS
This MIB module employs definitions from [RFC2578], [RFC2579], and
[RFC3411].
6.3. Documents Required for REFERENCE Clauses
This MIB module contains REFERENCE clauses making reference to
[RFC2865], [RFC3411], and [RFC5590].
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7. 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.
7.1. 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.
7.2. Actions upon Session Establishment Indication
7.2.1. 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;
Narayan, et al. Standards Track [Page 7]
RFC 6065 AAA-Enabled VACM December 2010
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.
7.2.2. 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.
7.2.3. 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
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RFC 6065 AAA-Enabled VACM December 2010
entry to fill in vacmGroupName, using a value of "volatile" for the
row's StorageType, and a value of "active" for its RowStatus.
7.2.4. 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.
7.3. 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.
7.3.1. 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.
Narayan, et al. Standards Track [Page 9]
RFC 6065 AAA-Enabled VACM December 2010
7.3.2. 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.
8. 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: isms@ietf.org"
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."
Narayan, et al. Standards Track [Page 10]
RFC 6065 AAA-Enabled VACM December 2010
::= { 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 }
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RFC 6065 AAA-Enabled VACM December 2010
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 }
Narayan, et al. Standards Track [Page 12]
RFC 6065 AAA-Enabled VACM December 2010
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
Narayan, et al. Standards Track [Page 13]
RFC 6065 AAA-Enabled VACM December 2010
9. 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.
9.1. 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.
Narayan, et al. Standards Track [Page 14]
RFC 6065 AAA-Enabled VACM December 2010
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.
9.2. 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.
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RFC 6065 AAA-Enabled VACM December 2010
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
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RFC 6065 AAA-Enabled VACM December 2010
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.
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RFC 6065 AAA-Enabled VACM December 2010
[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.
Narayan, et al. Standards Track [Page 18]
RFC 6065 AAA-Enabled VACM December 2010
Authors' Addresses
Kaushik Narayan
Cisco Systems, Inc.
10 West Tasman Drive
San Jose, CA 95134
USA
Phone: +1 408-526-8168
EMail: kaushik_narayan@yahoo.com
David Nelson
Elbrys Networks, Inc.
282 Corporate Drive, Unit #1,
Portsmouth, NH 03801
USA
Phone: +1 603-570-2636
EMail: d.b.nelson@comcast.net
Randy Presuhn (editor)
San Jose, CA 95120
USA
EMail: randy_presuhn@mindspring.com
Narayan, et al. Standards Track [Page 19]