Network Working Group                                         K. Narayan
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                               D. Nelson
Expires: January 7, 2011                           Elbrys Networks, Inc.
                                                         R. Presuhn, Ed.
                                                                    None
                                                            July 6, 2010


    Using Authentication, Authorization, and Accounting services to
  Dynamically Provision View-based Access Control Model  User-to-Group
                                Mappings
                   draft-ietf-isms-radius-vacm-07.txt

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).

   Comments are solicited and should be addressed to the working group's
   mailing list at isms@ietf.org.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 7, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The Internet-Standard Management Framework . . . . . . . . . .  3
   3.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     4.1.  Using AAA services with SNMP . . . . . . . . . . . . . . .  3
     4.2.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  4
   5.  Structure of the MIB Module  . . . . . . . . . . . . . . . . .  5
     5.1.  Textual Conventions  . . . . . . . . . . . . . . . . . . .  5
     5.2.  The Table Structure  . . . . . . . . . . . . . . . . . . .  5
   6.  Relationship to Other MIB Modules  . . . . . . . . . . . . . .  6
     6.1.  Relationship to the VACM MIB . . . . . . . . . . . . . . .  6
     6.2.  MIB modules required for IMPORTS . . . . . . . . . . . . .  6
   7.  Elements of Procedure  . . . . . . . . . . . . . . . . . . . .  6
     7.1.  Sequencing Requirements  . . . . . . . . . . . . . . . . .  6
     7.2.  Actions Upon Session Establishment Indication  . . . . . .  7
       7.2.1.  Creation of Entries in vacmAaaSecurityToGroupTable . .  7
       7.2.2.  Creation of Entries in vacmSecurityToGroupTable  . . .  8
       7.2.3.  Update of vacmGroupName  . . . . . . . . . . . . . . .  8
     7.3.  Actions Upon Session Termination Indication  . . . . . . .  8
       7.3.1.  Deletion of Entries from
               vacmAaaSecurityToGroupTable  . . . . . . . . . . . . .  9
       7.3.2.  Deletion of Entries from vacmSecurityToGroupTable  . .  9
   8.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     12.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17








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1.  Introduction

   This memo specifies a way to simplify the administration of the
   access rights granted to users of network management data.  It
   functions to dynamically provision selected View-Based Access Control
   Model (VACM) [RFC3415] MIB objects, based on information received
   from an Authentication, Authorization, and Accounting (AAA) service,
   such as RADIUS [RFC2865].

   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.


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", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


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.



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   The use case assumption here is that roles within an organization,
   which are reflected in VACM as groups and rules, 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 rules 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].

   The tmSessionID (along with its transport model prefix) [RFC5590] is
   a suitable identifier for a AAA-authorized "session".  This is
   because tmSessionID and tmSecurityName, assigned by a AAA-aware
   transport model, identify a specific transport session authorized to
   offer SNMP service, for which a principal has been AAA-authenticated.
   When a RADIUS-Management-Policy-ID Attribute (or equivalent) is bound
   to such a transport 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 behaviour.

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:




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   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, identified using a SecurityName, and
      provide the corresponding value of vacmGroupName to be used, based
      on information provided by the AAA service in use;

   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 a GroupName;

   o  the service provides an authenticated principal identifier (e.g.,
      the RADIUS User-Name Attribute [RFC2865]) which can be transformed
      to an equivalent principal identifier in the form of a
      SecurityName.


5.  Structure of the MIB Module

5.1.  Textual Conventions

   This MIB module makes use of the SnmpAdminString and
   SnmpSecurityModel 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.  This index structure was chosen to support use cases
   in which a given user could potentially have multiple concurrent
   sessions, and to support environments in which multiple security
   models might find concurrent usage.







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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].  The module also relies on the IANA registry defined in
   [RFC5590] for transport domain prefixes.


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-specific error cases not
   spelled out here, such as running out of memory.  By their nature,
   recovery in such cases will be implementation-specific.  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 critically 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 an SNMP Security Name
   [RFC3411].




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   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 is invoked for any SNMP
   PDUs from that session.

   If a session termination indication occurs before all invocations of
   the IsAccessAllowed() abstract service interface 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

   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 or equivalent;

   o  a session identifier, such as tmSessionID [RFC5590] along with the
      prefix for its transport domain, as a definitive identifier of the
      transport session that the AAA authorization is tied to;

   o  the RADIUS Management-Policy-Id Attribute or equivalent

   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.

7.2.1.  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;

   o  vacmAaaTransportModel = the one- to four-character registered
      prefix of the transport domain [RFC5590]




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   o  vacmAaaTransportSessionID = unique (at least within the the scope
      of a transport model) session identifier

   o  vacmAaaGroupName = RADIUS Management-Policy-Id Attribute or
      equivalent

   Otherwise, if the row already exists, update the vacmAaaGroupName
   with the value supplied.

7.2.2.  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
   vacmSecurityToGroupStorageType, and a value of "active" for
   vacmSecurityToGroupStatus.

   If a corresponding entry already exists in the
   vacmSecurityToGroupTable, and the row's StorageType is anything other
   than "volatile", or the RowStatus is anything other than "active",
   then a role (group) mapping for this user (principal) has already
   been put in place on this system, and will not be overridden.

7.2.3.  Update of vacmGroupName

   Whenever the value of an instance of vacmAaaGroupName is updated, if
   a corresponding entry exists in the vacmSecurityToGroupTable, and
   vacmSecurityToGroupStorageType is "volatile" and
   vacmSecurityToGroupStatus is "active", update the value of
   vacmGroupName with the value from vacmAaaGroupName.

   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 value being provided by RADIUS (or
   other 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
   supercede the one currently held there.

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



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   means of determining the SnmpSecurityModel, transport domain prefix,
   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, transport domain prefix, 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.

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
   specific.


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;

  snmpVacmAaaMIB    MODULE-IDENTITY
      LAST-UPDATED "201007040000Z"          -- 4 July, 2010
      ORGANIZATION "ISMS Working Group"
      CONTACT-INFO "WG-email:   isms@ietf.org"




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      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 XXXX;
                    see the RFC itself for full legal notices."

      REVISION "201007040000Z"
      DESCRIPTION "Initial version, published as RFC XXXX."
       ::= { mib-2 XXX }

  vacmAaaMIBObjects   OBJECT IDENTIFIER ::= { snmpVacmAaaMIB 1 }

  vacmAAAMIBConformance OBJECT IDENTIFIER ::= {snmpVacmAaaMIB 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 a GroupName has been provided
                   by an AAA service.  The GroupName (in VACM)
                   in turn identifies an access control policy
                   to be used for  the corresponding principals."
      ::= { 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 a GroupName
                   for a particular session.




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                   Each entry corresponds to a session.

                   Entries do not persist across reboots.

                   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."
      INDEX       {
                    vacmAaaSecurityModel,
                    vacmAaaSecurityName,
                    vacmAaaTransportModel,
                    vacmAaaTransportSessionID
                  }
      ::= { vacmAaaSecurityToGroupTable 1 }

  VacmAaaSecurityToGroupEntry ::= SEQUENCE
      {
          vacmAaaSecurityModel            SnmpSecurityModel,
          vacmAaaSecurityName             SnmpAdminString,
          vacmAaaTransportModel           SnmpAdminString,
          vacmAaaTransportSessionID       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 Security Name of the principal associated with
                   the AAA binding represented by this entry.
                   In RADIUS environments, this corresponds to
                   the User-Name Attribute."
      ::= { vacmAaaSecurityToGroupEntry 2 }

  vacmAaaTransportModel     OBJECT-TYPE
      SYNTAX       SnmpAdminString (SIZE(1..4))
      MAX-ACCESS   not-accessible



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      STATUS       current
      DESCRIPTION "The prefix of this session's transport domain."
      ::= { vacmAaaSecurityToGroupEntry 3 }

  vacmAaaTransportSessionID OBJECT-TYPE
      SYNTAX       Unsigned32
      MAX-ACCESS   not-accessible
      STATUS       current
      DESCRIPTION "A specific identifier of the session.
                   This value MUST be unique among all
                   currently open sessions within a transport model.
                   The value has no particular significance other
                   to distinguish sessions.  An example of a suitable
                   value would be tmSessionID."
      ::= { vacmAaaSecurityToGroupEntry 4 }

  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.

                   This group name is used to set the vacmGroupName
                   in the corresponding vacmSecurityToGroupEntry."
      ::= { vacmAaaSecurityToGroupEntry 5 }


  -- 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 which
                   implement the Extensions to the View-based Access
                   Control Model for use with RADIUS."
      MODULE    -- this module
          MANDATORY-GROUPS { vacmAaaGroup }

      ::= { vacmAaaMIBCompliances 1 }



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  -- 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 / group
                   mappings for VACM."
      ::= { vacmAaaMIBGroups 1 }


  END


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 over-ridden.  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.

   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



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      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 later 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 configured using SNMP, or the policy
   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 mis-identification in
   such cases may be undetectable by the SNMP engine or other software
   elements of the managed entity.

   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 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



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   o  vacmAaaTransportSessionID - 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
      ----------        -----------------------
      snmpVacmAaaMIB    { mib-2 XXX }


   Editor's Note (to be removed prior to publication): the IANA is
   requested to assign a value for "XXX" under the 'mib-2' subtree and
   to record the assignment in the SMI Numbers registry.  When the
   assignment has been made, the RFC Editor is asked to replace "XXX"
   (here and in the MIB module) with the assigned value and to remove
   this note.






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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


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



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              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: 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





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   Randy Presuhn (editor)
   None
   San Jose, CA  95120
   USA

   Email: randy_presuhn@mindspring.com













































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