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Network Working Group                                         K. NarayanRequest for Comments: 5608                           Cisco Systems, Inc.Category: Standards Track                                      D. Nelson                                                   Elbrys Networks, Inc.                                                             August 2009Remote Authentication Dial-In User Service (RADIUS) Usage forSimple Network Management Protocol (SNMP) Transport ModelsAbstract   This memo describes the use of a Remote Authentication Dial-In User   Service (RADIUS) authentication and authorization service with Simple   Network Management Protocol (SNMP) secure Transport Models to   authenticate users and authorize creation of secure transport   sessions.  While the recommendations of this memo are generally   applicable to a broad class of SNMP Transport Models, the examples   focus on the Secure Shell (SSH) Transport Model.Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents in effect on the date of   publication of this document (http://trustee.ietf.org/license-info).   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it mayNarayan & Nelson            Standards Track                     [Page 1]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Table of Contents1. Introduction ....................................................21.1. General ....................................................21.2. Requirements Language ......................................31.3. System Block Diagram .......................................31.4. RADIUS Operational Model ...................................31.5. RADIUS Usage with Secure Transports ........................51.6. Domain of Applicability ....................................51.7. SNMP Transport Models ......................................62. RADIUS Usage for SNMP Transport Models ..........................72.1. RADIUS Authentication for Transport Protocols ..............82.2. RADIUS Authorization for Transport Protocols ...............82.3. SNMP Service Authorization .................................93. Table of Attributes ............................................114. Security Considerations ........................................125. Acknowledgements ...............................................136. References .....................................................136.1. Normative References ......................................136.2. Informative References ....................................131.  Introduction1.1.  General   This memo describes the use of a Remote Authentication Dial-In User   Service (RADIUS) authentication and authorization service by Simple   Network Management Protocol (SNMP) secure Transport Models to   authenticate users and authorize creation of secure transport   sessions.  While the recommendations of this memo are generally   applicable to a broad class of SNMP Transport Models, the examples   focus on the Secure Shell Transport Model.   In the context of this document, a Network Access Server (NAS) is a   network device or host that contains an SNMP engine implementation,   utilizing SNMP Transport Models.  It is customary in SNMP documents   to indicate which subsystem performs specific processing tasks.  In   this document, we leave such decisions to the implementer, as is   customary for RADIUS documents, and simply specify NAS behavior.   Such processing would quite likely be implemented in the secure   transport module.Narayan & Nelson            Standards Track                     [Page 2]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 20091.2.  Requirements Language   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 [RFC2119].1.3.  System Block Diagram   A block diagram of the major system components referenced in this   document may be useful to understanding the text that follows.                                         +--------+              +......................... |RADIUS  |....+              .                          |Server  |    .            Shared                       +--------+    .            User                             |         .            Credentials             RADIUS   |      Shared              .                              |      RADIUS              .                              |      Secret              .                              |         .     +-------------+                  +-----------------+     | Network     |                  | RADIUS Client / |     | Management  |       SNMP       | SNMP Engine /   |     | Application |------------------| Network Device  |     +-------------+       SSH        +-----------------+                               Block Diagram   This diagram illustrates that a network management application   communicates with a network device, the managed entity, using SNMP   over SSH.  The network devices uses RADIUS to communicate with a   RADIUS server to authenticate the network management application (or   the user whose credentials that application provides) and to obtain   authorization information related to access via SNMP for purpose of   device management.  Other secure transport protocols might be used   instead of SSH.1.4.  RADIUS Operational Model   The RADIUS protocol [RFC2865] provides authentication and   authorization services for network access devices, usually referred   to as a Network Access Server (NAS).  The RADIUS protocol operates,   at the most simple level, as a request-response mechanism.  RADIUS   clients, within the NAS, initiate a transaction by sending a RADIUS   Access-Request message to a RADIUS server, with which the client   shares credentials.  The RADIUS server will respond with either an   Access-Accept message or an Access-Reject message.Narayan & Nelson            Standards Track                     [Page 3]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   RADIUS supports authentication methods compatible with plaintext   username and password mechanisms, MD5 Challenge/Response mechanisms,   Extensible Authentication Protocol (EAP) mechanisms, and HTTP Digest   mechanisms.  Upon presentation of identity and credentials, the user   is either accepted or rejected.  RADIUS servers indicate a successful   authentication by returning an Access-Accept message.  An Access-   Reject message indicates unsuccessful authentication.   Access-Accept messages are populated with one or more service   provisioning attributes, which control the type and extent of service   provided to the user at the NAS.  The authorization portion may be   thought of as service provisioning.  Based on the configuration of   the user's account on the RADIUS server, upon authentication, the NAS   is provided with instructions as to what type of service to provide   to the user.  When that service provisioning does not match the   capabilities of the NAS, or of the particular interface to the NAS   over which the user is requesting access,RFC 2865 [RFC2865] requires   that the NAS MUST reject the access request.RFC 2865 describes   service provisioning attributes for management access to a NAS, as   well as various terminal emulation and packet forwarding services on   the NAS.  This memo describes specific RADIUS service provisioning   attributes that are useful with secure transports and SNMP Transport   Models.   RADIUS servers are often deployed on an enterprise-wide or   organization-wide basis, covering a variety of disparate use cases.   In such deployments, all NASes and all users are serviced by a common   pool of RADIUS servers.  In many deployments, the RADIUS server will   handle requests from many different types of NASes with different   capabilities, and different types of interfaces, services, and   protocol support.   In order for a RADIUS server to make the correct authorization   decision in all cases, the server will often need to know something   about the type of NAS at which the user is requesting access, the   type of service that the user is requesting, and the role of the user   in the organization.  For example, many users may be authorized to   receive network access via a Remote Access Server (RAS), Virtual   Private Network (VPN) server, or LAN access switch.  Typically only a   small sub-set of all users are authorized to access the   administrative interfaces of network infrastructure devices, e.g.,   the Command Line Interface (CLI) or SNMP engine of switches and   routers.   In order for the RADIUS server to have information regarding the type   of access being requested, it is common for the NAS (i.e., the RADIUS   client) to include "hint" attributes in the RADIUS Access-Request   message, describing the NAS and the type of service being requested.Narayan & Nelson            Standards Track                     [Page 4]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   This document recommends appropriate "hint" attributes for the SNMP   service type.1.5.  RADIUS Usage with Secure Transports   Some secure transport protocols that can be used with SNMP Transport   Models have defined authentication protocols supporting several   authentication methods.  For example, the Secure Shell (SSH)   Authentication protocol [RFC4252] supports multiple methods   (including public key, password, and host-based) to authenticate SSH   clients.   SSH Server integration with RADIUS traditionally uses the username   and password mechanism.   Secure transport protocols do not, however, specify how the transport   interfaces to authentication clients, leaving such as implementation   specific.  For example, the "password" method of SSH authentication   primarily describes how passwords are acquired from the SSH client   and transported to the SSH server, the interpretation of the password   and validation against password databases is left to SSH server   implementations.  SSH server implementations often use the Pluggable   Authentication Modules [PAM] interface provided by operating systems   such as Linux and Solaris to integrate with password-based network   authentication mechanisms such as RADIUS, TACACS+ (Terminal Access   Controller Access-Control System Plus), Kerberos, etc.   Secure transports do not typically specify how to utilize   authorization information obtained from a AAA service, such as   RADIUS.  More often, user authentication is sufficient to cause the   secure transport server to begin delivering service to the user.   Access control in these situations is supplied by the application to   which the secure transport server session is attached.  For example,   if the application is a Linux shell, the user's access rights are   controlled by that user account's group membership and the file   system access protections.  This behavior does not closely follow the   traditional service provisioning model of AAA systems, such as   RADIUS.1.6.  Domain of Applicability   Most of the RADIUS Attributes referenced in this document have broad   applicability for provisioning remote management access to NAS   devices using SNMP.  However, the selection of secure transport   protocols has special considerations.  This document does not specify   details of the integration of secure transport protocols with a   RADIUS client in the NAS implementation.  However, there are   functional requirements for correct application of framed managementNarayan & Nelson            Standards Track                     [Page 5]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   protocols and secure transport protocols that will limit the   selection of such protocols that can be considered for use with   RADIUS.  Since the RADIUS user credentials are obtained by the RADIUS   client from the secure transport protocol server, or in some cases   directly from the SNMP engine, the secure transport protocol, and its   implementation in the NAS, MUST support forms of credentials that are   compatible with the authentication methods supported by RADIUS.   RADIUS currently supports the following user authentication methods,   although others may be added in the future:   o  Password -RFC 2865   o  CHAP (Challenge Handshake Authentication Protocol) -RFC 2865   o  ARAP (Apple Remote Access Protocol) -RFC 2869   o  EAP (Extensible Authentication Protocol) -RFC 2869,RFC 3579   o  HTTP Digest -RFC 5090   The secure transport protocols selected for use with RADIUS and SNMP   obviously need to support user authentication methods that are   compatible with those that exist in RADIUS.  The RADIUS   authentication methods most likely usable with these protocols are   Password, CHAP, and possibly HTTP Digest, with Password being the   distinct common denominator.  There are many secure transports that   support other, more robust, authentication mechanisms, such as public   key.  RADIUS has no support for public key authentication, except   within the context of an EAP Method.  The applicability statement for   EAP indicates that it is not intended for use as an application-layer   authentication mechanism, so its use with the mechanisms described in   this document is NOT RECOMMENDED.  In some cases, Password may be the   only compatible RADIUS authentication method available.1.7.  SNMP Transport Models   The Transport Subsystem for SNMP [RFC5590] defines a mechanism for   providing transport layer security (TLS) for SNMP, allowing protocols   such as SSH and TLS to be used to secure SNMP communication.  The   Transport Subsystem allows the modular definition of Transport Models   for multiple secure transport protocols.  Transport Models rely upon   the underlying secure transport for user authentication services.   The Transport Model (TM) then maps the authenticated identity to a   model-independent principal, which it stores in the tmStateReference.   When the selected security model is the Transport Security Model   (TSM), the expected behavior is for the securityName to be set by theNarayan & Nelson            Standards Track                     [Page 6]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   TSM from the authenticated principal information stored in the   tmStateReference by the TM.   The Secure Shell protocol provides a secure transport channel with   support for channel authentication via local accounts and integration   with various external authentication and authorization services such   as RADIUS, Kerberos, etc.  The Secure Shell Transport Model [RFC5592]   defines the use of the Secure Shell protocol as the basis for a   Transport Model.2.  RADIUS Usage for SNMP Transport Models   There are two use cases for RADIUS support of management access via   SNMP.  These are (a) service authorization and (b) access control   authorization.  RADIUS almost always involves user authentication as   prerequisite to authorization, and there is a user authentication   phase for each of these two use cases.  The first use case is   discussed in detail in this memo, while the second use case is a   topic of current research, and beyond the scope of this document.   This document describes the way in which RADIUS attributes and   messages are applied to the specific application area of SNMP   Transport Models.  User authentication and service authorization via   RADIUS are undertaken by the secure transport module, that underlies   the SNMP Transport Model.   User authentication for SNMP Transport Models has the same syntax and   semantics as user authentication for any other network service.  In   the context of SNMP, the "user" is thought of as a "principal" and   may represent a host, an application, or a human.   Service authorization allows a RADIUS server to authorize an   authenticated principal to use SNMP, optionally over a secure   transport, typically using an SNMP Transport Model.  This memo   describes mechanisms by which such information can be requested from   a RADIUS server and enforced within the NAS.  An SNMP architecture,   [RFC3411], does not make a distinction between user authentication   and service authorization.  In the case of existing, deployed   security models, such as the User-based Security Model (USM), this   distinction is not significant.  For SNMP Transport Models, this   distinction is relevant and important.   It is relevant because of the way in which SSH implementations have   traditionally integrated with RADIUS clients.  Those SSH   implementations traditionally seek to obtain user authentication   (e.g., validation of a username and password) from an outside   authentication service, often via a PAM-style interface.  The service   authorization in traditional SSH server implementations comes via the   restrictions that the operating system (OS) shell (and file system,Narayan & Nelson            Standards Track                     [Page 7]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   etc.) place on the user by means of access controls tied to the   username or the username's membership in various user groups.  These   OS-style access controls are distinct from the service provisioning   features of RADIUS.  If we wish to use existing SSH server   implementations, or slightly adapt them, for use with SNMP Transport   Models, and we wish to support RADIUS-provisioned service   authorization, we need to be aware that the RADIUS service   authorization information will need to be obtained by the relevant   SNMP models from the SSH module.   One reason that RADIUS-provisioned service authorization is important   is that in many deployments, the RADIUS server's back-end   authentication database contains credentials for many classes of   users, only a small portion of which may be authorized to access the   management interfaces of managed entities (NASes) via SNMP.  This is   in contrast to the way USM for SNMP works, in which all principals   entered to the local configuration data-store are authorized for   access to the managed entity.  In the absence of RADIUS-provisioned   service authorization, network management access may be granted to   unauthorized, but properly authenticated, users.  With SNMPv3, an   appropriately configured Access Control Model would serve to   alleviate the risk of unauthorized access.2.1.  RADIUS Authentication for Transport Protocols   This document will rely on implementation specific integration of the   transport protocols with RADIUS clients for user authentication.   It is REQUIRED that the integration of RADIUS clients with transport   protocols utilize appropriate "hint" attributes in RADIUS Access-   Request messages, to signal to the RADIUS server the type of service   being requested over the transport session.  Specific attributes for   use with SNMP Transport Models are recommended in this document.   RADIUS servers, compliant to this specification, MAY use RADIUS   "hint" attributes, as described herein, to inform the decision   whether to accept or reject the authentication request.2.2.  RADIUS Authorization for Transport Protocols   In compliance withRFC 2865, NASes MUST enforce implicitly mandatory   attributes, such as Service-Type, within an Access-Accept message.   NASes MUST treat Access-Accept messages that attempt to provision   unsupported services as if they were an Access-Reject.  NASes SHOULD   treat unknown attributes as if they were provisioning unsupported   services.  See [RFC5080] for additional details.Narayan & Nelson            Standards Track                     [Page 8]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   A NAS that is compliant to this specification MUST treat any RADIUS   Access-Accept message that provisions a level of transport protection   (e.g., SSH) that cannot be provided, and/or application service   (e.g., SNMP) that cannot be provided over that transport, as if an   Access-Reject message had been received instead.  The RADIUS Service-   Type Attribute is the primary indicator of the service being   provisioned, although other attributes may also convey service   provisioning information.   For traditional SSH usage, RADIUS servers typically provision   management access service, as SSH is often used to access the command   line shell of a host system, e.g., the NAS.RFC 2865 defines two   types of management access service attributes, one for privileged   access to the Command Line Interface (CLI) of the NAS and one for   non-privileged CLI access.  These traditional management access   services are not used with SNMP.  [RFC5607] describes further RADIUS   service provisioning attributes for management access to the NAS,   including SNMP access.2.3.  SNMP Service Authorization   The Transport Subsystem for SNMP [RFC5590] defines the notion of a   session, although the specifics of how sessions are managed is left   to Transport Models.  The Transport Subsystem defines some basic   requirements for transport protocols around creation and deletion of   sessions.  This memo specifies additional requirements for transport   protocols during session creation and for session termination.   RADIUS servers compliant to this specification MUST use RADIUS   service provisioning attributes, as described herein, to specify SNMP   access over a secure transport.  Such RADIUS servers MAY use RADIUS   "hint" attributes included in the Access-Request message, as   described herein, in determining what, if any, service to provision.   NASes compliant to this specification MUST use RADIUS service   provisioning attributes, as described in this section, when they are   present in a RADIUS Access-Accept message, to determine whether the   session can be created, and they MUST enforce the service   provisioning decisions of the RADIUS server.   The following RADIUS attributes MUST be used, as "hint" attributes   included in the Access-Request message to signal use of SNMP over a   secure transport (i.e., authPriv) to the RADIUS server:   1.  Service-Type with a value of Framed-Management.   2.  Framed-Management-Protocol with a value of SNMP.Narayan & Nelson            Standards Track                     [Page 9]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   3.  Management-Transport-Protection with a value of Integrity-       Confidentiality-Protection.   The following RADIUS attributes MUST be used in an Access-Accept   message to provision SNMP over a secure transport that provides both   integrity and confidentiality (i.e., authPriv):   1.  Service-Type with a value of Framed-Management.   2.  Framed-Management-Protocol with a value of SNMP.   3.  Management-Transport-Protection with a value of Integrity-       Confidentiality-Protection.   The following RADIUS attributes MUST be optionally used, to authorize   use of SNMP without protection (i.e., authNoPriv):   1.  Service-Type with a value of Framed-Management.   2.  Framed-Management-Protocol with a value of SNMP.   3.  Management-Transport-Protection with a value of No-Protection.   There are no combinations of RADIUS attributes that denote the   equivalent of SNMP noAuthNoPriv access, as RADIUS always involves the   authentication of a user (i.e., a principal) as a prerequisite for   authorization.  RADIUS can be used to provide an "Authorize-Only"   service, but only when the request contains a "cookie" from a   previous successful authentication with the same RADIUS server (i.e.,   the RADIUS State Attribute).   The following RADIUS attributes are used to limit the extent of a   secure transport session carrying SNMP traffic, in conjunction with   an SNMP Transport Model:   1.  Session-Timeout   2.  Inactivity-Timeout.   Refer to [RFC2865] for a detailed description of these attributes.   The Session-Timeout Attribute indicates the maximum number of seconds   that a session may exist before it is unconditionally disconnected.   The Inactivity-Timeout Attribute indicates the maximum number of   seconds that a transport session may exist without any protocol   activity (messages sent or received) before the session is   disconnected.  These timeouts are enforced by the NAS.Narayan & Nelson            Standards Track                    [Page 10]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 20093.  Table of Attributes   Table 1 provides a guide to which attributes may be found in which   kinds of packets, and in what quantity.   Access-   Request Accept Reject Challenge  #    Attribute   ---------------------------------------------------------------------   0-1     0        0        0       1   User-Name        [RFC2865]   0-1     0        0        0       2   User-Password    [RFC2865]   0-1 *   0        0        0       4   NAS-IP-Address   [RFC2865]   0-1 *   0        0        0      95   NAS-IPv6-Address [RFC3162]   0-1 *   0        0        0      32   NAS-Identifier   [RFC2865]   0-1     0-1      0        0       6   Service-Type     [RFC2865]   0-1     0-1      0        0-1    24   State            [RFC2865]   0       0-1      0        0      27   Session-Timeout  [RFC2865]   0       0-1      0        0      28   Idle-Timeout     [RFC2865]   0-1     0-1      0-1      0-1    80   Message-Authenticator [RFC3579]   0-1     0-1      0        0     133   Framed-Management-Protocol                                          [RFC5607]   0-1     0-1      0        0     134   Management-Transport-Protection                                          [RFC5607]                                  Table 1   Table 2 defines the meaning of the entries in Table 1.   0    This attribute MUST NOT be present in a packet.   0+   Zero or more instances of this attribute MAY be present in        a packet.   0-1  Zero or one instance of this attribute MAY be present in        a packet.   1    Exactly one instance of this attribute MUST be present in        a packet.   *    Only one of these attribute options SHOULD be included.                                  Table 2   SSH integration with RADIUS traditionally uses usernames and   passwords (with the User-Password Attribute), but other secure   transports could use other authentication mechanisms, and would   include RADIUS authentication attributes appropriate for that   mechanism instead of User-Password.   This document does not describe the usage of RADIUS Accounting or   Dynamic RADIUS Re-Authorization.  Such RADIUS usages are not   currently envisioned for SNMP, and are beyond the scope of this   document.Narayan & Nelson            Standards Track                    [Page 11]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 20094.  Security Considerations   This specification describes the use of RADIUS for purposes of   authentication and authorization.  Threats and security issues for   this application are described in [RFC3579] and [RFC3580]; security   issues encountered in roaming are described in [RFC2607].   Additional security considerations for use of SNMP with secure   Transport Models [RFC5590] and the Transport Security Model [RFC5591]   are found in the "Security Considerations" sections of the respective   documents.   If the SNMPv1 or SNMPv2c Security Model is used, then securityName   comes from the community name, as perRFC 3584.  If the User-based   Security Model is selected, then securityName is determined using   USM.  This may not be what is expected when using an SNMP secure   Transport Model with an external authentication service, such as   RADIUS.   Simultaneously using a secure transport with RADIUS authentication   and authorization, and the SNMPv1 or SNMPv2c or USM security models   is NOT RECOMMENDED.  See the "Coexistence, Security Parameters, and   Access Control" section of [RFC5590].   There are good reasons to provision USM access to supplement AAA-   based access, however.  When the network is under duress, or the AAA-   service is unreachable, for any reason, it is important to have   access credentials stored in the local configuration data-store of   the managed entity.  USM credentials are a likely way to fulfill this   requirement.  This is analogous to configuring a local "root"   password in the "/etc/passwd" file of a UNIX workstation, to be used   as a backup means of login, for times when the Network Information   Service (NIS) authentication service is unreachable.   The Message-Authenticator (80) Attribute [RFC3579] SHOULD be used   with RADIUS messages that are described in this memo.  This is useful   because the Message-Authenticator Attribute is the best available   mechanism in RADIUS as it stands today to provide tamper-evident   integrity protection of the service provisioning attributes in an   Access-Accept packet.  It is slightly less important for Access-   Request packets, although it may be desirable to protect any "hint"   attributes contained in those messages.  This protection mitigates   the fact that RADIUS messages are not encrypted and that attributes   could be added, deleted or modified by an adversary in a position to   intercept the packet.Narayan & Nelson            Standards Track                    [Page 12]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 20095.  Acknowledgements   The authors would like to acknowledge the contributions of David   Harrington and Juergen Schoenwaelder for numerous helpful discussions   in this space, and Wes Hardaker for his thoughtful review comments.6.  References6.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,              "Remote Authentication Dial In User Service (RADIUS)",RFC 2865, June 2000.   [RFC5080]  Nelson, D. and A. DeKok, "Common Remote Authentication              Dial In User Service (RADIUS) Implementation Issues and              Suggested Fixes",RFC 5080, December 2007.   [RFC5590]  Harrington, D. and J. Schoenwaelder, "Transport Subsystem              for the Simple Network Management Protocol (SNMP)",RFC 5590, June 2009.   [RFC5591]  Harrington, D. and W. Hardaker, "Transport Security Model              for Simple Network Management Protocol (SNMP)",RFC 5591,              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 2009.6.2.  Informative References   [PAM]      Samar, V. and R. Schemers, "UNIFIED LOGIN WITH PLUGGABLE              AUTHENTICATION MODULES (PAM)", Open GroupRFC 86.0,              October 1995,              <http://www.opengroup.org/rfc/mirror-rfc/rfc86.0.txt>.   [RFC2607]  Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy              Implementation in Roaming",RFC 2607, June 1999.   [RFC3162]  Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6",RFC 3162, August 2001.Narayan & Nelson            Standards Track                    [Page 13]

RFC 5608         RADIUS Usage for SNMP Transport Models      August 2009   [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.   [RFC3579]  Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication              Dial In User Service) Support For Extensible              Authentication Protocol (EAP)",RFC 3579, September 2003.   [RFC3580]  Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,              "IEEE 802.1X Remote Authentication Dial In User Service              (RADIUS) Usage Guidelines",RFC 3580, September 2003.   [RFC4252]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)              Authentication Protocol",RFC 4252, January 2006.   [RFC5592]  Harrington, D., Salowey, J., and W. Hardaker, "Secure              Shell Transport Model for 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   Portsmouth, NH  03801   USA   Phone: +1.603.570.2636   EMail: dnelson@elbrysnetworks.comNarayan & Nelson            Standards Track                    [Page 14]