rfc2741.txt

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Network Working Group                                          M. Daniele
Request for Comments: 2741                    Compaq Computer Corporation
Obsoletes: 2257                                                 B. Wijnen
Category: Standards Track          T.J. Watson Research Center, IBM Corp.
                                                          M. Ellison, Ed.
                                        Ellison Software Consulting, Inc.
                                                        D. Francisco. Ed.
                                                      Cisco Systems, Inc.
                                                             January 2000


                 Agent Extensibility (AgentX) Protocol
                               Version 1

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) The Internet Society (2000).  All Rights Reserved.

Abstract

   This memo defines a standardized framework for extensible SNMP
   agents.  It defines processing entities called master agents and
   subagents, a protocol (AgentX) used to communicate between them, and
   the elements of procedure by which the extensible agent processes
   SNMP protocol messages. This memo obsoletes RFC 2257.

Table of Contents

   1. Introduction.....................................................4
   2. The SNMP Management Framework....................................4
     2.1. A Note on Terminology........................................5
   3. Extending the MIB................................................5
     3.1. Motivation for AgentX........................................6
   4. AgentX Framework.................................................6
     4.1. AgentX Roles.................................................7
     4.2. Applicability................................................8
     4.3. Design Features of AgentX....................................9
     4.4. Non-Goals...................................................10





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   5. AgentX Encodings................................................11
     5.1. Object Identifier...........................................11
     5.2. SearchRange.................................................13
     5.3. Octet String................................................14
     5.4. Value Representation........................................15
   6. Protocol Definitions............................................17
     6.1. AgentX PDU Header...........................................17
       6.1.1. Context.................................................20
     6.2. AgentX PDUs.................................................20
       6.2.1. The agentx-Open-PDU.....................................20
       6.2.2. The agentx-Close-PDU....................................22
       6.2.3. The agentx-Register-PDU.................................23
       6.2.4. The agentx-Unregister-PDU...............................27
       6.2.5. The agentx-Get-PDU......................................29
       6.2.6. The agentx-GetNext-PDU..................................30
       6.2.7. The agentx-GetBulk-PDU..................................32
       6.2.8. The agentx-TestSet-PDU..................................34
       6.2.9. The agentx-CommitSet, -UndoSet, -CleanupSet PDUs........35
       6.2.10. The agentx-Notify-PDU..................................36
       6.2.11. The agentx-Ping-PDU....................................37
       6.2.12. The agentx-IndexAllocate-PDU...........................37
       6.2.13. The agentx-IndexDeallocate-PDU.........................38
       6.2.14. The agentx-AddAgentCaps-PDU............................39
       6.2.15. The agentx-RemoveAgentCaps-PDU.........................41
       6.2.16. The agentx-Response-PDU................................43
   7. Elements of Procedure...........................................45
     7.1. Processing AgentX Administrative Messages...................45
       7.1.1. Processing the agentx-Open-PDU..........................46
       7.1.2. Processing the agentx-IndexAllocate-PDU.................47
       7.1.3. Processing the agentx-IndexDeallocate-PDU...............49
       7.1.4. Processing the agentx-Register-PDU......................50
         7.1.4.1. Handling Duplicate and Overlapping Subtrees.........50
         7.1.4.2. Registering Stuff...................................51
           7.1.4.2.1. Registration Priority...........................51
           7.1.4.2.2. Index Allocation................................51
           7.1.4.2.3. Examples........................................53
       7.1.5. Processing the agentx-Unregister-PDU....................55
       7.1.6. Processing the agentx-AddAgentCaps-PDU..................55
       7.1.7. Processing the agentx-RemoveAgentCaps-PDU...............55
       7.1.8. Processing the agentx-Close-PDU.........................56
       7.1.9. Detecting Connection Loss...............................56
       7.1.10. Processing the agentx-Notify-PDU.......................56
       7.1.11. Processing the agentx-Ping-PDU.........................57
     7.2. Processing Received SNMP Protocol Messages..................58
       7.2.1. Dispatching AgentX PDUs.................................58
         7.2.1.1. agentx-Get-PDU......................................61
         7.2.1.2. agentx-GetNext-PDU..................................61
         7.2.1.3. agentx-GetBulk-PDU..................................62



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         7.2.1.4. agentx-TestSet-PDU..................................63
         7.2.1.5. Dispatch............................................64
       7.2.2. Subagent Processing.....................................64
       7.2.3. Subagent Processing of agentx-Get, GetNext, GetBulk-PDUs65
         7.2.3.1. Subagent Processing of the agentx-Get-PDU...........65
         7.2.3.2. Subagent Processing of the agentx-GetNext-PDU.......66
         7.2.3.3. Subagent Processing of the agentx-GetBulk-PDU.......66
       7.2.4. Subagent Processing of agentx-TestSet, -CommitSet,
              -UndoSet, -CleanupSet-PDUs..............................67
         7.2.4.1. Subagent Processing of the agentx-TestSet-PDU.......68
         7.2.4.2. Subagent Processing of the agentx-CommitSet-PDU.....69
         7.2.4.3. Subagent Processing of the agentx-UndoSet-PDU.......69
         7.2.4.4. Subagent Processing of the agentx-CleanupSet-PDU....70
       7.2.5. Master Agent Processing of AgentX Responses.............70
         7.2.5.1. Common Processing of All AgentX Response PDUs.......70
         7.2.5.2. Processing of Responses to agentx-Get-PDUs..........70
         7.2.5.3. Processing of Responses to agentx-GetNext-PDU and
                  agentx-GetBulk-PDU..................................71
         7.2.5.4. Processing of Responses to agentx-TestSet-PDUs......72
         7.2.5.5. Processing of Responses to agentx-CommitSet-PDUs....73
         7.2.5.6. Processing of Responses to agentx-UndoSet-PDUs......74
       7.2.6. Sending the SNMP Response-PDU...........................74
       7.2.7. MIB Views...............................................74
     7.3. State Transitions...........................................75
       7.3.1. Set Transaction States..................................75
       7.3.2. Transport Connection States.............................77
       7.3.3. Session States..........................................78
   8. Transport Mappings..............................................79
     8.1. AgentX over TCP.............................................79
       8.1.1. Well-known Values.......................................79
       8.1.2. Operation...............................................79
     8.2. AgentX over UNIX-domain Sockets.............................80
       8.2.1. Well-known Values.......................................80
       8.2.2. Operation...............................................80
   9. Security Considerations.........................................81
   10. Acknowledgements...............................................82
   11. Authors' and Editor's Addresses................................83
   12. References.....................................................84
   13. Notices........................................................86
   Appendix A. Changes relative to RFC 2257 ..........................87
   Full Copyright Statement ..........................................91










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1. Introduction

   This memo defines a standardized framework for extensible SNMP
   agents.  It defines processing entities called master agents and
   subagents, a protocol (AgentX) used to communicate between them, and
   the elements of procedure by which the extensible agent processes
   SNMP protocol messages.

   This memo obsoletes RFC 2257.  It is worth noting that most of the
   changes are for the purpose of clarification.  The only changes
   affecting AgentX protocol messages on the wire are:

      -  The agentx-Notify-PDU and agentx-Close-PDU now generate an
         agentx-Response-PDU

      -  Three new error codes are available: parseFailed(266),
         requestDenied(267), and processingError(268)

   Appendix A provides a detailed list of changes relative to RFC 2257.

   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 [27].

2. The SNMP Management Framework

   The SNMP Management Framework presently consists of five major
   components:

   An overall architecture, described in RFC 2571 [1].

   Mechanisms for describing and naming objects and events for the
   purpose of management. The first version of this Structure of
   Management Information (SMI) is called SMIv1 and described in STD 16,
   RFC 1155 [2], STD 16, RFC 1212 [3] and RFC 1215 [4]. The second
   version, called SMIv2, is described in STD 58, RFC 2578 [5], STD 58,
   RFC 2579 [6] and STD 58, RFC 2580 [7].

   Message protocols for transferring management information. The first
   version of the SNMP message protocol is called SNMPv1 and described
   in STD 15, RFC 1157 [8]. A second version of the SNMP message
   protocol, which is not an Internet standards track protocol, is
   called SNMPv2c and described in RFC 1901 [9] and RFC 1906 [10]. The
   third version of the message protocol is called SNMPv3 and described
   in RFC 1906 [10], RFC 2572 [11] and RFC 2574 [12].

   Protocol operations for accessing management information. The first
   set of protocol operations and associated PDU formats is described in



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   STD 15, RFC 1157 [8]. A second set of protocol operations and
   associated PDU formats is described in RFC 1905 [13].

   A set of fundamental applications described in RFC 2573 [14] and the
   view-based access control mechanism described in RFC 2575 [15].

   A more detailed introduction to the current SNMP Management Framework
   can be found in RFC 2570 [16].

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  Objects in the MIB are
   defined using the mechanisms defined in the SMI.

2.1. A Note on Terminology

   The term "variable" refers to an instance of a non-aggregate object
   type defined according to the conventions set forth in the SMIv2 (STD
   58, RFC 2578, [5]) or the textual conventions based on the SMIv2 (STD
   58, RFC 2579 [6]).  The term "variable binding" normally refers to
   the pairing of the name of a variable and its associated value.
   However, if certain kinds of exceptional conditions occur during
   processing of a retrieval request, a variable binding will pair a
   name and an indication of that exception.

   A variable-binding list is a simple list of variable bindings.

   The name of a variable is an OBJECT IDENTIFIER, which is the
   concatenation of the OBJECT IDENTIFIER of the corresponding object
   type together with an OBJECT IDENTIFIER fragment identifying the
   instance.  The OBJECT IDENTIFIER of the corresponding object-type is
   called the OBJECT IDENTIFIER prefix of the variable.

3. Extending the MIB

   New MIB modules that extend the Internet-standard MIB are
   continuously being defined by various IETF working groups.  It is
   also common for enterprises or individuals to create or extend
   enterprise-specific or experimental MIBs.

   As a result, managed devices are frequently complex collections of
   manageable components that have been independently installed on a
   managed node.  Each component provides instrumentation for the
   managed objects defined in the MIB module(s) it implements.

   The SNMP framework does not describe how the set of managed objects
   supported by a particular agent may be changed dynamically.





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3.1. Motivation for AgentX

   This very real need to dynamically extend the management objects
   within a node has given rise to a variety of "extensible agents",
   which typically comprise

      -  a "master" agent that is available on the standard transport
         address and that accepts SNMP protocol messages

      -  a set of "subagents" that each contain management
         instrumentation

      -  a protocol that operates between the master agent and
         subagents, permitting subagents to "connect" to the master
         agent, and the master agent to multiplex received SNMP protocol
         messages amongst the subagents.