rfc2257.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                         M. Daniele
Request for Comments: 2257                 Digital Equipment Corporation
Category: Standards Track                                      B. Wijnen
                                  T.J. Watson Research Center, IBM Corp.
                                                       D. Francisco, Ed.
                                                     Cisco Systems, Inc.
                                                            January 1998

                 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 (1998).  All Rights Reserved.

Table of Contents

   1 Introduction......................................................4

   2 The SNMP Framework................................................4
     2.1 A Note on Terminology.........................................4

   3 Extending the MIB.................................................5
     3.1 Motivation for AgentX.........................................5

   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

   5 AgentX Encodings.................................................10
     5.1 Object Identifier............................................11
     5.2 SearchRange..................................................13
     5.3 Octet String.................................................14
     5.4 Value Representation.........................................14

   6 Protocol Definitions.............................................16
     6.1 AgentX PDU Header............................................16



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RFC 2257                        AgentX                      January 1998


       6.1.1 Context..................................................19
     6.2 AgentX PDUs..................................................20
       6.2.1 The agentx-Open-PDU......................................20
       6.2.2 The agentx-Close-PDU.....................................21
       6.2.3 The agentx-Register-PDU..................................22
       6.2.4 The agentx-Unregister-PDU................................25
       6.2.5 The agentx-Get-PDU.......................................27
       6.2.6 The agentx-GetNext-PDU...................................29
       6.2.7 The agentx-GetBulk-PDU...................................30
       6.2.8 The agentx-TestSet-PDU...................................31
       6.2.9 The agentx-CommitSet, -UndoSet, -CleanupSet
             PDUs.....................................................33
       6.2.10 The agentx-Notify-PDU...................................33
       6.2.11 The agentx-Ping-PDU.....................................34
       6.2.12 The agentx-IndexAllocate-PDU............................35
       6.2.13 The agentx-IndexDeallocate-PDU..........................36
       6.2.14 The agentx-AddAgentCaps-PDU.............................37
       6.2.15 The agentx-RemoveAgentCaps-PDU..........................38
       6.2.16 The agentx-Response-PDU.................................39

   7 Elements of Procedure............................................41
     7.1 Processing AgentX Administrative Messages....................42
       7.1.1 Processing the agentx-Open-PDU...........................42
       7.1.2 Processing the agentx-IndexAllocate-PDU..................43
       7.1.3 Using the agentx-IndexAllocate-PDU.......................45
       7.1.4 Processing the agentx-IndexDeallocate-PDU................47
       7.1.5 Processing the agentx-Register-PDU.......................48
         7.1.5.1 Handling Duplicate OID Ranges........................50
       7.1.6 Processing the agentx-Unregister-PDU.....................51
       7.1.7 Processing the agentx-AddAgentCaps-PDU...................51
       7.1.8 Processing the agentx-RemoveAgentCaps-PDU................52
       7.1.9 Processing the agentx-Close-PDU..........................52
       7.1.10 Detecting Connection Loss...............................53
       7.1.11 Processing the agentx-Notify-PDU........................53
       7.1.12 Processing the agentx-Ping-PDU..........................54
     7.2 Processing Received SNMP Protocol Messages...................54
       7.2.1 Dispatching AgentX PDUs..................................55
         7.2.1.1 agentx-Get-PDU.......................................57
         7.2.1.2 agentx-GetNext-PDU...................................58
         7.2.1.3 agentx-GetBulk-PDU...................................59
         7.2.1.4 agentx-TestSet-PDU...................................60
         7.2.1.5 Dispatch.............................................60
       7.2.2 Subagent Processing of agentx-Get, GetNext,
             GetBulk-PDUs.............................................61
         7.2.2.1 Subagent Processing of the agentx-Get-PDU............61
         7.2.2.2 Subagent Processing of the
                 agentx-GetNext-PDU...................................62




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RFC 2257                        AgentX                      January 1998


         7.2.2.3 Subagent Processing of the
                 agentx-GetBulk-PDU...................................62
       7.2.3 Subagent Processing of agentx-TestSet,
             -CommitSet, -UndoSet, -CleanupSet-PDUs...................63
         7.2.3.1 Subagent Processing of the
                 agentx-TestSet-PDU...................................64
         7.2.3.2 Subagent Processing of the
                 agentx-CommitSet-PDU.................................65
         7.2.3.3 Subagent Processing of the
                 agentx-UndoSet-PDU...................................65
         7.2.3.4 Subagent Processing of the
                 agentx-CleanupSet-PDU................................65
       7.2.4 Master Agent Processing of AgentX Responses..............66
         7.2.4.1 Common Processing of All AgentX Response
                 PDUs.................................................66
         7.2.4.2 Processing of Responses to agentx-Get-PDUs...........66
         7.2.4.3 Processing of Responses to
                 agentx-GetNext-PDU and agentx-GetBulk-PDU............67
         7.2.4.4 Processing of Responses to
                 agentx-TestSet-PDUs..................................68
         7.2.4.5 Processing of Responses to
                 agentx-CommitSet-PDUs................................68
         7.2.4.6 Processing of Responses to
                 agentx-UndoSet-PDUs..................................69
       7.2.5 Sending the SNMP Response-PDU............................69
       7.2.6 MIB Views................................................69
     7.3 State Transitions............................................70
       7.3.1 Set Transaction States...................................70
       7.3.2 Transport Connection States..............................71
       7.3.3 Session States...........................................73

   8 Transport Mappings...............................................74
     8.1 AgentX over TCP..............................................74
       8.1.1 Well-known Values........................................74
       8.1.2 Operation................................................74
     8.2 AgentX over UNIX-domain Sockets..............................75
       8.2.1 Well-known Values........................................75
       8.2.2 Operation................................................75

   9 Security Considerations..........................................76

   10 Acknowledgements................................................77

   11 Authors' and Editor's Addresses.................................77

   12 References......................................................78

   13 Full Copyright Statement........................................80



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RFC 2257                        AgentX                      January 1998


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.

2.  The SNMP Framework

   A management system contains:  several (potentially many) nodes, each
   with a processing entity, termed an agent, which has access to
   management instrumentation; at least one management station; and, a
   management protocol, used to convey management information between
   the agents and management stations.  Operations of the protocol are
   carried out under an administrative framework which defines
   authentication, authorization, access control, and privacy policies.

   Management stations execute management applications which monitor and
   control managed elements.  Managed elements are devices such as
   hosts, routers, terminal servers, etc., which are monitored and
   controlled via access to their management information.

   Management information is viewed as a collection of managed objects,
   residing in a virtual information store, termed the Management
   Information Base (MIB).  Collections of related objects are defined
   in MIB modules.  These modules are written using a subset of OSI's
   Abstract Syntax Notation One (ASN.1) [1], termed the Structure of
   Management Information (SMI) (see RFC 1902 [2]).

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 SMI (RFC
   1902, [2]) or the textual conventions based on the SMI (RFC 1903
   [3]).  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





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RFC 2257                        AgentX                      January 1998


   instance.  The OBJECT IDENTIFIER of the corresponding object-type is
   called the OBJECT IDENTIFIER prefix of the variable.  For the purpose
   of exposition, the original Internet-standard

   Network Management Framework, as described in RFCs 1155 (STD 16),
   1157 (STD 15), and 1212 (STD 16), is termed the SNMP version 1
   framework (SNMPv1).  The current framework, as described in RFCs
   1902-1908, is termed the SNMP version 2 framework (SNMPv2).

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.

   Neither the SNMP version 1 nor version 2 framework describes how the
   set of managed objects supported by a particular agent may be changed
   dynamically.

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.

      - a set of tools to aid subagent development, and a runtime (API)
        environment that hides much of the protocol operation between a
        subagent and the master agent.






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RFC 2257                        AgentX                      January 1998


   The wide deployment of extensible SNMP agents, coupled with the lack
   of Internet standards in this area, makes it difficult to field
   SNMP-manageable applications.  A vendor may have to support several
   different subagent environments (APIs) in order to support different
   target platforms.

   It can also become quite cumbersome to configure subagents and
   (possibly multiple) master agents on a particular managed node.

   Specifying a standard protocol for agent extensibility (AgentX)
   provides the technical foundation required to solve both of these
   problems.  Independently developed AgentX-capable master agents and
   subagents will be able to interoperate at the protocol level.
   Vendors can continue to differentiate their products in all other
   respects.

4.  AgentX Framework

   Within the SNMP framework, a managed node contains a processing
   entity, called an agent, which has access to management information.

   Within the AgentX framework, an agent is further defined to consist
   of

      - a single processing entity called the master agent, which sends
        and receives SNMP protocol messages in an agent role (as
        specified by the SNMP version 1 and version 2 framework
        documents) but typically has little or no direct access to
        management information.