rfc3416.txt

开发snmp的开发包有两个开放的SNMP开发库

Network Working Group                            Editor of this version:
Request for Comments: 3416                                    R. Presuhn
STD: 62                                               BMC Software, Inc.
Obsoletes: 1905                             Authors of previous version:
Category: Standards Track                                        J. Case
                                                     SNMP Research, Inc.
                                                           K. McCloghrie
                                                     Cisco Systems, Inc.
                                                                 M. Rose
                                            Dover Beach Consulting, Inc.
                                                           S. Waldbusser
                                          International Network Services
                                                           December 2002


                Version 2 of the Protocol Operations for
             the Simple Network Management Protocol (SNMP)

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 (2002).  All Rights Reserved.

Abstract

   This document defines version 2 of the protocol operations for the
   Simple Network Management Protocol (SNMP).  It defines the syntax and
   elements of procedure for sending, receiving, and processing SNMP
   PDUs.  This document obsoletes RFC 1905.















Presuhn, et al.             Standards Track                     [Page 1]

RFC 3416              Protocol Operations for SNMP         December 2002


Table of Contents

   1. Introduction ................................................    3
   2. Overview ....................................................    4
   2.1. Management Information ....................................    4
   2.2. Retransmission of Requests ................................    4
   2.3. Message Sizes .............................................    4
   2.4. Transport Mappings ........................................    5
   2.5. SMIv2 Data Type Mappings ..................................    6
   3. Definitions .................................................    6
   4. Protocol Specification ......................................    9
   4.1. Common Constructs .........................................    9
   4.2. PDU Processing ............................................   10
   4.2.1. The GetRequest-PDU ......................................   10
   4.2.2. The GetNextRequest-PDU ..................................   11
   4.2.2.1. Example of Table Traversal ............................   12
   4.2.3. The GetBulkRequest-PDU ..................................   14
   4.2.3.1. Another Example of Table Traversal ....................   17
   4.2.4. The Response-PDU ........................................   18
   4.2.5. The SetRequest-PDU ......................................   19
   4.2.6. The SNMPv2-Trap-PDU .....................................   22
   4.2.7. The InformRequest-PDU ...................................   23
   5. Notice on Intellectual Property .............................   24
   6. Acknowledgments .............................................   24
   7. Security Considerations .....................................   26
   8. References ..................................................   26
   8.1. Normative References ......................................   26
   8.2. Informative References ....................................   27
   9. Changes from RFC 1905 .......................................   28
   10. Editor's Address ...........................................   30
   11. Full Copyright Statement ...................................   31




















Presuhn, et al.             Standards Track                     [Page 2]

RFC 3416              Protocol Operations for SNMP         December 2002


1.  Introduction

   The SNMP Management Framework at the time of this writing consists of
   five major components:

      -  An overall architecture, described in STD 62, RFC 3411
         [RFC3411].

      -  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 [RFC1155], STD 16, RFC 1212 [RFC1212] and RFC
         1215 [RFC1215].  The second version, called SMIv2, is described
         in STD 58, RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and
         STD 58, RFC 2580 [RFC2580].

      -  Message protocols for transferring management information.  The
         first version of the SNMP message protocol is called SNMPv1 and
         described in STD 15, RFC 1157 [RFC1157].  A second version of
         the SNMP message protocol, which is not an Internet standards
         track protocol, is called SNMPv2c and described in RFC 1901
         [RFC1901] and STD 62, RFC 3417 [RFC3417].  The third version of
         the message protocol is called SNMPv3 and described in STD 62,
         RFC 3417 [RFC3417], RFC 3412 [RFC3412] and RFC 3414 [RFC3414].

      -  Protocol operations for accessing management information.  The
         first set of protocol operations and associated PDU formats is
         described in STD 15, RFC 1157 [RFC1157].  A second set of
         protocol operations and associated PDU formats is described in
         this document.

      -  A set of fundamental applications described in STD 62, RFC 3413
         [RFC3413] and the view-based access control mechanism described
         in STD 62, RFC 3415 [RFC3415].

   A more detailed introduction to the SNMP Management Framework at the
   time of this writing can be found in RFC 3410 [RFC3410].

   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.

   This document, Version 2 of the Protocol Operations for the Simple
   Network Management Protocol, defines the operations of the protocol
   with respect to the sending and receiving of PDUs to be carried by
   the message protocol.





Presuhn, et al.             Standards Track                     [Page 3]

RFC 3416              Protocol Operations for SNMP         December 2002


2.  Overview

   SNMP entities supporting command generator or notification receiver
   applications (traditionally called "managers") communicate with SNMP
   entities supporting command responder or notification originator
   applications (traditionally called "agents").  The purpose of this
   protocol is the transport of management information and operations.

2.1.  Management Information

   The term "variable" refers to an instance of a non-aggregate object
   type defined according to the conventions set forth in the SMI
   [RFC2578] or the textual conventions based on the SMI [RFC2579].  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.

2.2.  Retransmission of Requests

   For all types of request in this protocol, the receiver is required
   under normal circumstances, to generate and transmit a response to
   the originator of the request.  Whether or not a request should be
   retransmitted if no corresponding response is received in an
   appropriate time interval, is at the discretion of the application
   originating the request.  This will normally depend on the urgency of
   the request.  However, such an application needs to act responsibly
   in respect to the frequency and duration of re-transmissions.  See
   BCP 41 [RFC2914] for discussion of relevant congestion control
   principles.

2.3.  Message Sizes

   The maximum size of an SNMP message is limited to the minimum of:

   (1)   the maximum message size which the destination SNMP entity can
         accept; and,





Presuhn, et al.             Standards Track                     [Page 4]

RFC 3416              Protocol Operations for SNMP         December 2002


   (2)   the maximum message size which the source SNMP entity can
         generate.

   The former may be known on a per-recipient basis; and in the absence
   of such knowledge, is indicated by transport domain used when sending
   the message.  The latter is imposed by implementation-specific local
   constraints.

   Each transport mapping for the SNMP indicates the minimum message
   size which a SNMP implementation must be able to produce or consume.
   Although implementations are encouraged to support larger values
   whenever possible, a conformant implementation must never generate
   messages larger than allowed by the receiving SNMP entity.

   One of the aims of the GetBulkRequest-PDU, specified in this
   protocol, is to minimize the number of protocol exchanges required to
   retrieve a large amount of management information.  As such, this PDU
   type allows an SNMP entity supporting command generator applications
   to request that the response be as large as possible given the
   constraints on message sizes.  These constraints include the limits
   on the size of messages which the SNMP entity supporting command
   responder applications can generate, and the SNMP entity supporting
   command generator applications can receive.

   However, it is possible that such maximum sized messages may be
   larger than the Path MTU of the path across the network traversed by
   the messages.  In this situation, such messages are subject to
   fragmentation.  Fragmentation is generally considered to be harmful
   [FRAG], since among other problems, it leads to a decrease in the
   reliability of the transfer of the messages.  Thus, an SNMP entity
   which sends a GetBulkRequest-PDU must take care to set its parameters
   accordingly, so as to reduce the risk of fragmentation.  In
   particular, under conditions of network stress, only small values
   should be used for max-repetitions.

2.4.  Transport Mappings

   It is important to note that the exchange of SNMP messages requires
   only an unreliable datagram service, with every message being
   entirely and independently contained in a single transport datagram.
   Specific transport mappings and encoding rules are specified
   elsewhere [RFC3417].  However, the preferred mapping is the use of
   the User Datagram Protocol [RFC768].








Presuhn, et al.             Standards Track                     [Page 5]

RFC 3416              Protocol Operations for SNMP         December 2002


2.5.  SMIv2 Data Type Mappings

   The SMIv2 [RFC2578] defines 11 base types (INTEGER, OCTET STRING,
   OBJECT IDENTIFIER, Integer32, IpAddress, Counter32, Gauge32,
   Unsigned32, TimeTicks, Opaque, Counter64) and the BITS construct.
   The SMIv2 base types are mapped to the corresponding selection type
   in the SimpleSyntax and ApplicationSyntax choices of the ASN.1 SNMP
   protocol definition.  Note that the INTEGER and Integer32 SMIv2 base
   types are mapped to the integer-value selection type of the
   SimpleSyntax choice.  Similarly, the Gauge32 and Unsigned32 SMIv2
   base types are mapped to the unsigned-integer-value selection type of
   the ApplicationSyntax choice.

   The SMIv2 BITS construct is mapped to the string-value selection type
   of the SimpleSyntax choice.  A BITS value is encoded as an OCTET
   STRING, in which all the named bits in (the definition of) the
   bitstring, commencing with the first bit and proceeding to the last
   bit, are placed in bits 8 (high order bit) to 1 (low order bit) of
   the first octet, followed by bits 8 to 1 of each subsequent octet in
   turn, followed by as many bits as are needed of the final subsequent
   octet, commencing with bit 8.  Remaining bits, if any, of the final
   octet are set to zero on generation and ignored on receipt.

3.  Definitions

   The PDU syntax is defined using ASN.1 notation [ASN1].

   SNMPv2-PDU DEFINITIONS ::= BEGIN

   ObjectName ::= OBJECT IDENTIFIER