rfc3412.txt

开发snmp的开发包有两个开放的SNMP开发库

Network Working Group                                            J. Case
Request for Comments: 3412                           SNMP Research, Inc.
STD: 62                                                    D. Harrington
Obsoletes: 2572                                       Enterasys Networks
Category: Standards Track                                     R. Presuhn
                                                      BMC Software, Inc.
                                                               B. Wijnen
                                                     Lucent Technologies
                                                           December 2002


               Message Processing and Dispatching 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 describes the Message Processing and Dispatching for
   Simple Network Management Protocol (SNMP) messages within the SNMP
   architecture.  It defines the procedures for dispatching potentially
   multiple versions of SNMP messages to the proper SNMP Message
   Processing Models, and for dispatching PDUs to SNMP applications.
   This document also describes one Message Processing Model - the
   SNMPv3 Message Processing Model.  This document obsoletes RFC 2572.
















Case, et al.                Standards Track                     [Page 1]

RFC 3412      Message Processing and Dispatching for SNMP  December 2002


Table of Contents

   1. Introduction ................................................    3
   2. Overview ....................................................    4
   2.1. The Dispatcher ............................................    5
   2.2. Message Processing Subsystem ..............................    5
   3. Elements of Message Processing and Dispatching ..............    6
   3.1. messageProcessingModel ....................................    6
   3.2. pduVersion ................................................    6
   3.3. pduType ...................................................    7
   3.4. sendPduHandle .............................................    7
   4. Dispatcher Elements of Procedure ............................    7
   4.1. Sending an SNMP Message to the Network ....................    7
   4.1.1. Sending a Request or Notification .......................    8
   4.1.2. Sending a Response to the Network .......................    9
   4.2. Receiving an SNMP Message from the Network ................   11
   4.2.1. Message Dispatching of received SNMP Messages ...........   11
   4.2.2. PDU Dispatching for Incoming Messages ...................   12
   4.2.2.1. Incoming Requests and Notifications ...................   13
   4.2.2.2. Incoming Responses ....................................   14
   4.3. Application Registration for Handling PDU types ...........   15
   4.4. Application Unregistration for Handling PDU Types .........   16
   5. Definitions .................................................   16
   5.1. Definitions for SNMP Message Processing and Dispatching ...   16
   6. The SNMPv3 Message Format ...................................   19
   6.1. msgVersion ................................................   20
   6.2. msgID .....................................................   20
   6.3. msgMaxSize ................................................   21
   6.4. msgFlags ..................................................   21
   6.5. msgSecurityModel ..........................................   24
   6.6. msgSecurityParameters .....................................   24
   6.7. scopedPduData .............................................   24
   6.8. scopedPDU .................................................   24
   6.8.1. contextEngineID .........................................   24
   6.8.2. contextName .............................................   25
   6.8.3. data ....................................................   25
   7. Elements of Procedure for v3MP ..............................   25
   7.1. Prepare an Outgoing SNMP Message ..........................   26
   7.2. Prepare Data Elements from an Incoming SNMP Message .......   32
   8. Intellectual Property .......................................   37
   9. Acknowledgements ............................................   38
   10. Security Considerations ....................................   39
   11. References .................................................   40
   11.1. Normative References .....................................   40
   11.2. Informative References ...................................   41
   12. Editors' Addresses .........................................   42
   13. Full Copyright Statement ...................................   43




Case, et al.                Standards Track                     [Page 2]

RFC 3412      Message Processing and Dispatching for SNMP  December 2002


1.  Introduction

   The Architecture for describing Internet Management Frameworks
   [RFC3411] describes that an SNMP engine is composed of:

      1) a Dispatcher
      2) a Message Processing Subsystem,
      3) a Security Subsystem, and
      4) an Access Control Subsystem.

   Applications make use of the services of these subsystems.

   It is important to understand the SNMP architecture and its
   terminology to understand where the Message Processing Subsystem and
   Dispatcher described in this document fit into the architecture and
   interact with other subsystems within the architecture.  The reader
   is expected to have read and understood the description of the SNMP
   architecture, defined in [RFC3411].

   The Dispatcher in the SNMP engine sends and receives SNMP messages.
   It also dispatches SNMP PDUs to SNMP applications.  When an SNMP
   message needs to be prepared or when data needs to be extracted from
   an SNMP message, the Dispatcher delegates these tasks to a message
   version-specific Message Processing Model within the Message
   Processing Subsystem.

   A Message Processing Model is responsible for processing an SNMP
   version-specific message and for coordinating the interaction with
   the Security Subsystem to ensure proper security is applied to the
   SNMP message being handled.

   Interactions between the Dispatcher, the Message Processing
   Subsystem, and applications are modeled using abstract data elements
   and abstract service interface primitives defined by the SNMP
   architecture.

   Similarly, interactions between the Message Processing Subsystem and
   the Security Subsystem are modeled using abstract data elements and
   abstract service interface primitives as defined by the SNMP
   architecture.

   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 BCP 14, RFC 2119.







Case, et al.                Standards Track                     [Page 3]

RFC 3412      Message Processing and Dispatching for SNMP  December 2002


2.  Overview

   The following illustration depicts the Message Processing in relation
   to SNMP applications, the Security Subsystem and Transport Mappings.

   +-------------------------------------------------------------------+
   | SNMP Entity                                                       |
   |                                                                   |
   | +---------------------------------------------------------------+ |
   | | Applications                                                  | |
   | | +-----------+  +--------------+                               | |
   | | | Command   |  | Notification |                               | |
   | | | Generator |  | Originator   | +-----------+ +--------------+| |
   | | +-----------+  +--------------+ | Proxy     | | Other        || |
   | | +-----------+  +--------------+ | Forwarder | |Application(s)|| |
   | | | Command   |  | Notification | +-----------+ +--------------+| |
   | | | Responder |  | Receiver     |                               | |
   | | +-----------+  +--------------+                               | |
   | +---------------------------------------------------------------+ |
   |        ^                ^               ^           ^             |
   |        |                |               |           |             |
   |        v                v               v           v             |
   |        +--------+-------+---------------+-----------+             |
   |                 ^                                                 |
   |                 |    +---------------------+  +-----------------+ |
   |                 |    | Message Processing  |  | Security        | |
   | Dispatcher      v    | Subsystem           |  | Subsystem       | |
   | +------------------+ |     +------------+  |  |                 | |
   | | PDU Dispatcher   | |  +->| v1MP     * |<--->| +-------------+ | |
   | |                  | |  |  +------------+  |  | | Other       | | |
   | |                  | |  |  +------------+  |  | | Security    | | |
   | |                  | |  +->| v2cMP    * |<--->| | Model       | | |
   | | Message          | |  |  +------------+  |  | +-------------+ | |
   | | Dispatcher  <-------->+                  |  |                 | |
   | |                  | |  |  +------------+  |  | +-------------+ | |
   | |                  | |  +->| v3MP     * |<--->| | User-based  | | |
   | | Transport        | |  |  +------------+  |  | | Security    | | |
   | | Mapping          | |  |  +------------+  |  | | Model       | | |
   | | (e.g., RFC 3417) | |  +->| otherMP  * |<--->| +-------------+ | |
   | +------------------+ |     +------------+  |  |                 | |
   |          ^           +---------------------+  +-----------------+ |
   |          |                                                        |
   +----------|--------------------------------------------------------+
              v
     +------------------+
     |   Network        |           * One or more models may be present.
     +------------------+




Case, et al.                Standards Track                     [Page 4]

RFC 3412      Message Processing and Dispatching for SNMP  December 2002


2.1.  The Dispatcher

   The Dispatcher is a key piece of an SNMP engine.  There is only one
   in an SNMP engine, and its job is to dispatch tasks to the multiple
   version-specific Message Processing Models, and to dispatch PDUs to
   various applications.

   For outgoing messages, an application provides a PDU to be sent, plus
   the data needed to prepare and send the message, and the application
   specifies which version-specific Message Processing Model will be
   used to prepare the message with the desired security processing.
   Once the message is prepared, the Dispatcher sends the message.

   For incoming messages, the Dispatcher determines the SNMP version of
   the incoming message and passes the message to the version-specific
   Message Processing Model to extract the components of the message and
   to coordinate the processing of security services for the message.
   After version-specific processing, the PDU Dispatcher determines
   which application, if any, should receive the PDU for processing and
   forwards it accordingly.

   The Dispatcher, while sending and receiving SNMP messages, collects
   statistics about SNMP messages and the behavior of the SNMP engine in
   managed objects to make them accessible to remote SNMP entities.
   This document defines these managed objects, the MIB module which
   contains them, and how these managed objects might be used to provide
   useful management.

2.2.  Message Processing Subsystem

   The SNMP Message Processing Subsystem is the part of an SNMP engine
   which interacts with the Dispatcher to handle the version-specific
   SNMP messages.  It contains one or more Message Processing Models.

   This document describes one Message Processing Model, the SNMPv3
   Message Processing Model, in Section 6.  The SNMPv3 Message
   Processing Model is defined in a separate section to show that
   multiple (independent) Message Processing Models can exist at the
   same time and that such Models can be described in different
   documents.  The SNMPv3 Message Processing Model can be replaced or
   supplemented with other Message Processing Models in the future.  Two
   Message Processing Models which are expected to be developed in the
   future are the SNMPv1 message format [RFC1157] and the SNMPv2c
   message format [RFC1901].  Others may be developed as needed.







Case, et al.                Standards Track                     [Page 5]

RFC 3412      Message Processing and Dispatching for SNMP  December 2002


3.  Elements of Message Processing and Dispatching

   See [RFC3411] for the definitions of:

      contextEngineID
      contextName
      scopedPDU
      maxSizeResponseScopedPDU
      securityModel
      securityName
      securityLevel
      messageProcessingModel

   For incoming messages, a version-specific message processing module
   provides these values to the Dispatcher.  For outgoing messages, an
   application provides these values to the Dispatcher.

   For some version-specific processing, the values may be extracted
   from received messages; for other versions, the values may be
   determined by algorithm, or by an implementation-defined mechanism.
   The mechanism by which the value is determined is irrelevant to the
   Dispatcher.

   The following additional or expanded definitions are for use within
   the Dispatcher.

3.1.  messageProcessingModel

   The value of messageProcessingModel identifies a Message Processing
   Model.  A Message Processing Model describes the version-specific
   procedures for extracting data from messages, generating messages,
   calling upon a securityModel to apply its security services to
   messages, for converting data from a version-specific message format
   into a generic format usable by the Dispatcher, and for converting
   data from Dispatcher format into a version-specific message format.

3.2.  pduVersion

   The value of pduVersion represents a specific version of protocol
   operation and its associated PDU formats, such as SNMPv1 or SNMPv2
   [RFC3416].  The values of pduVersion are specific to the version of
   the PDU contained in a message, and the PDUs processed by