rfc2271.txt

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Network Working Group                                      D. Harrington
Request for Comments: 2271                       Cabletron Systems, Inc.
Obsoletes: 2261                                               R. Presuhn
Category: Standards Track                             BMC Software, Inc.
                                                               B. Wijnen
                                               IBM T. J. Watson Research
                                                            January 1998

                     An Architecture for Describing
                       SNMP Management Frameworks

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.

IANA Note

   Due to a clerical error in the assignment of the snmpModules in this
   memo, this RFC provides the corrected number assignment for this
   protocol.  This memo obsoletes RFC 2261.

Abstract

   This document describes an architecture for describing SNMP
   Management Frameworks.  The architecture is designed to be modular to
   allow the evolution of the SNMP protocol standards over time.  The
   major portions of the architecture are an SNMP engine containing a
   Message Processing Subsystem, a Security Subsystem and an Access
   Control Subsystem, and possibly multiple SNMP applications which
   provide specific functional processing of management data.

Table of Contents

   1. Introduction ................................................    3
   1.1. Overview ..................................................    3
   1.2. SNMP ......................................................    4
   1.3. Goals of this Architecture ................................    5
   1.4. Security Requirements of this Architecture ................    6
   1.5. Design Decisions ..........................................    7
   2. Documentation Overview ......................................    8



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   2.1. Document Roadmap ..........................................   10
   2.2. Applicability Statement ...................................   10
   2.3. Coexistence and Transition ................................   10
   2.4. Transport Mappings ........................................   11
   2.5. Message Processing ........................................   11
   2.6. Security ..................................................   11
   2.7. Access Control ............................................   11
   2.8. Protocol Operations .......................................   12
   2.9. Applications ..............................................   12
   2.10. Structure of Management Information ......................   12
   2.11. Textual Conventions ......................................   13
   2.12. Conformance Statements ...................................   13
   2.13. Management Information Base Modules ......................   13
   2.13.1. SNMP Instrumentation MIBs ..............................   13
   2.14. SNMP Framework Documents .................................   13
   3. Elements of the Architecture ................................   14
   3.1. The Naming of Entities ....................................   14
   3.1.1. SNMP engine .............................................   15
   3.1.1.1. snmpEngineID ..........................................   16
   3.1.1.2. Dispatcher ............................................   16
   3.1.1.3. Message Processing Subsystem ..........................   16
   3.1.1.3.1. Message Processing Model ............................   17
   3.1.1.4. Security Subsystem ....................................   17
   3.1.1.4.1. Security Model ......................................   17
   3.1.1.4.2. Security Protocol ...................................   18
   3.1.2. Access Control Subsystem ................................   18
   3.1.2.1. Access Control Model ..................................   18
   3.1.3. Applications ............................................   18
   3.1.3.1. SNMP Manager ..........................................   19
   3.1.3.2. SNMP Agent ............................................   20
   3.2. The Naming of Identities ..................................   21
   3.2.1. Principal ...............................................   21
   3.2.2. securityName ............................................   21
   3.2.3. Model-dependent security ID .............................   22
   3.3. The Naming of Management Information ......................   22
   3.3.1. An SNMP Context .........................................   23
   3.3.2. contextEngineID .........................................   24
   3.3.3. contextName .............................................   24
   3.3.4. scopedPDU ...............................................   25
   3.4. Other Constructs ..........................................   25
   3.4.1. maxSizeResponseScopedPDU ................................   25
   3.4.2. Local Configuration Datastore ...........................   25
   3.4.3. securityLevel ...........................................   25
   4. Abstract Service Interfaces .................................   26
   4.1. Dispatcher Primitives .....................................   26
   4.1.1. Generate Outgoing Request or Notification ...............   26
   4.1.2. Process Incoming Request or Notification PDU ............   26
   4.1.3. Generate Outgoing Response ..............................   27



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   4.1.4. Process Incoming Response PDU ...........................   27
   4.1.5. Registering Responsibility for Handling SNMP PDUs .......   28
   4.2. Message Processing Subsystem Primitives ...................   28
   4.2.1. Prepare Outgoing SNMP Request or Notification Message ...   28
   4.2.2. Prepare an Outgoing SNMP Response Message ...............   29
   4.2.3. Prepare Data Elements from an Incoming SNMP Message .....   29
   4.3. Access Control Subsystem Primitives .......................   30
   4.4. Security Subsystem Primitives .............................   30
   4.4.1. Generate a Request or Notification Message ..............   30
   4.4.2. Process Incoming Message ................................   31
   4.4.3. Generate a Response Message .............................   31
   4.5. Common Primitives .........................................   32
   4.5.1. Release State Reference Information .....................   32
   4.6. Scenario Diagrams .........................................   32
   4.6.1. Command Generator or Notification Originator ............   32
   4.6.2. Scenario Diagram for a Command Responder Application ....   33
   5. Managed Object Definitions for SNMP Management Frameworks ...   35
   6. Intellectual Property .......................................   44
   7. Acknowledgements ............................................   45
   8. Security Considerations .....................................   46
   9. References ..................................................   46
   10. Editors' Addresses .........................................   48
   A. Guidelines for Model Designers ..............................   49
   A.1. Security Model Design Requirements ........................   49
   A.1.1. Threats .................................................   49
   A.1.2. Security Processing .....................................   50
   A.1.3. Validate the security-stamp in a received message .......   51
   A.1.4. Security MIBs ...........................................   51
   A.1.5. Cached Security Data ....................................   51
   A.2. Message Processing Model Design Requirements ..............   52
   A.2.1. Receiving an SNMP Message from the Network ..............   52
   A.2.2. Sending an SNMP Message to the Network ..................   52
   A.3. Application Design Requirements ...........................   53
   A.3.1. Applications that Initiate Messages .....................   53
   A.3.2. Applications that Receive Responses .....................   54
   A.3.3. Applications that Receive Asynchronous Messages .........   54
   A.3.4. Applications that Send Responses ........................   54
   A.4. Access Control Model Design Requirements ..................   55
   B. Full Copyright Statement ....................................   56

1.  Introduction

   1.1.  Overview

   This document defines a vocabulary for describing SNMP Management
   Frameworks, and an architecture for describing the major portions of
   SNMP Management Frameworks.




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   This document does not provide a general introduction to SNMP. Other
   documents and books can provide a much better introduction to SNMP.
   Nor does this document provide a history of SNMP. That also can be
   found in books and other documents.

   Section 1 describes the purpose, goals, and design decisions of this
   architecture.

   Section 2 describes various types of documents which define SNMP
   Frameworks, and how they fit into this architecture. It also provides
   a minimal road map to the documents which have previously defined
   SNMP frameworks.

   Section 3 details the vocabulary of this architecture and its pieces.
   This section is important for understanding the remaining sections,
   and for understanding documents which are written to fit within this
   architecture.

   Section 4 describes the primitives used for the abstract service
   interfaces between the various subsystems, models and applications
   within this architecture.

   Section 5 defines a collection of managed objects used to instrument
   SNMP entities within this architecture.

   Sections 6, 7, 8, and 9 are administrative in nature.

   Appendix A contains guidelines for designers of Models which are
   expected to fit within this 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 [RFC2119].

1.2.  SNMP

   An SNMP management system contains:

      -  several (potentially many) nodes, each with an SNMP entity
         containing command responder and notification originator
         applications, which have access to management instrumentation
         (traditionally called agents);

      -  at least one SNMP entity containing command generator and/or
         notification receiver applications (traditionally called a
         manager) and,





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      -  a management protocol, used to convey management information
         between the SNMP entities.

   SNMP entities executing command generator and notification receiver
   applications 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.

   It is the purpose of this document to define an architecture which
   can evolve to realize effective management in a variety of
   configurations and environments. The architecture has been designed
   to meet the needs of implementations of:

      -  minimal SNMP entities with command responder and/or
         notification originator applications (traditionally called SNMP
         agents),

      -  SNMP entities with proxy forwarder applications (traditionally
         called SNMP proxy agents),

      -  command line driven SNMP entities with command generator and/or
         notification receiver applications (traditionally called SNMP
         command line managers),

      -  SNMP entities with  command generator and/or notification
         receiver, plus command responder and/or notification originator
         applications (traditionally called SNMP mid-level managers or
         dual-role entities),

      -  SNMP entities with command generator and/or notification
         receiver and possibly other types of applications for managing
         a potentially very large number of managed nodes (traditionally
         called (network) management stations).

1.3.  Goals of this Architecture

   This architecture was driven by the following goals:

      -  Use existing materials as much as possible. It is heavily based
         on previous work, informally known as SNMPv2u and SNMPv2*.

      -  Address the need for secure SET support, which is considered
         the most important deficiency in SNMPv1 and SNMPv2c.

      -  Make it possible to move portions of the architecture forward
         in the standards track, even if consensus has not been reached
         on all pieces.




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      -  Define an architecture that allows for longevity of the SNMP
         Frameworks that have been and will be defined.

      -  Keep SNMP as simple as possible.

      -  Make it relatively inexpensive to deploy a minimal conforming
         implementation.

      -  Make it possible to upgrade portions of SNMP as new approaches
         become available, without disrupting an entire SNMP framework.

      -  Make it possible to support features required in large
         networks, but make the expense of supporting a feature directly