





Network Working Group                                            J. Case
Request for Comments: 2570                           SNMP Research, Inc.
Category: Informational                                         R. Mundy
                                    TIS Labs at Network Associates, Inc.
                                                              D. Partain
                                                                Ericsson
                                                              B. Stewart
                                                           Cisco Systems
                                                              April 1999

                    Introduction to Version 3 of the
             Internet-standard Network Management Framework



Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

   The purpose of this document is to provide an overview of the third
   version of the Internet-standard Management Framework, termed the
   SNMP version 3 Framework (SNMPv3).  This Framework is derived from
   and builds upon both the original Internet-standard Management
   Framework (SNMPv1) and the second Internet-standard Management
   Framework (SNMPv2).

   The architecture is designed to be modular to allow the evolution of
   the Framework over time.

Table of Contents

   1 Introduction .....................................................2
   2 The Internet Standard Management Framework .......................3
   2.1 Basic Structure and Components .................................3
   2.2 Architecture of the Internet Standard Management Framework .....3
   3 The SNMPv1 Management Framework ..................................4
   3.1 The SNMPv1 Data Definition Language ............................5
   3.2 Management Information .........................................6
   3.3 Protocol Operations ............................................6
   3.4 SNMPv1 Security and Administration .............................6



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   4 The SNMPv2 Management Framework ..................................7
   5 The SNMPv3 Working Group .........................................8
   6 SNMPv3 Framework Module Specifications ..........................10
   6.1 Data Definition Language ......................................10
   6.2 MIB Modules ...................................................11
   6.3 Protocol Operations and Transport Mappings ....................12
   6.4 SNMPv3 Security and Administration ............................12
   7 Document Summaries ..............................................13
   7.1 Structure of Management Information ...........................13
   7.1.1 Base SMI Specification ......................................13
   7.1.2 Textual Conventions .........................................14
   7.1.3 Conformance Statements ......................................15
   7.2 Protocol Operations ...........................................15
   7.3 Transport Mappings ............................................15
   7.4 Protocol Instrumentation ......................................16
   7.5 Architecture / Security and Administration ....................16
   7.6 Message Processing and Dispatch (MPD) .........................16
   7.7 SNMP Applications .............................................17
   7.8 User-based Security Model (USM) ...............................17
   7.9 View-based Access Control (VACM) ..............................18
   7.10 SNMPv3 Coexistence and Transition ............................18
   8 Security Considerations .........................................19
   9 Editors' Addresses ..............................................19
   10 References .....................................................20
   11 Full Copyright Statement .......................................23

1 Introduction

   This document is an introduction to the third version of the
   Internet-standard Management Framework, termed the SNMP version 3
   Management Framework (SNMPv3) and has multiple purposes.

   First, it describes the relationship between the SNMP version 3
   (SNMPv3) specifications and the specifications of the SNMP version 1
   (SNMPv1) Management Framework, the SNMP version 2 (SNMPv2) Management
   Framework, and the Community-based Administrative Framework for
   SNMPv2.

   Second, it provides a roadmap to the multiple documents which contain
   the relevant specifications.

   Third, this document provides a brief easy-to-read summary of the
   contents of each of the relevant specification documents.

   This document is intentionally tutorial in nature and, as such, may
   occasionally be "guilty" of oversimplification.  In the event of a
   conflict or contradiction between this document and the more detailed
   documents for which this document is a roadmap, the specifications in



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   the more detailed documents shall prevail.

   Further, the detailed documents attempt to maintain separation
   between the various component modules in order to specify well-
   defined interfaces between them.  This roadmap document, however,
   takes a different approach and attempts to provide an integrated view
   of the various component modules in the interest of readability.

2 The Internet Standard Management Framework

   The third version of the Internet Standard Management Framework (the
   SNMPv3 Framework) is derived from and builds upon both the original
   Internet-standard Management Framework (SNMPv1) and the second
   Internet-standard Management Framework (SNMPv2).

   All versions (SNMPv1, SNMPv2, and SNMPv3) of the Internet Standard
   Management Framework share the same basic structure and components.
   Furthermore, all versions of the specifications of the Internet
   Standard Management Framework follow the same architecture.

2.1 Basic Structure and Components

   An enterprise deploying the Internet Standard Management Framework
   contains four basic components:

     * several (typically many) managed nodes, each with an SNMP entity
       which provides remote access to management instrumentation
       (traditionally called an agent);

     * at least one SNMP entity with management applications (typically
       called a manager),

     * a management protocol used to convey management information
       between the SNMP entities, and

     * management information.

   The management protocol is used to convey management information
   between SNMP entities such as managers and agents.

   This basic structure is common to all versions of the Internet
   Standard Management Framework; i.e., SNMPv1, SNMPv2, and SNMPv3.

2.2 Architecture of the Internet Standard Management Framework

   The specifications of the Internet Standard Management Framework are
   based on a modular architecture.  This framework is more than just a
   protocol for moving data.  It consists of:



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     * a data definition language,

     * definitions of management information (the Management
       Information Base, or MIB),

     * a protocol definition, and

     * security and administration.

   Over time, as the Framework has evolved from SNMPv1, through SNMPv2,
   to SNMPv3, the definitions of each of these architectural components
   have become richer and more clearly defined, but the fundamental
   architecture has remained consistent.

   One prime motivator for this modularity was to enable the ongoing
   evolution of the Framework as is documented in RFC 1052 [14].  When
   originally envisioned, this capability was to be used to ease the
   transition from SNMP-based management of internets to management
   based on OSI protocols.  To this end, the framework was architected
   with a protocol-independent data definition language and Management
   Information Base along with a MIB-independent protocol.  This
   separation was designed to allow the SNMP-based protocol to be
   replaced without requiring the management information to be redefined
   or reinstrumented.  History has shown that the selection of this
   architecture was the right decision for the wrong reason -- it turned
   out that this architecture has eased the transition from SNMPv1 to
   SNMPv2 and from SNMPv2 to SNMPv3 rather than easing the transition
   away from management based on the Simple Network Management Protocol.

   The SNMPv3 Framework builds and extends these architectural
   principles by:

     * building on these four basic architectural components, in some
       cases incorporating them from the SNMPv2 Framework by reference,
       and

     * by using these same layering principles in the definition of new
       capabilities in the security and administration portion of the
       architecture.

   Those who are familiar with the architecture of the SNMPv1 Management
   Framework and the SNMPv2 Management Framework will find many familiar
   concepts in the architecture of the SNMPv3 Management Framework.
   However, in some cases, the terminology may be somewhat different.







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3 The SNMPv1 Management Framework

   The original Internet-standard Network Management Framework (SNMPv1)
   is defined in the following documents:

     * STD 16, RFC 1155 [1] which defines the Structure of Management
       Information (SMI), the mechanisms used for describing and naming
       objects for the purpose of management.

     * STD 16, RFC 1212 [2] which defines a more concise description
       mechanism for describing and naming management information objects,
       but which is wholly consistent with the SMI.

     * STD 15, RFC 1157 [3] which defines the Simple Network Management
       Protocol (SNMP), the protocol used for network access to managed
       objects and event notification. Note this document also defines an
       initial set of event notifications.

   Additionally, two documents are generally considered to be companions
   to these three:

     * STD 17, RFC 1213 [13] which contains definitions for the base
       set of management information

     * RFC 1215 [25] defines a concise description mechanism for
       defining event notifications, which are called traps in the SNMPv1
       protocol. It also specifies the generic traps from RFC 1157 in the
       concise notation.

   These documents describe the four parts of the first version of the
   SNMP Framework.

3.1 The SNMPv1 Data Definition Language

   The first two and the last document describe the SNMPv1 data
   definition language.   Note that due to the initial requirement that
   the SMI be protocol-independent, the first two SMI documents do not
   provide a means for defining event notifications (traps).  Instead,
   the SNMP protocol document defines a few standardized event
   notifications (generic traps) and provides a means for additional
   event notifications to be defined. The last document specifies a
   straight-forward approach towards defining event notifications used
   with the SNMPv1 protocol. At the time that it was written, use of
   traps in the Internet-standard network management framework was
   controversial.  As such, RFC 1215 was put forward with the status of
   "Informational", which was never updated because it was believed that
   the second version of the SNMP Framework would replace the first
   version.  Note that the SNMPv1 data definition language is sometimes



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   referred to as SMIv1.

3.2 Management Information

   The data definition language described in the first two documents was
   first used to define the now-historic MIB-I as specified in RFC 1066
   [12], and was subsequently used to define MIB-II as specified in RFC
   1213 [13].

   Later, after the publication of MIB-II, a different approach to
   management information definition was taken from the earlier approach
   of having a single committee staffed by generalists work on a single
   document to define the Internet-standard MIB.  Rather, many mini-MIB
   documents were produced in a parallel and distributed fashion by
   groups chartered to produce a specification for a focused portion of
   the Internet-standard MIB and staffed by personnel with expertise in
   those particular areas ranging from various aspects of network
   management, to system management, and application management.

3.3 Protocol Operations

   The third document, STD 15, describes the SNMPv1 protocol operations
   performed by protocol data units (PDUs) on lists of variable bindings
   and describes the format of SNMPv1 messages. The operators defined by
   SNMPv1 are:  get, get-next, get-response, set-request, and trap.
   Typical layering of SNMP on a connectionless transport service is
   also defined.

3.4 SNMPv1 Security and Administration

   STD 15 also describes an approach to security and administration.
   Many of these concepts are carried forward and some, particularly
   security, are extended by the SNMPv3 Framework.

   The SNMPv1 Framework describes the encapsulation of SNMPv1 PDUs in
   SNMP messages between SNMP entities and distinguishes between
   application entities and protocol entities.  In SNMPv3, these are
   renamed applications and engines, respectively.

   The SNMPv1 Framework also introduces the concept of an authentication
   service supporting one or more authentication schemes.  In addition
   to authentication, SNMPv3 defines the additional security capability
   referred to as privacy.  (Note: some literature from the security
   community would describe SNMPv3 security capabilities as providing
   data integrity, source authenticity, and confidentiality.)  The
   modular nature of the SNMPv3 Framework permits both changes and
   additions to the security capabilities.




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   Finally, the SNMPv1 Framework introduces access control based on a
   concept called an SNMP MIB view.  The SNMPv3 Framework specifies a
   fundamentally similar concept called view-based access control.  With
   this capability, SNMPv3 provides the means for controlling access to
   information on managed devices.

   However, while the SNMPv1 Framework anticipated the definition of
   multiple authentication schemes, it did not define any such schemes
   other than a trivial authentication scheme based on community
   strings.  This was a known fundamental weakness in the SNMPv1
   Framework but it was thought at that time that the definition of
   commercial grade security might be contentious in its design and
   difficult to get approved because "security" means many different
   things to different people.  To that end, and because some users do
   not require strong authentication, the SNMPv1 architected an
   authentication service as a separate block to be defined "later" and
   the SNMPv3 Framework provides an architecture for use within that
   block as well as a definition for its subsystems.

4 The SNMPv2 Management Framework

   The SNMPv2 Management Framework is fully described in [4-9] and
   coexistence and transition issues relating to SNMPv1 and SNMPv2 are
   discussed in [10].

   SNMPv2 provides several advantages over SNMPv1, including:

     * expanded data types (e.g., 64 bit counter)

     * improved efficiency and performance (get-bulk operator)

     * confirmed event notification (inform operator)

     * richer error handling (errors and exceptions)

     * improved sets, especially row creation and deletion

     * fine tuning of the data definition language

   However, the SNMPv2 Framework, as described in these documents, is
   incomplete in that it does not meet the original design goals of the
   SNMPv2 project.  The unmet goals included provision of security and
   administration delivering so-called "commercial grade" security with

     * authentication:  origin identification, message integrity,
       and some aspects of replay protection;

     * privacy:  confidentiality;



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     * authorization and access control; and

     * suitable remote configuration and administration capabilities
       for these features.

   The SNMPv3 Management Framework, as described in this document and
   the companion documents, addresses these significant deficiencies.

5 The SNMPv3 Working Group

   This document, and its companion documents, were produced by the
   SNMPv3 Working Group of the Internet Engineering Task Force (IETF).
   The SNMPv3 Working Group was chartered to prepare recommendations for
   the next generation of SNMP.  The goal of the Working Group was to
   produce the necessary set of documents that provide a single standard
   for the next generation of core SNMP functions.  The single, most
   critical need in the next generation is a definition of security and
   administration that makes SNMP-based management transactions secure
   in a way which is useful for users who wish to use SNMPv3 to manage
   networks, the systems that make up those networks, and the
   applications which reside on those systems, including manager-to-
   agent, agent-to-manager, and manager-to-manager transactions.

   In the several years prior to the chartering of the Working Group,
   there were a number of activities aimed at incorporating security and
   other improvements to SNMP.  These efforts included:

     * "SNMP Security" circa 1991-1992 [RFC 1351 - RFC 1353],

     * "SMP" circa 1992-1993,

     * "The Party-based SNMPv2" circa 1993-1995 [RFC 1441 - RFC 1452].

   Each of these efforts incorporated commercial grade, industrial
   strength security including authentication, privacy, authorization,
   view-based access control, and administration, including remote
   configuration.

   These efforts fed the development of the SNMPv2 Management Framework
   as described in RFCs 1902 - 1908.  However, the Framework described
   in those RFCs had no standards-based security and administrative
   framework of its own; rather, it was associated with multiple
   security and administrative frameworks, including:

     * "The Community-based SNMPv2" (SNMPv2c) [RFC 1901],

     * "SNMPv2u" [RFCs 1909 - 1910] and




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     * "SNMPv2*".

   SNMPv2c had the endorsement of the IETF but no security and
   administration whereas both SNMPv2u and SNMPv2* had security but
   lacked the endorsement of the IETF.

   The SNMPv3 Working Group was chartered to produce a single set of
   specifications for the next generation of SNMP, based upon a
   convergence of the concepts and technical elements of SNMPv2u and
   SNMPv2*, as was suggested by an advisory team which was formed to
   provide a single recommended approach for SNMP evolution.

   In so doing, the Working Group charter defined the following
   objectives:

     * accommodate the wide range of operational environments with
       differing management demands;

     * facilitate the need to transition from previous, multiple
       protocols to SNMPv3;

     * facilitate the ease of setup and maintenance activities.

   In the initial work of the SNMPv3 Working Group, the group focused on
   security and administration, including

     * authentication and privacy,

     * authorization and view-based access control, and

     * standards-based remote configuration of the above.

   The SNMPv3 Working Group did not "reinvent the wheel," but reused the
   SNMPv2 Draft Standard documents, i.e., RFCs 1902 through 1908 for
   those portions of the design that were outside the focused scope.

   Rather, the primary contributors to the SNMPv3 Working Group, and the
   Working Group in general, devoted their considerable efforts to
   addressing the missing link -- security and administration -- and in
   the process made invaluable contributions to the state-of-the-art of
   management.

   They produced a design based on a modular architecture with
   evolutionary capabilities with emphasis on layering.  As a result,
   SNMPv3 can be thought of as SNMPv2 with additional security and
   administration capabilities.





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   In doing so, the Working Group achieved the goal of producing a
   single specification which has not only the endorsement of the IETF
   but also has security and administration.

6 SNMPv3 Framework Module Specifications

   The specification of the SNMPv3 Management Framework is partitioned
   in a modular fashion among several documents.  It is the intention of
   the SNMPv3 Working Group that, with proper care, any or all of the
   individual documents can be revised, upgraded, or replaced as
   requirements change, new understandings are obtained, and new
   technologies become available.

   Whenever feasible, the initial document set which defines the SNMPv3
   Management Framework leverages prior investments defining and
   implementing the SNMPv2 Management Framework by incorporating by
   reference each of the specifications of the SNMPv2 Management
   Framework.

   The SNMPv3 Framework augments those specifications with
   specifications for security and administration for SNMPv3.

   The documents which specify the SNMPv3 Management Framework follow
   the same architecture as those of the prior versions and can be
   organized for expository purposes into four main categories as
   follows:

     * the data definition language,

     * Management Information Base (MIB) modules,

     * protocol operations, and

     * security and administration.

   The first three sets of documents are incorporated from SNMPv2.  The
   fourth set of documents are new to SNMPv3, but, as described
   previously, build on significant prior related works.

6.1 Data Definition Language

   The specifications of the data definition language includes STD 58,
   RFC 2578, "Structure of Management Information Version 2 (SMIv2)"
   [26], and related specifications.  These documents are updates of
   RFCs 1902 - 1904 [4-6] which have evolved independently from the
   other parts of the framework and were republished as STD 58, RFCs
   2578 - 2580 [26-28] when promoted from Draft Standard.




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   The Structure of Management Information (SMIv2) defines fundamental
   data types, an object model, and the rules for writing and revising
   MIB modules.  Related specifications include STD 58, RFCs 2579, 2580.
   The updated data definition language is sometimes referred to as
   SMIv2.

   STD 58, RFC 2579, "Textual Conventions for SMIv2" [27], defines an
   initial set of shorthand abbreviations which are available for use
   within all MIB modules for the convenience of human readers and
   writers.

   STD 58, RFC 2580, "Conformance Statements for SMIv2" [28], defines
   the format for compliance statements which are used for describing
   requirements for agent implementations and capability statements
   which can be used to document the characteristics of particular
   implementations.

6.2 MIB Modules

   MIB modules usually contain object definitions, may contain
   definitions of event notifications, and sometimes include compliance
   statements specified in terms of appropriate object and event
   notification groups.  As such, MIB modules define the management
   information maintained by the instrumentation in managed nodes, made
   remotely accessible by management agents, conveyed by the management
   protocol, and manipulated by management applications.

   MIB modules are defined according the rules defined in the documents
   which specify the data definition language, principally the SMI as
   supplemented by the related specifications.

   There is a large and growing number of standards-based MIB modules,
   as defined in the periodically updated list of standard protocols
   [STD 1, RFC 2400].  As of this writing, there are nearly 100
   standards-based MIB modules with a total number of defined objects
   approaching 10,000.  In addition, there is an even larger and growing
   number of enterprise-specific MIB modules defined unilaterally by
   various vendors, research groups, consortia, and the like resulting
   in an unknown and virtually uncountable number of defined objects.

   In general, management information defined in any MIB module,
   regardless of the version of the data definition language used, can
   be used with any version of the protocol.  For example, MIB modules
   defined in terms of the SNMPv1 SMI (SMIv1) are compatible with the
   SNMPv3 Management Framework and can be conveyed by the protocols
   specified therein.  Furthermore, MIB modules defined in terms of the
   SNMPv2 SMI (SMIv2) are compatible with SNMPv1 protocol operations and
   can be conveyed by it.  However, there is one noteworthy exception:



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   the Counter64 datatype which can be defined in a MIB module defined
   in SMIv2 format but which cannot be conveyed by an SNMPv1 protocol
   engine.

6.3 Protocol Operations and Transport Mappings

   The specifications for the protocol operations and transport mappings
   of the SNMPv3 Framework are incorporated by reference to the two
   SNMPv2 Framework documents.

   The specification for protocol operations is found in RFC 1905,
   "Protocol Operations for Version 2 of the Simple Network Management
   Protocol (SNMPv2)" [7].  The SNMPv3 Framework is designed to allow
   various portions of the architecture to evolve independently.  For
   example, it might be possible for a new specification of protocol
   operations to be defined within the Framework to allow for additional
   protocol operations.

   The specification of transport mappings is found in RFC 1906,
   "Transport Mappings for Version 2 of the Simple Network Management
   Protocol (SNMPv2)" [8].

6.4 SNMPv3 Security and Administration

   The SNMPv3 document series defined by the SNMPv3 Working Group
   consists of seven documents at this time:

      RFC 2570, "Introduction to Version 3 of the Internet-standard
      Network Management Framework", which is this document.

      RFC 2571, "An Architecture for Describing SNMP Management
      Frameworks" [15], describes the overall architecture with special
      emphasis on the architecture for security and administration.

      RFC 2572, "Message Processing and Dispatching for the Simple
      Network Management Protocol (SNMP)" [16], describes the possibly
      multiple message processing models and the dispatcher portion that
      can be a part of an SNMP protocol engine.

      RFC 2573, "SNMP Applications" [17], describes the five types of
      applications that can be associated with an SNMPv3 engine and
      their elements of procedure.

      RFC 2574, "The User-Based Security Model for Version 3 of the
      Simple Network Management Protocol (SNMPv3)" [18], describes the
      threats, mechanisms, protocols, and supporting data used to
      provide SNMP message-level security.




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      RFC 2575, "View-based Access Control Model for the Simple Network
      Management Protocol (SNMP)" [19], describes how view-based access
      control can be applied within command responder and notification
      originator applications.

      The Work in Progress, "Coexistence between Version 1, Version 2,
      and Version 3 of the Internet-standard Network Management
      Framework" [20], describes coexistence between the SNMPv3
      Management Framework, the SNMPv2 Management Framework, and the
      original SNMPv1 Management Framework.

7 Document Summaries

   The following sections provide brief summaries of each document with
   slightly more detail than is provided in the overviews above.

7.1 Structure of 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 in the SNMP MIB module
   language, which contains elements of OSI's Abstract Syntax Notation
   One (ASN.1) [11] language.   STD 58, RFCs 2578, 2579, 2580, together
   define the MIB module language, specify the base data types for
   objects, specify a core set of short-hand specifications for data
   types called textual conventions, and specify a few administrative
   assignments of object identifier (OID) values.

   The SMI is divided into three parts:  module definitions, object
   definitions, and notification definitions.

   (1)  Module definitions are used when describing information modules.
        An ASN.1 macro, MODULE-IDENTITY, is used to convey concisely the
        semantics of an information module.

   (2)  Object definitions are used when describing managed objects.  An
        ASN.1 macro, OBJECT-TYPE, is used to convey concisely the syntax
        and semantics of a managed object.

   (3)  Notification definitions are used when describing unsolicited
        transmissions of management information.  An ASN.1 macro,
        NOTIFICATION-TYPE, is used to convey concisely the syntax and
        semantics of a notification.







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7.1.1 Base SMI Specification

   STD 58, RFC 2578 specifies the base data types for the MIB module
   language, which include: Integer32, enumerated integers, Unsigned32,
   Gauge32, Counter32,  Counter64, TimeTicks, INTEGER, OCTET STRING,
   OBJECT IDENTIFIER, IpAddress, Opaque, and BITS. It also assigns
   values to several object identifiers.  STD 58, RFC 2578 further
   defines the following constructs of the MIB module language:

     * IMPORTS to allow the specification of items that are used
       in a MIB module, but defined in another MIB module.

     * MODULE-IDENTITY to specify for a MIB module a description
       and administrative information such as contact and revision
       history.

     * OBJECT-IDENTITY and OID value assignments to specify a
       an OID value.

     * OBJECT-TYPE to specify the data type, status, and the semantics
       of managed objects.

     * SEQUENCE type assignment to list the columnar objects in
       a table.

     * NOTIFICATION-TYPE construct to specify an event notification.

7.1.2 Textual Conventions

   When designing a MIB module, it is often useful to specify in a
   short-hand way the semantics for a set of objects with similar
   behavior.  This is done by defining a new data type using a base data
   type specified in the SMI.  Each new type has a different name, and
   specifies a base type with more restrictive semantics.  These newly
   defined types are termed textual conventions, and are used for the
   convenience of humans reading a MIB module and potentially by
   "intelligent" management applications.  It is the purpose of STD 58,
   RFC 2579, Textual Conventions for SMIv2 [27], to define the
   construct, TEXTUAL-CONVENTION, of the MIB module language used to
   define such new types and to specify an initial set of textual
   conventions available to all MIB modules.










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7.1.3 Conformance Statements

   It may be useful to define the acceptable lower-bounds of
   implementation, along with the actual level of implementation
   achieved.  It is the purpose of STD 58, RFC 2580, Conformance
   Statements for SMIv2 [28], to define the constructs of the MIB module
   language used for these purposes.  There are two kinds of constructs:

   (1)  Compliance statements are used when describing requirements for
        agents with respect to object and event notification
        definitions.  The MODULE-COMPLIANCE construct is used to convey
        concisely such requirements.

   (2)  Capability statements are used when describing capabilities of
        agents with respect to object and event notification
        definitions.  The AGENT-CAPABILITIES construct is used to convey
        concisely such capabilities.

   Finally, collections of related objects and collections of related
   event notifications are grouped together to form a unit of
   conformance.  The OBJECT-GROUP construct is used to convey concisely
   the objects in and the semantics of an object group. The
   NOTIFICATION-GROUP construct is used to convey concisely the event
   notifications in and the semantics of an event notification group.

7.2 Protocol Operations

   The management protocol provides for the exchange of messages which
   convey management information between the agents and the management
   stations.  The form of these messages is a message "wrapper" which
   encapsulates a Protocol Data Unit (PDU).

   It is the purpose of RFC 1905, Protocol Operations for SNMPv2 [7], to
   define the operations of the protocol with respect to the sending and
   receiving of the PDUs.

7.3 Transport Mappings

   SNMP Messages may be used over a variety of protocol suites.  It is
   the purpose of RFC 1906, Transport Mappings for SNMPv2 [8], to define
   how SNMP messages maps onto an initial set of transport domains.
   Other mappings may be defined in the future.

   Although several mappings are defined, the mapping onto UDP is the
   preferred mapping.  As such, to provide for the greatest level of
   interoperability, systems which choose to deploy other mappings
   should also provide for proxy service to the UDP mapping.




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7.4 Protocol Instrumentation

   It is the purpose of RFC 1907, the Management Information Base for
   SNMPv2 document [9] to define managed objects which describe the
   behavior of an SNMPv2 entity.

7.5 Architecture / Security and Administration

   It is the purpose of RFC 2571, "An Architecture for Describing SNMP
   Management Frameworks" [15], to define an architecture for specifying
   SNMP Management Frameworks.  While addressing general architectural
   issues, it focuses on aspects related to security and administration.
   It defines a number of terms used throughout the SNMPv3 Management
   Framework and, in so doing, clarifies and extends the naming of

     * engines and applications,

     * entities (service providers such as the engines in agents
       and managers),

     * identities (service users), and

     * management information, including support for multiple
       logical contexts.

   The document contains a small MIB module which is implemented by all
   authoritative SNMPv3 protocol engines.

7.6 Message Processing and Dispatch (MPD)

   RFC 2572, "Message Processing and Dispatching for the Simple Network
   Management Protocol (SNMP)" [16], describes the Message Processing
   and Dispatching for 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.

   It is expected that an SNMPv3 protocol engine MUST support at least
   one Message Processing Model.  An SNMPv3 protocol engine MAY support
   more than one, for example in a multi-lingual system which provides
   simultaneous support of SNMPv3 and SNMPv1 and/or SNMPv2c.








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7.7 SNMP Applications

   It is the purpose of RFC 2573, "SNMP Applications" to describe the
   five types of applications which can be associated with an SNMP
   engine.  They are: Command Generators, Command Responders,
   Notification Originators, Notification Receivers, and Proxy
   Forwarders.

   The document also defines MIB modules for specifying targets of
   management operations (including notifications), for notification
   filtering, and for proxy forwarding.

7.8 User-based Security Model (USM)

   RFC 2574, the "User-based Security Model (USM) for version 3 of the
   Simple Network Management Protocol (SNMPv3)" describes the User-based
   Security Model for SNMPv3.  It defines the Elements of Procedure for
   providing SNMP message-level security.

   The document describes the two primary and two secondary threats
   which are defended against by the User-based Security Model.  They
   are:  modification of information, masquerade, message stream
   modification, and disclosure.

   The USM utilizes MD5 [21] and the Secure Hash Algorithm [22] as keyed
   hashing algorithms [23] for digest computation to provide data
   integrity

     * to directly protect against data modification attacks,

     * to indirectly provide data origin authentication, and

     * to defend against masquerade attacks.

   The USM uses loosely synchronized monotonically increasing time
   indicators to defend against certain message stream modification
   attacks.  Automatic clock synchronization mechanisms based on the
   protocol are specified without dependence on third-party time sources
   and concomitant security considerations.

   The USM uses the Data Encryption Standard (DES) [24] in the cipher
   block chaining mode (CBC) if disclosure protection is desired.
   Support for DES in the USM is optional, primarily because export and
   usage restrictions in many countries make it difficult to export and
   use products which include cryptographic technology.






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   The document also includes a MIB suitable for remotely monitoring and
   managing the configuration parameters for the USM, including key
   distribution and key management.

   An entity may provide simultaneous support for multiple security
   models as well as multiple authentication and privacy protocols.  All
   of the protocols used by the USM are based on pre-placed keys, i.e.,
   private key mechanisms.  The SNMPv3 architecture permits the use of
   asymmetric mechanisms and protocols (commonly called "public key
   cryptography") but as of this writing, no such SNMPv3 security models
   utilizing public key cryptography have been published.

7.9 View-based Access Control (VACM)

   The purpose of RFC 2575, the "View-based Access Control Model (VACM)
   for the Simple Network Management Protocol (SNMP)" is to describe the
   View-based Access Control Model for use in the SNMP architecture.
   The VACM can simultaneously be associated in a single engine
   implementation with multiple Message Processing Models and multiple
   Security Models.

   It is architecturally possible to have multiple, different, Access
   Control Models active and present simultaneously in a single engine
   implementation, but this is expected to be *_very_* rare in practice
   and *_far_* less common than simultaneous support for multiple
   Message Processing Models and/or multiple Security Models.

7.10 SNMPv3 Coexistence and Transition

   The purpose of "Coexistence between Version 1, Version 2, and Version
   3 of the Internet-standard Network Management Framework" is to
   describe coexistence between the SNMPv3 Management Framework, the
   SNMPv2 Management Framework, and the original SNMPv1 Management
   Framework.  In particular, this document describes four aspects of
   coexistence:

     *  Conversion of MIB documents from SMIv1 to SMIv2 format

     *  Mapping of notification parameters

     *  Approaches to coexistence between entities which support
        the various versions of SNMP in a multi-lingual network, in
        particular the processing of protocol operations in
        multi-lingual implementations, as well as behavior of
        proxy implementations






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     *  The SNMPv1 Message Processing Model and Community-Based
        Security Model, which provides mechanisms for adapting
        SNMPv1 and SNMPv2c into the View-Based Access Control Model
        (VACM) [19]

8 Security Considerations

   As this document is primarily a roadmap document, it introduces no
   new security considerations.  The reader is referred to the relevant
   sections of each of the referenced documents for information about
   security considerations.

9 Editors' Addresses

   Jeffrey Case
   SNMP Research, Inc.
   3001 Kimberlin Heights Road
   Knoxville, TN 37920-9716
   USA
   Phone:  +1 423 573 1434
   EMail:  case@snmp.com

   Russ Mundy
   TIS Labs at Network Associates
   3060 Washington Rd
   Glenwood, MD 21738
   USA
   Phone:  +1 301 854 6889
   EMail:  mundy@tislabs.com

   David Partain
   Ericsson Radio Systems
   Research and Innovation
   P.O. Box 1248
   SE-581 12 Linkoping
   Sweden
   Phone:  +46 13 28 41 44
   EMail:  David.Partain@ericsson.com

   Bob Stewart
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134-1706
   U.S.A.
   Phone:  +1 603 654 6923
   EMail:  bstewart@cisco.com





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10 References

   [1]  Rose, M. and K. McCloghrie, "Structure and Identification of
        Management Information for TCP/IP-based internets", STD 16, RFC
        1155, May 1990.

   [2]  Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16,
        RFC 1212, March 1991.

   [3]  Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple
        Network Management Protocol", STD 15, RFC 1157, May 1990.

   [4]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
        Waldbusser, "Structure of Management Information for Version 2
        of the Simple Network Management Protocol (SNMPv2)", RFC 1902,
        January 1996.

   [5]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
        Waldbusser, "Textual Conventions for Version 2 of the Simple
        Network Management Protocol (SNMPv2)", RFC 1903, January 1996.

   [6]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
        Waldbusser, "Conformance Statements for Version 2 of the Simple
        Network Management Protocol (SNMPv2)", RFC 1904, January 1996.

   [7]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and S.
        Waldbusser, "Protocol Operations for Version 2 of the Simple
        Network Management Protocol (SNMPv2)", RFC 1905, January 1996.

   [8]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and S.
        Waldbusser, "Transport Mappings for Version 2 of the Simple
        Network Management Protocol (SNMPv2)", RFC 1906, January 1996.

   [9]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and S.
        Waldbusser, "Management Information Base for Version 2 of the
        Simple Network Management Protocol (SNMPv2)", RFC 1907, January
        1996.

   [10] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M. and S.
        Waldbusser, "Coexistence between Version 1 and Version 2 of the
        Internet-standard Network Management Framework", RFC 1908,
        January 1996.

   [11] Information processing systems - Open Systems Interconnection -
        Specification of Abstract Syntax Notation One (ASN.1),
        International Organization for Standardization.  International
        Standard 8824, (December, 1987).




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   [12] McCloghrie, K. and M. Rose, "Management Information Base for
        Network Management of TCP/IP-based Internets", RFC 1066, August
        1988.

   [13] McCloghrie, K. and M. Rose, "Management Information Base for
        Network Management of TCP/IP-based internets:  MIB-II, STD 17,
        RFC 1213, March 1991.

   [14] Cerf, V., "IAB Recommendations for the Development of Internet
        Network Management Standards", RFC 1052, April 1988.

   [15] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
        Describing SNMP Management Frameworks", RFC 2571, April 1999.

   [16] Case, J., Harrington, D., Presuhn, R. and B. Wijnen, "Message
        Processing and Dispatching for the Simple Network Management
        Protocol (SNMP)", RFC 2572, April 1999.

   [17] Levi, D., Meyer, P. and B. Stewart, "SNMP Applications", RFC
        2573, April 1999.

   [18] Blumenthal, U. and B. Wijnen, "The User-Based Security Model for
        Version 3 of the Simple Network Management Protocol (SNMPv3)",
        RFC 2574, April 1999.

   [19] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
        Control Model for the Simple Network Management Protocol
        (SNMP)", RFC 2575, April 1999.

   [20] Frye, R., Levi, D., Routhier, S., and B. Wijnen, "Coexistence
        between Version 1, Version 2, and Version 3 of the Internet-
        standard Network Management Framework", Work in Progress.

   [21] Rivest, R., "Message Digest Algorithm MD5", RFC 1321, April
        1992.

   [22] Secure Hash Algorithm. NIST FIPS 180-1, (April, 1995)
        http://csrc.nist.gov/fips/fip180-1.txt (ASCII)
        http://csrc.nist.gov/fips/fip180-1.ps  (Postscript)

   [23] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:  Keyed-Hashing
        for Message Authentication", RFC 2104, February 1997.

   [24] Data Encryption Standard, National Institute of Standards and
        Technology.  Federal Information Processing Standard (FIPS)
        Publication 46-1.  Supersedes FIPS Publication 46, (January,
        1977; reaffirmed January, 1988).




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   [25] Rose, M., "A Convention for Defining Traps for use with the
        SNMP", RFC 1215, March 1991.

   [26] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
        M. and S. Waldbusser, "Structure of Management Information
        Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

   [27] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
        M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58,
        RFC 2579, April 1999.

   [28] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
        M. and S. Waldbusser, "Conformance Statements for SMIv2", STD
        58, RFC 2580, April 1999.





































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11 Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

Acknowledgement

   Funding for the RFC Editor function is currently provided by
   the Internet Society.



















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