rfc1157.txt

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Network Working Group                                            J. Case
Request for Comments:  1157                                SNMP Research
Obsoletes:  RFC 1098                                            M. Fedor
                                       Performance Systems International
                                                          M. Schoffstall
                                       Performance Systems International
                                                                J. Davin
                                     MIT Laboratory for Computer Science
                                                                May 1990


              A Simple Network Management Protocol (SNMP)

                           Table of Contents

   1. Status of this Memo ...................................    2
   2. Introduction ..........................................    2
   3. The SNMP Architecture .................................    5
   3.1 Goals of the Architecture ............................    5
   3.2 Elements of the Architecture .........................    5
   3.2.1 Scope of Management Information ....................    6
   3.2.2 Representation of Management Information ...........    6
   3.2.3 Operations Supported on Management Information .....    7
   3.2.4 Form and Meaning of Protocol Exchanges .............    8
   3.2.5 Definition of Administrative Relationships .........    8
   3.2.6 Form and Meaning of References to Managed Objects ..   12
   3.2.6.1 Resolution of Ambiguous MIB References ...........   12
   3.2.6.2 Resolution of References across MIB Versions......   12
   3.2.6.3 Identification of Object Instances ...............   12
   3.2.6.3.1 ifTable Object Type Names ......................   13
   3.2.6.3.2 atTable Object Type Names ......................   13
   3.2.6.3.3 ipAddrTable Object Type Names ..................   14
   3.2.6.3.4 ipRoutingTable Object Type Names ...............   14
   3.2.6.3.5 tcpConnTable Object Type Names .................   14
   3.2.6.3.6 egpNeighTable Object Type Names ................   15
   4. Protocol Specification ................................   16
   4.1 Elements of Procedure ................................   17
   4.1.1 Common Constructs ..................................   19
   4.1.2 The GetRequest-PDU .................................   20
   4.1.3 The GetNextRequest-PDU .............................   21
   4.1.3.1 Example of Table Traversal .......................   23
   4.1.4 The GetResponse-PDU ................................   24
   4.1.5 The SetRequest-PDU .................................   25
   4.1.6 The Trap-PDU .......................................   27
   4.1.6.1 The coldStart Trap ...............................   28
   4.1.6.2 The warmStart Trap ...............................   28
   4.1.6.3 The linkDown Trap ................................   28
   4.1.6.4 The linkUp Trap ..................................   28



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   4.1.6.5 The authenticationFailure Trap ...................   28
   4.1.6.6 The egpNeighborLoss Trap .........................   28
   4.1.6.7 The enterpriseSpecific Trap ......................   29
   5. Definitions ...........................................   30
   6. Acknowledgements ......................................   33
   7. References ............................................   34
   8. Security Considerations................................   35
   9. Authors' Addresses.....................................   35

1.  Status of this Memo

   This RFC is a re-release of RFC 1098, with a changed "Status of this
   Memo" section plus a few minor typographical corrections.  This memo
   defines a simple protocol by which management information for a
   network element may be inspected or altered by logically remote
   users.  In particular, together with its companion memos which
   describe the structure of management information along with the
   management information base, these documents provide a simple,
   workable architecture and system for managing TCP/IP-based internets
   and in particular the Internet.

   The Internet Activities Board recommends that all IP and TCP
   implementations be network manageable.  This implies implementation
   of the Internet MIB (RFC-1156) and at least one of the two
   recommended management protocols SNMP (RFC-1157) or CMOT (RFC-1095).
   It should be noted that, at this time, SNMP is a full Internet
   standard and CMOT is a draft standard.  See also the Host and Gateway
   Requirements RFCs for more specific information on the applicability
   of this standard.

   Please refer to the latest edition of the "IAB Official Protocol
   Standards" RFC for current information on the state and status of
   standard Internet protocols.

   Distribution of this memo is unlimited.

2.  Introduction

   As reported in RFC 1052, IAB Recommendations for the Development of
   Internet Network Management Standards [1], a two-prong strategy for
   network management of TCP/IP-based internets was undertaken.  In the
   short-term, the Simple Network Management Protocol (SNMP) was to be
   used to manage nodes in the Internet community.  In the long-term,
   the use of the OSI network management framework was to be examined.
   Two documents were produced to define the management information: RFC
   1065, which defined the Structure of Management Information (SMI)
   [2], and RFC 1066, which defined the Management Information Base
   (MIB) [3].  Both of these documents were designed so as to be



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   compatible with both the SNMP and the OSI network management
   framework.

   This strategy was quite successful in the short-term: Internet-based
   network management technology was fielded, by both the research and
   commercial communities, within a few months.  As a result of this,
   portions of the Internet community became network manageable in a
   timely fashion.

   As reported in RFC 1109, Report of the Second Ad Hoc Network
   Management Review Group [4], the requirements of the SNMP and the OSI
   network management frameworks were more different than anticipated.
   As such, the requirement for compatibility between the SMI/MIB and
   both frameworks was suspended.  This action permitted the operational
   network management framework, the SNMP, to respond to new operational
   needs in the Internet community by producing documents defining new
   MIB items.

   The IAB has designated the SNMP, SMI, and the initial Internet MIB to
   be full "Standard Protocols" with "Recommended" status.  By this
   action, the IAB recommends that all IP and TCP implementations be
   network manageable and that the implementations that are network
   manageable are expected to adopt and implement the SMI, MIB, and
   SNMP.

   As such, the current network management framework for TCP/IP- based
   internets consists of:  Structure and Identification of Management
   Information for TCP/IP-based Internets, which describes how managed
   objects contained in the MIB are defined as set forth in RFC 1155
   [5]; Management Information Base for Network Management of TCP/IP-
   based Internets, which describes the managed objects contained in the
   MIB as set forth in RFC 1156 [6]; and, the Simple Network Management
   Protocol, which defines the protocol used to manage these objects, as
   set forth in this memo.

   As reported in RFC 1052, IAB Recommendations for the Development of
   Internet Network Management Standards [1], the Internet Activities
   Board has directed the Internet Engineering Task Force (IETF) to
   create two new working groups in the area of network management.  One
   group was charged with the further specification and definition of
   elements to be included in the Management Information Base (MIB).
   The other was charged with defining the modifications to the Simple
   Network Management Protocol (SNMP) to accommodate the short-term
   needs of the network vendor and operations communities, and to align
   with the output of the MIB working group.

   The MIB working group produced two memos, one which defines a
   Structure for Management Information (SMI) [2] for use by the managed



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   objects contained in the MIB.  A second memo [3] defines the list of
   managed objects.

   The output of the SNMP Extensions working group is this memo, which
   incorporates changes to the initial SNMP definition [7] required to
   attain alignment with the output of the MIB working group.  The
   changes should be minimal in order to be consistent with the IAB's
   directive that the working groups be "extremely sensitive to the need
   to keep the SNMP simple."  Although considerable care and debate has
   gone into the changes to the SNMP which are reflected in this memo,
   the resulting protocol is not backwardly-compatible with its
   predecessor, the Simple Gateway Monitoring Protocol (SGMP) [8].
   Although the syntax of the protocol has been altered, the original
   philosophy, design decisions, and architecture remain intact.  In
   order to avoid confusion, new UDP ports have been allocated for use
   by the protocol described in this memo.



































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3.  The SNMP Architecture

   Implicit in the SNMP architectural model is a collection of network
   management stations and network elements.  Network management
   stations execute management applications which monitor and control
   network elements.  Network elements are devices such as hosts,
   gateways, terminal servers, and the like, which have management
   agents responsible for performing the network management functions
   requested by the network management stations.  The Simple Network
   Management Protocol (SNMP) is used to communicate management
   information between the network management stations and the agents in
   the network elements.

3.1.  Goals of the Architecture

   The SNMP explicitly minimizes the number and complexity of management
   functions realized by the management agent itself.  This goal is
   attractive in at least four respects:

      (1)  The development cost for management agent software
           necessary to support the protocol is accordingly reduced.

      (2)  The degree of management function that is remotely
           supported is accordingly increased, thereby admitting
           fullest use of internet resources in the management task.

      (3)  The degree of management function that is remotely
           supported is accordingly increased, thereby imposing the
           fewest possible restrictions on the form and
           sophistication of management tools.

      (4)  Simplified sets of management functions are easily
           understood and used by developers of network management
           tools.

   A second goal of the protocol is that the functional paradigm for
   monitoring and control be sufficiently extensible to accommodate
   additional, possibly unanticipated aspects of network operation and
   management.

   A third goal is that the architecture be, as much as possible,
   independent of the architecture and mechanisms of particular hosts or
   particular gateways.

3.2.  Elements of the Architecture

   The SNMP architecture articulates a solution to the network
   management problem in terms of:



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      (1)  the scope of the management information communicated by
           the protocol,

      (2)  the representation of the management information
           communicated by the protocol,

      (3)  operations on management information supported by the
           protocol,

      (4)  the form and meaning of exchanges among management
           entities,

      (5)  the definition of administrative relationships among
           management entities, and

      (6)  the form and meaning of references to management
           information.

3.2.1.  Scope of Management Information

   The scope of the management information communicated by operation of
   the SNMP is exactly that represented by instances of all non-
   aggregate object types either defined in Internet-standard MIB or
   defined elsewhere according to the conventions set forth in
   Internet-standard SMI [5].

   Support for aggregate object types in the MIB is neither required for
   conformance with the SMI nor realized by the SNMP.

3.2.2.  Representation of Management Information

   Management information communicated by operation of the SNMP is
   represented according to the subset of the ASN.1 language [9] that is
   specified for the definition of non-aggregate types in the SMI.

   The SGMP adopted the convention of using a well-defined subset of the
   ASN.1 language [9].  The SNMP continues and extends this tradition by
   utilizing a moderately more complex subset of ASN.1 for describing
   managed objects and for describing the protocol data units used for
   managing those objects.  In addition, the desire to ease eventual
   transition to OSI-based network management protocols led to the
   definition in the ASN.1 language of an Internet-standard Structure of
   Management Information (SMI) [5] and Management Information Base
   (MIB) [6].  The use of the ASN.1 language, was, in part, encouraged
   by the successful use of ASN.1 in earlier efforts, in particular, the
   SGMP.  The restrictions on the use of ASN.1 that are part of the SMI
   contribute to the simplicity espoused and validated by experience
   with the SGMP.



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