rfc1098.txt

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Network Working Group                                            J. Case
Request for Comments: 1098          University of Tennessee at Knoxville
Obsoletes: RFC 1067                                             M. Fedor
                                                          NYSERNet, Inc.
                                                          M. Schoffstall
                                        Rensselaer Polytechnic Institute
                                                                C. Davin
                                     MIT Laboratory for Computer Science
                                                              April 1989


              A Simple Network Management Protocol (SNMP)

                           Table of Contents

   1. Status of this Memo ...................................    2
   2. Introduction ..........................................    2
   3. The SNMP Architecture .................................    4
   3.1 Goals of the Architecture ............................    4
   3.2 Elements of the Architecture .........................    4
   3.2.1 Scope of Management Information ....................    5
   3.2.2 Representation of Management Information ...........    5
   3.2.3 Operations Supported on Management Information .....    6
   3.2.4 Form and Meaning of Protocol Exchanges .............    7
   3.2.5 Definition of Administrative Relationships .........    7
   3.2.6 Form and Meaning of References to Managed Objects ..   11
   3.2.6.1 Resolution of Ambiguous MIB References ...........   11
   3.2.6.2 Resolution of References across MIB Versions......   11
   3.2.6.3 Identification of Object Instances ...............   11
   3.2.6.3.1 ifTable Object Type Names ......................   12
   3.2.6.3.2 atTable Object Type Names ......................   12
   3.2.6.3.3 ipAddrTable Object Type Names ..................   13
   3.2.6.3.4 ipRoutingTable Object Type Names ...............   13
   3.2.6.3.5 tcpConnTable Object Type Names .................   13
   3.2.6.3.6 egpNeighTable Object Type Names ................   14
   4. Protocol Specification ................................   15
   4.1 Elements of Procedure ................................   16
   4.1.1 Common Constructs ..................................   18
   4.1.2 The GetRequest-PDU .................................   19
   4.1.3 The GetNextRequest-PDU .............................   20
   4.1.3.1 Example of Table Traversal .......................   22
   4.1.4 The GetResponse-PDU ................................   23
   4.1.5 The SetRequest-PDU .................................   24
   4.1.6 The Trap-PDU .......................................   26
   4.1.6.1 The coldStart Trap ...............................   27
   4.1.6.2 The warmStart Trap ...............................   27
   4.1.6.3 The linkDown Trap ................................   27
   4.1.6.4 The linkUp Trap ..................................   27



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RFC 1098                          SNMP                        April 1989


   4.1.6.5 The authenticationFailure Trap ...................   27
   4.1.6.6 The egpNeighborLoss Trap .........................   27
   4.1.6.7 The enterpriseSpecific Trap ......................   28
   5. Definitions ...........................................   29
   6. Acknowledgements ......................................   32
   7. References ............................................   33

1.  Status of this Memo

   This RFC is a re-release of RFC 1067, with a changed "Status of this
   Memo" section.  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 initial 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 (IAB) has designated two different
   network management protocols with the same status of "Draft Standard"
   and "Recommended".

   The two protocols are the Common Management Information Services and
   Protocol over TCP/IP (CMOT) [9], and the Simple Network Management
   Protocol (SNMP) (this memo).

   The IAB intends each of these two protocols to receive the attention
   of implementers and experimenters.  The IAB seeks reports of
   experience with these two protocols from system builders and users.

   By this action, the IAB recommends that all IP and TCP
   implementations be network manageable (e.g., implement the Internet
   MIB [3]) and that the implementations that are network manageable are
   expected to adopt and implement at least one of these two Internet
   Draft Standards.

   Distribution of this memo is unlimited.

2.  Introduction

   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 is charged with the further specification and definition of
   elements to be included in the Management Information Base (MIB).
   The other is charged with defining the modifications to the Simple
   Network Management Protocol (SNMP) to accommodate the short-term



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   needs of the network vendor and operations communities, and to align
   with the output of the MIB working group.

   The MIB working group has produced two memos, one which defines a
   Structure for Management Information (SMI) [2] for use by the managed
   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 [4] 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) [5].
   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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RFC 1098                          SNMP                        April 1989


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 [2].

   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 [6] 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 [6].  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) [2] and Management Information Base
   (MIB) [3].  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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   Also for the sake of simplicity, the SNMP uses only a subset of the
   basic encoding rules of ASN.1 [7].  Namely, all encodings use the
   definite-length form.  Further, whenever permissible, non-constructor
   encodings are used rather than constructor encodings.  This
   restriction applies to all aspects of ASN.1 encoding, both for the
   top-level protocol data units and the data objects they contain.

3.2.3.  Operations Supported on Management Information

   The SNMP models all management agent functions as alterations or
   inspections of variables.  Thus, a protocol entity on a logically
   remote host (possibly the network element itself) interacts with the
   management agent resident on the network element in order to retrieve
   (get) or alter (set) variables.  This strategy has at least two
   positive consequences:

      (1)  It has the effect of limiting the number of essential
           management functions realized by the management agent to
           two: one operation to assign a value to a specified
           configuration or other parameter and another to retrieve
           such a value.

      (2)  A second effect of this decision is to avoid introducing
           into the protocol definition support for imperative
           management commands:  the number of such commands is in
           practice ever-increasing, and the semantics of such
           commands are in general arbitrarily complex.

   The strategy implicit in the SNMP is that the monitoring of network
   state at any significant level of detail is accomplished primarily by
   polling for appropriate information on the part of the monitoring
   center(s).  A limited number of unsolicited messages (traps) guide
   the timing and focus of the polling.  Limiting the number of
   unsolicited messages is consistent with the goal of simplicity and
   minimizing the amount of traffic generated by the network management
   function.

   The exclusion of imperative commands from the set of explicitly
   supported management functions is unlikely to preclude any desirable
   management agent operation.  Currently, most commands are requests
   either to set the value of some parameter or to retrieve such a
   value, and the function of the few imperative commands currently
   supported is easily accommodated in an asynchronous mode by this
   management model.  In this scheme, an imperative command might be
   realized as the setting of a parameter value that subsequently
   triggers the desired action.  For example, rather than implementing a
   "reboot command," this action might be invoked by simply setting a
   parameter indicating the number of seconds until system reboot.