rfc1525.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                          E. Decker
Request for Comments: 1525                           cisco Systems, Inc.
Obsoletes: 1286                                            K. McCloghrie
Category: Standards Track                       Hughes LAN Systems, Inc.
                                                             P. Langille
                                                                     DEC
                                                          A. Rijsinghani
                                                                     DEC
                                                          September 1993


                   Definitions of Managed Objects for
                         Source Routing Bridges

Status of this Memo

   This RFC 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" for the standardization state and status
   of this protocol.  Distribution of this memo is unlimited.

Table of Contents

   1. Introduction .........................................    2
   2. The Network Management Framework .....................    2
   2.1 Object Definitions ..................................    2
   3. Overview .............................................    2
   3.1 Structure of MIB ....................................    3
   3.1.1 The dot1dSr Group .................................    4
   3.1.2 The dot1dPortPair Group ...........................    4
   3.2 Relationship to Other MIBs ..........................    5
   3.2.1 Relationship to the Bridge MIB ....................    5
   3.2.2 Relationship to the 'system' group ................    5
   3.2.3 Relationship to the 'interfaces' group ............    5
   4. Changes from RFC 1286 ................................    6
   5. Definitions ..........................................    7
   5.1 Groups in the SR MIB ................................    7
   5.2 The dot1dSr Group Definitions .......................    7
   5.3 The dot1dPortPair Group Definitions .................   14
   6. Acknowledgments ......................................   16
   7. References ...........................................   16
   8. Security Considerations ..............................   18
   9. Authors' Addresses ...................................   18







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1.  Introduction

   This memo defines a portion of the Management Information Base (MIB)
   for use with network management protocols in TCP/IP based internets.
   In particular, it defines objects for managing source routing and
   source routing transparent bridges.  These bridges are also required
   to implement relevant groups in the Bridge MIB [6].

   This MIB supersedes the dot1dSr group of objects published in an
   earlier version of the Bridge MIB, RFC 1286.  Changes have primarily
   been made to track changes in the IEEE 802.5M SRT Addendum to the
   IEEE 802.1D Standard for MAC Bridges.

2.  The Network Management Framework

   The Internet-standard Network Management Framework consists of three
   components.  They are:

      o    STD 16, RFC 1155 which defines the SMI, the mechanisms used for
           describing and naming objects for the purpose of
           management.  STD 16, RFC 1212 defines a more concise description
           mechanism, which is wholly consistent with the SMI.

      o    STD 17, RFC 1213 defines MIB-II, the core set of managed objects
           for the Internet suite of protocols.

      o    STD 15, RFC 1157 which defines the SNMP, the protocol used for
           network access to managed objects.

   The Framework permits new objects to be defined for the purpose of
   experimentation and evaluation.

2.1.  Object Definitions

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  Objects in the MIB are
   defined using the subset of Abstract Syntax Notation One (ASN.1)
   defined in the SMI.  In particular, each object object type is named
   by an OBJECT IDENTIFIER, an administratively assigned name.  The
   object type together with an object instance serves to uniquely
   identify a specific instantiation of the object.  For human
   convenience, we often use a textual string, termed the descriptor, to
   refer to the object type.

3.  Overview

   A common device present in many networks is the Bridge.  This device
   is used to connect Local Area Network segments below the network



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   layer.  There are two major modes defined for this bridging;
   transparent and source route.  The transparent method of bridging is
   defined in the IEEE 802.1d MAC Bridge specification [11].  Source
   route bridging has been defined by I.B.M. and is described in the
   Token Ring Architecture Reference [12], as well as the IEEE 802.5M
   SRT Bridge Operations Addendum [14] to 802.1d.  This memo defines
   objects needed for management of a source routing bridge, and is an
   extension to the SNMP Bridge MIB [6].

   An explicit attempt was made to keep this MIB as simple as possible.
   This was accomplished by applying the following criteria to objects
   proposed for inclusion:

      (1)  Start with a small set of essential objects and add only
           as further objects are needed.

      (2)  Require objects be essential for either fault or
           configuration management.

      (3)  Consider evidence of current use and/or utility.

      (4)  Limit the total of objects.

      (5)  Exclude objects which are simply derivable from others in
           this or other MIBs.

      (6)  Avoid causing critical sections to be heavily
           instrumented.  The guideline that was followed is one
           counter per critical section per layer.

3.1.  Structure of MIB

   Objects in this MIB are arranged into groups.  Each group is
   organized as a set of related objects.  The overall structure and
   assignment of objects to their groups is shown below.  Where
   appropriate, the corresponding management object name found in IEEE
   802.1d [11] and IEEE 802.5M [14] is also included.

    SR Bridge MIB Name              IEEE Name

      dot1dSr
        PortTable
          Port
          HopCount                    SourceRoutingPort
                                        .PortHopCount
          LocalSegment                  .SegmentNumber
          BridgeNum                     .BridgeNumber
          TargetSegment



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          LargestFrame                  .LargestFrameSize
          STESpanMode                   .LimitedBroadcastMode
          SpecInFrames                BridgePort
                                        .ValidSRFramesReceived
          SpecOutFrames                 .ValidSRForwardedOutbound
          ApeInFrames
          ApeOutFrames                  .BroadcastFramesForwarded
          SteInFrames
          SteOutFrames                  .BroadcastFramesForwarded
          SegmentMismatchDiscards       .DiscardInvalidRI
          DuplicateSegmentDiscards      .LanIdMismatch
          HopCountExceededDiscards      .FramesDiscardedHopCountExceeded

   The following IEEE management objects have not been included in the
   SR Bridge MIB for the indicated reasons.

    IEEE Object                     Disposition

    SourceRoutingPort
                                    The following objects were NOT
                                    included in this MIB because they
                                    are redundant or not considered
                                    useful.
        .LimitedBroadcastEnable
        .DiscardLackOfBuffers
        .DiscardErrorDetails
        .DiscardTargetLANInoperable
        .ValidSRDiscardedInbound
        .BroadcastBytesForwarded
        .NonBroadcastBytesForwarded
        .FramesNotReceivedDueToCongestion
        .FramesDiscardedDueToInternalError

3.1.1.  The dot1dSr Group

   This group contains the objects that describe the entity's state with
   respect to source route bridging.  If source routing is not
   supported, this group will not be implemented.  This group is
   applicable to source route only, and SRT bridges.

3.1.2.  The dot1dPortPair Group

   Implementation of this group is optional.  This group is implemented
   by those bridges that support the port-pair multiport model of the
   source route bridging mode as defined in the IEEE 802.5M SRT Addendum
   to 802.1d.





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3.2.  Relationship to Other MIBs

   As described above, some IEEE 802.1d management objects have not been
   included in this MIB because they overlap with objects in other MIBs
   applicable to a bridge implementing this MIB.  In particular, it is
   assumed that a bridge implementing this MIB will also implement (at
   least) the Bridge MIB and the 'system' group and the 'interfaces'
   group defined in MIB-II [4].

3.2.1.  Relationship to the Bridge MIB

   The Bridge MIB [6] must be implemented by all bridges, including
   transparent, SR and SRT bridges.  The SR bridge MIB is an extension
   to the Bridge MIB.

3.2.2.  Relationship to the 'system' group

   In MIB-II, the 'system' group is defined as being mandatory for all
   systems such that each managed entity contains one instance of each
   object in the 'system' group.  Thus, those objects apply to the
   entity as a whole irrespective of whether the entity's sole
   functionality is bridging, or whether bridging is only a subset of
   the entity's functionality.

3.2.3.  Relationship to the 'interfaces' group

   In MIB-II, the 'interfaces' group is defined as being mandatory for
   all systems and contains information on an entity's interfaces, where
   each interface is thought of as being attached to a `subnetwork'.
   (Note that this term is not to be confused with `subnet' which refers
   to an addressing partitioning scheme used in the Internet suite of
   protocols.)  The term 'segment' is used in this memo to refer to such
   a subnetwork.

   Implicit in this MIB is the notion of ports on a bridge.  Each of
   these ports is associated with one interface of the 'interfaces'
   group, and in most situations, each port is associated with a
   different interface. However, there are situations in which multiple
   ports are associated with the same interface.  An example of such a
   situation would be several ports, each corresponding one-to-one with
   several X.25 virtual circuits, but all on the same interface.

   Each port is uniquely identified by a port number.  A port number has
   no mandatory relationship to an interface number, but in the simple
   case, a port number will have the same value as the corresponding
   interface's interface number.





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   Some entities provide other services in addition to bridging with
   respect to the data sent and received by their interfaces.  In such
   situations, only a subset of the data sent/received on an interface
   is within the domain of the entity's bridging functionality.  This
   subset is considered to be delineated according to a set of
   protocols, with some protocols being bridged, and other protocols not
   being bridged.  For example, in an entity which exclusively performed
   bridging, all protocols would be considered as being bridged, whereas
   in an entity which performed IP routing on IP datagrams and only
   bridged other protocols, only the non-IP data would be considered as
   being bridged.

   Thus, this MIB (and in particular, its counters) are applicable only
   to that subset of the data on an entity's interfaces which is
   sent/received for a protocol being bridged.  All such data is
   sent/received via the ports of the bridge.

4.  Changes from RFC 1286

   In addition to being separated from the Bridge MIB into a separate
   document, the following changes were implemented as a result of
   feedback from IEEE 802.5M:

          (1)  Changed syntax of dot1dSrPortLargestFrame to INTEGER in
               order to allow for having 64 possible values as described
               in draft 7 of the SR Addendum.  Listed all legal values
               in description.

          (2)  Updated syntax of dot1dSrPort, used to index into
               dot1dSrPortTable, to use the range (1..65535).

          (3)  Added a counter to dot1dSrPortTable to count occurrences
               of duplicate LAN IDs or Tree errors.

          (4)  Added a counter to dot1dSrPortTable to count LAN ID
               mismatches.

          (5)  Added text to dot1dSrPortSpecInFrames and
               dot1dSrPortSpecOutFrames clarifying that they are also
               referred to as Source Routed Frames.

          (6)  Added text to dot1dSrPortApeInFrames and
               dot1dSrPortApeOutFrames clarifying that they are also
               referred to as All Routes Explorer frames.

          (7)  Added a scalar variable to the dot1dSr group to indicate
               whether the bridge uses 3 bit or 6 bit length negotiation
               fields.