rfc1354.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                                           F. Baker
Request For Comments: 1354                                           ACC
                                                               July 1992


                        IP Forwarding Table MIB

Status of this Memo

   This RFC specifies an IAB standards track protocol for the Internet
   community, and requests discussion and suggestions for improvements.
   Please refer to the current edition of the "IAB Official Protocol
   Standards" for the standardization state and status of this protocol.
   Distribution of this memo is unlimited.

Abstract

   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 routes in the IP
   Internet.

   It is proposed that the ipRouteTable defined by MIB-II (RFC 1213) be
   deprecated and replaced with this table.  This adds the ability to
   set or display multi-path routes, and varying routes by network
   management policy.

Table of Contents

   1. The Network Management Framework ............................    1
   2. Objects .....................................................    2
   2.1 Format of Definitions ......................................    2
   3. Overview ....................................................    3
   3.1 Structure of MIB ...........................................    3
   4. Definitions .................................................    4
   4.1 IP Forwarding Table ........................................    4
   5. Acknowledgements ............................................   11
   6. References ..................................................   11
   7. Security Considerations........................................ 12
   8. Author's Address............................................... 12

1.  The Network Management Framework

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

   RFC 1155 which defines the SMI, the mechanisms used for describing
   and naming objects for the purpose of management.  RFC 1212 defines a



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   more concise description mechanism, which is wholly consistent with
   the SMI.

   RFC 1156 which defines MIB-I, the core set of managed objects for the
   Internet suite of protocols.  RFC 1213 defines MIB-II, an evolution
   of MIB-I based on implementation experience and new operational
   requirements.

   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.  Objects

   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) [7]
   defined in the SMI.  In particular, each object has a name, a syntax,
   and an encoding.  The name is an object identifier, an
   administratively assigned name, which specifies an object type.  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 OBJECT
   DESCRIPTOR, to also refer to the object type.

   The syntax of an object type defines the abstract data structure
   corresponding to that object type.  The ASN.1 language is used for
   this purpose.  However, the SMI [3] purposely restricts the ASN.1
   constructs which may be used.  These restrictions are explicitly made
   for simplicity.

   The encoding of an object type is simply how that object type is
   represented using the object type's syntax.  Implicitly tied to the
   notion of an object type's syntax and encoding is how the object type
   is represented when being transmitted on the network.

   The SMI specifies the use of the basic encoding rules of ASN.1 [8],
   subject to the additional requirements imposed by the SNMP.

2.1.  Format of Definitions

   Section 4 contains contains the specification of all object types
   contained in this MIB module.  The object types are defined using the
   conventions defined in the SMI, as amended by the extensions
   specified in [9].




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3.  Overview

3.1.  Structure of MIB

   The IP Forwarding Table is quite analogous to the older ipRoute
   Table.  The principal differences are:

      (1)  It is somewhat re-organized, for aesthetic reasons,

      (2)  It has the Next Hop Autonomous System Number, useful
           primarily to the administrators of regional networks,

      (3)  It is instanced by Policy and Next Hop as well as by
           ultimate destination.  Thus, multiple multipath routes
           can be managed, not just a single route, along with the
           circumstances under which the any given route might be
           chosen.

4.  Definitions

     RFC1354-MIB DEFINITIONS ::= BEGIN

     IMPORTS
             Gauge, IpAddress
                     FROM RFC1155-SMI
             mib-2, ip
                     FROM RFC1213-MIB
             OBJECT-TYPE
                     FROM RFC-1212;

     --  This MIB module uses the extended OBJECT-TYPE macro as
     --  defined in [9].
     ipForward  OBJECT IDENTIFIER ::= { ip 24 }

         ipForwardNumber OBJECT-TYPE
             SYNTAX   Gauge
             ACCESS   read-only
             STATUS   mandatory
             DESCRIPTION
                "The number of current  ipForwardTable  entries
                that are not invalid."
             ::= { ipForward 1 }


     --  IP Forwarding Table

     --  The IP Forwarding Table obsoletes and replaces the ipRoute
     --  Table current in MIB-I and MIB-II.  It adds knowledge of



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     --  the autonomous system of the next hop, multiple next hop
     --  support, and policy routing support.


         ipForwardTable OBJECT-TYPE
             SYNTAX   SEQUENCE OF IpForwardEntry
             ACCESS   not-accessible
             STATUS   mandatory
             DESCRIPTION
                "This entity's IP Routing table."
             REFERENCE
                "RFC 1213 Section 6.6, The IP Group"
             ::= { ipForward 2 }


         ipForwardEntry OBJECT-TYPE
             SYNTAX   IpForwardEntry
             ACCESS   not-accessible
             STATUS   mandatory
             DESCRIPTION
                "A particular route to  a  particular  destina-
                tion, under a particular policy."
             INDEX {
                 ipForwardDest,
                 ipForwardProto,
                 ipForwardPolicy,
                 ipForwardNextHop
                 }
             ::= { ipForwardTable 1 }


         IpForwardEntry ::=
             SEQUENCE {
                 ipForwardDest
                     IpAddress,
                 ipForwardMask
                     IpAddress,
                 ipForwardPolicy
                     INTEGER,
                 ipForwardNextHop
                     IpAddress,
                 ipForwardIfIndex
                     INTEGER,
                 ipForwardType
                     INTEGER,
                 ipForwardProto
                     INTEGER,
                 ipForwardAge



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                     INTEGER,
                 ipForwardInfo
                     OBJECT IDENTIFIER,
                 ipForwardNextHopAS
                     INTEGER,
                 ipForwardMetric1
                     INTEGER,
                 ipForwardMetric2
                     INTEGER,
                 ipForwardMetric3
                     INTEGER,
                 ipForwardMetric4
                     INTEGER,
                 ipForwardMetric5
                     INTEGER
             }

         ipForwardDest OBJECT-TYPE
             SYNTAX   IpAddress
             ACCESS   read-only
             STATUS   mandatory
             DESCRIPTION
                "The destination IP address of this route.   An
                entry  with  a value of 0.0.0.0 is considered a
                default route.

                This object may not take a Multicast (Class  D)
                address value.

                Any assignment (implicit or  otherwise)  of  an
                instance  of  this  object to a value x must be
                rejected if the bitwise logical-AND of  x  with
                the  value of the corresponding instance of the
                ipForwardMask object is not equal to x."
             ::= { ipForwardEntry 1 }


         ipForwardMask OBJECT-TYPE
             SYNTAX   IpAddress
             ACCESS   read-write
             STATUS   mandatory
             DESCRIPTION
                "Indicate the mask to be logical-ANDed with the
                destination  address  before  being compared to
                the value  in  the  ipForwardDest  field.   For
                those  systems  that  do  not support arbitrary
                subnet masks, an agent constructs the value  of
                the  ipForwardMask  by  reference to the IP Ad-



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                dress Class.

                Any assignment (implicit or  otherwise)  of  an
                instance  of  this  object to a value x must be
                rejected if the bitwise logical-AND of  x  with
                the  value of the corresponding instance of the
                ipForwardDest object is not equal to ipForward-
                Dest."
             DEFVAL { '00000000'h }      -- 0.0.0.0
             ::= { ipForwardEntry 2 }


         -- The following convention is included for specification
         -- of TOS Field contents.  At this time, the Host Requirements
         -- and the Router Requirements documents disagree on the width
         -- of the TOS field.  This mapping describes the Router
         -- Requirements mapping, and leaves room to widen the TOS field
         -- without impact to fielded systems.

         ipForwardPolicy OBJECT-TYPE
             SYNTAX   INTEGER
             ACCESS   read-only
             STATUS   mandatory
             DESCRIPTION
                "The general set of conditions that would cause
                the  selection  of  one multipath route (set of
                next hops for a given destination) is  referred
                to as 'policy'.

                Unless the mechanism indicated by ipForwardPro-
                to specifies otherwise, the policy specifier is
                the IP TOS Field.  The encoding of IP TOS is as
                specified  by  the  following convention.  Zero
                indicates the default path if no more  specific
                policy applies.

                +-----+-----+-----+-----+-----+-----+-----+-----+
                |                 |                       |     |
                |   PRECEDENCE    |    TYPE OF SERVICE    |  0  |
                |                 |                       |     |
                +-----+-----+-----+-----+-----+-----+-----+-----+

                         IP TOS                IP TOS
                    Field     Policy      Field     Policy
                    Contents    Code      Contents    Code
                    0 0 0 0  ==>   0      0 0 0 1  ==>   2
                    0 0 1 0  ==>   4      0 0 1 1  ==>   6
                    0 1 0 0  ==>   8      0 1 0 1  ==>  10



Baker                                                           [Page 6]