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RFC 2864 - The Inverted Stack Table Extension to the Interfaces

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Network Working Group                                      K. McCloghrie
Request for Comments: 2864                                 Cisco Systems
Category: Standards Track                                      G. Hanson
                                                  ADC Telecommunications
                                                               June 2000

     The Inverted Stack Table Extension to the Interfaces Group MIB

Status of this Memo

   This document 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" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Table of Contents

   1 Introduction ..................................................  1
   2 The SNMP Network Management Framework .........................  1
   3 Interface Sub-Layers and the ifStackTable .....................  3
   4 Definitions ...................................................  4
   5 Acknowledgements ..............................................  7
   6 References ....................................................  7
   7 Security Considerations .......................................  8
   8 Authors' Addresses ............................................  9
   9 Notice on Intellectual Property ............................... 10
   10 Full Copyright Statement ..................................... 11

1.  Introduction

   This memo defines a portion of the Management Information Base (MIB)
   for use with network management protocols in the Internet community.
   In particular, it describes managed objects which provide an inverted
   mapping of the interface stack table used for managing network

2.  The SNMP Network Management Framework

   The SNMP Management Framework presently consists of five major

    o An overall architecture, described in RFC 2571 [1].

    o Mechanisms for describing and naming objects and events for the
      purpose of management.  The first version of this Structure of
      Management Information (SMI) is called SMIv1 and described in STD
      16, RFC 1155 [2], STD 16, RFC 1212 [3] and RFC 1215 [4].  The
      second version, called SMIv2, is described in STD 58, which
      consists of RFC 2578 [5], RFC 2579 [6] and RFC 2580 [7].

    o Message protocols for transferring management information.  The
      first version of the SNMP message protocol is called SNMPv1 and
      described in STD 15, RFC 1157 [8].  A second version of the SNMP
      message protocol, which is not an Internet standards track
      protocol, is called SNMPv2c and described in RFC 1901 [9] and RFC
      1906 [10].  The third version of the message protocol is called
      SNMPv3 and described in RFC 1906 [10], RFC 2572 [11] and RFC 2574

    o Protocol operations for accessing management information.  The
      first set of protocol operations and associated PDU formats is
      described in STD 15, RFC 1157 [8].  A second set of protocol
      operations and associated PDU formats is described in RFC 1905

    o A set of fundamental applications described in RFC 2573 [14] and
      the view-based access control mechanism described in RFC 2575

   A more detailed introduction to the current SNMP Management Framework
   can be found in RFC 2570 [18].

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  Objects in the MIB are
   defined using the mechanisms defined in the SMI.

   This memo specifies a MIB module that is compliant to the SMIv2.  A
   MIB conforming to the SMIv1 can be produced through the appropriate
   translations.  The resulting translated MIB must be semantically
   equivalent, except where objects or events are omitted because no
   translation is possible (e.g., use of Counter64).  Some machine
   readable information in SMIv2 will be converted into textual
   descriptions in SMIv1 during the translation process.  However, this
   loss of machine readable information is not considered to change the
   semantics of the MIB.

3.  Interface Sub-Layers and the ifStackTable

   MIB-II [16] defines objects for managing network interfaces by
   providing a generic interface definition together with the ability to
   define media-specific extensions.  The generic objects are known as
   the 'interfaces' group.

   Experience in defining media-specific extensions showed the need to
   distinguish between the multiple sub-layers beneath the
   internetwork-layer.  Consider, for example, an interface with PPP
   running over an HDLC link which uses a RS232-like connector.  Each of
   these sub-layers has its own media-specific MIB module.

   The latest definition of the 'interfaces' group in the IF-MIB [17]
   satisfies this need by having each sub-layer be represented by its
   own conceptual row in the ifTable.  It also defines an additional MIB
   table, the ifStackTable, to identify the "superior" and "subordinate"
   sub-layers through ifIndex "pointers" to the appropriate conceptual
   rows in the ifTable.

   Each conceptual row in the ifStackTable represents a relationship
   between two interfaces, where this relationship is that the "higher-
   layer" interface runs "on top" of the "lower-layer" interface.  For
   example, if a PPP module operated directly over a serial interface,
   the PPP module would be a "higher layer" to the serial interface, and
   the serial interface would be a "lower layer" to the PPP module.
   This concept of "higher-layer" and "lower-layer" is the same as
   embodied in the definitions of the ifTable's packet counters.

   The ifStackTable is INDEX-ed by the ifIndex values of the two
   interfaces involved in the relationship.  By necessity, one of these
   ifIndex values must come first, and the IF-MIB chose to have the
   higher-layer interface first, and the lower-layer interface second.
   Due to this, it is straight-forward for a Network Management
   application to read a subset of the ifStackTable and thereby
   determine the interfaces which run underneath a particular interface.
   However, to determine which interfaces run on top of a particular
   interface, a Network Management application has no alternative but to
   read the whole table.  This is very inefficient when querying a
   device which has many interfaces, and many conceptual rows in its

   This MIB provides an inverted Interfaces Stack Table, the
   ifInvStackTable.  While it contains no additional information beyond
   that already contained in the ifStackTable, the ifInvStackTable has
   the ifIndex values in its INDEX clause in the reverse order, i.e.,
   the lower-layer interface first, and the higher-layer interface
   second.  As a result, the ifInvStackTable is an inverted version of

   the same information contained in the ifStackTable.  Thus, the
   ifInvStackTable provides an efficient means for a Network Management
   application to read a subset of the ifStackTable and thereby
   determine which interfaces run on top of a particular interface.

4.  Definitions


  RowStatus                                FROM SNMPv2-TC
  ifStackHigherLayer, ifStackLowerLayer    FROM IF-MIB;

  LAST-UPDATED "200006140000Z"
  ORGANIZATION "IETF Interfaces MIB Working Group"
          "   Keith McCloghrie
              Cisco Systems, Inc.
              170 West Tasman Drive
              San Jose, CA  95134-1706

          "The MIB module which provides the Inverted Stack Table for
          interface sub-layers."
  REVISION      "200006140000Z"
          "Initial revision, published as RFC 2864"
  ::= { mib-2 77 }

ifInvMIBObjects OBJECT IDENTIFIER ::= { ifInvertedStackMIB 1 }

--           The Inverted Interface Stack Group

ifInvStackTable  OBJECT-TYPE
   SYNTAX        SEQUENCE OF IfInvStackEntry
   MAX-ACCESS    not-accessible
   STATUS        current
          "A table containing information on the relationships between

          the multiple sub-layers of network interfaces.  In
          particular, it contains information on which sub-layers run
          'underneath' which other sub-layers, where each sub-layer
          corresponds to a conceptual row in the ifTable.  For
          example, when the sub-layer with ifIndex value x runs
          underneath the sub-layer with ifIndex value y, then this
          table contains:


          For each ifIndex value, z, which identifies an active
          interface, there are always at least two instantiated rows
          in this table associated with z.  For one of these rows, z
          is the value of ifStackHigherLayer; for the other, z is the
          value of ifStackLowerLayer.  (If z is not involved in
          multiplexing, then these are the only two rows associated
          with z.)

          For example, two rows exist even for an interface which has
          no others stacked on top or below it:


          This table contains exactly the same number of rows as the
          ifStackTable, but the rows appear in a different order."
          "ifStackTable of RFC 2863"
   ::= { ifInvMIBObjects 1 }

ifInvStackEntry  OBJECT-TYPE
   SYNTAX        IfInvStackEntry
   MAX-ACCESS    not-accessible
   STATUS        current
          "Information on a particular relationship between two sub-
          layers, specifying that one sub-layer runs underneath the
          other sub-layer.  Each sub-layer corresponds to a conceptual
          row in the ifTable."
   INDEX { ifStackLowerLayer, ifStackHigherLayer }
   ::= { ifInvStackTable 1 }

IfInvStackEntry ::=
      ifInvStackStatus       RowStatus

ifInvStackStatus  OBJECT-TYPE

  SYNTAX         RowStatus
  MAX-ACCESS     read-only
  STATUS         current
          "The status of the relationship between two sub-layers.

          An instance of this object exists for each instance of the
          ifStackStatus object, and vice versa.  For example, if the
          variable ifStackStatus.H.L exists, then the variable
          ifInvStackStatus.L.H must also exist, and vice versa.  In
          addition, the two variables always have the same value.

          However, unlike ifStackStatus, the ifInvStackStatus object
          is NOT write-able.  A network management application wishing
          to change a relationship between sub-layers H and L cannot
          do so by modifying the value of ifInvStackStatus.L.H, but
          must instead modify the value of ifStackStatus.H.L.  After
          the ifStackTable is modified, the change will be reflected
          in this table."
  ::= { ifInvStackEntry 1 }

-- conformance information

ifInvConformance OBJECT IDENTIFIER ::= { ifInvMIBObjects 2 }

ifInvGroups      OBJECT IDENTIFIER ::= { ifInvConformance 1 }
ifInvCompliances OBJECT IDENTIFIER ::= { ifInvConformance 2 }

-- compliance statements

  STATUS  current
          "The compliance statement for SNMP entities which provide
          inverted information on the layering of network interfaces."

  MODULE  -- this module
      MANDATORY-GROUPS { ifInvStackGroup }

      OBJECT       ifInvStackStatus
      SYNTAX       INTEGER { active(1) }
          "Support is only required for 'active'."

      MANDATORY-GROUPS { ifStackGroup2 }

  ::= { ifInvCompliances 1 }

-- units of conformance

ifInvStackGroup    OBJECT-GROUP
  OBJECTS { ifInvStackStatus }
  STATUS  current
          "A collection of objects providing inverted information on
          the layering of MIB-II interfaces."
  ::= { ifInvGroups 1 }


5.  Acknowledgements

   This memo has been produced by the IETF's Interfaces MIB working-

6.  References

   [1]  Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
        Describing SNMP Management Frameworks", RFC 2571, January 1998.

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

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

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

   [5]  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.

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

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

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

   [9]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
        Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901,
        January 1996.

   [10] 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.

   [11] Case, J., Harrington D., Presuhn R. and B. Wijnen, "Message
        Processing and Dispatching for the Simple Network Management
        Protocol (SNMP)", RFC 2572, January 1998.

   [12] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM)
        for version 3 of the Simple Network Management Protocol
        (SNMPv3)", RFC 2574, January 1998.

   [13] 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.

   [14] Levi, D., Meyer, P. and B. Stewart, "SNMP Applications", RFC
        2573, January 1998.

   [15] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
        Control Model (VACM) for the Simple Network Management Protocol
        (SNMP)", RFC 2575, January 1998.

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

   [17] McCloghrie, K. and F. Kastenholz, "The Interface Group MIB", RFC
        2863, June 2000.

   [18] Case, J., Mundy, R., Partain, D. and B. Stewart, "Introduction
        to Version 3 of the Internet-standard Network Management
        Framework", RFC 2570, April 1999.

7.  Security Considerations

   There are no management objects defined in this MIB that have a MAX-
   ACCESS clause of read-write and/or read-create.  So, if this MIB is
   implemented correctly, then there is no risk that an intruder can
   alter or create any management objects of this MIB via direct SNMP
   SET operations.

   SNMPv1 by itself is not a secure environment.  Even if the network
   itself is secure (for example by using IPSec), even then, there is no
   control as to who on the secure network is allowed to access and
   GET/SET (read/change/create/delete) the objects in this MIB.

   It is recommended that the implementers consider the security
   features as provided by the SNMPv3 framework.  Specifically, the use
   of the User-based Security Model RFC 2574 [12] and the View- based
   Access Control Model RFC 2575 [15] is recommended.

   It is then a customer/user responsibility to ensure that the SNMP
   entity giving access to an instance of this MIB, is properly
   configured to give access to the objects only to those principals
   (users) that have legitimate rights to indeed GET or SET
   (change/create/delete) them.

8.  Authors' Addresses

   Keith McCloghrie
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134-1706

   Phone: 408-526-5260
   EMail: kzm@cisco.com

   Gary Hanson
   ADC Telecommunications
   14375 NW Science Park Drive
   Portland, Oregon, 97229

   Phone: (800)733-5511 x6333
   EMail: gary_hanson@adc.com

9.  Notice on Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
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   proprietary rights by implementors or users of this specification can
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   The IETF invites any interested party to bring to its attention any
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   this standard.  Please address the information to the IETF Executive

10.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

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