rfc2863.txt

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Network Working Group                                      K. McCloghrie
Request for Comments: 2863                                 Cisco Systems
Obsoletes: 2233                                            F. Kastenholz
Category: Standards Track                                 Argon Networks
                                                               June 2000


                        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 .................................................    2
   2 The SNMP Network Management Framework ........................    2
   3 Experience with the Interfaces Group .........................    3
   3.1 Clarifications/Revisions ...................................    4
   3.1.1 Interface Sub-Layers .....................................    4
   3.1.2 Guidance on Defining Sub-layers ..........................    7
   3.1.3 Virtual Circuits .........................................    8
   3.1.4 Bit, Character, and Fixed-Length Interfaces ..............    8
   3.1.5 Interface Numbering ......................................   10
   3.1.6 Counter Size .............................................   14
   3.1.7 Interface Speed ..........................................   16
   3.1.8 Multicast/Broadcast Counters .............................   17
   3.1.9 Trap Enable ..............................................   17
   3.1.10 Addition of New ifType values ...........................   18
   3.1.11 InterfaceIndex Textual Convention .......................   18
   3.1.12 New states for IfOperStatus .............................   18
   3.1.13 IfAdminStatus and IfOperStatus ..........................   19
   3.1.14 IfOperStatus in an Interface Stack ......................   21
   3.1.15 Traps ...................................................   21
   3.1.16 ifSpecific ..............................................   23
   3.1.17 Creation/Deletion of Interfaces .........................   23
   3.1.18 All Values Must be Known ................................   24
   4 Media-Specific MIB Applicability .............................   24
   5 Overview .....................................................   25
   6 Interfaces Group Definitions .................................   26



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   7 Acknowledgements .............................................   64
   8 References ...................................................   64
   9 Security Considerations ......................................   66
   10 Authors' Addresses ..........................................   67
   11 Changes from RFC 2233 .......................................   67
   12 Notice on Intellectual Property .............................   68
   13 Full Copyright Statement ....................................   69

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 used for managing Network
   Interfaces.  This memo discusses the 'interfaces' group of MIB-II
   [17], especially the experience gained from the definition of
   numerous media-specific MIB modules for use in conjunction with the '
   interfaces' group for managing various sub-layers beneath the
   internetwork-layer.  It specifies clarifications to, and extensions
   of, the architectural issues within the MIB-II model of the '
   interfaces' group.  This memo obsoletes RFC 2233, the previous
   version of the Interfaces Group MIB.

   The key words "MUST" and "MUST NOT" in this document are to be
   interpreted as described in RFC 2119 [16].

2.  The SNMP Network Management Framework

   The SNMP Management Framework presently consists of five major
   components:

      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 [12].




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      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
         [13].

      o  A set of fundamental applications described in RFC 2573 [14]
         and the view-based access control mechanism described in RFC
         2575 [15].

   A more detailed introduction to the current SNMP Management Framework
   can be found in RFC 2570 [22].

   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.  Experience with the Interfaces Group

   One of the strengths of internetwork-layer protocols such as IP [18]
   is that they are designed to run over any network interface.  In
   achieving this, IP considers any and all protocols it runs over as a
   single "network interface" layer.  A similar view is taken by other
   internetwork-layer protocols.  This concept is represented in MIB-II
   by the 'interfaces' group which defines a generic set of managed
   objects such that any network interface can be managed in an
   interface-independent manner through these managed objects.  The '
   interfaces' group provides the means for additional managed objects
   specific to particular types of network interface (e.g., a specific
   medium such as Ethernet) to be defined as extensions to the '
   interfaces' group for media-specific management.  Since the
   standardization of MIB-II, many such media-specific MIB modules have
   been defined.

   Experience in defining these media-specific MIB modules has shown
   that the model defined by MIB-II is too simplistic and/or static for
   some types of media-specific management.  As a result, some of these
   media-specific MIB modules assume an evolution or loosening of the



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   model.  This memo documents and standardizes that evolution of the
   model and fills in the gaps caused by that evolution.  This memo also
   incorporates the interfaces group extensions documented in RFC 1229
   [19].

3.1.  Clarifications/Revisions

   There are several areas for which experience has indicated that
   clarification, revision, or extension of the model would be helpful.
   The following sections discuss the changes in the interfaces group
   adopted by this memo in each of these areas.

   In some sections, one or more paragraphs contain discussion of
   rejected alternatives to the model adopted in this memo.  Readers not
   familiar with the MIB-II model and not interested in the rationale
   behind the new model may want to skip these paragraphs.

3.1.1.  Interface Sub-Layers

   Experience in defining media-specific management information has
   shown the need to distinguish between the multiple sub-layers beneath
   the internetwork-layer.  In addition, there is a need to manage these
   sub-layers in devices (e.g., MAC-layer bridges) which are unaware of
   which, if any, internetwork protocols run over these sub-layers.  As
   such, a model of having a single conceptual row in the interfaces
   table (MIB-II's ifTable) represent a whole interface underneath the
   internetwork-layer, and having a single associated media-specific MIB
   module (referenced via the ifType object) is too simplistic.  A
   further problem arises with the value of the ifType object which has
   enumerated values for each type of interface.

   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.  If all of this is represented by
   a single conceptual row in the ifTable, then an enumerated value for
   ifType is needed for that specific combination which maps to the
   specific combination of media-specific MIBs.  Furthermore, such a
   model still lacks a method to describe the relationship of all the
   sub-layers of the MIB stack.

   An associated problem is that of upward and downward multiplexing of
   the sub-layers.  An example of upward multiplexing is MLP (Multi-
   Link-Procedure) which provides load-sharing over several serial lines
   by appearing as a single point-to-point link to the sub-layer(s)
   above.  An example of downward multiplexing would be several
   instances of PPP, each framed within a separate X.25 virtual circuit,





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   all of which run over one fractional T1 channel, concurrently with
   other uses of the T1 link.  The MIB structure must allow these sorts
   of relationships to be described.

   Several solutions for representing multiple sub-layers were rejected.
   One was to retain the concept of one conceptual row for all the sub-
   layers of an interface and have each media-specific MIB module
   identify its "superior" and "subordinate" sub-layers through OBJECT
   IDENTIFIER "pointers".  This scheme would have several drawbacks: the
   superior/subordinate pointers would be contained in the media-
   specific MIB modules; thus, a manager could not learn the structure
   of an interface without inspecting multiple pointers in different MIB
   modules; this would be overly complex and only possible if the
   manager had knowledge of all the relevant media-specific MIB modules;
   MIB modules would all need to be retrofitted with these new
   "pointers"; this scheme would not adequately address the problem of
   upward and downward multiplexing; and finally, enumerated values of
   ifType would be needed for each combination of sub-layers.  Another
   rejected solution also retained the concept of one conceptual row for
   all the sub-layers of an interface but had a new separate MIB table
   to identify the "superior" and "subordinate" sub-layers and to
   contain OBJECT IDENTIFIER "pointers" to the media-specific MIB module
   for each sub-layer.  Effectively, one conceptual row in the ifTable
   would represent each combination of sub-layers between the
   internetwork-layer and the wire.  While this scheme has fewer
   drawbacks, it still would not support downward multiplexing, such as
   PPP over MLP: observe that MLP makes two (or more) serial lines
   appear to the layers above as a single physical interface, and thus
   PPP over MLP should appear to the internetwork-layer as a single
   interface; in contrast, this scheme would result in two (or more)
   conceptual rows in the ifTable, both of which the internetwork-layer
   would run over.  This scheme would also require enumerated values of
   ifType for each combination of sub-layers.

   The solution adopted by this memo is to have an individual conceptual
   row in the ifTable to represent each sub-layer, and have a new
   separate MIB table (the ifStackTable, see section 6 below) to