SGI Developer Toolbox 6.1/SGI Developer Toolbox 6.1 - Disc 4.iso/documents/RFC/rfc1573.txt

Text File | 1994-08-01 | 123KB | 3,084 lines

Network Working Group                                      K. McCloghrie
Request for Comments: 1573                            Hughes LAN Systems
Obsoletes: 1229                                            F. Kastenholz
Category: Standards Track                                   FTP Software
                                                            January 1994


              Evolution of the Interfaces Group of MIB-II

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.

Table of Contents

   1. Introduction .............................................    2
   2. The SNMPv2 Network Management Framework ..................    2
   2.1 Object Definitions ......................................    3
   3 Experience with the Interfaces Group ......................    3
   3.1 Areas of Clarification/Revision .........................    3
   3.1.1 Interface Numbering ...................................    4
   3.1.2 Interface Sub-Layers ..................................    4
   3.1.3 Virtual Circuits ......................................    5
   3.1.4 Bit, Character, and Fixed-Length Interfaces ...........    5
   3.1.5 Counter Size ..........................................    5
   3.1.6 Interface Speed .......................................    6
   3.1.7 Multicast/Broadcast Counters ..........................    6
   3.1.8 Addition of New ifType values .........................    6
   3.1.9 ifSpecific ............................................    6
   3.2 Clarifications/Revisions ................................    7
   3.2.1 Interface Numbering ...................................    7
   3.2.2 Interface Sub-Layers ..................................    8
   3.2.3 Guidance on Defining Sub-layers .......................   11
   3.2.4 Virtual Circuits ......................................   12
   3.2.5 Bit, Character, and Fixed-Length Interfaces ...........   12
   3.2.6 Counter Size ..........................................   14
   3.2.7 Interface Speed .......................................   16
   3.2.8 Multicast/Broadcast Counters ..........................   16
   3.2.9 Trap Enable ...........................................   17
   3.2.10 Addition of New ifType values ........................   17
   3.2.11 InterfaceIndex Textual Convention ....................   17
   3.2.12 IfAdminStatus and IfOperStatus .......................   18
   3.2.13 Traps ................................................   19
   3.2.14 ifSpecific ...........................................   20



McCloghrie & Kastenholz                                         [Page 1]

RFC 1573               Interfaces Group Evolution           January 1994


   3.3 Media-Specific MIB Applicability ........................   20
   4. Overview .................................................   21
   5. IANAifType Definition ....................................   22
   6. Interfaces Group Definitions .............................   24
   7. Acknowledgements .........................................   53
   8. References ...............................................   53
   9. Security Considerations ..................................   55
   10. Authors' Addresses.......................................   55

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, 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
   proposes clarifications to, and extensions of, the architectural
   issues within the current model used for the 'interfaces' group.

   This memo also includes a MIB module.  As well as including new MIB
   definitions to support the architectural extensions, this MIB module
   also re-specifies the 'interfaces' group of MIB-II in a manner which
   is both compliant to the SNMPv2 SMI and semantically-identical to the
   existing SNMPv1-based definitions.

2.  The SNMPv2 Network Management Framework

   The SNMPv2 Network Management Framework consists of four major
   components.  They are:

      o    RFC 1442 which defines the SMI, the mechanisms used for
           describing and naming objects for the purpose of management.

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

      o    RFC 1445 which defines the administrative and other
           architectural aspects of the framework.

      o    RFC 1448 which defines the protocol used for network access
           to managed objects.

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



McCloghrie & Kastenholz                                         [Page 2]

RFC 1573               Interfaces Group Evolution           January 1994


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.  Experience with the Interfaces Group

   One of the strengths of internetwork-layer protocols such as IP [6]
   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 have assumed an evolution or loosening of
   the model.  This memo is a proposal to document and standardize the
   evolution of the model and to fill in the gaps caused by that
   evolution.

   A previous effort to extend the interfaces group resulted in the
   publication of RFC 1229 [7].  As part of defining the evolution of
   the interfaces group, this memo applies that evolution to, and
   thereby incorporates, the RFC 1229 extensions.

3.1.  Areas of Clarification/Revision

   There are several areas for which experience indicates that
   clarification, revision, or extension of the model would be helpful.
   The next sections discuss these.




McCloghrie & Kastenholz                                         [Page 3]

RFC 1573               Interfaces Group Evolution           January 1994


3.1.1.  Interface Numbering

   MIB-II defines an object, ifNumber, whose value represents:

     "The number of network interfaces (regardless of their
     current state) present on this system."

   Each interface is identified by a unique value of the ifIndex object,
   and the description of ifIndex constrains its value as follows:

     "Its value ranges between 1 and the value of ifNumber.  The
     value for each interface must remain constant at least from
     one re-initialization of the entity's network management
     system to the next re-initialization."

   This constancy requirement on the value of ifIndex for a particular
   interface is vital for efficient management.  However, an increasing
   number of devices allow for the dynamic addition/removal of network
   interfaces.  One example of this is a dynamic ability to configure
   the use of SLIP/PPP over a character-oriented port.  For such dynamic
   additions/removals, the combination of the constancy requirement and
   the restriction that the value of ifIndex is less than ifNumber is
   problematic.

3.1.2.  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, there is
   still a lack of 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



McCloghrie & Kastenholz                                         [Page 4]

RFC 1573               Interfaces Group Evolution           January 1994


   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,
   all of which run over one fractional T1 channel, concurrently with
   other uses of the T1 link.  The current MIB structure does not allow
   for these sorts of relationships to be described.

3.1.3.  Virtual Circuits

   Several of the sub-layers for which media-specific MIB modules have
   been defined are connection oriented (e.g., Frame Relay, X.25).
   Experience has shown that each effort to define such a MIB module
   revisits the question of whether separate conceptual rows in the
   ifTable are needed for each virtual circuit.  Most, if not all, of
   these efforts to date have decided to have all virtual circuits
   reference a single conceptual row in the ifTable.

3.1.4.  Bit, Character, and Fixed-Length Interfaces

   RS-232 is an example of a character-oriented sub-layer over which
   (e.g., through use of PPP) IP datagrams can be sent.  Due to the
   packet-based nature of many of the objects in the ifTable, experience
   has shown that it is not appropriate to have a character-oriented
   sub-layer represented by a (whole) conceptual row in the ifTable.

   Experience has also shown that it is sometimes desirable to have some
   management information for bit-oriented interfaces, which are
   similarly difficult to represent by a (whole) conceptual row in the
   ifTable.  For example, to manage the channels of a DS1 circuit, where
   only some of the channels are carrying packet-based data.

   A further complication is that some subnetwork technologies transmit
   data in fixed length transmission units.  One example of such a
   technology is cell relay, and in particular Asynchronous Transfer
   Mode (ATM), which transmits data in fixed-length cells.  Representing
   such a interface as a packet-based interface produces redundant
   objects if the relationship between the number of packets and the
   number of octets in either direction is fixed by the size of the
   transmission unit (e.g., the size of a cell).

3.1.5.  Counter Size

   As the speed of network media increase, the minimum time in which a
   32 bit counter will wrap decreases.  For example, on an Ethernet, a
   stream of back-to-back, full-size packets will cause ifInOctets to
   wrap in just over 57 minutes.  For a T3 line, the minimum wrap-time



McCloghrie & Kastenholz                                         [Page 5]

RFC 1573               Interfaces Group Evolution           January 1994


   is just over 12 minutes.  For FDDI, it will wrap in 5.7 minutes.  For
   a 1-gigabit medium, the counter might wrap in as little as 34
   seconds.  Requiring that interfaces be polled frequently enough not
   to miss a counter wrap will be increasingly problematic.

3.1.6.  Interface Speed

   Network speeds are increasing.  The range of ifSpeed is limited to
   reporting a maximum speed of (2**31)-1 bits/second, or approximately
   2.2Gbs.  SONET defines an OC-48 interface, which is defined at
   operating at 48 times 51 Mbs, which is a speed in excess of 2.4gbits.
   Thus, ifSpeed will be of diminishing utility over the next several
   years.

3.1.7.  Multicast/Broadcast Counters

   The counters in the ifTable for packets addressed to a multicast or
   the broadcast address, are combined as counters of non-unicast
   packets.  In contrast, the ifExtensions MIB [7] defines one set of
   counters for multicast, and a separate set for broadcast packets.
   With the separate counters, the original combined counters become
   redundant.

3.1.8.  Addition of New ifType values

   Over time new ifType enumerated values have been needed for new
   interface types.  With the syntax of ifType being defined in a MIB,
   this requires the new MIB to be re-issued in order to define the new
   values.  In the past, re-issuing of the MIB has occurred only after
   several years.

3.1.9.  ifSpecific

   The original definition of the OBJECT IDENTIFIER value of ifSpecific
   was not sufficently clear.  As a result, different implementors have
   used it differently, and confusion has resulted.  Some
   implementations have the value of ifSpecific be the OBJECT IDENTIFIER
   that defines the media-specific MIB, i.e., the "foo" of:

          foo OBJECT IDENTIFIER ::= { transmission xxx }

   while others have it be the OBJECT IDENTIFIER of the table or entry
   in the appropriate media-specific MIB (e.g. fooTable or fooEntry),
   while still others have it be the OBJECT IDENTIFIER of the index
   object of the table's row, including instance identifier (e.g.,
   fooIfIndex.ifIndex).  A definition based on the latter would not be
   sufficient unless it also allowed for media-specific MIBs which
   include several tables, where each table has its own, different,



McCloghrie & Kastenholz                                         [Page 6]

RFC 1573               Interfaces Group Evolution           January 1994


   indexing.

3.2.  Clarifications/Revisions

   The following clarifications and/or revisions are proposed.

3.2.1.  Interface Numbering

   One solution to the interface numbering problem would be to redefine
   ifNumber to be the largest value of ifIndex, but the utility of such
   an object is questionable, and such a re-definition would require
   ifNumber to be deprecated.  Thus, an improvement would be to
   deprecate ifNumber and not replace it.  However, the deprecation of
   ifNumber would require a change to that portion of ifIndex's
   definition which refers to ifNumber.  So, since the definition of
   ifIndex must be changed anyway in order to solve the problem, changes
   to ifNumber do not benefit the solution.

   The solution adopted in this memo is to delete the requirement that
   the value of ifIndex must be less than the value of ifNumber, and to
   retain ifNumber with its current definition.  It could be argued that
   this is a change in the semantics of ifIndex; however, all existing
   implementations conform to this new definition, and in the interests
   of not requiring changes in existing implementations and in the many
   existing media-specific MIBs, it is proposed that this change does
   not require ifIndex to be deprecated.

   This solution also results in the possibility of "holes" in the
   ifTable (i.e., the ifIndex values of conceptual rows in the ifTable
   are not necessarily contiguous), but SNMP's GetNext (and SNMPv2's
   GetBulk) operation easily deals with such holes.  The value of
   ifNumber still represents the number of conceptual rows, which
   increases/decreases as new interfaces are dynamically added/removed.
   The vital constancy requirement is met by requiring that after an
   interface is dynamically removed, its ifIndex value is not re-used
   (by a different dynamically added interface) until after the
   following re-initialization of the network management system.  This
   avoids the need for a priori assignment of ifIndex values for all
   possible interfaces which might be added dynamically.

   The exact meaning of a "different" interface is hard to define, and
   there will be gray areas.  One important criterion is that a
   management station, not noticing that an interface has gone away and
   another come into existence, should not be confused when it
   calculates the difference between the counter values retrieved on
   successive polls for a particular ifIndex value.  However, any firm
   definition in this document would likely to turn out to be
   inadequate.  Instead, the following guidelines are offered to allow



McCloghrie & Kastenholz                                         [Page 7]

RFC 1573               Interfaces Group Evolution           January 1994


   implementors to choose what "different" means in their particular
   situation.

   A previously-unused value of ifIndex should be assigned to a
   dynamically added interface if:

      (1)  the assignment of a previously-used ifIndex value to the
           interface could result in a discontinuity in the values of
           ifTable counters for that value of ifIndex; or,

      (2)  an agent has no knowledge of whether the interface is the
           "same" or "different" from a previous interface incarnation.

   Because of the restriction of the value of ifIndex to be less than
   ifNumber, interfaces have been numbered with small integer values.
   This has led to the ability by humans to use the ifIndex values as
   (somewhat) user-friendly names for network interfaces (e.g.,
   "interface number 3").  With the relaxation of the restriction on the
   value of ifIndex, there is now the possibility that ifIndex values
   could be assigned as very large numbers (e.g., memory addresses).
   Such numbers would be much less user-friendly.

   Therefore, this memo recommends that ifIndex values still be assigned
   as (relatively) small integer values starting at 1, even though the
   values in use at any one time are not necessarily contiguous.  (Note
   that this makes remembering which values have been assigned easy for
   agents which dynamically add new interfaces.)

   This proposed change introduces a new problem of its own.
   Previously, there usually was a simple, direct, mapping of interfaces
   to the physical ports on systems.  This mapping would be based on the
   ifIndex value.  However, by removing the previous restrictions on the
   values allowed for ifIndex, along with the interface sub-layer
   concept (see the following section), mapping from interfaces to
   physical ports becomes increasingly problematic.

   To address this issue, a new object, ifName, is added to the MIB.
   This object contains the device's name for the interface of which the
   relevant entry in the ifTable is a component.  For example, if a
   router has an interface named wan1, which is composed of PPP running
   over an RS-232 port, the ifName objects for the corresponding PPP and
   RS-232 entries in the ifTable will contain the string "wan1".

3.2.2.  Interface Sub-Layers

   One possible but not recommended solution to the problem of
   representing multiple sub-layers would be to retain the concept of
   one conceptual row for all the sub-layers of an interface and have



McCloghrie & Kastenholz                                         [Page 8]

RFC 1573               Interfaces Group Evolution           January 1994


   each media-specific MIB module identify its "superior" and
   "subordinate" sub-layers through OBJECT IDENTIFIER "pointers".  The
   drawbacks of this scheme are: 1) the superior/subordinate pointers
   are contained in the media-specific MIB modules, and thus, a manager
   could not learn the structure of an interface, without inspecting
   multiple pointers in different MIB modules; this is overly complex
   and only possible if the manager has knowledge of all the relevant
   media-specific MIB modules; 2) current MIB modules would all need to
   be retrofitted with these new "pointers"; 3) this scheme does not
   adequately address the problem of upward and downward multiplexing;
   and 4) enumerated values of ifType are needed for each combination of
   sub-layers.

   Another possible but not recommended scheme would be to retain the
   concept of one conceptual row for all the sub-layers of an interface
   and have a new separate MIB table to identify the "superior" and
   "subordinate" sub-layers which contain OBJECT IDENTIFIER "pointers"
   to media-specific MIB module(s) 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 does not support downward
   multiplexing, such as PPP over MLP; since MLP makes two (or more)
   serial lines appear to the layers above as a single physical
   interface, PPP over MLP should appear to the internetwork-layer as a
   single interface.  However, this scheme would result in two (or more)
   conceptual rows in the ifTable and the internetwork-layer would run
   over both of them.  This scheme also requires enumerated values of
   ifType for each combination of sub-layers.

   The solution adopted in 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 5 of this memo) to
   identify the "superior" and "subordinate" sub-layers through INTEGER
   "pointers" to the appropriate conceptual rows in the ifTable.  This
   solution supports both upward and downward multiplexing.  It also
   allows the IANAIfType to Media-Specific MIB mapping to identify the
   media-specific MIB module for each sub- layer.  The new table
   (ifStackTable) need be referenced only to obtain information about
   layering.  Enumerated values for ifType are required for each sub-
   layer only, not for combinations of them.

   However, this solution does require that the descriptions of some
   objects in the ifTable (specifically, ifType, ifPhysAddress,
   ifInUcastPkts, and ifOutUcastPkts) be generalized so as to apply to
   any sub-layer (rather than only to a sub-layer immediately beneath
   the network layer, as at present).  It also requires that some
   objects (specifically, ifSpeed) need to have appropriate values
   identified for use when a generalized definition does not apply to a



McCloghrie & Kastenholz                                         [Page 9]

RFC 1573               Interfaces Group Evolution           January 1994


   particular sub-layer.

   In addition, this adopted solution makes no requirement that a
   device, in which a sub-layer is instrumented by a conceptual row of
   the ifTable, be aware of whether an internetwork protocol runs on top
   of (i.e., at some layer above) that sub-layer.  In fact, the counters
   of packets received on an interface are defined as counting the
   number "delivered to a higher-layer protocol".  This meaning of
   "higher-layer" includes:

      (1)  Delivery to a forwarding module which accepts
           packets/frames/octets and forwards them on at the same
           protocol layer.  For example, for the purposes of this
           definition, the forwarding module of a MAC-layer bridge is
           considered as a "higher-layer" to the MAC-layer of each port
           on the bridge.

      (2)  Delivery to a higher sub-layer within a interface stack.  For
           example, for the purposes of this definition, if a PPP module
           operated directly over a serial interface, the PPP module
           would be considered the higher sub-layer to the serial
           interface.

      (3)  Delivery to a higher protocol layer which does not do packet
           forwarding for sub-layers that are "at the top of" the
           interface stack.  For example, for the purposes of this
           definition, the local IP module would be considered the
           higher layer to a SLIP serial interface.

   Similarly, for output, the counters of packets transmitted out an
   interface are defined as counting the number "that higher-level
   protocols requested to be transmitted".  This meaning of "higher-
   layer" includes:

      (1)  A forwarding module, at the same protocol layer, which
           transmits packets/frames/octets that were received on an
           different interface.  For example, for the purposes of this
           definition, the forwarding module of a MAC-layer bridge is
           considered as a "higher-layer" to the MAC-layer of each port
           on the bridge.

      (2)  The next higher sub-layer within an interface stack.  For
           example, for the purposes of this definition, if a PPP module
           operated directly over a serial interface, the PPP module
           would be a "higher layer" to the serial interface.






McCloghrie & Kastenholz                                        [Page 10]

RFC 1573               Interfaces Group Evolution           January 1994


      (3)  For sub-layers that are "at the top of" the interface stack,
           a higher element in the network protocol stack.  For example,
           for the purposes of this definition, the local IP module
           would be considered the higher layer to an Ethernet
           interface.

3.2.3.  Guidance on Defining Sub-layers

   The designer of a media-specific MIB must decide whether to divide
   the interface into sub-layers, and if so, how to make the divisions.
   The following guidance is offered to assist the media-specific MIB
   designer in these decisions.

   In general, the number of entries in the ifTable should be kept to
   the minimum required for network management.  In particular, a group
   of related interfaces should be treated as a single interface with
   one entry in the ifTable providing that:

      (1)  None of the group of interfaces performs multiplexing for any
           other interface in the agent,

      (2)  There is a meaningful and useful way for all of the ifTable's
           information (e.g., the counters, and the status variables),
           and all of the ifTable's capabilities (e.g., write access to
           ifAdminStatus), to apply to the group of interfaces as a
           whole.

   Under these circumstances, there should be one entry in the ifTable
   for such a group of interfaces, and any internal structure which
   needs to be represented to network management should be captured in a
   MIB module specific to the particular type of interface.

   Note that application of bullet 2 above to the ifTable's ifType
   object requires that there is a meaningful media-specific MIB and a
   meaningful ifType value which apply to the group of interfaces as a
   whole.  For example, it is not appropriate to treat an HDLC sub-layer
   and an RS-232 sub-layer as a single ifTable entry when the media-
   specific MIBs and the ifType values for HDLC and RS-232 are separate
   (rather than combined).

   Note that the sub-layers of an interface on one device will sometimes
   be different to the sub-layers of the interconnected interface of
   another device.  A simple example of this is a frame-relay DTE
   interface which connects to a frameRelayService interface, where the
   DTE interface has a different ifType value and media-specific MIB to
   the DCE interface.

   Also note that a media-specific MIB may mandate that a particular



McCloghrie & Kastenholz                                        [Page 11]

RFC 1573               Interfaces Group Evolution           January 1994


   ifTable counter does not apply and that its value must always be 0,
   signifying that the applicable event can not and does not occur for
   that type of interface; for example, ifInMulticastPkts and
   ifOutMulticastPkts on an interface type which has no multicast
   capability.  In other circumstances, an agent must not always return
   0 for any counter just because its implementation is incapable of
   detecting occurrences of the particular event; instead, it must
   return a noSuchName/noSuchObject error/exception when queried for the
   counter, even if this prevents the implementation from complying with
   the relevant MODULE-COMPLIANCE macro.

   These guidelines are just that - guidelines.  The designer of a
   media-specific MIB is free to lay out the MIB in whatever SMI
   conformant manner is desired.  However, in so doing, the media-
   specific MIB MUST completely specify the sub-layering model used for
   the MIB, and provide the assumptions, reasoning, and rationale used
   to develop that model.

3.2.4.  Virtual Circuits

   This memo strongly recommends that connection-oriented sub-layers do
   not have a conceptual row in the ifTable for each virtual circuit.
   This avoids the proliferation of conceptual rows, especially those
   which have considerable redundant information.  (Note, as a
   comparison, that connection-less sub-layers do not have conceptual
   rows for each remote address.)  There may, however, be circumstances
   under which it is appropriate for a virtual circuit of a connection-
   oriented sub-layer to have its own conceptual row in the ifTable; an
   example of this might be PPP over an X.25 virtual circuit.  The MIB
   in section 6 of this memo supports such circumstances.

   If a media-specific MIB wishes to assign an entry in the ifTable to
   each virtual circuit, the MIB designer must present the rationale for
   this decision in the media-specific MIB's specification.

3.2.5.  Bit, Character, and Fixed-Length Interfaces

   About half the objects in the ifTable are applicable to every type of
   interface: packet-oriented, character-oriented, and bit-oriented.  Of
   the other half, two are applicable to both character-oriented and
   packet-oriented interfaces, and the rest are applicable only to
   packet-oriented interfaces.  Thus, while it is desirable for
   consistency to be able to represent any/all types of interfaces in
   the ifTable, it is not possible to implement the full ifTable for
   bit- and character-oriented sub-layers.

   One possible but not recommended solution to this problem would be to
   split the ifTable into two (or more) new MIB tables, one of which



McCloghrie & Kastenholz                                        [Page 12]

RFC 1573               Interfaces Group Evolution           January 1994


   would contain objects that are relevant only to packet-oriented
   interfaces (e.g., PPP), and another that may be used by all
   interfaces.  This is highly undesirable since it would require
   changes in every agent implementing the ifTable (i.e., just about
   every existing SNMP agent).

   The solution adopted in this memo builds upon the fact that
   compliance statements in SNMPv2 (in contrast to SNMPv1) refer to
   object groups, where object groups are explicitly defined by listing
   the objects they contain.  Thus, in SNMPv2, multiple compliance
   statements can be specified, one for all interfaces and additional
   ones for specific types of interfaces.  The separate compliance
   statements can be based on separate object groups, where the object
   group for all interfaces can contain only those objects from the
   ifTable which are appropriate for every type of interfaces.  Using
   this solution, every sub-layer can have its own conceptual row in the
   ifTable.

   Thus, section 6 of this memo contains definitions of the objects of
   the existing 'interfaces' group of MIB-II, in a manner which is both
   SNMPv2-compliant and semantically-equivalent to the existing MIB-II
   definitions.  With equivalent semantics, and with the BER ("on the
   wire") encodings unchanged, these definitions retain the same OBJECT
   IDENTIFIER values as assigned by MIB-II.  Thus, in general, no
   rewrite of existing agents which conform to MIB-II and the
   ifExtensions MIB is required.

   In addition, this memo defines several object groups for the purposes
   of defining which objects apply to which types of interface:

      (1)  the ifGeneralGroup.  This group contains those objects
           applicable to all types of network interfaces, including
           bit-oriented interfaces.

      (2)  the ifPacketGroup.  This group contains those objects
           applicable to packet-oriented network interfaces.

      (3)  the ifFixedLengthGroup.  This group contains the objects
           applicable not only to character-oriented interfaces, such as
           RS-232, but also to those subnetwork technologies, such as
           cell-relay/ATM, which transmit data in fixed length
           transmission units.  As well as the octet counters, there are
           also a few other counters (e.g., the error counters) which
           are useful for this type of interface, but are currently
           defined as being packet-oriented.  To accommodate this, the
           definitions of these counters are generalized to apply to
           character-oriented interfaces and fixed-length-transmission
           interfaces.



McCloghrie & Kastenholz                                        [Page 13]

RFC 1573               Interfaces Group Evolution           January 1994


   It should be noted that the octet counters in the ifTable aggregate
   octet counts for unicast and non-unicast packets into a single octet
   counter per direction (received/transmitted).  Thus, with the above
   definition of fixed-length-transmission interfaces, where such
   interfaces which support non-unicast packets, separate counts of
   unicast and multicast/broadcast transmissions can only be maintained
   in a media-specific MIB module.

3.2.6.  Counter Size

   Two approaches to addressing the shrinking minimum counter-wrap time
   problem were evaluated.  Counters could be scaled, for example,
   ifInOctets could be changed to count received octets in, e.g., 1024
   byte blocks.  Alternatively, the size of the counter could be
   increased.

   Scaling the counters was rejected.  While it provides acceptable
   performance at high count rates, at low rates it suffers.  If there
   is little traffic on an interface, there might be a significant
   interval before enough counts occur to cause a counter to be
   incremented.  Traffic would then appear to be very bursty, leading to
   incorrect conclusions of the network's performance.

   The alternative, which this memo adopts, is to provide expanded, 64
   bit, counters.  These counters are provided in new "high capacity"
   groups,

   The old, 32-bit, counters have not been deprecated.  The 64-bit
   counters are to be used only when the 32-bit counters do not provide
   enough capacity; that is, the 32 bit counters could wrap too fast.

   For interfaces that operate at 20,000,000 (20 million) bits per
   second or less, 32-bit byte and packet counters MUST be used.  For
   interfaces that operate faster than 20,000,000 bits/second, and
   slower than 650,000,000 bits/second, 32-bit packet counters MUST be
   used and 64-bit octet counters MUST be used.  For interfaces that
   operate at 650,000,000 bits/second or faster, both 64-bit packet
   counters AND 64-bit octet counters MUST be used.

   These speed steps were chosen as reasonable compromises based on the
   following:

      (1)  The cost of maintaining 64-bit counters is relatively high,
           so minimizing the number of agents which must support them is
           desirable.  Common interfaces (such as Ethernet) should not
           require them.





McCloghrie & Kastenholz                                        [Page 14]

RFC 1573               Interfaces Group Evolution           January 1994


      (2)  64-bit counters are a new feature, introduced in SNMPv2.  It
           is reasonable to expect that support for them will be spotty
           for the immediate future.  Thus, we wish to limit them to as
           few systems as possible.  This, in effect, means that 64-bit
           counters should be limited to higher speed interfaces.
           Ethernet (10,000,000 bps) and Token Ring (16,000,000 bps) are
           fairly wide-spread so it seems reasonable to not require 64-
           bit counters for these interfaces.

      (3)  The 32-bit octet counters will wrap in the following times,
           for the following interfaces (when transmitting maximum-sized
           packets back-to-back):

           -   Ethernet: 57 minutes,

           -   16 megabit Token Ring: 36 minutes,

           -   A US T3 line (45 megabits): 12 minutes,

           -   FDDI: 5.7 minutes

      (4)  The 32-bit packet counters wraps in about 57 minutes when
           64-byte packets are transmitted back-to-back on a 650,000,000
           bit/second link.

           As an aside, a 1-terabit (1,000 gigabits) link will cause a
           64 bit octet counter to wrap in just under 5 years.
           Conversely, an 81,000,000 terabit/second link is required to
           cause a 64-bit counter to wrap in 30 minutes.  We believe
           that, while technology rapidly marches forward, this link
           speed will not be achieved for at least several years,
           leaving sufficient time to evaluate the introduction of 96
           bit counters.

   When 64-bit counters are in use, the 32-bit counters MUST still be
   available.  They will report the low 32-bits of the associated 64-bit
   count (e.g., ifInOctets will report the least significant 32 bits of
   ifHCInOctets).  This enhances inter-operability with existing
   implementations at a very minimal cost to agents.

   The new "high capacity" groups are:

      (1)  the ifHCFixedLengthGroup for character-oriented/fixed-length
           interfaces, and the ifHCPacketGroup for packet-based
           interfaces; both of these groups include 64 bit counters for
           octets, and





McCloghrie & Kastenholz                                        [Page 15]

RFC 1573               Interfaces Group Evolution           January 1994


      (2)  the ifVHCPacketGroup for packet-based interfaces; this group
           includes 64 bit counters for octets and packets.

3.2.7.  Interface Speed

   In order to deal with increasing interface speeds, we have added an
   ifHighSpeed object.

   This object reports the speed of the interface in 1,000,000 (1
   million) bits/second units.  Thus, the true speed of the interface
   will be the value reported by this object, plus or minus 500,000
   bits/second.

   Other alternatives considered were:

      (1)  Making the interface speed a 64-bit gauge.  This was rejected
           since the current SMI does not allow such a syntax.

           Furthermore, even if 64-bit gauges were available, their use
           would require additional complexity in agents due to an
           increased requirement for 64-bit operations.

      (2)  We also considered making "high-32 bit" and "low-32-bit"
           objects which, when combined, would be a 64-bit value.  This
           simply seemed overly complex for what we are trying to do.

           Furthermore, a full 64-bits of precision does not seem
           necessary.  The value of ifHighSpeed will be the only report
           of interface speed for interfaces that are faster than
           4,294,967,295 bits per second.  At this speed, the
           granularity of ifHighSpeed will be 1,000,000 bits per second,
           thus the error will be 1/4294, or about 0.02%.  This seems
           reasonable.

      (3)  Adding a "scale" object, which would define the units which
           ifSpeed's value is.

           This would require two additional objects; one for the
           scaling object, and one to replace the current ifSpeed.  This
           later object is required since the semantics of ifSpeed would
           be significantly altered, and manager stations which do not
           understand the new semantics would be confused.

3.2.8.  Multicast/Broadcast Counters

   To avoid the redundancy of counting all non-unicast packets as well
   as having individual multicast and broadcast packet counters, we
   deprecate the use of the non-unicast counters, which can be derived



McCloghrie & Kastenholz                                        [Page 16]

RFC 1573               Interfaces Group Evolution           January 1994


   from the values of the others.

   For the output broadcast and multicast counters defined in RFC 1229,
   their definitions varied slightly from the packet counters in the
   ifTable, in that they did not count errors/discarded packets.  To
   align the definitions better, the old counters are deprecated and
   replaced by new definitions.  Counters with 64 bits of range are also
   needed, as explained above.

3.2.9.  Trap Enable

   In the multi-layer interface model, each sub-layer for which there is
   an entry in the ifTable can generate linkUp/Down Traps.  Since
   interface state changes would tend to propagate through the interface
   (from top to bottom, or bottom to top), it is likely that several
   traps would be generated for each linkUp/Down occurrence.

   It is desirable to provide a mechanism for manager stations to
   control the generation of these traps.  To this end, the
   ifLinkUpDownTrapEnable object has been added.  This object allows
   managers to limit generation of traps to just the sub-layers of
   interest.

   The default setting should limit the number of traps generated to one
   per interface per linkUp/Down event.  Furthermore, it seems that the
   conditions that cause these state changes that are of most interest
   to network managers occur at the lowest level of an interface stack.
   Therefore we specify that by default, only the lowest sub-layer of
   the interface generate traps.

3.2.10.  Addition of New ifType values

   The syntax of ifType is changed to be a textual convention, such that
   the enumerated integer values are now defined in the textual
   convention, IANAifType, which can be re-specified (with additional
   values) without issuing a new version of this document.  The Internet
   Assigned Number Authority (IANA) is responsible for the assignment of
   all Internet numbers, including various SNMP-related numbers, and
   specifically, new ifType values.  Thus, this document defines two MIB
   modules: one to define the MIB for the 'interfaces' group, and a
   second to define the first version of the IANAifType textual
   convention.  The latter will be periodically re-issued by the IANA.

3.2.11.  InterfaceIndex Textual Convention

   A new textual convention, InterfaceIndex, has been defined.  This
   textual convention "contains" all of the semantics of the ifIndex
   object.  This allows other mib modules to easily import the semantics



McCloghrie & Kastenholz                                        [Page 17]

RFC 1573               Interfaces Group Evolution           January 1994


   of ifIndex.

3.2.12.  IfAdminStatus and IfOperStatus

   A new state has been added to ifOperStatus: dormant.  This state
   indicates that the relevant interface is not actually in a condition
   to pass packets (i.e., up) but is in a "pending" state, waiting for
   some external event.  For "on-demand" interfaces, this new state
   identifies the situation where the interface is waiting for events to
   place it in the up state.  Examples of such events might be:

      (1)  having packets to transmit before establishing a connection
           to a remote system.

      (2)  having a remote system establish a connection to the
           interface (e.g., dialing up to a slip-server).

   The down state now has two meanings, depending on the value of
   ifAdminStatus.

      (1)  If ifAdminStatus is not down and ifOperStatus is down, then a
           fault condition is presumed to exist on the interface.

      (2)  If ifAdminStatus is down, then ifOperStatus will normally
           also be down, i.e., there is not (necessarily) a fault
           condition on the interface.

   Note that when ifAdminStatus transitions to down, ifOperStatus will
   normally also transition to down.  In this situation, it is possible
   that ifOperStatus's transition will not occur immediately, but rather
   after a small time lag to complete certain operations before going
   "down"; for example, it might need to finish transmitting a packet.
   If a manager station finds that ifAdminStatus is down and
   ifOperStatus is not down for a particular interface, the manager
   station should wait a short while and check again.  If the condition
   still exists only then should it raise an error indication.
   Naturally, it should also ensure that ifLastChange has not changed
   during this interval.

   Whenever an interface table entry is created (usually as a result of
   system initialization), the relevant instance of ifAdminStatus is set
   to down, and presumably ifOperStatus will also be down.

   An interface may be enabled in two ways: either as a result of
   explicit management action (e.g., setting ifAdminStatus to up) or as
   a result of the managed system's initialization process.  When
   ifAdminStatus changes to the up state, the related ifOperStatus
   should do one of the following:



McCloghrie & Kastenholz                                        [Page 18]

RFC 1573               Interfaces Group Evolution           January 1994


      (1)  Change to the up state if and only if the interface is able
           to send and receive packets.

      (2)  Change to the dormant state if and only if the interface is
           found to be operable, but the interface is waiting for other,
           external, events to occur before it can transmit or receive
           packets.  Presumably when the expected events occur, the
           interface will then transition to the up state.

      (3)  Remain in the down state if an error or other fault condition
           is detected on the interface.

      (4)  Change to the unknown state if, for some reason, the state of
           the interface can not be ascertained.

      (5)  Change to the testing state if some test(s) must be performed
           on the interface.  Presumably after completion of the test,
           the interface's state will change to up, dormant, or down, as
           appropriate.

3.2.13.  Traps

   The exact definition of when linkUp and linkDown traps are generated,
   has been changed to reflect the changes to ifAdminStatus and
   ifOperStatus.

   LinkUp and linkDown traps are generated just after ifOperStatus
   leaves, or just before it enters, the down state, respectively.  The
   wording of the conditions under which a linkDown trap is generated
   was explicitly chosen to allow a node with only one interface to
   transmit the linkDown trap before that interface goes down.

   Operational experience seems to indicate that manager stations are
   most concerned with an interface being in the down state and the fact
   that this state may indicate a failure.  It seemed most useful to
   instrument either transitions into/out of the up state or the down
   state.

   Instrumenting transitions into or out of the up state has the
   drawback that an on-demand interface might have many transitions
   between up and dormant, leading to many linkUp traps and no linkDown
   traps.  Furthermore, if a node's only interface is the on-demand
   interface, then a transition to dormant will entail generation of a
   trap, necessitating bringing the link to the up state (and a linkUp
   trap)!!

   On the other hand, instrumenting transitions into or out of the down
   state has the advantages:



McCloghrie & Kastenholz                                        [Page 19]

RFC 1573               Interfaces Group Evolution           January 1994


      (1)  A transition into the down state will occur when an error is
           detected on an interface.  Error conditions are presumably of
           great interest to network managers.

      (2)  Departing the down state generally indicates that the
           interface is going to either up or dormant, both of which are
           considered "healthy" states.

   Furthermore, it is believed that generarating traps on transitions
   into or out of the down state is generally consistent with current
   usage and interpretation of these traps by manager stations.

   Therefore, this memo defines that it is the transitions into/out of
   the down state which generate traps.

   Obviously, if a failure condition is present on a node with a single
   interface, the linkDown trap will probably not be succesfully
   transmitted since the interface through which it must be transmitted
   has failed.

3.2.14.  ifSpecific

   The current definition of ifSpecific is not explicit enough.  The
   only definition that can both be made explicit and can cover all the
   useful situations (see section 3.1.9) is to have ifSpecific be the
   most general value for the media-specific MIB module (the first
   example given section in 3.1.9).  This effectively makes it redundant
   because it contains no more information than is provided by ifType.
   For this reason, ifSpecific has been deprecated.

3.3.  Media-Specific MIB Applicability

   The exact use and semantics of many objects in this MIB are open to
   some interpretation.  This is a result of the generic nature of this
   MIB.  It is not always possible to come up with specific,
   unambiguous, text that covers all cases and yet preserve the generic
   nature of the MIB.

   Therefore, it is incumbent upon a media-specific MIB designer to,
   wherever necessary, clarify the use of the objects in this MIB with
   respect to the media-specific MIB.

   Specific areas of clarification include:

   Layering Model
        The media-specific MIB designer MUST completely and
        unambiguously specify the layering model used.  Each
        individual sub-layer must be identified.



McCloghrie & Kastenholz                                        [Page 20]

RFC 1573               Interfaces Group Evolution           January 1994


   Virtual Circuits
        The media-specific MIB designer MUST specify whether virtual
        circuits are assigned entries in the ifTable or not.  If they
        are, compelling rationale must be presented.

   ifTestTable
        The media-specific MIB designer MUST specify the
        applicability of the ifTestTable.

   ifRcvAddressTable
        The media-specific MIB designer MUST specify the
        applicability of the ifRcvAddressTable.

   ifType
        For each of the ifType values to which the media-specific MIB
        applies, it must specify the mapping of ifType values to
        media-specific MIB module(s) and instances of MIB objects
        within those modules.

   However, wherever this interface MIB is specific in the semantics,
   DESCRIPTION, or applicability of objects, the media-specific MIB
   designer MUST NOT change said semantics, DESCRIPTION, or
   applicability.

4.  Overview

   This MIB consists of 5 tables:

   ifTable
        This table is the ifTable from MIB-II.

   ifXTable
        This table contains objects that have been added to the
        Interface MIB as a result of the Interface Evolution effort,
        or replacements for objects of the original, MIB-II, ifTable
        that were deprecated because the semantics of said objects
        have significantly changed.  This table also contains objects
        that were previously in the ifExtnsTable.

   ifStackTable
        This table contains objects that define the relationships
        among the sub-layers of an interface.

   ifTestTable
        This table contains objects that are used to perform tests on
        interfaces.  This table is a generic table.  The designers of
        media-specific MIBs must define exactly how this table
        applies to their specific MIB.



McCloghrie & Kastenholz                                        [Page 21]

RFC 1573               Interfaces Group Evolution           January 1994


        This table replaces the interface test table defined in
        RFC1229 [7].  The significant change is the replacement of
        the ifExtnsTestCommunity (and ifExtnsTestContext which would
        also have been required for SNMPv2) and ifExtnsTestRequestId
        objects, by the new ifTestId, ifTestStatus, and ifTestOwner
        objects.

   ifRcvAddressTable
        This table contains objects that are used to define the
        media-level addresses which this interface will receive.
        This table is a generic table.  The designers of media-
        specific MIBs must define exactly how this table applies to
        their specific MIB.

5.  IANAifType Definition

   IANAifType-MIB DEFINITIONS ::= BEGIN

   IMPORTS
       MODULE-IDENTITY, OBJECT-TYPE        FROM SNMPv2-SMI
       TEXTUAL-CONVENTION                  FROM SNMPv2-TC;

   ianaifType MODULE-IDENTITY
       LAST-UPDATED "9311082155Z"
       ORGANIZATION "IANA"
       CONTACT-INFO

                  "        Internet Assigned Numbers Authority

                   Postal: USC/Information Sciences Institute
                           4676 Admiralty Way, Marina del Rey, CA 90292

                   Tel:    [phone]
                   E-Mail: [e-mail]"
       DESCRIPTION
               "The MIB module which defines the IANAifType textual
               convention, and thus the enumerated values of the
               ifType object defined in MIB-II's ifTable."
       ::= { mib-2 30 }


   IANAifType ::= TEXTUAL-CONVENTION
       STATUS       current
       DESCRIPTION
               "This data type is used as the syntax of the ifType
               object in the (updated) definition of MIB-II's
               ifTable.




McCloghrie & Kastenholz                                        [Page 22]

RFC 1573               Interfaces Group Evolution           January 1994


               The definition of this textual convention with the
               addition of newly assigned values is published
               periodically by the IANA, in either the Assigned
               Numbers RFC, or some derivative of it specific to
               Internet Network Management number assignments.  (The
               latest arrangements can be obtained by contacting the
               IANA.)

               Requests for new values should be made to IANA via
               email ([e-mail]).

               The relationship between the assignment of ifType
               values and of OIDs to particular media-specific MIBs
               is solely the purview of IANA and is subject to change
               without notice.  Quite often, a media-specific MIB's
               OID-subtree assignment within MIB-II's 'transmission'
               subtree will be the same as its ifType value.
               However, in some circumstances this will not be the
               case, and implementors must not pre-assume any
               specific relationship between ifType values and
               transmission subtree OIDs."
       SYNTAX  INTEGER {
                   other(1),          -- none of the following
                   regular1822(2),
                   hdh1822(3),
                   ddnX25(4),
                   rfc877x25(5),
                   ethernetCsmacd(6),
                   iso88023Csmacd(7),
                   iso88024TokenBus(8),
                   iso88025TokenRing(9),
                   iso88026Man(10),
                   starLan(11),
                   proteon10Mbit(12),
                   proteon80Mbit(13),
                   hyperchannel(14),
                   fddi(15),
                   lapb(16),
                   sdlc(17),
                   ds1(18),           -- DS1/E1 (RFC 1406)
                   e1(19),            -- obsolete
                   basicISDN(20),
                   primaryISDN(21),
                   propPointToPointSerial(22), -- proprietary serial
                   ppp(23),
                   softwareLoopback(24),
                   eon(25),            -- CLNP over IP (RFC 1070)
                   ethernet3Mbit(26),



McCloghrie & Kastenholz                                        [Page 23]

RFC 1573               Interfaces Group Evolution           January 1994


                   nsip(27),           -- XNS over IP
                   slip(28),           -- generic SLIP
                   ultra(29),          -- ULTRA technologies
                   ds3(30),            -- T-3
                   sip(31),            -- SMDS
                   frameRelay(32),    -- DTE only
                   rs232(33),
                   para(34),           -- parallel-port
                   arcnet(35),         -- arcnet
                   arcnetPlus(36),     -- arcnet plus
                   atm(37),            -- ATM cells
                   miox25(38),
                   sonet(39),          -- SONET or SDH
                   x25ple(40),
                   iso88022llc(41),
                   localTalk(42),
                   smdsDxi(43),
                   frameRelayService(44),  -- Frame relay DCE
                   v35(45),
                   hssi(46),
                   hippi(47),
                   modem(48),          -- Generic modem
                   aal5(49),           -- AAL5 over ATM
                   sonetPath(50),
                   sonetVT(51),
                   smdsIcip(52),       -- SMDS InterCarrier Interface
                   propVirtual(53),    -- proprietary virtual/internal
                   propMultiplexor(54) -- proprietary multiplexing
               }

   END

6.  Interfaces Group Definitions

   IF-MIB DEFINITIONS ::= BEGIN

   IMPORTS
       MODULE-IDENTITY, OBJECT-TYPE, Counter32, Gauge32,
       Integer32, TimeTicks,
       NOTIFICATION-TYPE                        FROM SNMPv2-SMI
       TEXTUAL-CONVENTION, DisplayString,
       PhysAddress, TruthValue, RowStatus,
       AutonomousType, TestAndIncr              FROM SNMPv2-TC
       MODULE-COMPLIANCE, OBJECT-GROUP          FROM SNMPv2-CONF
       IANAifType                               FROM IANAifType-MIB
       interfaces                               FROM RFC-1213;





McCloghrie & Kastenholz                                        [Page 24]

RFC 1573               Interfaces Group Evolution           January 1994


   ifMIB MODULE-IDENTITY
       LAST-UPDATED "9311082155Z"
       ORGANIZATION "IETF Interfaces MIB Working Group"
       CONTACT-INFO

                  "        Keith McCloghrie

                   Postal: Hughes LAN Systems
                           1225 Charleston Road, Mountain View, CA 94043

                   Tel:    [phone]
                   E-Mail: [e-mail]


                           Frank Kastenholz

                   Postal: FTP Software
                           2 High Street, North Andover, MA 01845

                   Tel:    [phone]
                   E-Mail: [e-mail]"
       DESCRIPTION
               "The MIB module to describe generic objects for
               network interface sub-layers.  This MIB is an updated
               version of MIB-II's ifTable, and incorporates the
               extensions defined in RFC 1229."
       ::= { mib-2 31 }

   ifMIBObjects OBJECT IDENTIFIER ::= { ifMIB 1 }

   -- OwnerString has the same semantics as used in RFC 1271

   OwnerString ::= TEXTUAL-CONVENTION
       DISPLAY-HINT "255a"
       STATUS       current
       DESCRIPTION
               "This data type is used to model an administratively
               assigned name of the owner of a resource.  This
               information is taken from the NVT ASCII character set.
               It is suggested that this name contain one or more of
               the following: ASCII form of the manager station's
               transport address, management station name (e.g.,
               domain name), network management personnel's name,
               location, or phone number.  In some cases the agent
               itself will be the owner of an entry.  In these cases,
               this string shall be set to a string starting with
               'agent'."
       SYNTAX       OCTET STRING (SIZE(0..255))



McCloghrie & Kastenholz                                        [Page 25]

RFC 1573               Interfaces Group Evolution           January 1994


   -- InterfaceIndex contains the semantics of ifIndex and
   -- should be used for any objects defined on other mib
   -- modules that need these semantics.

   InterfaceIndex ::= TEXTUAL-CONVENTION
       DISPLAY-HINT "d"
       STATUS       current
       DESCRIPTION
               "A unique value, greater than zero, for each interface
               or interface sub-layer in the managed system.  It is
               recommended that values are assigned contiguously
               starting from 1.  The value for each interface sub-
               layer must remain constant at least from one re-
               initialization of the entity's network management
               system to the next re-initialization."
       SYNTAX       Integer32

   ifNumber  OBJECT-TYPE
       SYNTAX      Integer32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of network interfaces (regardless of their
               current state) present on this system."
       ::= { interfaces 1 }


   -- the Interfaces table

   -- The Interfaces table contains information on the entity's
   -- interfaces.  Each sub-layer below the internetwork-layer
   -- of a network interface is considered to be an interface.

   ifTable OBJECT-TYPE
       SYNTAX      SEQUENCE OF IfEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
               "A list of interface entries.  The number of entries
               is given by the value of ifNumber."
       ::= { interfaces 2 }

   ifEntry OBJECT-TYPE
       SYNTAX      IfEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
               "An entry containing management information applicable



McCloghrie & Kastenholz                                        [Page 26]

RFC 1573               Interfaces Group Evolution           January 1994


               to a particular interface."
       INDEX   { ifIndex }
       ::= { ifTable 1 }

   IfEntry ::=
       SEQUENCE {
           ifIndex                 InterfaceIndex,
           ifDescr                 DisplayString,
           ifType                  IANAifType,
           ifMtu                   Integer32,
           ifSpeed                 Gauge32,
           ifPhysAddress           PhysAddress,
           ifAdminStatus           INTEGER,
           ifOperStatus            INTEGER,
           ifLastChange            TimeTicks,
           ifInOctets              Counter32,
           ifInUcastPkts           Counter32,
           ifInNUcastPkts          Counter32,  -- deprecated
           ifInDiscards            Counter32,
           ifInErrors              Counter32,
           ifInUnknownProtos       Counter32,
           ifOutOctets             Counter32,
           ifOutUcastPkts          Counter32,
           ifOutNUcastPkts         Counter32,  -- deprecated
           ifOutDiscards           Counter32,
           ifOutErrors             Counter32,
           ifOutQLen               Gauge32,    -- deprecated
           ifSpecific              OBJECT IDENTIFIER -- deprecated
       }


   ifIndex OBJECT-TYPE
       SYNTAX      InterfaceIndex
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "A unique value, greater than zero, for each
               interface.  It is recommended that values are assigned
               contiguously starting from 1.  The value for each
               interface sub-layer must remain constant at least from
               one re-initialization of the entity's network
               management system to the next re-initialization."
       ::= { ifEntry 1 }

   ifDescr OBJECT-TYPE
       SYNTAX      DisplayString (SIZE (0..255))
       MAX-ACCESS  read-only
       STATUS      current



McCloghrie & Kastenholz                                        [Page 27]

RFC 1573               Interfaces Group Evolution           January 1994


       DESCRIPTION
               "A textual string containing information about the
               interface.  This string should include the name of the
               manufacturer, the product name and the version of the
               interface hardware/software."
       ::= { ifEntry 2 }

   ifType OBJECT-TYPE
       SYNTAX      IANAifType
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The type of interface.  Additional values for ifType
               are assigned by the Internet Assigned Numbers
               Authority (IANA), through updating the syntax of the
               IANAifType textual convention."
       ::= { ifEntry 3 }

   ifMtu OBJECT-TYPE
       SYNTAX      Integer32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The size of the largest packet which can be
               sent/received on the interface, specified in octets.
               For interfaces that are used for transmitting network
               datagrams, this is the size of the largest network
               datagram that can be sent on the interface."
       ::= { ifEntry 4 }

   ifSpeed OBJECT-TYPE
       SYNTAX      Gauge32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "An estimate of the interface's current bandwidth in
               bits per second.  For interfaces which do not vary in
               bandwidth or for those where no accurate estimation
               can be made, this object should contain the nominal
               bandwidth.  If the bandwidth of the interface is
               greater than the maximum value reportable by this
               object then this object should report its maximum
               value (4,294,967,295) and ifHighSpeed must be used to
               report the interace's speed.  For a sub-layer which
               has no concept of bandwidth, this object should be
               zero."
       ::= { ifEntry 5 }




McCloghrie & Kastenholz                                        [Page 28]

RFC 1573               Interfaces Group Evolution           January 1994


   ifPhysAddress OBJECT-TYPE
       SYNTAX      PhysAddress
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The interface's address at its protocol sub-layer.
               The interface's media-specific MIB must define the bit
               and byte ordering and format of the value contained by
               this object.  For interfaces which do not have such an
               address (e.g., a serial line), this object should
               contain an octet string of zero length."
       ::= { ifEntry 6 }

   ifAdminStatus OBJECT-TYPE
       SYNTAX  INTEGER {
                   up(1),       -- ready to pass packets
                   down(2),
                   testing(3)   -- in some test mode
               }
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
               "The desired state of the interface.  The testing(3)
               state indicates that no operational packets can be
               passed.  When a managed system initializes, all
               interfaces start with ifAdminStatus in the down(2)
               state.  As a result of either explicit management
               action or per configuration information retained by
               the managed system, ifAdminStatus is then changed to
               either the up(1) or testing(3) states (or remains in
               the down(2) state)."
       ::= { ifEntry 7 }

   ifOperStatus OBJECT-TYPE
       SYNTAX  INTEGER {
                   up(1),       -- ready to pass packets
                   down(2),
                   testing(3),  -- in some test mode
                   unknown(4),  -- status can not be determined
                                -- for some reason.
                   dormant(5)
               }
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The current operational state of the interface.  The
               testing(3) state indicates that no operational packets
               can be passed.  If ifAdminStatus is down(2) then



McCloghrie & Kastenholz                                        [Page 29]

RFC 1573               Interfaces Group Evolution           January 1994


               ifOperStatus should be down(2).  If ifAdminStatus is
               changed to up(1) then ifOperStatus should change to
               up(1) if the interface is ready to transmit and
               receive network traffic; it should change to
               dormant(5) if the interface is waiting for external
               actions (such as a serial line waiting for an
               incomming connection); it should remain in the down(2)
               state if and only if there is a fault that prevents if
               from going to the up(1) state."
       ::= { ifEntry 8 }

   ifLastChange OBJECT-TYPE
       SYNTAX      TimeTicks
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The value of sysUpTime at the time the interface
               entered its current operational state.  If the current
               state was entered prior to the last re-initialization
               of the local network management subsystem, then this
               object contains a zero value."
       ::= { ifEntry 9 }

   ifInOctets OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of octets received on the interface,
               including framing characters."
       ::= { ifEntry 10 }

   ifInUcastPkts OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of packets, delivered by this sub-layer to
               a higher (sub-)layer, which were not addressed to a
               multicast or broadcast address at this sub-layer."
       ::= { ifEntry 11 }

   ifInNUcastPkts OBJECT-TYPE
       SYNTAX  Counter32
       MAX-ACCESS  read-only
       STATUS      deprecated
       DESCRIPTION
               "The number of packets, delivered by this sub-layer to



McCloghrie & Kastenholz                                        [Page 30]

RFC 1573               Interfaces Group Evolution           January 1994


               a higher (sub-)layer, which were addressed to a
               multicast or broadcast address at this sub-layer.
               This object is deprecated in favour of
               ifInMulticastPkts and ifInBroadcastPkts."
       ::= { ifEntry 12 }

   ifInDiscards OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of inbound packets which were chosen to be
               discarded even though no errors had been detected to
               prevent their being deliverable to a higher-layer
               protocol.  One possible reason for discarding such a
               packet could be to free up buffer space."
       ::= { ifEntry 13 }

   ifInErrors OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "For packet-oriented interfaces, the number of inbound
               packets that contained errors preventing them from
               being deliverable to a higher-layer protocol.  For
               character-oriented or fixed-length interfaces, the
               number of inbound transmission units that contained
               errors preventing them from being deliverable to a
               higher-layer protocol."
       ::= { ifEntry 14 }

   ifInUnknownProtos OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "For packet-oriented interfaces, the number of packets
               received via the interface which were discarded
               because of an unknown or unsupported protocol.  For
               character-oriented or fixed-length interfaces which
               support protocol multiplexing the number of
               transmission units received via the interface which
               were discarded because of an unknown or unsupported
               protocol.  For any interface which does not support
               protocol multiplexing, this counter will always be 0."
       ::= { ifEntry 15 }




McCloghrie & Kastenholz                                        [Page 31]

RFC 1573               Interfaces Group Evolution           January 1994


   ifOutOctets OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of octets transmitted out of the
               interface, including framing characters."
       ::= { ifEntry 16 }

   ifOutUcastPkts OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION

               "The total number of packets that higher-level
               protocols requested be transmitted, and which were not
               addressed to a multicast or broadcast address at this
               sub-layer, including those that were discarded or not
               sent."
       ::= { ifEntry 17 }

   ifOutNUcastPkts OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      deprecated
       DESCRIPTION
               "The total number of packets that higher-level
               protocols requested be transmitted, and which were
               addressed to a multicast or broadcast address at this
               sub-layer, including those that were discarded or not
               sent.

               This object is deprecated in favour of
               ifOutMulticastPkts and ifOutBroadcastPkts."
       ::= { ifEntry 18 }

   ifOutDiscards OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of outbound packets which were chosen to
               be discarded even though no errors had been detected
               to prevent their being transmitted.  One possible
               reason for discarding such a packet could be to free
               up buffer space."
       ::= { ifEntry 19 }



McCloghrie & Kastenholz                                        [Page 32]

RFC 1573               Interfaces Group Evolution           January 1994


   ifOutErrors OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "For packet-oriented interfaces, the number of
               outbound packets that could not be transmitted because
               of errors.  For character-oriented or fixed-length
               interfaces, the number of outbound transmission units
               that could not be transmitted because of errors."
       ::= { ifEntry 20 }

   ifOutQLen OBJECT-TYPE
       SYNTAX      Gauge32
       MAX-ACCESS  read-only
       STATUS      deprecated
       DESCRIPTION
               "The length of the output packet queue (in packets)."
       ::= { ifEntry 21 }

   ifSpecific OBJECT-TYPE
       SYNTAX      OBJECT IDENTIFIER
       MAX-ACCESS  read-only
       STATUS      deprecated
       DESCRIPTION
               "A reference to MIB definitions specific to the
               particular media being used to realize the interface.
               It is recommended that this value point to an instance
               of a MIB object in the media-specific MIB, i.e., that
               this object have the semantics associated with the
               InstancePointer textual convention defined in RFC
               1443.  In fact, it is recommended that the media-
               specific MIB specify what value ifSpecific should/can
               take for values of ifType.  If no MIB definitions
               specific to the particular media are available, the
               value should be set to the OBJECT IDENTIFIER { 0 0 }."
       ::= { ifEntry 22 }


   --
   --   Extension to the interface table
   --
   -- This table replaces the ifExtnsTable table.
   --

   ifXTable        OBJECT-TYPE
       SYNTAX      SEQUENCE OF IfXEntry
       MAX-ACCESS  not-accessible



McCloghrie & Kastenholz                                        [Page 33]

RFC 1573               Interfaces Group Evolution           January 1994


       STATUS      current
       DESCRIPTION
               "A list of interface entries.  The number of entries
               is given by the value of ifNumber.  This table
               contains additional objects for the interface table."
       ::= { ifMIBObjects 1 }

   ifXEntry        OBJECT-TYPE
       SYNTAX      IfXEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
               "An entry containing additional management information
               applicable to a particular interface."
       AUGMENTS    { ifEntry }
       ::= { ifXTable 1 }

   IfXEntry ::=
       SEQUENCE {
           ifName                  DisplayString,
           ifInMulticastPkts       Counter32,
           ifInBroadcastPkts       Counter32,
           ifOutMulticastPkts      Counter32,
           ifOutBroadcastPkts      Counter32,
           ifHCInOctets            Counter64,
           ifHCInUcastPkts         Counter64,
           ifHCInMulticastPkts     Counter64,
           ifHCInBroadcastPkts     Counter64,
           ifHCOutOctets           Counter64,
           ifHCOutUcastPkts        Counter64,
           ifHCOutMulticastPkts    Counter64,
           ifHCOutBroadcastPkts    Counter64,
           ifLinkUpDownTrapEnable  INTEGER,
           ifHighSpeed             Gauge32,
           ifPromiscuousMode       TruthValue,
           ifConnectorPresent      TruthValue
       }


   ifName OBJECT-TYPE
       SYNTAX      DisplayString
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The textual name of the interface.  The value of this
               object should be the name of the interface as assigned
               by the local device and should be suitable for use in
               commands entered at the device's `console'.  This



McCloghrie & Kastenholz                                        [Page 34]

RFC 1573               Interfaces Group Evolution           January 1994


               might be a text name, such as `le0' or a simple port
               number, such as `1', depending on the interface naming
               syntax of the device.  If several entries in the
               ifTable together represent a single interface as named
               by the device, then each will have the same value of
               ifName.  If there is no local name, or this object is
               otherwise not applicable, then this object contains a
               0-length string."
       ::= { ifXEntry 1 }

   ifInMulticastPkts OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of packets, delivered by this sub-layer to
               a higher (sub-)layer, which were addressed to a
               multicast address at this sub-layer.  For a MAC layer
               protocol, this includes both Group and Functional
               addresses."
       ::= { ifXEntry 2 }

   ifInBroadcastPkts OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of packets, delivered by this sub-layer to
               a higher (sub-)layer, which were addressed to a
               broadcast address at this sub-layer."
       ::= { ifXEntry 3 }

   ifOutMulticastPkts OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of packets that higher-level
               protocols requested be transmitted, and which were
               addressed to a multicast address at this sub-layer,
               including those that were discarded or not sent.  For
               a MAC layer protocol, this includes both Group and
               Functional addresses."
       ::= { ifXEntry 4 }

   ifOutBroadcastPkts OBJECT-TYPE
       SYNTAX      Counter32
       MAX-ACCESS  read-only



McCloghrie & Kastenholz                                        [Page 35]

RFC 1573               Interfaces Group Evolution           January 1994


       STATUS      current
       DESCRIPTION
               "The total number of packets that higher-level
               protocols requested be transmitted, and which were
               addressed to a broadcast address at this sub-layer,
               including those that were discarded or not sent."
       ::= { ifXEntry 5 }

   --
   -- High Capacity Counter objects.  These objects are all

   -- 64 bit versions of the "basic" ifTable counters.  These
   -- objects all have the same basic semantics as their 32-bit
   -- counterparts, however, their syntax has been extended
   -- to 64 bits.
   --

   ifHCInOctets OBJECT-TYPE
       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of octets received on the interface,
               including framing characters.  This object is a 64-bit
               version of ifInOctets."
       ::= { ifXEntry 6 }

   ifHCInUcastPkts OBJECT-TYPE
       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of packets, delivered by this sub-layer to
               a higher (sub-)layer, which were not addressed to a
               multicast or broadcast address at this sub-layer.
               This object is a 64-bit version of ifInUcastPkts."
       ::= { ifXEntry 7 }

   ifHCInMulticastPkts OBJECT-TYPE
       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of packets, delivered by this sub-layer to
               a higher (sub-)layer, which were addressed to a
               multicast address at this sub-layer.  For a MAC layer
               protocol, this includes both Group and Functional
               addresses.  This object is a 64-bit version of



McCloghrie & Kastenholz                                        [Page 36]

RFC 1573               Interfaces Group Evolution           January 1994


               ifInMulticastPkts."
       ::= { ifXEntry 8 }

   ifHCInBroadcastPkts OBJECT-TYPE
       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of packets, delivered by this sub-layer to
               a higher (sub-)layer, which were addressed to a
               broadcast address at this sub-layer.  This object is a
               64-bit version of ifInBroadcastPkts."
       ::= { ifXEntry 9 }

   ifHCOutOctets OBJECT-TYPE
       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of octets transmitted out of the
               interface, including framing characters.  This object
               is a 64-bit version of ifOutOctets."
       ::= { ifXEntry 10 }

   ifHCOutUcastPkts OBJECT-TYPE
       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of packets that higher-level
               protocols requested be transmitted, and which were not
               addressed to a multicast or broadcast address at this
               sub-layer, including those that were discarded or not
               sent.  This object is a 64-bit version of
               ifOutUcastPkts."
       ::= { ifXEntry 11 }

   ifHCOutMulticastPkts OBJECT-TYPE
       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of packets that higher-level
               protocols requested be transmitted, and which were
               addressed to a multicast address at this sub-layer,
               including those that were discarded or not sent.  For
               a MAC layer protocol, this includes both Group and
               Functional addresses.  This object is a 64-bit version



McCloghrie & Kastenholz                                        [Page 37]

RFC 1573               Interfaces Group Evolution           January 1994


               of ifOutMulticastPkts."
       ::= { ifXEntry 12 }

   ifHCOutBroadcastPkts OBJECT-TYPE
       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of packets that higher-level
               protocols requested be transmitted, and which were
               addressed to a broadcast address at this sub-layer,
               including those that were discarded or not sent.  This
               object is a 64-bit version of ifOutBroadcastPkts."
       ::= { ifXEntry 13 }

   ifLinkUpDownTrapEnable  OBJECT-TYPE
       SYNTAX      INTEGER { enabled(1), disabled(2) }
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
               "Indicates whether linkUp/linkDown traps should be
               generated for this interface.

               By default, this object should have the value
               enabled(1) for interfaces which do not operate on
               'top' of any other interface (as defined in the
               ifStackTable), and disabled(2) otherwise."
       ::= { ifXEntry 14 }

   ifHighSpeed OBJECT-TYPE
       SYNTAX      Gauge32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "An estimate of the interface's current bandwidth in
               units of 1,000,000 bits per second.  If this object
               reports a value of `n' then the speed of the interface
               is somewhere in the range of `n-500,000' to
               `n+499,999'.  For interfaces which do not vary in
               bandwidth or for those where no accurate estimation
               can be made, this object should contain the nominal
               bandwidth.  For a sub-layer which has no concept of
               bandwidth, this object should be zero."
       ::= { ifXEntry 15 }

   ifPromiscuousMode  OBJECT-TYPE
       SYNTAX      TruthValue
       MAX-ACCESS  read-write



McCloghrie & Kastenholz                                        [Page 38]

RFC 1573               Interfaces Group Evolution           January 1994


       STATUS      current
       DESCRIPTION
               "This object has a value of false(2) if this interface
               only accepts packets/frames that are addressed to this
               station.  This object has a value of true(1) when the
               station accepts all packets/frames transmitted on the
               media.  The value true(1) is only legal on certain
               types of media.  If legal, setting this object to a
               value of true(1) may require the interface to be reset
               before becoming effective.

               The value of ifPromiscuousMode does not affect the
               reception of broadcast and multicast packets/frames by
               the interface."
       ::= { ifXEntry 16 }

   ifConnectorPresent   OBJECT-TYPE
       SYNTAX      TruthValue
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "This object has the value 'true(1)' if the interface
               sublayer has a physical connector and the value
               'false(2)' otherwise."
       ::= { ifXEntry 17 }


   --           The Interface Stack Group
   --
   -- Implementation of this group is mandatory for all systems
   --

   ifStackTable  OBJECT-TYPE
        SYNTAX        SEQUENCE OF IfStackEntry
        MAX-ACCESS    not-accessible
        STATUS        current
        DESCRIPTION
               "The table containing information on the relationships
               between the multiple sub-layers of network interfaces.
               In particular, it contains information on which sub-
               layers run 'on top of' which other sub-layers.  Each
               sub-layer corresponds to a conceptual row in the
               ifTable."
        ::= { ifMIBObjects 2 }


   ifStackEntry  OBJECT-TYPE
        SYNTAX        IfStackEntry



McCloghrie & Kastenholz                                        [Page 39]

RFC 1573               Interfaces Group Evolution           January 1994


        MAX-ACCESS    not-accessible
        STATUS        current
        DESCRIPTION
               "Information on a particular relationship between two
               sub-layers, specifying that one sub-layer runs on
               'top' of the other sub-layer.  Each sub-layer
               corresponds to a conceptual row in the ifTable."
        INDEX { ifStackHigherLayer, ifStackLowerLayer }
        ::= { ifStackTable 1 }


   IfStackEntry ::=
       SEQUENCE {
           ifStackHigherLayer  Integer32,
           ifStackLowerLayer   Integer32,
           ifStackStatus       RowStatus
        }


   ifStackHigherLayer  OBJECT-TYPE
        SYNTAX        Integer32
        MAX-ACCESS    not-accessible
        STATUS        current
        DESCRIPTION
               "The value of ifIndex corresponding to the higher
               sub-layer of the relationship, i.e., the sub-layer
               which runs on 'top' of the sub-layer identified by the
               corresponding instance of ifStackLowerLayer.  If there
               is no higher sub-layer (below the internetwork layer),
               then this object has the value 0."
        ::= { ifStackEntry 1 }


   ifStackLowerLayer  OBJECT-TYPE
        SYNTAX        Integer32
        MAX-ACCESS    not-accessible
        STATUS        current
        DESCRIPTION
               "The value of ifIndex corresponding to the lower sub-
               layer of the relationship, i.e., the sub-layer which
               runs 'below' the sub-layer identified by the
               corresponding instance of ifStackHigherLayer.  If
               there is no lower sub-layer, then this object has the
               value 0."
        ::= { ifStackEntry 2 }


   ifStackStatus  OBJECT-TYPE



McCloghrie & Kastenholz                                        [Page 40]

RFC 1573               Interfaces Group Evolution           January 1994


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

               Changing the value of this object from 'active' to
               'notInService' or 'destroy' will likely have
               consequences up and down the interface stack.  Thus,
               write access to this object is likely to be
               inappropriate for some types of interfaces, and many
               implementations will choose not to support write-
               access for any type of interface."
       ::= { ifStackEntry 3 }


   --
   --    The Interface Test Table
   --
   -- This group of objects is optional.  However, a media-specific
   -- MIB may make implementation of this group mandatory.
   --
   -- This table replaces the ifExtnsTestTable
   --

   ifTestTable   OBJECT-TYPE
       SYNTAX      SEQUENCE OF IfTestEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
               "This table contains one entry per interface.  It
               defines objects which allow a network manager to
               instruct an agent to test an interface for various
               faults.  Tests for an interface are defined in the
               media-specific MIB for that interface.  After invoking
               a test, the object ifTestResult can be read to
               determine the outcome.  If an agent can not perform
               the test, ifTestResult is set to so indicate.  The
               object ifTestCode can be used to provide further
               test-specific or interface-specific (or even
               enterprise-specific) information concerning the
               outcome of the test.  Only one test can be in progress
               on each interface at any one time.  If one test is in
               progress when another test is invoked, the second test
               is rejected.  Some agents may reject a test when a
               prior test is active on another interface.




McCloghrie & Kastenholz                                        [Page 41]

RFC 1573               Interfaces Group Evolution           January 1994


               Before starting a test, a manager-station must first
               obtain 'ownership' of the entry in the ifTestTable for
               the interface to be tested.  This is accomplished with
               the ifTestId and ifTestStatus objects as follows:

            try_again:
                get (ifTestId, ifTestStatus)
                while (ifTestStatus != notInUse)
                    /*
                     * Loop while a test is running or some other
                     * manager is configuring a test.
                     */
                    short delay
                    get (ifTestId, ifTestStatus)
                }

                /*
                 * Is not being used right now -- let's compete
                 * to see who gets it.
                 */
                lock_value = ifTestId

                if ( set(ifTestId = lock_value, ifTestStatus = inUse,
                         ifTestOwner = 'my-IP-address') == FAILURE)
                    /*
                     * Another manager got the ifTestEntry -- go
                     * try again
                     */
                    goto try_again;

                /*
                 * I have the lock
                 */
                set up any test parameters.

                /*
                 * This starts the test
                 */
                set(ifTestType = test_to_run);

                wait for test completion by polling ifTestResult

                when test completes, agent sets ifTestResult
                     agent also sets ifTestStatus = 'notInUse'

                retrieve any additional test results, and ifTestId

                if (ifTestId == lock_value+1) results are valid



McCloghrie & Kastenholz                                        [Page 42]

RFC 1573               Interfaces Group Evolution           January 1994


              A manager station first retrieves the value of the
              appropriate ifTestId and ifTestStatus objects,
              periodically repeating the retrieval if necessary,
              until the value of ifTestStatus is 'notInUse'.  The
              manager station then tries to set the same ifTestId
              object to the value it just retrieved, the same
              ifTestStatus object to 'inUse', and the corresponding
              ifTestOwner object to a value indicating itself.  If
              the set operation succeeds then the manager has
              obtained ownership of the ifTestEntry, and the value of
              the ifTestId object is incremented by the agent (per
              the semantics of TestAndIncr).  Failure of the set
              operation indicates that some other manager has
              obtained ownership of the ifTestEntry.

              Once ownership is obtained, any test parameters can be
              setup, and then the test is initiated by setting
              ifTestType.  On completion of the test, the agent sets
              ifTestStatus to 'notInUse'.  Once this occurs, the
              manager can retrieve the results.  In the (rare) event
              that the invocation of tests by two network managers
              were to overlap, then there would be a possibility that
              the first test's results might be overwritten by the
              second test's results prior to the first results being
              read.  This unlikely circumstance can be detected by a
              network manager retrieving ifTestId at the same time as
              retrieving the test results, and ensuring that the
              results are for the desired request.

              If ifTestType is not set within an abnormally long
              period of time after ownership is obtained, the agent
              should time-out the manager, and reset the value of the
              ifTestStatus object back to 'notInUse'.  It is
              suggested that this time-out period be 5 minutes.

              In general, a management station must not retransmit a
              request to invoke a test for which it does not receive
              a response; instead, it properly inspects an agent's
              MIB to determine if the invocation was successful.
              Only if the invocation was unsuccessful, is the
              invocation request retransmitted.

              Some tests may require the interface to be taken off-
              line in order to execute them, or may even require the
              agent to reboot after completion of the test.  In these
              circumstances, communication with the management
              station invoking the test may be lost until after
              completion of the test.  An agent is not required to



McCloghrie & Kastenholz                                        [Page 43]

RFC 1573               Interfaces Group Evolution           January 1994


              support such tests.  However, if such tests are
              supported, then the agent should make every effort to
              transmit a response to the request which invoked the
              test prior to losing communication.  When the agent is
              restored to normal service, the results of the test are
              properly made available in the appropriate objects.
              Note that this requires that the ifIndex value assigned
              to an interface must be unchanged even if the test
              causes a reboot.  An agent must reject any test for
              which it cannot, perhaps due to resource constraints,
              make available at least the minimum amount of
              information after that test completes."
       ::= { ifMIBObjects 3 }

   ifTestEntry OBJECT-TYPE
       SYNTAX       IfTestEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION
               "An entry containing objects for invoking tests on an
               interface."
       AUGMENTS  { ifEntry }
       ::= { ifTestTable 1 }

   IfTestEntry ::=
       SEQUENCE {
           ifTestId           TestAndIncr,
           ifTestStatus       INTEGER,
           ifTestType         AutonomousType,
           ifTestResult       INTEGER,
           ifTestCode         OBJECT IDENTIFIER,
           ifTestOwner        OwnerString
       }

   ifTestId         OBJECT-TYPE
       SYNTAX       TestAndIncr
       MAX-ACCESS   read-write
       STATUS       current
       DESCRIPTION
               "This object identifies the current invocation of the
               interface's test."
       ::= { ifTestEntry 1 }

   ifTestStatus     OBJECT-TYPE
       SYNTAX       INTEGER { notInUse(1), inUse(2) }
       MAX-ACCESS   read-write
       STATUS       current
       DESCRIPTION



McCloghrie & Kastenholz                                        [Page 44]

RFC 1573               Interfaces Group Evolution           January 1994


               "This object indicates whether or not some manager
               currently has the necessary 'ownership' required to
               invoke a test on this interface.  A write to this
               object is only successful when it changes its value
               from 'notInUse(1)' to 'inUse(2)'.  After completion of
               a test, the agent resets the value back to
               'notInUse(1)'."
       ::= { ifTestEntry 2 }

   ifTestType       OBJECT-TYPE
       SYNTAX       AutonomousType
       MAX-ACCESS   read-write
       STATUS       current
       DESCRIPTION
               "A control variable used to start and stop operator-
               initiated interface tests.  Most OBJECT IDENTIFIER
               values assigned to tests are defined elsewhere, in
               association with specific types of interface.
               However, this document assigns a value for a full-
               duplex loopback test, and defines the special meanings
               of the subject identifier:

                   noTest  OBJECT IDENTIFIER ::= { 0 0 }

               When the value noTest is written to this object, no
               action is taken unless a test is in progress, in which
               case the test is aborted.  Writing any other value to
               this object is only valid when no test is currently in
               progress, in which case the indicated test is
               initiated.

               When read, this object always returns the most recent
               value that ifTestType was set to.  If it has not been
               set since the last initialization of the network
               management subsystem on the agent, a value of noTest
               is returned."
       ::= { ifTestEntry 3 }

   ifTestResult  OBJECT-TYPE
       SYNTAX       INTEGER {
                        none(1),          -- no test yet requested
                        success(2),
                        inProgress(3),
                        notSupported(4),
                        unAbleToRun(5),   -- due to state of system
                        aborted(6),
                        failed(7)
                    }



McCloghrie & Kastenholz                                        [Page 45]

RFC 1573               Interfaces Group Evolution           January 1994


       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION
               "This object contains the result of the most recently
               requested test, or the value none(1) if no tests have
               been requested since the last reset.  Note that this
               facility provides no provision for saving the results
               of one test when starting another, as could be
               required if used by multiple managers concurrently."
       ::= { ifTestEntry 4 }

   ifTestCode  OBJECT-TYPE
       SYNTAX       OBJECT IDENTIFIER
       MAX-ACCESS   read-only
       STATUS       current
       DESCRIPTION
               "This object contains a code which contains more
               specific information on the test result, for example
               an error-code after a failed test.  Error codes and
               other values this object may take are specific to the
               type of interface and/or test.  The value may have the
               semantics of either the AutonomousType or
               InstancePointer textual conventions as defined in RFC
               1443.  The identifier:

                   testCodeUnknown  OBJECT IDENTIFIER ::= { 0 0 }

               is defined for use if no additional result code is
               available."
       ::= { ifTestEntry 5 }

   ifTestOwner      OBJECT-TYPE
       SYNTAX       OwnerString
       MAX-ACCESS   read-write
       STATUS       current
       DESCRIPTION
               "The entity which currently has the 'ownership'
               required to invoke a test on this interface."
       ::= { ifTestEntry 6 }


   --   Generic Receive Address Table
   --
   -- This group of objects is mandatory for all types of
   -- interfaces which can receive packets/frames addressed to
   -- more than one address.
   --
   -- This table replaces the ifExtnsRcvAddr table.  The main



McCloghrie & Kastenholz                                        [Page 46]

RFC 1573               Interfaces Group Evolution           January 1994


   -- difference is that this table makes use of the RowStatus
   -- textual convention, while ifExtnsRcvAddr did not.

   ifRcvAddressTable  OBJECT-TYPE
       SYNTAX      SEQUENCE OF IfRcvAddressEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
               "This table contains an entry for each address
               (broadcast, multicast, or uni-cast) for which the
               system will receive packets/frames on a particular
               interface, except as follows:

               - for an interface operating in promiscuous mode,
               entries are only required for those addresses for
               which the system would receive frames were it not
               operating in promiscuous mode.

               - for 802.5 functional addresses, only one entry is
               required, for the address which has the functional
               address bit ANDed with the bit mask of all functional
               addresses for which the interface will accept frames."
       ::= { ifMIBObjects 4 }

   ifRcvAddressEntry  OBJECT-TYPE
       SYNTAX      IfRcvAddressEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
               "A list of objects identifying an address for which
               the system will accept packets/frames on the
               particular interface identified by the index value
               ifIndex."
       INDEX  { ifIndex, ifRcvAddressAddress }
       ::= { ifRcvAddressTable 1 }

   IfRcvAddressEntry ::=
       SEQUENCE {
           ifRcvAddressAddress   PhysAddress,
           ifRcvAddressStatus    RowStatus,
           ifRcvAddressType      INTEGER
       }

   ifRcvAddressAddress OBJECT-TYPE
       SYNTAX      PhysAddress
       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION



McCloghrie & Kastenholz                                        [Page 47]

RFC 1573               Interfaces Group Evolution           January 1994


               "An address for which the system will accept
               packets/frames on this entry's interface."
       ::= { ifRcvAddressEntry 1 }

   ifRcvAddressStatus OBJECT-TYPE
       SYNTAX      RowStatus
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
               "This object is used to create and delete rows in the
               ifRcvAddressTable."

       ::= { ifRcvAddressEntry 2 }

   ifRcvAddressType OBJECT-TYPE
       SYNTAX      INTEGER {
                       other(1),
                       volatile(2),
                       nonVolatile(3)
                   }

       MAX-ACCESS  read-create
       STATUS      current
       DESCRIPTION
               "This object has the value nonVolatile(3) for those
               entries in the table which are valid and will not be
               deleted by the next restart of the managed system.
               Entries having the value volatile(2) are valid and
               exist, but have not been saved, so that will not exist
               after the next restart of the managed system.  Entries
               having the value other(1) are valid and exist but are
               not classified as to whether they will continue to
               exist after the next restart."

       DEFVAL  { volatile }

       ::= { ifRcvAddressEntry 3 }


   -- definition of interface-related traps.

   linkDown NOTIFICATION-TYPE
       OBJECTS { ifIndex, ifAdminStatus, ifOperStatus }
       STATUS  current
       DESCRIPTION
               "A linkDown trap signifies that the SNMPv2 entity,
               acting in an agent role, has detected that the
               ifOperStatus object for one of its communication links



McCloghrie & Kastenholz                                        [Page 48]

RFC 1573               Interfaces Group Evolution           January 1994


               is about to transition into the down state."
       ::= { snmpTraps 3 }

   linkUp NOTIFICATION-TYPE
       OBJECTS { ifIndex, ifAdminStatus, ifOperStatus }
       STATUS  current
       DESCRIPTION
               "A linkUp trap signifies that the SNMPv2 entity,
               acting in an agent role, has detected that the
               ifOperStatus object for one of its communication links
               has transitioned out of the down state."
       ::= { snmpTraps 4 }


   -- conformance information

   ifConformance OBJECT IDENTIFIER ::= { ifMIB 2 }

   ifGroups      OBJECT IDENTIFIER ::= { ifConformance 1 }
   ifCompliances OBJECT IDENTIFIER ::= { ifConformance 2 }


   -- compliance statements

   ifCompliance MODULE-COMPLIANCE
       STATUS  current
       DESCRIPTION
               "The compliance statement for SNMPv2 entities which
               have network interfaces."

       MODULE  -- this module
           MANDATORY-GROUPS { ifGeneralGroup, ifStackGroup }

           GROUP       ifFixedLengthGroup
           DESCRIPTION
               "This group is mandatory for all network interfaces
               which are character-oriented or transmit data in
               fixed-length transmission units."

           GROUP       ifHCFixedLengthGroup
           DESCRIPTION
               "This group is mandatory only for those network
               interfaces which are character-oriented or transmit
               data in fixed-length transmission units, and for which
               the value of the corresponding instance of ifSpeed is
               greater than 20,000,000 bits/second."

           GROUP       ifPacketGroup



McCloghrie & Kastenholz                                        [Page 49]

RFC 1573               Interfaces Group Evolution           January 1994


           DESCRIPTION
               "This group is mandatory for all network interfaces
               which are packet-oriented."

           GROUP       ifHCPacketGroup
           DESCRIPTION
               "This group is mandatory only for those network
               interfaces which are packet-oriented and for which the
               value of the corresponding instance of ifSpeed is
               greater than 650,000,000 bits/second."
           GROUP       ifTestGroup
           DESCRIPTION
               "This group is optional.  Media-specific MIBs which
               require interface tests are strongly encouraged to use
               this group for invoking tests and reporting results.
               A medium specific MIB which has mandatory tests may
               make implementation of this group mandatory."

           GROUP       ifRcvAddressGroup
           DESCRIPTION
               "The applicability of this group MUST be defined by
               the media-specific MIBs.  Media-specific MIBs must
               define the exact meaning, use, and semantics of the
               addresses in this group."

           OBJECT      ifLinkUpDownTrapEnable
           MIN-ACCESS  read-only
           DESCRIPTION
               "Write access is not required."

           OBJECT      ifPromiscuousMode
           MIN-ACCESS  read-only
           DESCRIPTION
               "Write access is not required."

           OBJECT      ifStackStatus
           SYNTAX      INTEGER { active(1) } -- subset of RowStatus
           MIN-ACCESS  read-only
           DESCRIPTION
               "Write access is not required, and only one of the six
               enumerated values for the RowStatus textual convention
               need be supported, specifically: active(1)."

           OBJECT       ifAdminStatus
           SYNTAX       INTEGER { up(1), down(2) }
           MIN-ACCESS   read-only
           DESCRIPTION
               "Write access is not required, nor is support for the



McCloghrie & Kastenholz                                        [Page 50]

RFC 1573               Interfaces Group Evolution           January 1994


               value testing(3)."
       ::= { ifCompliances 1 }


   -- units of conformance

   ifGeneralGroup    OBJECT-GROUP
       OBJECTS { ifDescr, ifType, ifSpeed, ifPhysAddress,
                 ifAdminStatus, ifOperStatus, ifLastChange,
                 ifLinkUpDownTrapEnable, ifConnectorPresent,
                 ifHighSpeed, ifName }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information
               applicable to all network interfaces."
       ::= { ifGroups 1 }

   -- the following five groups are mutually exclusive; at most
   -- one of these groups is implemented for any interface

   ifFixedLengthGroup    OBJECT-GROUP
       OBJECTS { ifInOctets, ifOutOctets, ifInUnknownProtos,
                 ifInErrors, ifOutErrors }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information
               specific to non-high speed, character-oriented or
               fixed-length-transmission network interfaces.  (Non-
               high speed interfaces transmit and receive at speeds
               less than or equal to 20,000,000 bits/second.)"
       ::= { ifGroups 2 }

   ifHCFixedLengthGroup    OBJECT-GROUP
       OBJECTS { ifHCInOctets, ifHCOutOctets,
                 ifInOctets, ifOutOctets, ifInUnknownProtos,
                 ifInErrors, ifOutErrors }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information
               specific to high speed (greater than 20,000,000
               bits/second) character-oriented or fixed-length-
               transmission network interfaces."
       ::= { ifGroups 3 }

   ifPacketGroup    OBJECT-GROUP
       OBJECTS { ifInOctets, ifOutOctets, ifInUnknownProtos,
                 ifInErrors, ifOutErrors,
                 ifMtu, ifInUcastPkts, ifInMulticastPkts,



McCloghrie & Kastenholz                                        [Page 51]

RFC 1573               Interfaces Group Evolution           January 1994


                 ifInBroadcastPkts, ifInDiscards,
                 ifOutUcastPkts, ifOutMulticastPkts,
                 ifOutBroadcastPkts, ifOutDiscards,
                 ifPromiscuousMode }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information
               specific to non-high speed, packet-oriented network
               interfaces.  (Non-high speed interfaces transmit and
               receive at speeds less than or equal to 20,000,000
               bits/second.)"
       ::= { ifGroups 4 }

   ifHCPacketGroup    OBJECT-GROUP
       OBJECTS { ifHCInOctets, ifHCOutOctets,
                 ifInOctets, ifOutOctets, ifInUnknownProtos,
                 ifInErrors, ifOutErrors,
                 ifMtu, ifInUcastPkts, ifInMulticastPkts,
                 ifInBroadcastPkts, ifInDiscards,
                 ifOutUcastPkts, ifOutMulticastPkts,
                 ifOutBroadcastPkts, ifOutDiscards,
                 ifPromiscuousMode }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information
               specific to high speed (greater than 20,000,000
               bits/second but less than or equal to 650,000,000
               bits/second) packet-oriented network interfaces."
       ::= { ifGroups 5 }

   ifVHCPacketGroup    OBJECT-GROUP
       OBJECTS { ifHCInUcastPkts, ifHCInMulticastPkts,
                 ifHCInBroadcastPkts, ifHCOutUcastPkts,
                 ifHCOutMulticastPkts, ifHCOutBroadcastPkts,
                 ifHCInOctets, ifHCOutOctets,
                 ifInOctets, ifOutOctets, ifInUnknownProtos,
                 ifInErrors, ifOutErrors,
                 ifMtu, ifInUcastPkts, ifInMulticastPkts,
                 ifInBroadcastPkts, ifInDiscards,
                 ifOutUcastPkts, ifOutMulticastPkts,
                 ifOutBroadcastPkts, ifOutDiscards,
                 ifPromiscuousMode }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information
               specific to higher speed (greater than 650,000,000
               bits/second) packet-oriented network interfaces."
       ::= { ifGroups 6 }



McCloghrie & Kastenholz                                        [Page 52]

RFC 1573               Interfaces Group Evolution           January 1994


   ifRcvAddressGroup    OBJECT-GROUP
       OBJECTS { ifRcvAddressStatus, ifRcvAddressType }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information on the
               multiple addresses which an interface receives."
       ::= { ifGroups 7 }

   ifTestGroup    OBJECT-GROUP
       OBJECTS { ifTestId, ifTestStatus, ifTestType,
                 ifTestResult, ifTestCode, ifTestOwner }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing the ability to
               invoke tests on an interface."
       ::= { ifGroups 8 }

   ifStackGroup    OBJECT-GROUP
       OBJECTS { ifStackStatus }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information on the
               layering of MIB-II interfaces."
       ::= { ifGroups 9 }

   END

7.  Acknowledgements

   This memo has been produced by the IETF's Interfaces MIB Working
   Group.

   The initial proposal to the working group was the result of
   conversations and discussions with many people, including at least
   the following: Fred Baker, Ted Brunner, Chuck Davin, Jeremy Greene,
   Marshall Rose, Kaj Tesink, and Dean Throop.

8.  References

   [1] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Structure
       of Management Information for version 2 of the Simple Network
       Management Protocol (SNMPv2)", RFC 1442, SNMP Research, Inc.,
       Hughes LAN Systems, Dover Beach Consulting, Inc., Carnegie Mellon
       University, April 1993.

   [2] Galvin, J., and K. McCloghrie, "Administrative Model for version
       2 of the Simple Network Management Protocol (SNMPv2)", RFC 1445,
       Trusted Information Systems, Hughes LAN Systems, April 1993.



McCloghrie & Kastenholz                                        [Page 53]

RFC 1573               Interfaces Group Evolution           January 1994


   [3] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Protocol
       Operations for version 2 of the Simple Network Management
       Protocol (SNMPv2)", RFC 1448, SNMP Research, Inc., Hughes LAN
       Systems, Dover Beach Consulting, Inc., Carnegie Mellon
       University, April 1993.

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

   [5] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple
       Network Management Protocol", RFC 1157, SNMP Research,
       Performance Systems International, Performance Systems
       International, MIT Laboratory for Computer Science, May 1990.

   [6] Postel, J., "Internet Protocol", STD 5, RFC 791, USC/Information
       Sciences Institute, September 1981.

   [7] McCloghrie, K., "Extensions to the Generic-Interface MIB", RFC
       1229, Hughes LAN Systems, May 1991.

   [8] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Textual
       Conventions for version 2 of the Simple Network Management
       Protocol (SNMPv2)", RFC 1443, SNMP Research, Inc., Hughes LAN
       Systems, Dover Beach Consulting, Inc., Carnegie Mellon
       University, April 1993.
























McCloghrie & Kastenholz                                        [Page 54]

RFC 1573               Interfaces Group Evolution           January 1994


9.  Security Considerations

   Security issues are not discussed in this memo.

10.  Authors' Addresses

   Keith McCloghrie
   Hughes LAN Systems
   1225 Charleston Rd,
   Mountain View, Ca 94043

   Phone: [phone]
   EMail: [e-mail]


   Frank Kastenholz
   FTP Software
   2 High Street
   North Andover, Mass. USA 01845

   Phone: [phone]
   EMail: [e-mail]





























McCloghrie & Kastenholz                                        [Page 55]