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Versions: 01 02 03 04 05 rfc2233                                        
Draft                  Interfaces Group MIB           January 1996



                     The Interfaces Group MIB

                         30 January 1996


                   draft-ietf-ifmib-mib-02.txt


                         Keith McCloghrie
                          Cisco Systems
                          kzm@cisco.com

                       Frank J. Kastenholz
                           FTP Software
                          kasten@ftp.com





                       Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups.  Note that other groups may also
distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time.  It is inappropriate to use Internet-
Drafts as reference material or to cite them other than as ``work
in progress.''

To learn the current status of any Internet-Draft, please check
the ``1id-abstracts.txt'' listing contained in the Internet-
Drafts Shadow Directories on ds.internic.net (US East Coast),
nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or
munnari.oz.au (Pacific Rim).











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1.  Introduction

This memo defines an experimental 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 specifies clarifications to, and extensions of, the
architectural issues within the previous 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.


1.1.  Change Log

This section tracks changes made to the revisions of the Internet
Drafts of this document.  It will be deleted when the document is
published as an RFC.

28 January 1996

The following changes were made for the version of the document
dated 28 January 1996. These changes were made based on the output
of the working group's meeting at the Dallas IETF meeting.

(1)  Changed ifStackLastChange to be a scalar object.

(2)  Updated the definition of ifAlias.

(3)  Added text contrasting the use of ifDescr, ifName and
     ifAlias.

(4)  Added section on the creation/deletion of interfaces.

(5)  Added section on how an interface's ifOperStatus depends on
     the states of the interfaces below it in the interface stack.





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(6)  Added clarification that a defective interface which
     periodically tests itself does not transition to the
     ifOperStatus=testing state while that testing is in progress.

26 November 1995

The following changes were made for the version of the document
dated 26 November 1995. These changes were made based on the
output of the working group's meeting at the Stockholm IETF
meeting.

(1)  Added the ifAlias, ifStackLastChange and ifTableLastChange
     objects.

(2)  Defined new group definitions to contain the new objects, and
     defined a new conformance definition.  Deprecated the old
     group and conformance definitions.

(3)  Corrected the MAX-ACCESS clause values for
     ifRcvAddressAddress, ifRcvAddressStatus and ifStackStatus.

(4)  Deprecated the ifTestTable and ifTestGroup.

(5)  Removed (to be defined elsewhere) the IANAifType-MIB MIB
     Module.

(6)  Re-arranged and combined the previous sections 3.1 and 3.2.

(7)  Minor editorial changes.





















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2.  The SNMP Network Management Framework

The SNMP Network Management Framework presently consists of three
major components.  They are:

o    RFC 1902 which defines the SMI, the mechanisms used for
     describing and naming objects for the purpose of management.

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

o    RFC 1157 and RFC 1905 which define two versions of the
     protocol used for network access to managed objects.

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


2.1.  Object Definitions

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





















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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 assume an evolution or loosening
of the model.  This memo documents and standardizes that evolution
of the model and fills in the gaps caused by that evolution.  This
memo also incorporates the interfaces group extensions documented
in RFC 1229 [7].

3.1.  Clarifications/Revisions

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

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

3.1.1.  Interface Sub-Layers

Experience in defining media-specific management information has
shown the need to distinguish between the multiple sub-layers
beneath the internetwork-layer.  In addition, there is a need to
manage these sub-layers in devices (e.g., MAC-layer bridges) which
are unaware of which, if any, internetwork protocols run over





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these sub-layers.  As such, a model of having a single conceptual
row in the interfaces table (MIB-II's ifTable) represent a whole
interface underneath the internetwork-layer, and having a single
associated media-specific MIB module (referenced via the ifType
object) is too simplistic.  A further problem arises with the
value of the ifType object which has enumerated values for each
type of interface.

Consider, for example, an interface with PPP running over an HDLC
link which uses a RS232-like connector.  Each of these sub-layers
has its own media-specific MIB module.  If all of this is
represented by a single conceptual row in the ifTable, then an
enumerated value for ifType is needed for that specific
combination which maps to the specific combination of media-
specific MIBs.  Furthermore, such a model still lacks a method to
describe the relationship of all the sub-layers of the MIB stack.

An associated problem is that of upward and downward multiplexing
of the sub-layers.  An example of upward multiplexing is MLP
(Multi-Link-Procedure) which provides load-sharing over several
serial lines by appearing as a single point-to-point link to the
sub-layer(s) above.  An example of downward multiplexing would be
several instances of PPP, each framed within a separate X.25
virtual circuit, all of which run over one fractional T1 channel,
concurrently with other uses of the T1 link.  The MIB structure
must allow these sorts of relationships to be described.

Several solutions for representing multiple sub-layers were
rejected.  One was to retain the concept of one conceptual row for
all the sub-layers of an interface and have each media-specific
MIB module identify its "superior" and "subordinate" sub-layers
through OBJECT IDENTIFIER "pointers".  This scheme would have
several drawbacks: the superior/subordinate pointers would be
contained in the media-specific MIB modules; thus, a manager could
not learn the structure of an interface without inspecting
multiple pointers in different MIB modules; this would be overly
complex and only possible if the manager had knowledge of all the
relevant media-specific MIB modules; MIB modules would all need to
be retrofitted with these new "pointers"; this scheme would not
adequately address the problem of upward and downward
multiplexing; and finally, enumerated values of ifType would be
needed for each combination of sub-layers.  Another rejected
solution also retained the concept of one conceptual row for all
the sub-layers of an interface but had a new separate MIB table to
identify the "superior" and "subordinate" sub-layers and to





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contain OBJECT IDENTIFIER "pointers" to the media-specific MIB
module for each sub-layer.  Effectively, one conceptual row in the
ifTable would represent each combination of sub-layers between the
internetwork-layer and the wire.  While this scheme has fewer
drawbacks, it still would not support downward multiplexing, such
as PPP over MLP: observe that MLP makes two (or more) serial lines
appear to the layers above as a single physical interface, and
thus PPP over MLP should appear to the internetwork-layer as a
single interface; in contrast, this scheme would result in two (or
more) conceptual rows in the ifTable, both of which the
internetwork-layer would run over.  This scheme would also require
enumerated values of ifType for each combination of sub-layers.

The solution adopted by this memo is to have an individual
conceptual row in the ifTable to represent each sub-layer, and
have a new separate MIB table (the ifStackTable, see section 5
below) 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, allows the IANAifType to Media-Specific MIB mapping
to identify the media-specific MIB module for that sub-layer, such
that the new table need only be referenced to obtain information
about layering, and it only requires enumerated values of ifType
for each sub-layer, not for combinations of them.  However, it
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 previously), plus some (specifically, ifSpeed) which need
to have appropriate values identified for use when a generalized
definition does not apply to a 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





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     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.

(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.

3.1.2.  Guidance on Defining Sub-layers

The designer of a media-specific MIB must decide whether to divide
the interface into sub-layers or not, and if so, how to make the
divisions.  The following guidance is offered to assist the
media-specific MIB designer in these decisions.







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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.

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 doing so, 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.









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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.

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 5 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.

3.1.4.  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





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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).

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.

A rejected solution to this problem would be to split the ifTable
into two (or more) new MIB tables, one of which 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 5 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.







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

(1)  the ifGeneralInformationGroup.  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.

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.

3.1.5.  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





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     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.

Redefining ifNumber to be the largest value of ifIndex was
rejected since it would not help.  Such a re-definition would
require ifNumber to be deprecated and the utility of the redefined
object would be questionable.  Alternatively, ifNumber could be
deprecated and not replaced.  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 just 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.
This is a minor change in the semantics of ifIndex; however, all
existing agent implementations conform to this new definition, and
in the interests of not requiring changes to existing agent
implementations and to the many existing media-specific MIBs, this
memo assumes that this change does not require ifIndex to be
deprecated.  Experience indicates that this assumption does
"break" a few management applications, but this is considered
preferable to breaking all agent implementations.

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





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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 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)  an agent has no knowledge of whether the interface is the
     "same" or "different" to a previously incarnated interface,
     or

(2)  an agent knows that the interface is the "same" as a
     previously incarnated interface, but the assignment of the
     previously-used ifIndex value to the interface could result
     in a discontinuity in the values of ifTable counters for that
     value of ifIndex.

     Note that discontinuities in the values of ifTable counters
     can be avoided if an implementation is able to retain the
     counter values when an interface goes away and restore them
     on the interface's re-appearance.

Note that ifIndex values may change to identify different
interfaces upon a re-initialization (e.g., a reboot) of the agent,
which can be detected by the value of sysUpTime being reset to
zero.  Note also that some agents support multiple "naming
scopes", i.e., for an SNMPv1 agent, multiple values of the SNMPv1
community string.  For such an agent (e.g., a CNM agent which
supports a different subset of interfaces for different
customers), there is no required relationship between the ifIndex
values which identify interfaces in one naming scope and those
which identify interfaces in another naming scope.  It is the
agent's choice as to whether the same or different ifIndex values
identify the same or different interfaces in different naming
scopes.






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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)

A new problem is introduced by representing each sub-layer as an
ifTable entry.  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 having
an ifTable entry for each interface sub-layer, 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 local name (e.g., the name used
at the device's local console) for the interface of which the
relevant entry in the ifTable is a component.  For example,
consider a router having an interface composed of PPP running over
an RS-232 port.  If the router uses the name "wan1" for the
(combined) interface, then the ifName objects for the
corresponding PPP and RS-232 entries in the ifTable would both
have the value "wan1".  On the other hand, if the router uses the
name "wan1.1" for the PPP interface and "wan1.2" for the RS-232
port, then the ifName objects for the corresponding PPP and RS-232
entries in the ifTable would have the values "wan1.1" and
"wan1.2", respectively.

In contrast, the existing ifDescr object is intended to contain a
description of an interface, whereas another new object, ifAlias,
provides a location in which a network management application can
store a non-volatile interface-naming value of its own choice.
The ifAlias object allows a network manager to give one or more
interfaces their own unique names, irrespective of any interface-
stack relationship.  Further, the ifAlias name is non-volatile,
and thus an interface must retain its assigned ifAlias value
across reboots, even if an agent chooses a new ifIndex value for





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the interface.

3.1.6.  Counter Size

As the speed of network media increase, the minimum time in which
a 32 bit counter will wrap decreases.  For example, a 10Mbs stream
of back-to-back, full-size packets causes ifInOctets to wrap in
just over 57 minutes; at 100Mbs, the minimum wrap time is 5.7
minutes, and at 1Gbs, the minimum is 34 seconds.  Requiring that
interfaces be polled frequently enough not to miss a counter wrap
is increasingly problematic.

A rejected solution to this problem was to scale the counters; for
example, ifInOctets could be changed to count received octets in,
e.g., 1024 byte blocks.  While it would provide acceptable
functionality at high rates of the counted-events, at low rates it
suffers.  If there is little traffic on an interface, there might
be a significant interval before enough of the counted-events
occur to cause the scaled counter to be incremented.  Traffic
would then appear to be very bursty, leading to incorrect
conclusions of the network's performance.

Instead, this memo adopts 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, when 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, 64-bit packet
counters AND 64-bit octet counters MUST be used.

These speed thresholds 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 10Mbs Ethernet) should
     not require them.







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(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):

     -   10Mbs Ethernet: 57 minutes,

     -   16Mbs Token Ring: 36 minutes,

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

     -   FDDI: 5.7 minutes

(4)  The 32-bit packet counters wrap 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/second (1,000 Gbs) 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





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

3.1.7.  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 2.4Gbs.  Thus, ifSpeed is insufficient for the future,
and this memo defines an additional object: ifHighSpeed.

The ifHighSpeed 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 (but rejected) 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





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     understand the new semantics would be confused.

3.1.8.  Multicast/Broadcast Counters

In MIB-II, the ifTable counters for multicast and broadcast
packets are combined as counters of non-unicast packets.  In
contrast, the ifExtensions MIB [7] defined one set of counters for
multicast, and a separate set for broadcast packets.  With the
separate counters, the original combined counters become
redundant.  To avoid this redundancy, the non-unicast counters are
deprecated.

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.  Thus, this memo defines new objects with better aligned
definitions.  Counters with 64 bits of range are also needed, as
explained above.

3.1.9.  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 state changes 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.

3.1.10.  Addition of New ifType values

Over time, there is the need to add new ifType enumerated values
for new interface types.  If the syntax of ifType were defined in





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the MIB in section 5, then a new version of this MIB would have to
be re-issued in order to define new values.  In the past, re-
issuing of a MIB has occurred only after several years.

Therefore, 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, defined in a
different document.  This allows additional values to be
documented without having to re-issue 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.

3.1.11.  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 of ifIndex.


3.1.12.  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





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     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 (i.e. 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:

(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 change 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.







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3.1.13.  IfOperStatus in an Interface Stack

When an interface is a part of an interface-stack, but is not the
lowest interface in the stack, then:

(1)  ifOperStatus has the value 'down' while all interfaces below
     it in the stack are either 'down', 'unknown' or 'testing'.

(2)  ifOperStatus has the value 'dormant' if one or more
     interfaces below it in the stack are 'dormant', and all
     others below it are either 'down', 'unknown' or 'testing'.

(3)  ifOperStatus has the value 'up' if it is able to pass packets
     due to one or more interfaces below it in the stack being
     'up', irrespective of whether other interfaces below it are
     'down', 'dormant', 'unknown' or 'testing'.

3.1.14.  Traps

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

Operational experience indicates that management stations are most
concerned with an interface being in the down state and the fact
that this state may indicate a failure.  Thus, it is most useful
to instrument transitions into/out of either the up state or the
down state.

Instrumenting transitions into or out of the up state was rejected
since it would have the drawback that a 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 demand interface, then a transition to dormant
would entail generation of a linkDown 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:

(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.







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(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 generating 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 LinkUp and linkDown traps are
generated just after ifOperStatus leaves, or just before it
enters, the down state, respectively.

Note that this definition allows a node with only one interface to
transmit a linkDown trap before that interface goes down.  (Of
course, when the interface is going down because of a failure
condition, the linkDown trap probably cannot be successfully
transmitted anyway.)

Some interfaces perform a link "training" function when trying to
bring the interface up.  In the event that such an interface were
defective, then the training function would fail and the interface
would remain down, and the training function might be repeated at
appropriate intervals.  If the interface, while performing this
training function, were considered to the in the testing state,
then linkUp and linkDown traps would be generated for each start
and end of the training function.  This is not the intent of the
linkUp and linkDown traps, and therefore, while performing such a
training function, the interface's state should be represented as
down.

3.1.15.  ifSpecific

The original definition of the OBJECT IDENTIFIER value of
ifSpecific was not sufficiently 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 OBJECT IDENTIFIER of the specific 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





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latter would not be sufficient unless it also allowed for media-
specific MIBs which include several tables, where each table has
its own (different) indexing.

The only definition that can both be made explicit and can cover
all the useful situations is to have ifSpecific be the most
general value for the media-specific MIB module (the first example
given above).  This effectively makes it redundant because it
contains no more information than is provided by ifType.  Thus,
ifSpecific has been deprecated.

3.1.16.  Creation/Deletion of Interfaces

While some interfaces, for example, most physical interfaces,
cannot be created via network management, other interfaces such as
logical interfaces sometimes can be.  The ifTable contains only
generic information about an interface.  Almost all 'create-able'
interfaces have other, media-specific, information through which
configuration parameters may be supplied prior to creating such an
interface.  Thus, the ifTable does not itself support the creation
or deletion of an interface (i.e., it has no RowStatus [2]
column).  Rather, if a particular interface type supports the
dynamic creation and/or deletion of an interface of that type,
then that media-specific MIB should include an appropriate
RowStatus object (see the ATM LAN-Emulation Client MIB [8] for an
example of a MIB which does this).  Typically, when such a
RowStatus object is created/deleted, then the conceptual row in
the ifTable appears/disappears as a by-product, and an ifIndex
value (chosen by the agent) is stored in an appropriate object in
the media-specific MIB.

3.1.17.  All Values Must be Known

There are a number of situations where an agent does not know the
value of one or more objects for a particular interface.  In all
such circumstances, an agent MUST NOT instantiate an object with
an incorrect value; rather, it MUST respond with the appropriate
error/exception condition (e.g., noSuchInstance for SNMPv2).

One example is where an agent is unable to count the occurrences
defined by one (or more) of the ifTable counters.  In this
circumstance, the agent MUST NOT instantiate the particular
counter with a value of, say, zero.  To do so would be to provide
mis-information to a network management application reading the
zero value, and thereby assuming that there have been no





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occurrences of the event (e.g., no input errors because ifInErrors
is always zero).

Sometimes the lack of knowledge of an object's value is temporary.
For example, when the MTU of an interface is a configured value
and a device dynamically learns the configured value through
(after) exchanging messages over the interface (e.g., ATM LAN-
Emulation [8]).  In such a case, the value is not known until
after the ifTable entry has already been created.  In such a case,
the ifTable entry should be created without an instance of the
object whose value is unknown; later, when the value becomes
known, the missing object can then be instantiated (e.g., the
instance of ifMtu is only instantiated once the interface's MTU
becomes known).

As a result of this "known values" rule, management applications
MUST be able to cope with the responses to retrieving the object
instances within a conceptual row of the ifTable revealing that
some of the row's columnar objects are missing/not available.































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4.  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 preserves 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, as must the
     ifStackTable's portrayal of the relationship(s) between the
     sub-layers.

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.

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.










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5.  Overview

This MIB consists of 4 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.

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.

























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6.  Interfaces Group Definitions

IF-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE, Counter32, Gauge32, Counter64,
    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
    snmpTraps                                FROM SNMPv2-MIB
    IANAifType                               FROM IANAifType-MIB
    mib-2, interfaces                        FROM RFC1213-MIB;


ifMIB MODULE-IDENTITY
    LAST-UPDATED "9601232155Z"
    ORGANIZATION "IETF Interfaces MIB Working Group"
    CONTACT-INFO
            "   Keith McCloghrie
                Cisco Systems, Inc.
                170 West Tasman Drive
                San Jose, CA  95134-1706
                US

                408-526-5260
                kzm@cisco.com"
    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."
    REVISION      "9602282155Z"
    DESCRIPTION
            "Revisions made by the Interfaces MIB WG."
    REVISION      "9311082155Z"
    DESCRIPTION
            "Initial revision, published as part of RFC 1573."
    ::= { mib-2 31 }


ifMIBObjects OBJECT IDENTIFIER ::= { ifMIB 1 }






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-- 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))

-- 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















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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 }

ifTableLastChange  OBJECT-TYPE
    SYNTAX      TimeTicks
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
            "The value of sysUpTime at the time of the last
            creation or deletion of an entry in the ifTable.  If
            the number of entries has been unchanged since the
            last re-initialization of the local network management
            subsystem, then this object contains a zero value."
    ::= { ifMIBObjects 5 }


-- 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
            to a particular interface."
    INDEX   { ifIndex }





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    ::= { 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





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    STATUS      current
    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





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            has no concept of bandwidth, this object should be
            zero."
    ::= { ifEntry 5 }

ifPhysAddress OBJECT-TYPE
    SYNTAX      PhysAddress
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
            "The interface's address at its protocol sub-layer.
            For example, for an 802.x interface, this object
            normally contains a MAC address.  The interface's
            media-specific MIB must define the bit and byte
            ordering and the format of the value of 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





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                             -- 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
            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 incoming
            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





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    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
            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 }






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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 }

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





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            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 }

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





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            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
            1903.  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
    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,





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        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,
        ifAlias                 DisplayString
    }


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
            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
            zero-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





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            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
    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.
--





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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
            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 }






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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
            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,





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            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
    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





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            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 }

ifAlias   OBJECT-TYPE
    SYNTAX      DisplayString (SIZE(0..64))
    MAX-ACCESS  read-write
    STATUS      current
    DESCRIPTION
            "This object is an 'alias' name for the interface as
            specified by a network manager, and provides a non-
            volatile 'handle' for the interface.

            On the first instantiation of an interface, the value
            of ifAlias associated with that interface is the
            zero-length string.  As and when a value is written
            into an instance of ifAlias through a network
            management set operation, then the agent must retain
            the supplied value in the ifAlias instance associated
            with the same interface for as long as that interface
            remains instantiated, including across all re-
            initializations/reboots of the network management
            system, including those which result in a change of
            the interface's ifIndex value.

            An example of the value which a network manager might
            store in this object for a WAN interface is the
            (Telco's) circuit number/identifier of the interface.

            Some agents may support write-access only for
            interfaces having particular values of ifType.  An





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            agent which supports write access to this object is
            required to keep the value in non-volatile storage,
            but it may limit the length of new values depending on
            how much storage is already occupied by the current
            values for other interfaces."
    ::= { ifXEntry 18 }












































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--           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, where
            each sub-layer corresponds to a conceptual row in the
            ifTable.  For example, when the sub-layer with ifIndex
            value x runs over the sub-layer with ifIndex value y,
            then this table contains:

              ifStackStatus.x.y=active

            For each ifIndex value, I, which identifies an active
            interface, there are always at least two instantiated
            rows in this table associated with I.  For one of
            these rows, I is the value of ifStackHigherLayer; for
            the other, I is the value of ifStackLowerLayer.

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

             ifStackStatus.0.x=active
             ifStackStatus.x.0=active "
     ::= { ifMIBObjects 2 }


ifStackEntry  OBJECT-TYPE
     SYNTAX        IfStackEntry
     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 }





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     ::= { 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
    SYNTAX         RowStatus
    MAX-ACCESS     read-create
    STATUS         current
    DESCRIPTION
            "The status of the relationship between two sub-





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            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 }

ifStackLastChange OBJECT-TYPE
    SYNTAX         TimeTicks
    MAX-ACCESS     read-only
    STATUS         current
    DESCRIPTION
            "The value of sysUpTime at the time of the last change
            of the (whole) interface stack.  A change of the
            interface stack is defined to be any creation,
            deletion, or change in value of any instance of
            ifStackStatus.  If the interface stack has been
            unchanged since the last re-initialization of the
            local network management subsystem, then this object
            contains a zero value."
    ::= { ifMIBObjects 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
-- 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





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            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.

            A system is normally able to use any unicast address
            which corresponds to an entry in this table as a
            source address."
    ::= { 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  not-accessible
    STATUS      current
    DESCRIPTION
            "An address for which the system will accept
            packets/frames on this entry's interface."
    ::= { ifRcvAddressEntry 1 }






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ifRcvAddressStatus OBJECT-TYPE
    SYNTAX      RowStatus
    MAX-ACCESS  read-create
    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 }


















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-- 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
            is about to enter the down state."
    ::= { snmpTraps 3 }

linkUp 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
            has left the down state."
    ::= { snmpTraps 4 }





























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-- conformance information

ifConformance OBJECT IDENTIFIER ::= { ifMIB 2 }

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


-- compliance statements

ifCompliance2 MODULE-COMPLIANCE
    STATUS  current
    DESCRIPTION
            "The compliance statement for SNMPv2 entities which
            have network interfaces."

    MODULE  -- this module
        MANDATORY-GROUPS { ifGeneralInformationGroup, ifStackGroup2 }

        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
        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."






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        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
            value testing(3)."

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

    ::= { ifCompliances 2 }












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-- units of conformance

ifGeneralInformationGroup    OBJECT-GROUP
    OBJECTS { ifDescr, ifType, ifSpeed, ifPhysAddress,
              ifAdminStatus, ifOperStatus, ifLastChange,
              ifLinkUpDownTrapEnable, ifConnectorPresent,
              ifHighSpeed, ifName, ifNumber, ifAlias,
              ifTableLastChange }
    STATUS  current
    DESCRIPTION
            "A collection of objects providing information
            applicable to all network interfaces."
    ::= { ifGroups 10 }

-- 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 (non-high speed interfaces
            transmit and receive at speeds less than or equal to
            20,000,000 bits/second) character-oriented or fixed-
            length-transmission network interfaces."
    ::= { 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,





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





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            specific to higher speed (greater than 650,000,000
            bits/second) packet-oriented network interfaces."
    ::= { ifGroups 6 }

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 }

ifStackGroup2    OBJECT-GROUP
    OBJECTS { ifStackStatus, ifStackLastChange }
    STATUS  current
    DESCRIPTION
            "A collection of objects providing information on the
            layering of MIB-II interfaces."
    ::= { ifGroups 11 }































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-- Deprecated Definitions - Objects


--
--    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      deprecated
    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.

            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.





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                  */
                 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

           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





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           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
           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





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           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       deprecated
    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       deprecated
    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       deprecated
    DESCRIPTION
            "This object indicates whether or not some manager





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            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       deprecated
    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),





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                     failed(7)
                 }
    MAX-ACCESS   read-only
    STATUS       deprecated
    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       deprecated
    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
            1903.  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       deprecated
    DESCRIPTION
            "The entity which currently has the 'ownership'
            required to invoke a test on this interface."
    ::= { ifTestEntry 6 }









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-- Deprecated Definitions - Groups


ifGeneralGroup    OBJECT-GROUP
    OBJECTS { ifDescr, ifType, ifSpeed, ifPhysAddress,
              ifAdminStatus, ifOperStatus, ifLastChange,
              ifLinkUpDownTrapEnable, ifConnectorPresent,
              ifHighSpeed, ifName }
    STATUS  deprecated
    DESCRIPTION
            "A collection of objects deprecated in favour of
            ifGeneralInformationGroup."
    ::= { ifGroups 1 }


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


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


ifOldObjectsGroup    OBJECT-GROUP
    OBJECTS { ifInNUcastPkts, ifOutNUcastPkts,
              ifOutQLen, ifSpecific }
    STATUS  deprecated
    DESCRIPTION
            "The collection of objects deprecated from the
            original MIB-II interfaces group."
    ::= { ifGroups 12 }


-- Deprecated Definitions - Compliance





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ifCompliance MODULE-COMPLIANCE
    STATUS  deprecated
    DESCRIPTION
            "The previous 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
        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





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

END


















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7.  Acknowledgements

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

The original proposal evolved from 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.









































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8.  References

[1]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
     S. Waldbusser, "Structure of Management Information for
     version 2 of the Simple Network Management Protocol
     (SNMPv2)", RFC 1902, January 1996.


[2]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
     S. Waldbusser, "Textual Conventions for version 2 of the
     Simple Network Management Protocol (SNMPv2)", RFC 1903,
     January 1996.


[3]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
     S. Waldbusser, "Protocol Operations for version 2 of the
     Simple Network Management Protocol (SNMPv2)", RFC 1905,
     January 1996.


[4]  McCloghrie, K., and M. Rose, "Management Information Base for
     Network Management of TCP/IP-based internets - MIB-II", 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]  J. Postel, "Internet Protocol", RFC 791, Information Sciences
     Institute, USC, September 1981.


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


[8]  ATM Forum Technical Committee, "LAN Emulation Client
     Management: Version 1.0 Specification", af-lane-0044.000, ATM
     Forum, September 1995.







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9.  Security Considerations

Security issues are not discussed in this memo.


10.  Authors' Address

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

     Phone: 408-526-5260
     Email: kzm@cisco.com"


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

     Phone: (508)685-4000
     Email: kasten@ftp.com



























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Table of Contents


1 Introduction ..............................................    2
1.1 Change Log ..............................................    2
2 The SNMP Network Management Framework .....................    4
2.1 Object Definitions ......................................    4
3 Experience with the Interfaces Group ......................    5
3.1 Clarifications/Revisions ................................    5
3.1.1 Interface Sub-Layers ..................................    5
3.1.2 Guidance on Defining Sub-layers .......................    8
3.1.3 Virtual Circuits ......................................   10
3.1.4 Bit, Character, and Fixed-Length Interfaces ...........   10
3.1.5 Interface Numbering ...................................   12
3.1.6 Counter Size ..........................................   16
3.1.7 Interface Speed .......................................   18
3.1.8 Multicast/Broadcast Counters ..........................   19
3.1.9 Trap Enable ...........................................   19
3.1.10 Addition of New ifType values ........................   19
3.1.11 InterfaceIndex Textual Convention ....................   20
3.1.12 IfAdminStatus and IfOperStatus .......................   20
3.1.13 IfOperStatus in an Interface Stack ...................   22
3.1.14 Traps ................................................   22
3.1.15 ifSpecific ...........................................   23
3.1.16 Creation/Deletion of Interfaces ......................   24
3.1.17 All Values Must be Known .............................   24
4 Media-Specific MIB Applicability ..........................   26
5 Overview ..................................................   27
6 Interfaces Group Definitions ..............................   28
7 Acknowledgements ..........................................   66
8 References ................................................   67
9 Security Considerations ...................................   68
10 Authors' Address .........................................   68

















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