The Interfaces Group MIB using SMIv2

Status of this Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright © The Internet Society (1997). All Rights Reserved.

Table of Contents

   1 Introduction ..............................................    2
   2 The SNMP Network Management Framework .....................    2
   2.1 Object Definitions ......................................    3
   3 Experience with the Interfaces Group ......................    3
   3.1 Clarifications/Revisions ................................    3
   3.1.1 Interface Sub-Layers ..................................    4
   3.1.2 Guidance on Defining Sub-layers .......................    6
   3.1.3 Virtual Circuits ......................................    8
   3.1.4 Bit, Character, and Fixed-Length Interfaces ...........    8
   3.1.5 Interface Numbering ...................................   10
   3.1.6 Counter Size ..........................................   14
   3.1.7 Interface Speed .......................................   16
   3.1.8 Multicast/Broadcast Counters ..........................   17
   3.1.9 Trap Enable ...........................................   18
   3.1.10 Addition of New ifType values ........................   18
   3.1.11 InterfaceIndex Textual Convention ....................   18
   3.1.12 New states for IfOperStatus ..........................   19
   3.1.13 IfAdminStatus and IfOperStatus .......................   20
   3.1.14 IfOperStatus in an Interface Stack ...................   21
   3.1.15 Traps ................................................   21
   3.1.16 ifSpecific ...........................................   23
   3.1.17 Creation/Deletion of Interfaces ......................   24
   3.1.18 All Values Must be Known .............................   24
   4 Media-Specific MIB Applicability ..........................   25
   
   5 Overview ..................................................   26
   6 Interfaces Group Definitions ..............................   26
   7 Acknowledgements ..........................................   64
   8 References ................................................   64
   9 Security Considerations ...................................   65
   10 Authors' Addresses .......................................   65
   11 Full Copyright Statement .................................   66

1. Introduction

This memo defines a portion of the Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, it describes managed objects used for managing Network Interfaces.

This memo discusses the 'interfaces' group of MIB-II, especially the experience gained from the definition of numerous media- specific MIB modules for use in conjunction with the 'interfaces' group for managing various sub-layers beneath the internetwork- layer. It 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 that is both compliant to the SNMPv2 SMI and semantically- identical to the existing SNMPv1-based definitions.

The key words "MUST" and "MUST NOT" in this document are to be interpreted as described in RFC 2119 [10].

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    STD 17, RFC 1213 defines MIB-II, the core set of managed
        objects for the Internet suite of protocols.
   
   o    STD 15, 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.

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

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

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).

Subject to the above, it is appropriate to assign an ifIndex value to any interface that can occur in an interface stack (in the ifStackTable) where the bottom of the stack is a physical interface (ifConnectorPresent has the value 'true') and there is a layer-3 or other application that "points down" to the top of this stack. An example of an application that points down to the top of the stack is the Character MIB [9].

Note that the sub-layers of an interface on one device will sometimes be different from the sub-layers of the interconnected interface of another device; for example, for a frame-relay DTE interface connected a frameRelayService interface, the inter- connected DTE and DCE interfaces have different ifType values and media-specific MIBs.

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.

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 6 of this memo supports such circumstances.

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

3.1.4. Bit, Character, and Fixed-Length Interfaces

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

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

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

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

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

(1) the 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 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 requirement for constancy (between re-initializations) of an interface's ifIndex value 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 assignment (in advance) of ifIndex values for all possible interfaces that might be added dynamically. The exact meaning of a "different" interface is hard to define, and there will be gray areas. Any firm definition in this document would likely to turn out to be inadequate. Instead, implementors must choose what it means in their particular situation, subject to the following rules:

(1) a previously-unused value of ifIndex must be assigned to a

dynamically added interface if an agent has no knowledge of

whether the interface is the "same" or "different" to a

previously incarnated interface.

(2) a management station, not noticing that an interface has gone

away and another has come into existence, must not be confused when calculating the difference between the counter values retrieved on successive polls for a particular ifIndex value.

When the new interface is the same as an old interface, but a discontinuity in the value of the interface's counters cannot be avoided, the ifTable has (until now) required that a new ifIndex value be assigned to the returning interface. That is, either all counter values have had to be retained during the absence of an interface in order to use the same ifIndex value on that interface's return, or else a new ifIndex value has had to be assigned to the returning interface. Both alternatives have proved to be burdensome to some implementations:

   (1)  maintaining the counter values may not be possible (e.g., if
        they are maintained on removable hardware),

(2) using a new ifIndex value presents extra work for management

applications. While the potential need for such extra work

is unavoidable on agent re-initializations, it is desirable

to avoid it between re-initializations.

To address this, a new object, ifCounterDiscontinuityTime, has been defined to record the time of the last discontinuity in an interface's counters. By monitoring the value of this new object, a management application can now detect counter discontinuities without the ifIndex value of the interface being changed. Thus, an agent which implements this new object should, when a new interface is the same as an old interface, retain that interface's ifIndex value and update if necessary the interface's value of ifCounterDiscontinuityTime. With this new object, a management application must, when calculating differences between counter values retrieved on successive polls, discard any calculated difference for which the value of ifCounterDiscontinuityTime is different for the two polls. (Note that this test must be performed in addition to the normal checking of sysUpTime to detect an agent re-initialization.) Since such discards are a waste of network management processing and bandwidth, an agent should not update the value of ifCounterDiscontinuityTime unless absolutely necessary.

While defining this new object is a change in the semantics of the ifTable counter objects, it is impractical to deprecate and redefine all these counters because of their wide deployment and importance. Also, a survey of implementations indicates that many agents and management applications do not correctly implement this aspect of the current semantics (because of the burdensome issues mentioned above), such that the practical implications of such a change is small. Thus, this breach of the SMI's rules is considered to be acceptable.

Note, however, that the addition of ifCounterDiscontinuityTime does not change the fact that:

It is necessary at certain times for the assignment of ifIndex values to change on a reinitialization of the agent (such as a reboot).

The possibility of ifIndex value re-assignment must be accommodated by a management application whenever the value of sysUpTime is reset to zero.

Note also that some agents support multiple "naming scopes", e.g., 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.

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. As an another example, consider an agent which responds to SNMP queries concerning an interface on some other (proxied) device: if such a proxied device associates a particular identifier with an interface, then it is appropriate to use this identifier as the value of the interface's ifName, since the local console in this case is that of the proxied device.

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 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, say, 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.

(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

(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 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 the MIB in section 6, 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. New states for IfOperStatus

   Three new states have been added to ifOperStatus: 'dormant', 
   'notPresent', and 'lowerLayerDown'.

The dormant state indicates that the relevant interface is not actually in a condition to pass packets (i.e., it is not "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 notPresent state is a refinement on the down state which indicates that the relevant interface is down specifically because some component (typically, a hardware component) is not present in the managed system. Examples of use of the notPresent state are:

(1) to allow an interface's conceptual row including its counter

values to be retained across a "hot swap" of a card/module, and/or

(2) to allow an interface's conceptual row to be created, and

thereby enable interfaces to be pre-configured prior to

installation of the hardware needed to make the interface

operational.

Agents are not required to support interfaces in the notPresent state. However, from a conceptual viewpoint, when a row in the ifTable is created, it first enters the notPresent state and then subsequently transitions into the down state; similarly, when a row in the ifTable is deleted, it first enters the notPresent state and then subsequently the object instances are deleted. For an agent with no support for notPresent, both of these transitions (from the notPresent state to the down state, and from the notPresent state to the instances being removed) are immediate, i.e., the transition does not last long enough to be recorded by ifOperStatus. Even for those agents which do support interfaces in the notPresent state, the length of time and conditions under which an interface stays in the notPresent state is implementation-specific.

The lowerLayerDown state is also a refinement on the down state. This new state indicates that this interface runs "on top of" one or more other interfaces (see ifStackTable) and that this interface is down specifically because one or more of these lower-layer interfaces are down.

3.1.13. IfAdminStatus and IfOperStatus

The down state of ifOperStatus 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 (or notPresent) i.e., there is not (necessarily) a fault condition on the interface.

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

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

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

(1) Change to the up state if and only if the interface is able

to send and receive packets.

(2) Change to the lowerLayerDown state if and only if the

interface is prevented from entering the up state because of the state of one or more of the interfaces beneath it in the interface stack.

(3) 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.

(4) Remain in the down state if an error or other fault condition

is detected on the interface.

(5) Change to the unknown state if, for some reason, the state of

the interface can not be ascertained.

(6) 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.

(7) Remain in the notPresent state if interface components are

missing.

3.1.14. 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 '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', 'notPresent', 'lowerLayerDown', 'unknown' or
        'testing'.

(2) ifOperStatus may have the value 'up' or 'dormant' if one or

more interfaces below it in the stack are 'dormant', and all

others below it are either 'down', 'dormant', 'notPresent',

'lowerLayerDown', 'unknown' or 'testing'.

(3) ifOperStatus has the value 'lowerLayerDown' while all

interfaces below it in the stack are either 'down', 'notPresent', 'lowerLayerDown', or 'testing'.

3.1.15. 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 (to/from all other states except notPresent) has the advantages:

(1) A transition into the down state (from a state other than

notPresent) will occur when an error is detected on an interface. Error conditions are presumably of great interest to network managers.

(2) Departing the down state (to a state other than the

notPresent 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 (except to/from the notPresent state) is generally consistent with current usage and interpretation of these traps by manager stations.

Transitions to/from the notPresent state are concerned with the insertion and removal of hardware, and are outside the scope of these traps.

Therefore, this memo defines that LinkUp and linkDown traps are generated on just after ifOperStatus leaves, or just before it enters, the down state, respectively; except that LinkUp and linkDown traps never generated on transitions to/from the notPresent state.

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.

An exception to the above generation of linkUp/linkDown traps on changes in ifOperStatus, occurs when an interface is "flapping", i.e., when it is rapidly oscillating between the up and down states. If traps were generated for each such oscillation, the network and the network management system would be flooded with unnecessary traps. In such a situation, the agent should rate- limit its generation of traps.

3.1.16. ifSpecific

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

foo OBJECT IDENTIFIER ::= { transmission xxx }

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

3.1.17. 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 (specifically, 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.

3.1.18. 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 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.

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.

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.

6. Interfaces Group Definitions

IF-MIB DEFINITIONS ::= BEGIN

IMPORTS

       MODULE-IDENTITY, OBJECT-TYPE, Counter32, Gauge32, Counter64,
       Integer32, TimeTicks, mib-2,
       NOTIFICATION-TYPE                        FROM SNMPv2-SMI
       TEXTUAL-CONVENTION, DisplayString,
       PhysAddress, TruthValue, RowStatus,
       TimeStamp, AutonomousType, TestAndIncr   FROM SNMPv2-TC
       MODULE-COMPLIANCE, OBJECT-GROUP          FROM SNMPv2-CONF
       snmpTraps                                FROM SNMPv2-MIB
       IANAifType                               FROM IANAifType-MIB;

ifMIB MODULE-IDENTITY

       LAST-UPDATED "9611031355Z"
       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 }
   
   interfaces   OBJECT IDENTIFIER ::= { mib-2 2 }

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 (1..2147483647)

InterfaceIndexOrZero ::= TEXTUAL-CONVENTION

       DISPLAY-HINT "d"
       STATUS       current
       DESCRIPTION
               "This textual convention is an extension of the
               InterfaceIndex convention.  The latter defines a
               greater than zero value used to identify an interface
               or interface sub-layer in the managed system.  This
               extension permits the additional value of zero.  the
               value zero is object-specific and must therefore be
               defined as part of the description of any object which
               uses this syntax.  Examples of the usage of zero might
               include situations where interface was unknown, or
               when none or all interfaces need to be referenced."
       SYNTAX       Integer32 (0..2147483647)
   
   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 }
       
       ::= { ifTable 1 }

IfEntry ::=

SEQUENCE {

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

ifIndex OBJECT-TYPE

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

ifDescr OBJECT-TYPE

       SYNTAX      DisplayString (SIZE (0..255))
       MAX-ACCESS  read-only
       
       STATUS      current
       DESCRIPTION
               "A textual string containing information about the
               interface.  This string should include the name of the
               manufacturer, the product name and the version of the
               interface hardware/software."
       ::= { ifEntry 2 }

ifType OBJECT-TYPE

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

ifMtu OBJECT-TYPE

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

ifSpeed OBJECT-TYPE

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

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
                                 -- for some reason.
                   dormant(5),
                   notPresent(6),    -- some component is missing
                   lowerLayerDown(7) -- down due to state of
                                     -- lower-layer interface(s)
               }
       
       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 it from
               going to the up(1) state; it should remain in the
               notPresent(6) state if the interface has missing
               (typically, hardware) components."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { ifEntry 10 }

ifInUcastPkts OBJECT-TYPE

       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The number of packets, delivered by this sub-layer to
               a higher (sub-)layer, which were not addressed to a
               multicast or broadcast address at this sub-layer.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.

Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime.

               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.

Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime."

       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { ifEntry 14 }

ifInUnknownProtos OBJECT-TYPE

       SYNTAX      Counter32
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "For packet-oriented interfaces, the number of packets
               received via the interface which were discarded
               because of an unknown or unsupported protocol.  For
               character-oriented or fixed-length interfaces that
               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 that does not support
               protocol multiplexing, this counter will always be 0.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { ifEntry 17 }

ifOutNUcastPkts OBJECT-TYPE

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

Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime.

               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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { ifEntry 20 }

ifOutQLen OBJECT-TYPE

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

ifSpecific OBJECT-TYPE

       SYNTAX      OBJECT IDENTIFIER
       MAX-ACCESS  read-only
       STATUS      deprecated
       DESCRIPTION
               "A reference to MIB definitions specific to the
               particular media being used to realize the interface.
               It is recommended that this value point to an instance
               of a MIB object in the media-specific MIB, i.e., that
               this object have the semantics associated with the
               InstancePointer textual convention defined in RFC
               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,
           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,
           ifCounterDiscontinuityTime TimeStamp
       }

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.  Note that for an agent which responds to SNMP
               queries concerning an interface on some other
               (proxied) device, then the value of ifName for such an
               interface is the proxied device's local name for it.
       
               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
               protocol, this includes both Group and Functional
               addresses.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.

Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime."

       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { ifXEntry 5 }

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

ifHCInOctets OBJECT-TYPE

       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current

DESCRIPTION

"The total number of octets received on the interface, including framing characters. This object is a 64-bit version of ifInOctets.

               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.

Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of

               ifCounterDiscontinuityTime."
       ::= { ifXEntry 9 }

ifHCOutOctets OBJECT-TYPE

       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of octets transmitted out of the
               interface, including framing characters.  This object
               is a 64-bit version of ifOutOctets.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { ifXEntry 12 }

ifHCOutBroadcastPkts OBJECT-TYPE

       SYNTAX      Counter64
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The total number of packets that higher-level
               protocols requested be transmitted, and which were
               addressed to a broadcast address at this sub-layer,
               including those that were discarded or not sent.  This
               object is a 64-bit version of ifOutBroadcastPkts.
       
               Discontinuities in the value of this counter can occur
               at re-initialization of the management system, and at
               other times as indicated by the value of
               ifCounterDiscontinuityTime."
       ::= { 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
               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
               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 }

ifCounterDiscontinuityTime OBJECT-TYPE

       SYNTAX      TimeStamp
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
               "The value of sysUpTime on the most recent occasion at
               which any one or more of this interface's counters
               suffered a discontinuity.  The relevant counters are
               the specific instances associated with this interface
               of any Counter32 or Counter64 object contained in the
               ifTable or ifXTable.  If no such discontinuities have
               occurred since the last re-initialization of the local
               management subsystem, then this object contains a zero
               value."
       ::= { ifXEntry 19 }
   
   --           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. (If I is not involved in multiplexing, then these are the only two rows associated with I.)

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 }
        ::= { 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-
               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
               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 }

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 }

-- 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 from some other state
               (but not from the notPresent state).  This other state
               is indicated by the included value of ifOperStatus."
       ::= { 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
               left the down state and transitioned into some other
               state (but not into the notPresent state).  This other
               state is indicated by the included value of
               ifOperStatus."
       ::= { snmpTraps 4 }
   
   -- 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,
                              ifCounterDiscontinuityGroup }
       
           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       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 }

-- units of conformance

   ifGeneralInformationGroup    OBJECT-GROUP
       OBJECTS { ifIndex, 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,
                 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
               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 }
   
   ifCounterDiscontinuityGroup  OBJECT-GROUP
       OBJECTS { ifCounterDiscontinuityTime }
       STATUS  current
       DESCRIPTION
               "A collection of objects providing information
               specific to interface counter discontinuities."
       ::= { ifGroups 13 }
   
   -- 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.
                     */
                    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 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 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
               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),
                        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 }
   
   -- 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

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
               "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

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.

8. References

   [1]  Case, J., McCloghrie, K., Rose, M., and
        S. Waldbusser, "Structure of Management Information for
        version 2 of the Simple Network Management Protocol
        (SNMPv2)", RFC 1902, January 1996.
   
   [2]  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]  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", STD
        17, RFC 1213, March 1991.
   
   [5]  Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple
        Network Management Protocol", STD 15, RFC 1157, May 1990.
   
   [6]  Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
   
   [7]  McCloghrie, K., "Extensions to the Generic-Interface MIB", RFC
        1229, May 1991.
   
   [8]  ATM Forum Technical Committee, "LAN Emulation Client
        Management: Version 1.0 Specification", af-lane-0044.000, ATM
        Forum, September 1995.
   
   [9]  Stewart, B., "Definitions of Managed Objects for Character
        Stream Devices using SMIv2", RFC 1658, July 1994.
   
   [10] Bradner, S., "Key words for use in RFCs to Indicate
        Requirements Levels", RFC 2119, March 1997.

9. Security Considerations

This MIB contains both readable objects whose values provide the number and status of a device's network interfaces, and write-able objects which allow an administrator to control the interfaces and to perform tests on the interfaces. Unauthorized access to the readable objects is relatively innocuous. Unauthorized access to the write- able objects could cause a denial of service, or in combination with other (e.g., physical) security breaches, could cause unauthorized connectivity to a device.

10. Authors' Addresses

   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

11. Full Copyright Statement

Copyright © The Internet Society (1997). All Rights Reserved.

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.