Network Working Group K. McCloghrie
Request for Comments: 1573 Hughes LAN Systems
Obsoletes: 1229 F. Kastenholz
Category: Standards Track FTP Software
January 1994
Evolution of the Interfaces Group of MIB-II
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Table of Contents
1. IntrodUCtion ............................................. 2
2. The SNMPv2 Network Management Framework .................. 2
2.1 Object Definitions ...................................... 3
3 EXPerience with the Interfaces Group ...................... 3
3.1 Areas of Clarification/Revision ......................... 3
3.1.1 Interface Numbering ................................... 4
3.1.2 Interface Sub-Layers .................................. 4
3.1.3 Virtual Circuits ...................................... 5
3.1.4 Bit, Character, and Fixed-Length Interfaces ........... 5
3.1.5 Counter Size .......................................... 5
3.1.6 Interface Speed ....................................... 6
3.1.7 Multicast/Broadcast Counters .......................... 6
3.1.8 Addition of New ifType values ......................... 6
3.1.9 ifSpecific ............................................ 6
3.2 Clarifications/Revisions ................................ 7
3.2.1 Interface Numbering ................................... 7
3.2.2 Interface Sub-Layers .................................. 8
3.2.3 Guidance on Defining Sub-layers ....................... 11
3.2.4 Virtual Circuits ...................................... 12
3.2.5 Bit, Character, and Fixed-Length Interfaces ........... 12
3.2.6 Counter Size .......................................... 14
3.2.7 Interface Speed ....................................... 16
3.2.8 Multicast/Broadcast Counters .......................... 16
3.2.9 Trap Enable ........................................... 17
3.2.10 Addition of New ifType values ........................ 17
3.2.11 InterfaceIndex Textual Convention .................... 17
3.2.12 IfAdminStatus and IfOperStatus ....................... 18
3.2.13 Traps ................................................ 19
3.2.14 ifSpecific ........................................... 20
3.3 Media-Specific MIB Applicability ........................ 20
4. Overview ................................................. 21
5. IANAifType Definition .................................... 22
6. Interfaces Group Definitions ............................. 24
7. Acknowledgements ......................................... 53
8. References ............................................... 53
9. Security Considerations .................................. 55
10. Authors" Addresses....................................... 55
1. Introduction
This memo defines a portion of the Management Information Base (MIB)
for use with network management protocols in the Internet community.
In particular, it describes managed objects used for managing Network
Interfaces.
This memo discusses the "interfaces" group of MIB-II, especially the
experience gained from the definition of numerous media-specific MIB
modules for use in conjunction with the "interfaces" group for
managing various sub-layers beneath the internetwork-layer. It
proposes clarifications to, and extensions of, the architectural
issues within the current model used for the "interfaces" group.
This memo also includes a MIB module. As well as including new MIB
definitions to support the architectural extensions, this MIB module
also re-specifies the "interfaces" group of MIB-II in a manner which
is both compliant to the SNMPv2 SMI and semantically-identical to the
existing SNMPv1-based definitions.
2. The SNMPv2 Network Management Framework
The SNMPv2 Network Management Framework consists of four major
components. They are:
o RFC1442 which defines the SMI, the mechanisms used for
describing and naming objects for the purpose of management.
o STD 17, RFC1213 defines MIB-II, the core set of managed
objects for the Internet suite of protocols.
o RFC1445 which defines the administrative and other
architectural ASPects of the framework.
o RFC1448 which defines the protocol used for network Access
to managed objects.
The Framework permits new objects to be defined for the purpose of
experimentation and evaluation.
2.1. Object Definitions
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. Objects in the MIB are
defined using the subset of Abstract Syntax Notation One (ASN.1)
defined in the SMI. In particular, each object object type is named
by an OBJECT IDENTIFIER, an administratively assigned name. The
object type together with an object instance serves to uniquely
identify a specific instantiation of the object. For human
convenience, we often use a textual string, termed the descriptor, to
refer to the object type.
3. Experience with the Interfaces Group
One of the strengths of internetwork-layer protocols such as IP [6]
is that they are designed to run over any network interface. In
achieving this, IP considers any and all protocols it runs over as a
single "network interface" layer. A similar view is taken by other
internetwork-layer protocols. This concept is represented in MIB-II
by the "interfaces" group which defines a generic set of managed
objects such that any network interface can be managed in an
interface-independent manner through these managed objects. The
"interfaces" group provides the means for additional managed objects
specific to particular types of network interface (e.g., a specific
medium such as Ethernet) to be defined as extensions to the
"interfaces" group for media-specific management. Since the
standardization of MIB-II, many such media-specific MIB modules have
been defined.
Experience in defining these media-specific MIB modules has shown
that the model defined by MIB-II is too simplistic and/or static for
some types of media-specific management. As a result, some of these
media-specific MIB modules have assumed an evolution or loosening of
the model. This memo is a proposal to document and standardize the
evolution of the model and to fill in the gaps caused by that
evolution.
A previous effort to extend the interfaces group resulted in the
publication of RFC1229 [7]. As part of defining the evolution of
the interfaces group, this memo applies that evolution to, and
thereby incorporates, the RFC1229 extensions.
3.1. Areas of Clarification/Revision
There are several areas for which experience indicates that
clarification, revision, or extension of the model would be helpful.
The next sections discuss these.
3.1.1. Interface Numbering
MIB-II defines an object, ifNumber, whose value represents:
"The number of network interfaces (regardless of their
current state) present on this system."
Each interface is identified by a unique value of the ifIndex object,
and the description of ifIndex constrains its value as follows:
"Its value ranges between 1 and the value of ifNumber. The
value for each interface must remain constant at least from
one re-initialization of the entity"s network management
system to the next re-initialization."
This constancy requirement on the value of ifIndex for a particular
interface is vital for efficient management. However, an increasing
number of devices allow for the dynamic addition/removal of network
interfaces. One example of this is a dynamic ability to configure
the use of SLIP/PPP over a character-oriented port. For such dynamic
additions/removals, the combination of the constancy requirement and
the restriction that the value of ifIndex is less than ifNumber is
problematic.
3.1.2. Interface Sub-Layers
Experience in defining media-specific management information has
shown the need to distinguish between the multiple sub-layers beneath
the internetwork-layer. In addition, there is a need to manage these
sub-layers in devices (e.g., MAC-layer bridges) which are unaware of
which, if any, internetwork protocols run over these sub-layers. As
such, a model of having a single conceptual row in the interfaces
table (MIB-II"s ifTable) represent a whole interface underneath the
internetwork-layer, and having a single associated media-specific MIB
module (referenced via the ifType object) is too simplistic. A
further problem arises with the value of the ifType object which has
enumerated values for each type of interface.
Consider, for example, an interface with PPP running over an HDLC
link which uses a RS232-like connector. Each of these sub-layers has
its own media-specific MIB module. If all of this is represented by
a single conceptual row in the ifTable, then an enumerated value for
ifType is needed for that specific combination which maps to the
specific combination of media-specific MIBs. Furthermore, there is
still a lack of a method to describe the relationship of all the
sub-layers of the MIB stack.
An associated problem is that of upward and downward multiplexing of
the sub-layers. An example of upward multiplexing is MLP (Multi-
Link-Procedure) which provides load-sharing over several serial lines
by appearing as a single point-to-point link to the sub-layer(s)
above. An example of downward multiplexing would be several
instances of PPP, each framed within a separate X.25 virtual circuit,
all of which run over one fractional T1 channel, concurrently with
other uses of the T1 link. The current MIB structure does not allow
for these sorts of relationships to be described.
3.1.3. Virtual Circuits
Several of the sub-layers for which media-specific MIB modules have
been defined are connection oriented (e.g., Frame Relay, X.25).
Experience has shown that each effort to define such a MIB module
revisits the question of whether separate conceptual rows in the
ifTable are needed for each virtual circuit. Most, if not all, of
these efforts to date have decided to have all virtual circuits
reference a single conceptual row in the ifTable.
3.1.4. Bit, Character, and Fixed-Length Interfaces
RS-232 is an example of a character-oriented sub-layer over which
(e.g., through use of PPP) IP datagrams can be sent. Due to the
packet-based nature of many of the objects in the ifTable, experience
has shown that it is not appropriate to have a character-oriented
sub-layer represented by a (whole) conceptual row in the ifTable.
Experience has also shown that it is sometimes desirable to have some
management information for bit-oriented interfaces, which are
similarly difficult to represent by a (whole) conceptual row in the
ifTable. For example, to manage the channels of a DS1 circuit, where
only some of the channels are carrying packet-based data.
A further complication is that some subnetwork technologies transmit
data in fixed length transmission units. One example of such a
technology is cell relay, and in particular Asynchronous Transfer
Mode (ATM), which transmits data in fixed-length cells. Representing
such a interface as a packet-based interface produces redundant
objects if the relationship between the number of packets and the
number of octets in either direction is fixed by the size of the
transmission unit (e.g., the size of a cell).
3.1.5. Counter Size
As the speed of network media increase, the minimum time in which a
32 bit counter will wrap decreases. For example, on an Ethernet, a
stream of back-to-back, full-size packets will cause ifInOctets to
wrap in just over 57 minutes. For a T3 line, the minimum wrap-time
is just over 12 minutes. For FDDI, it will wrap in 5.7 minutes. For
a 1-gigabit medium, the counter might wrap in as little as 34
seconds. Requiring that interfaces be polled frequently enough not
to miss a counter wrap will be increasingly problematic.
3.1.6. Interface Speed
Network speeds are increasing. The range of ifSpeed is limited to
reporting a maximum speed of (2**31)-1 bits/second, or approximately
2.2Gbs. SONET defines an OC-48 interface, which is defined at
operating at 48 times 51 Mbs, which is a speed in excess of 2.4gbits.
Thus, ifSpeed will be of diminishing utility over the next several
years.
3.1.7. Multicast/Broadcast Counters
The counters in the ifTable for packets addressed to a multicast or
the broadcast address, are combined as counters of non-unicast
packets. In contrast, the ifExtensions MIB [7] defines one set of
counters for multicast, and a separate set for broadcast packets.
With the separate counters, the original combined counters become
redundant.
3.1.8. Addition of New ifType values
Over time new ifType enumerated values have been needed for new
interface types. With the syntax of ifType being defined in a MIB,
this requires the new MIB to be re-issued in order to define the new
values. In the past, re-issuing of the MIB has occurred only after
several years.
3.1.9. ifSpecific
The original definition of the OBJECT IDENTIFIER value of ifSpecific
was not sufficently clear. As a result, different implementors have
used it differently, and confusion has resulted. Some
implementations have the value of ifSpecific be the OBJECT IDENTIFIER
that defines the media-specific MIB, i.e., the "foo" of:
foo OBJECT IDENTIFIER ::= { transmission xxx }
while others have it be the OBJECT IDENTIFIER of the table or entry
in the appropriate media-specific MIB (e.g. fooTable or fooEntry),
while still others have it be the OBJECT IDENTIFIER of the index
object of the table"s row, including instance identifier (e.g.,
fooIfIndex.ifIndex). A definition based on the latter would not be
sufficient unless it also allowed for media-specific MIBs which
include several tables, where each table has its own, different,
indexing.
3.2. Clarifications/Revisions
The following clarifications and/or revisions are proposed.
3.2.1. Interface Numbering
One solution to the interface numbering problem would be to redefine
ifNumber to be the largest value of ifIndex, but the utility of such
an object is questionable, and such a re-definition would require
ifNumber to be deprecated. Thus, an improvement would be to
deprecate ifNumber and not replace it. However, the deprecation of
ifNumber would require a change to that portion of ifIndex"s
definition which refers to ifNumber. So, since the definition of
ifIndex must be changed anyway in order to solve the problem, changes
to ifNumber do not benefit the solution.
The solution adopted in this memo is to delete the requirement that
the value of ifIndex must be less than the value of ifNumber, and to
retain ifNumber with its current definition. It could be argued that
this is a change in the semantics of ifIndex; however, all existing
implementations conform to this new definition, and in the interests
of not requiring changes in existing implementations and in the many
existing media-specific MIBs, it is proposed that this change does
not require ifIndex to be deprecated.
This solution also results in the possibility of "holes" in the
ifTable (i.e., the ifIndex values of conceptual rows in the ifTable
are not necessarily contiguous), but SNMP"s GetNext (and SNMPv2"s
GetBulk) operation easily deals with such holes. The value of
ifNumber still represents the number of conceptual rows, which
increases/decreases as new interfaces are dynamically added/removed.
The vital constancy requirement is met by requiring that after an
interface is dynamically removed, its ifIndex value is not re-used
(by a different dynamically added interface) until after the
following re-initialization of the network management system. This
avoids the need for a priori assignment of ifIndex values for all
possible interfaces which might be added dynamically.
The exact meaning of a "different" interface is hard to define, and
there will be gray areas. One important criterion is that a
management station, not noticing that an interface has gone away and
another come into existence, should not be confused when it
calculates the difference between the counter values retrieved on
successive polls for a particular ifIndex value. However, any firm
definition in this document would likely to turn out to be
inadequate. Instead, the following guidelines are offered to allow
implementors to choose what "different" means in their particular
situation.
A previously-unused value of ifIndex should be assigned to a
dynamically added interface if:
(1) the assignment of a previously-used ifIndex value to the
interface could result in a discontinuity in the values of
ifTable counters for that value of ifIndex; or,
(2) an agent has no knowledge of whether the interface is the
"same" or "different" from a previous interface incarnation.
Because of the restriction of the value of ifIndex to be less than
ifNumber, interfaces have been numbered with small integer values.
This has led to the ability by humans to use the ifIndex values as
(somewhat) user-friendly names for network interfaces (e.g.,
"interface number 3"). With the relaxation of the restriction on the
value of ifIndex, there is now the possibility that ifIndex values
could be assigned as very large numbers (e.g., memory addresses).
Such numbers would be much less user-friendly.
Therefore, this memo recommends that ifIndex values still be assigned
as (relatively) small integer values starting at 1, even though the
values in use at any one time are not necessarily contiguous. (Note
that this makes remembering which values have been assigned easy for
agents which dynamically add new interfaces.)
This proposed change introduces a new problem of its own.
Previously, there usually was a simple, direct, mapping of interfaces
to the physical ports on systems. This mapping would be based on the
ifIndex value. However, by removing the previous restrictions on the
values allowed for ifIndex, along with the interface sub-layer
concept (see the following section), mapping from interfaces to
physical ports becomes increasingly problematic.
To address this issue, a new object, ifName, is added to the MIB.
This object contains the device"s name for the interface of which the
relevant entry in the ifTable is a component. For example, if a
router has an interface named wan1, which is composed of PPP running
over an RS-232 port, the ifName objects for the corresponding PPP and
RS-232 entries in the ifTable will contain the string "wan1".
3.2.2. Interface Sub-Layers
One possible but not recommended solution to the problem of
representing multiple sub-layers would be to retain the concept of
one conceptual row for all the sub-layers of an interface and have
each media-specific MIB module identify its "superior" and
"subordinate" sub-layers through OBJECT IDENTIFIER "pointers". The
drawbacks of this scheme are: 1) the superior/subordinate pointers
are contained in the media-specific MIB modules, and thus, a manager
could not learn the structure of an interface, without inspecting
multiple pointers in different MIB modules; this is overly complex
and only possible if the manager has knowledge of all the relevant
media-specific MIB modules; 2) current MIB modules would all need to
be retrofitted with these new "pointers"; 3) this scheme does not
adequately address the problem of upward and downward multiplexing;
and 4) enumerated values of ifType are needed for each combination of
sub-layers.
Another possible but not recommended scheme would be to retain the
concept of one conceptual row for all the sub-layers of an interface
and have a new separate MIB table to identify the "superior" and
"subordinate" sub-layers which contain OBJECT IDENTIFIER "pointers"
to media-specific MIB module(s) for each sub-layer. Effectively, one
conceptual row in the ifTable would represent each combination of
sub-layers between the internetwork-layer and the wire. While this
scheme has fewer drawbacks, it does not support downward
multiplexing, such as PPP over MLP; since MLP makes two (or more)
serial lines appear to the layers above as a single physical
interface, PPP over MLP should appear to the internetwork-layer as a
single interface. However, this scheme would result in two (or more)
conceptual rows in the ifTable and the internetwork-layer would run
over both of them. This scheme also requires enumerated values of
ifType for each combination of sub-layers.
The solution adopted in this memo is to have an individual conceptual
row in the ifTable to represent each sub-layer and have a new
separate MIB table (the ifStackTable, see section 5 of this memo) to
identify the "superior" and "subordinate" sub-layers through INTEGER
"pointers" to the appropriate conceptual rows in the ifTable. This
solution supports both upward and downward multiplexing. It also
allows the IANAIfType to Media-Specific MIB mapping to identify the
media-specific MIB module for each sub- layer. The new table
(ifStackTable) need be referenced only to oBTain information about
layering. Enumerated values for ifType are required for each sub-
layer only, not for combinations of them.
However, this solution does require that the descriptions of some
objects in the ifTable (specifically, ifType, ifPhysAddress,
ifInUcastPkts, and ifOutUcastPkts) be generalized so as to apply to
any sub-layer (rather than only to a sub-layer immediately beneath
the network layer, as at present). It also requires that some
objects (specifically, ifSpeed) need to have appropriate values
identified for use when a generalized definition does not apply to a
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.
3.2.3. Guidance on Defining Sub-layers
The designer of a media-specific MIB must decide whether to divide
the interface into sub-layers, and if so, how to make the divisions.
The following guidance is offered to assist the media-specific MIB
designer in these decisions.
In general, the number of entries in the ifTable should be kept to
the minimum required for network management. In particular, a group
of related interfaces should be treated as a single interface with
one entry in the ifTable providing that:
(1) None of the group of interfaces performs multiplexing for any
other interface in the agent,
(2) There is a meaningful and useful way for all of the ifTable"s
information (e.g., the counters, and the status variables),
and all of the ifTable"s capabilities (e.g., write access to
ifAdminStatus), to apply to the group of interfaces as a
whole.
Under these circumstances, there should be one entry in the ifTable
for such a group of interfaces, and any internal structure which
needs to be represented to network management should be captured in a
MIB module specific to the particular type of interface.
Note that application of bullet 2 above to the ifTable"s ifType
object requires that there is a meaningful media-specific MIB and a
meaningful ifType value which apply to the group of interfaces as a
whole. For example, it is not appropriate to treat an HDLC sub-layer
and an RS-232 sub-layer as a single ifTable entry when the media-
specific MIBs and the ifType values for HDLC and RS-232 are separate
(rather than combined).
Note that the sub-layers of an interface on one device will sometimes
be different to the sub-layers of the interconnected interface of
another device. A simple example of this is a frame-relay DTE
interface which connects to a frameRelayService interface, where the
DTE interface has a different ifType value and media-specific MIB to
the DCE interface.
Also note that a media-specific MIB may mandate that a particular
ifTable counter does not apply and that its value must always be 0,
signifying that the applicable event can not and does not occur for
that type of interface; for example, ifInMulticastPkts and
ifOutMulticastPkts on an interface type which has no multicast
capability. In other circumstances, an agent must not always return
0 for any counter just because its implementation is incapable of
detecting occurrences of the particular event; instead, it must
return a noSuchName/noSuchObject error/exception when queried for the
counter, even if this prevents the implementation from complying with
the relevant MODULE-COMPLIANCE macro.
These guidelines are just that - guidelines. The designer of a
media-specific MIB is free to lay out the MIB in whatever SMI
conformant manner is desired. However, in so doing, the media-
specific MIB MUST completely specify the sub-layering model used for
the MIB, and provide the assumptions, reasoning, and rationale used
to develop that model.
3.2.4. Virtual Circuits
This memo strongly recommends that connection-oriented sub-layers do
not have a conceptual row in the ifTable for each virtual circuit.
This avoids the proliferation of conceptual rows, especially those
which have considerable redundant information. (Note, as a
comparison, that connection-less sub-layers do not have conceptual
rows for each remote address.) There may, however, be circumstances
under which it is appropriate for a virtual circuit of a connection-
oriented sub-layer to have its own conceptual row in the ifTable; an
example of this might be PPP over an X.25 virtual circuit. The MIB
in section 6 of this memo supports such circumstances.
If a media-specific MIB wishes to assign an entry in the ifTable to
each virtual circuit, the MIB designer must present the rationale for
this decision in the media-specific MIB"s specification.
3.2.5. Bit, Character, and Fixed-Length Interfaces
About half the objects in the ifTable are applicable to every type of
interface: packet-oriented, character-oriented, and bit-oriented. Of
the other half, two are applicable to both character-oriented and
packet-oriented interfaces, and the rest are applicable only to
packet-oriented interfaces. Thus, while it is desirable for
consistency to be able to represent any/all types of interfaces in
the ifTable, it is not possible to implement the full ifTable for
bit- and character-oriented sub-layers.
One possible but not recommended solution to this problem would be to
split the ifTable into two (or more) new MIB tables, one of which
would contain objects that are relevant only to packet-oriented
interfaces (e.g., PPP), and another that may be used by all
interfaces. This is highly undesirable since it would require
changes in every agent implementing the ifTable (i.e., just about
every existing SNMP agent).
The solution adopted in this memo builds upon the fact that
compliance statements in SNMPv2 (in contrast to SNMPv1) refer to
object groups, where object groups are explicitly defined by listing
the objects they contain. Thus, in SNMPv2, multiple compliance
statements can be specified, one for all interfaces and additional
ones for specific types of interfaces. The separate compliance
statements can be based on separate object groups, where the object
group for all interfaces can contain only those objects from the
ifTable which are appropriate for every type of interfaces. Using
this solution, every sub-layer can have its own conceptual row in the
ifTable.
Thus, section 6 of this memo contains definitions of the objects of
the existing "interfaces" group of MIB-II, in a manner which is both
SNMPv2-compliant and semantically-equivalent to the existing MIB-II
definitions. With equivalent semantics, and with the BER ("on the
wire") encodings unchanged, these definitions retain the same OBJECT
IDENTIFIER values as assigned by MIB-II. Thus, in general, no
rewrite of existing agents which conform to MIB-II and the
ifExtensions MIB is required.
In addition, this memo defines several object groups for the purposes
of defining which objects apply to which types of interface:
(1) the ifGeneralGroup. This group contains those objects
applicable to all types of network interfaces, including
bit-oriented interfaces.
(2) the ifPacketGroup. This group contains those objects
applicable to packet-oriented network interfaces.
(3) the ifFixedLengthGroup. This group contains the objects
applicable not only to character-oriented interfaces, such as
RS-232, but also to those subnetwork technologies, such as
cell-relay/ATM, which transmit data in fixed length
transmission units. As well as the octet counters, there are
also a few other counters (e.g., the error counters) which
are useful for this type of interface, but are currently
defined as being packet-oriented. To accommodate this, the
definitions of these counters are generalized to apply to
character-oriented interfaces and fixed-length-transmission
interfaces.
It should be noted that the octet counters in the ifTable aggregate
octet counts for unicast and non-unicast packets into a single octet
counter per direction (received/transmitted). Thus, with the above
definition of fixed-length-transmission interfaces, where such
interfaces which support non-unicast packets, separate counts of
unicast and multicast/broadcast transmissions can only be maintained
in a media-specific MIB module.
3.2.6. Counter Size
Two approaches to addressing the shrinking minimum counter-wrap time
problem were evaluated. Counters could be scaled, for example,
ifInOctets could be changed to count received octets in, e.g., 1024
byte blocks. Alternatively, the size of the counter could be
increased.
Scaling the counters was rejected. While it provides acceptable
performance at high count rates, at low rates it suffers. If there
is little traffic on an interface, there might be a significant
interval before enough counts occur to cause a counter to be
incremented. Traffic would then appear to be very bursty, leading to
incorrect conclusions of the network"s performance.
The alternative, which this memo adopts, is to provide expanded, 64
bit, counters. These counters are provided in new "high capacity"
groups,
The old, 32-bit, counters have not been deprecated. The 64-bit
counters are to be used only when the 32-bit counters do not provide
enough capacity; that is, the 32 bit counters could wrap too fast.
For interfaces that operate at 20,000,000 (20 million) bits per
second or less, 32-bit byte and packet counters MUST be used. For
interfaces that operate faster than 20,000,000 bits/second, and
slower than 650,000,000 bits/second, 32-bit packet counters MUST be
used and 64-bit octet counters MUST be used. For interfaces that
operate at 650,000,000 bits/second or faster, both 64-bit packet
counters AND 64-bit octet counters MUST be used.
These speed steps were chosen as reasonable compromises based on the
following:
(1) The cost of maintaining 64-bit counters is relatively high,
so minimizing the number of agents which must support them is
desirable. Common interfaces (such as Ethernet) should not
require them.
(2) 64-bit counters are a new feature, introduced in SNMPv2. It
is reasonable to expect that support for them will be spotty
for the immediate future. Thus, we wish to limit them to as
few systems as possible. This, in effect, means that 64-bit
counters should be limited to higher speed interfaces.
Ethernet (10,000,000 bps) and Token Ring (16,000,000 bps) are
fairly wide-spread so it seems reasonable to not require 64-
bit counters for these interfaces.
(3) The 32-bit octet counters will wrap in the following times,
for the following interfaces (when transmitting maximum-sized
packets back-to-back):
- Ethernet: 57 minutes,
- 16 megabit Token Ring: 36 minutes,
- A US T3 line (45 megabits): 12 minutes,
- FDDI: 5.7 minutes
(4) The 32-bit packet counters wraps in about 57 minutes when
64-byte packets are transmitted back-to-back on a 650,000,000
bit/second link.
As an aside, a 1-terabit (1,000 gigabits) link will cause a
64 bit octet counter to wrap in just under 5 years.
Conversely, an 81,000,000 terabit/second link is required to
cause a 64-bit counter to wrap in 30 minutes. We believe
that, while technology rapidly marches forward, this link
speed will not be achieved for at least several years,
leaving sufficient time to evaluate the introduction of 96
bit counters.
When 64-bit counters are in use, the 32-bit counters MUST still be
available. They will report the low 32-bits of the associated 64-bit
count (e.g., ifInOctets will report the least significant 32 bits of
ifHCInOctets). This enhances inter-operability with existing
implementations at a very minimal cost to agents.
The new "high capacity" groups are:
(1) the ifHCFixedLengthGroup for character-oriented/fixed-length
interfaces, and the ifHCPacketGroup for packet-based
interfaces; both of these groups include 64 bit counters for
octets, and
(2) the ifVHCPacketGroup for packet-based interfaces; this group
includes 64 bit counters for octets and packets.
3.2.7. Interface Speed
In order to deal with increasing interface speeds, we have added an
ifHighSpeed object.
This object reports the speed of the interface in 1,000,000 (1
million) bits/second units. Thus, the true speed of the interface
will be the value reported by this object, plus or minus 500,000
bits/second.
Other alternatives considered were:
(1) Making the interface speed a 64-bit gauge. This was rejected
since the current SMI does not allow such a syntax.
Furthermore, even if 64-bit gauges were available, their use
would require additional complexity in agents due to an
increased requirement for 64-bit operations.
(2) We also considered making "high-32 bit" and "low-32-bit"
objects which, when combined, would be a 64-bit value. This
simply seemed overly complex for what we are trying to do.
Furthermore, a full 64-bits of precision does not seem
necessary. The value of ifHighSpeed will be the only report
of interface speed for interfaces that are faster than
4,294,967,295 bits per second. At this speed, the
granularity of ifHighSpeed will be 1,000,000 bits per second,
thus the error will be 1/4294, or about 0.02%. This seems
reasonable.
(3) Adding a "scale" object, which would define the units which
ifSpeed"s value is.
This would require two additional objects; one for the
scaling object, and one to replace the current ifSpeed. This
later object is required since the semantics of ifSpeed would
be significantly altered, and manager stations which do not
understand the new semantics would be confused.
3.2.8. Multicast/Broadcast Counters
To avoid the redundancy of counting all non-unicast packets as well
as having individual multicast and broadcast packet counters, we
deprecate the use of the non-unicast counters, which can be derived
from the values of the others.
For the output broadcast and multicast counters defined in RFC1229,
their definitions varied slightly from the packet counters in the
ifTable, in that they did not count errors/discarded packets. To
align the definitions better, the old counters are deprecated and
replaced by new definitions. Counters with 64 bits of range are also
needed, as explained above.
3.2.9. Trap Enable
In the multi-layer interface model, each sub-layer for which there is
an entry in the ifTable can generate linkUp/Down Traps. Since
interface state changes would tend to propagate through the interface
(from top to bottom, or bottom to top), it is likely that several
traps would be generated for each linkUp/Down occurrence.
It is desirable to provide a mechanism for manager stations to
control the generation of these traps. To this end, the
ifLinkUpDownTrapEnable object has been added. This object allows
managers to limit generation of traps to just the sub-layers of
interest.
The default setting should limit the number of traps generated to one
per interface per linkUp/Down event. Furthermore, it seems that the
conditions that cause these state changes that are of most interest
to network managers occur at the lowest level of an interface stack.
Therefore we specify that by default, only the lowest sub-layer of
the interface generate traps.
3.2.10. Addition of New ifType values
The syntax of ifType is changed to be a textual convention, such that
the enumerated integer values are now defined in the textual
convention, IANAifType, which can be re-specified (with additional
values) without issuing a new version of this document. The Internet
Assigned Number Authority (IANA) is responsible for the assignment of
all Internet numbers, including various SNMP-related numbers, and
specifically, new ifType values. Thus, this document defines two MIB
modules: one to define the MIB for the "interfaces" group, and a
second to define the first version of the IANAifType textual
convention. The latter will be periodically re-issued by the IANA.
3.2.11. InterfaceIndex Textual Convention
A new textual convention, InterfaceIndex, has been defined. This
textual convention "contains" all of the semantics of the ifIndex
object. This allows other mib modules to easily import the semantics
of ifIndex.
3.2.12. IfAdminStatus and IfOperStatus
A new state has been added to ifOperStatus: dormant. This state
indicates that the relevant interface is not actually in a condition
to pass packets (i.e., up) but is in a "pending" state, waiting for
some external event. For "on-demand" interfaces, this new state
identifies the situation where the interface is waiting for events to
place it in the up state. Examples of such events might be:
(1) having packets to transmit before establishing a connection
to a remote system.
(2) having a remote system establish a connection to the
interface (e.g., dialing up to a slip-server).
The down state now has two meanings, depending on the value of
ifAdminStatus.
(1) If ifAdminStatus is not down and ifOperStatus is down, then a
fault condition is presumed to exist on the interface.
(2) If ifAdminStatus is down, then ifOperStatus will normally
also be down, i.e., there is not (necessarily) a fault
condition on the interface.
Note that when ifAdminStatus transitions to down, ifOperStatus will
normally also transition to down. In this situation, it is possible
that ifOperStatus"s transition will not occur immediately, but rather
after a small time lag to complete certain operations before going
"down"; for example, it might need to finish transmitting a packet.
If a manager station finds that ifAdminStatus is down and
ifOperStatus is not down for a particular interface, the manager
station should wait a short while and check again. If the condition
still exists only then should it raise an error indication.
Naturally, it should also ensure that ifLastChange has not changed
during this interval.
Whenever an interface table entry is created (usually as a result of
system initialization), the relevant instance of ifAdminStatus is set
to down, and presumably ifOperStatus will also be down.
An interface may be enabled in two ways: either as a result of
explicit management action (e.g., setting ifAdminStatus to up) or as
a result of the managed system"s initialization process. When
ifAdminStatus changes to the up state, the related ifOperStatus
should do one of the following:
(1) Change to the up state if and only if the interface is able
to send and receive packets.
(2) Change to the dormant state if and only if the interface is
found to be operable, but the interface is waiting for other,
external, events to occur before it can transmit or receive
packets. Presumably when the expected events occur, the
interface will then transition to the up state.
(3) Remain in the down state if an error or other fault condition
is detected on the interface.
(4) Change to the unknown state if, for some reason, the state of
the interface can not be ascertained.
(5) Change to the testing state if some test(s) must be performed
on the interface. Presumably after completion of the test,
the interface"s state will change to up, dormant, or down, as
appropriate.
3.2.13. Traps
The exact definition of when linkUp and linkDown traps are generated,
has been changed to reflect the changes to ifAdminStatus and
ifOperStatus.
LinkUp and linkDown traps are generated just after ifOperStatus
leaves, or just before it enters, the down state, respectively. The
Wording of the conditions under which a linkDown trap is generated
was explicitly chosen to allow a node with only one interface to
transmit the linkDown trap before that interface goes down.
Operational experience seems to indicate that manager stations are
most concerned with an interface being in the down state and the fact
that this state may indicate a failure. It seemed most useful to
instrument either transitions into/out of the up state or the down
state.
Instrumenting transitions into or out of the up state has the
drawback that an on-demand interface might have many transitions
between up and dormant, leading to many linkUp traps and no linkDown
traps. Furthermore, if a node"s only interface is the on-demand
interface, then a transition to dormant will entail generation of a
trap, necessitating bringing the link to the up state (and a linkUp
trap)!!
On the other hand, instrumenting transitions into or out of the down
state has the advantages:
(1) A transition into the down state will occur when an error is
detected on an interface. Error conditions are presumably of
great interest to network managers.
(2) Departing the down state generally indicates that the
interface is going to either up or dormant, both of which are
considered "healthy" states.
Furthermore, it is believed that generarating traps on transitions
into or out of the down state is generally consistent with current
usage and interpretation of these traps by manager stations.
Therefore, this memo defines that it is the transitions into/out of
the down state which generate traps.
Obviously, if a failure condition is present on a node with a single
interface, the linkDown trap will probably not be succesfully
transmitted since the interface through which it must be transmitted
has failed.
3.2.14. ifSpecific
The current definition of ifSpecific is not explicit enough. The
only definition that can both be made explicit and can cover all the
useful situations (see section 3.1.9) is to have ifSpecific be the
most general value for the media-specific MIB module (the first
example given section in 3.1.9). This effectively makes it redundant
because it contains no more information than is provided by ifType.
For this reason, ifSpecific has been deprecated.
3.3. Media-Specific MIB Applicability
The exact use and semantics of many objects in this MIB are open to
some interpretation. This is a result of the generic nature of this
MIB. It is not always possible to come up with specific,
unambiguous, text that covers all cases and yet preserve the generic
nature of the MIB.
Therefore, it is incumbent upon a media-specific MIB designer to,
wherever necessary, clarify the use of the objects in this MIB with
respect to the media-specific MIB.
Specific areas of clarification include:
Layering Model
The media-specific MIB designer MUST completely and
unambiguously specify the layering model used. Each
individual sub-layer must be identified.
Virtual Circuits
The media-specific MIB designer MUST specify whether virtual
circuits are assigned entries in the ifTable or not. If they
are, compelling rationale must be presented.
ifTestTable
The media-specific MIB designer MUST specify the
applicability of the ifTestTable.
ifRcvAddressTable
The media-specific MIB designer MUST specify the
applicability of the ifRcvAddressTable.
ifType
For each of the ifType values to which the media-specific MIB
applies, it must specify the mapping of ifType values to
media-specific MIB module(s) and instances of MIB objects
within those modules.
However, wherever this interface MIB is specific in the semantics,
DESCRIPTION, or applicability of objects, the media-specific MIB
designer MUST NOT change said semantics, DESCRIPTION, or
applicability.
4. Overview
This MIB consists of 5 tables:
ifTable
This table is the ifTable from MIB-II.
ifXTable
This table contains objects that have been added to the
Interface MIB as a result of the Interface Evolution effort,
or replacements for objects of the original, MIB-II, ifTable
that were deprecated because the semantics of said objects
have significantly changed. This table also contains objects
that were previously in the ifExtnsTable.
ifStackTable
This table contains objects that define the relationships
among the sub-layers of an interface.
ifTestTable
This table contains objects that are used to perform tests on
interfaces. This table is a generic table. The designers of
media-specific MIBs must define exactly how this table
applies to their specific MIB.
This table replaces the interface test table defined in
RFC1229 [7]. The significant change is the replacement of
the ifExtnsTestCommunity (and ifExtnsTestContext which would
also have been required for SNMPv2) and ifExtnsTestRequestId
objects, by the new ifTestId, ifTestStatus, and ifTestOwner
objects.
ifRcvAddressTable
This table contains objects that are used to define the
media-level addresses which this interface will receive.
This table is a generic table. The designers of media-
specific MIBs must define exactly how this table applies to
their specific MIB.
5. IANAifType Definition
IANAifType-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE FROM SNMPv2-SMI
TEXTUAL-CONVENTION FROM SNMPv2-TC;
ianaifType MODULE-IDENTITY
LAST-UPDATED "9311082155Z"
ORGANIZATION "IANA"
CONTACT-INFO
" Internet Assigned Numbers Authority
Postal: USC/Information Sciences Institute
4676 Admiralty Way, Marina del Rey, CA 90292
Tel: +1 310 822 1511
E-Mail: iana@isi.edu"
DESCRIPTION
"The MIB module which defines the IANAifType textual
convention, and thus the enumerated values of the
ifType object defined in MIB-II"s ifTable."
::= { mib-2 30 }
IANAifType ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION
"This data type is used as the syntax of the ifType
object in the (updated) definition of MIB-II"s
ifTable.
The definition of this textual convention with the
addition of newly assigned values is published
periodically by the IANA, in either the Assigned
Numbers RFC, or some derivative of it specific to
Internet Network Management number assignments. (The
latest arrangements can be obtained by contacting the
IANA.)
Requests for new values should be made to IANA via
email (iana@isi.edu).
The relationship between the assignment of ifType
values and of OIDs to particular media-specific MIBs
is solely the purview of IANA and is subject to change
without notice. Quite often, a media-specific MIB"s
OID-subtree assignment within MIB-II"s "transmission"
subtree will be the same as its ifType value.
However, in some circumstances this will not be the
case, and implementors must not pre-assume any
specific relationship between ifType values and
transmission subtree OIDs."
SYNTAX INTEGER {
other(1), -- none of the following
regular1822(2),
hdh1822(3),
ddnX25(4),
rfc877x25(5),
ethernetCsmacd(6),
iso88023Csmacd(7),
iso88024TokenBus(8),
iso88025TokenRing(9),
iso88026Man(10),
starLan(11),
proteon10Mbit(12),
proteon80Mbit(13),
hyperchannel(14),
fddi(15),
lapb(16),
sdlc(17),
ds1(18), -- DS1/E1 (RFC1406)
e1(19), -- obsolete
basicISDN(20),
primaryISDN(21),
propPointToPointSerial(22), -- proprietary serial
ppp(23),
softwareLoopback(24),
eon(25), -- CLNP over IP (RFC1070)
ethernet3Mbit(26),
nsip(27), -- XNS over IP
slip(28), -- generic SLIP
ultra(29), -- ULTRA technologies
ds3(30), -- T-3
sip(31), -- SMDS
frameRelay(32), -- DTE only
rs232(33),
para(34), -- parallel-port
arcnet(35), -- arcnet
arcnetPlus(36), -- arcnet plus
atm(37), -- ATM cells
miox25(38),
sonet(39), -- SONET or SDH
x25ple(40),
iso88022llc(41),
localTalk(42),
smdsDxi(43),
frameRelayService(44), -- Frame relay DCE
v35(45),
hssi(46),
hippi(47),
modem(48), -- Generic modem
aal5(49), -- AAL5 over ATM
sonetPath(50),
sonetVT(51),
smdsIcip(52), -- SMDS InterCarrier Interface
propVirtual(53), -- proprietary virtual/internal
propMultiplexor(54) -- proprietary multiplexing
}
END
6. Interfaces Group Definitions
IF-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, Counter32, Gauge32,
Integer32, TimeTicks,
NOTIFICATION-TYPE FROM SNMPv2-SMI
TEXTUAL-CONVENTION, DisplayString,
PhysAddress, TruthValue, RowStatus,
AutonomousType, TestAndIncr FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF
IANAifType FROM IANAifType-MIB
interfaces FROM RFC-1213
ifMIB MODULE-IDENTITY
LAST-UPDATED "9311082155Z"
ORGANIZATION "IETF Interfaces MIB Working Group"
CONTACT-INFO
" Keith McCloghrie
Postal: Hughes LAN Systems
1225 Charleston Road, Mountain View, CA 94043
Tel: +1 415 966 7934
E-Mail: kzm@hls.com
Frank Kastenholz
Postal: FTP Software
2 High Street, North Andover, MA 01845
Tel: +1 508 685 4000
E-Mail: kasten@ftp.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 RFC1229."
::= { mib-2 31 }
ifMIBObjects OBJECT IDENTIFIER ::= { ifMIB 1 }
-- OwnerString has the same semantics as used in RFC1271
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
ifNumber OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of network interfaces (regardless of their
current state) present on this system."
::= { interfaces 1 }
-- the Interfaces table
-- The Interfaces table contains information on the entity"s
-- interfaces. Each sub-layer below the internetwork-layer
-- of a network interface is considered to be an interface.
ifTable OBJECT-TYPE
SYNTAX SEQUENCE OF IfEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A list of interface entries. The number of entries
is given by the value of ifNumber."
::= { interfaces 2 }
ifEntry OBJECT-TYPE
SYNTAX IfEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry containing management information applicable
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.
The interface"s media-specific MIB must define the bit
and byte ordering and format of the value contained by
this object. For interfaces which do not have such an
address (e.g., a serial line), this object should
contain an octet string of zero length."
::= { ifEntry 6 }
ifAdminStatus OBJECT-TYPE
SYNTAX INTEGER {
up(1), -- ready to pass packets
down(2),
testing(3) -- in some test mode
}
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"The desired state of the interface. The testing(3)
state indicates that no operational packets can be
passed. When a managed system initializes, all
interfaces start with ifAdminStatus in the down(2)
state. As a result of either explicit management
action or per configuration information retained by
the managed system, ifAdminStatus is then changed to
either the up(1) or testing(3) states (or remains in
the down(2) state)."
::= { ifEntry 7 }
ifOperStatus OBJECT-TYPE
SYNTAX INTEGER {
up(1), -- ready to pass packets
down(2),
testing(3), -- in some test mode
unknown(4), -- status can not be determined
-- for some reason.
dormant(5)
}
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The current operational state of the interface. The
testing(3) state indicates that no operational packets
can be passed. If ifAdminStatus is down(2) then
ifOperStatus should be down(2). If ifAdminStatus is
changed to up(1) then ifOperStatus should change to
up(1) if the interface is ready to transmit and
receive network traffic; it should change to
dormant(5) if the interface is waiting for external
actions (such as a serial line waiting for an
incomming connection); it should remain in the down(2)
state if and only if there is a fault that prevents if
from going to the up(1) state."
::= { ifEntry 8 }
ifLastChange OBJECT-TYPE
SYNTAX TimeTicks
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime at the time the interface
entered its current operational state. If the current
state was entered prior to the last re-initialization
of the local network management subsystem, then this
object contains a zero value."
::= { ifEntry 9 }
ifInOctets OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The total number of octets received on the interface,
including framing characters."
::= { ifEntry 10 }
ifInUcastPkts OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of packets, delivered by this sub-layer to
a higher (sub-)layer, which were not addressed to a
m