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Draft Interfaces Group Evolution May 1993
Evolution of the Interfaces Group of MIB-II
1 June 1993
Keith McCloghrie
Hughes LAN Systems
kzm@hls.com
Frank J. Kastenholz
FTP Software
kasten@ftp.com
Status of this Memo
This document is an Internet Draft. Internet Drafts are
working documents of the Internet Engineering Task Force
(IETF), its Areas, and its Working Groups. Note that other
groups may also distribute working documents as Internet
Drafts.
Internet Drafts are valid for a maximum of six months and may
be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet Drafts as reference
material or to cite them other than as a "work in progress".
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1. Introduction
MIB-II [3] is the core set of managed objects defined for use
by network management of the Internet suite of protocols.
MIB-II was defined using the SNMPv1 Network Management
Framework.
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 experimental 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.
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2. The SNMPv2 Network Management Framework
The SNMPv2 Network Management Framework consists of four major
components. They are:
o RFC 1441 which defines the SMI, the mechanisms used for
describing and naming objects for the purpose of
management.
o RFC 1213 defines MIB-II, the core set of managed objects
for the Internet suite of protocols.
o RFC 1445 which defines the administrative and other
architectural aspects of the framework.
o RFC 1448 which defines the protocol used for network
access to managed objects.
The Framework permits new objects to be defined for the
purpose of experimentation and evaluation.
2.1. Object Definitions
Managed objects are accessed via a virtual information store,
termed the Management Information Base or MIB. Objects in the
MIB are defined using the subset of Abstract Syntax Notation
One (ASN.1) defined in the SMI. In particular, each object
object type is named by an OBJECT IDENTIFIER, an
administratively assigned name. The object type together with
an object instance serves to uniquely identify a specific
instantiation of the object. For human convenience, we often
use a textual string, termed the descriptor, to refer to the
object type.
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3. Experience with the Interfaces Group
One of the strengths of internetwork-layer protocols such as
IP [6] is that they are designed to run over any network
interface. In achieving this, IP considers any and all
protocols it runs over as a single "network interface" layer.
A similar view is be 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/loosening of the model. This memo is a
proposal to document/standardize the evolution of the model
and to fill in the gaps caused by that evolution.
3.1. Areas of Clarification/Revision
There are four areas for which experience indicates that
clarification or revision 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:
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"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 by the ifSpecific 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, and that row's ifSpecific variable can
"point" to only one of the three media-specific MIB modules.
Furthermore, even if there was a convention for deciding which
MIB module is referenced by ifSpecific then 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
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multiplexing of the sub-layers. An example of upward
multiplexing is MLP (Multi-Link) 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 running
over a Frame Relay virtual circuit, all of which run over the
same ISDN B channel. 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 and Character Oriented 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.
3.2. Clarifications/Revisions
The following clarifications and/or revisions are proposed.
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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 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. 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
another 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.
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
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would be much less user-friendly. Therefore, this memo
recommends that ifIndex values still be assigned as small
integer values starting at 1, even though the values in use at
any one time are not necessarily contiguous. (Note that this
makes it easy for agents which dynamically add new interfaces,
to remember which values have been assigned.)
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)
that 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 and to contain OBJECT
IDENTIFIER "pointers" to media-specific MIBs. 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 would
deprecate the use of ifSpecific and it still 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; this scheme,
however, would result in two (or more) conceptual rows in the
ifTable, both of which the internetwork-layer would run over.
This scheme also requires enumerated values of ifType for each
combination of sub-layers.
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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 4
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, allows the ifSpecific
pointer in each conceptual row of the ifTable to point to 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 at present), 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.
3.2.3. Virtual Circuits
This memo recommends that, in general, 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 a Frame
Relay virtual circuit. The MIB in section 4 of this memo
supports such circumstances.
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3.2.4. Bit and Character Oriented 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, the following section 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, no rewrite of
existing agents is required.
Three new object groups are defined: the ifGeneralGroup
containing those objects applicable to all types of network
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interfaces; the ifCharacterGroup containing those objects
applicable to character-oriented (but not packet-oriented)
network interfaces; and the ifPacketGroup containing those
objects applicable only to packet-oriented network interfaces.
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4. Definitions
IF-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, Counter32, Gauge32,
Integer32, TimeTicks, experimental FROM SNMPv2-SMI
DisplayString, PhysAddress, RowStatus FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF
mib-2, interfaces FROM RFC-1213;
-- combining the experimental parts of this MIB with the
-- existing ifExtensions MIB (RFC 1229) should be considered.
-- ifExtensions is defined in RFC 1239 as { mib-2 12 }
ifMIB MODULE-IDENTITY
LAST-UPDATED "9305262355Z"
ORGANIZATION "IETF Interfaces MIB Working Group"
CONTACT-INFO
" Keith McCloghrie
Hughes LAN Systems
1225 Charleston Road
Mountain View, Ca. 94043
Tel: 415-966-7934
Fax: 415-966-7980
E-mail: kzm@hls.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."
::= { experimental xx }
ifMIBObjects OBJECT IDENTIFIER ::= { ifMIB 1 }
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-- the Interfaces group
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 Integer32,
ifDescr DisplayString,
ifType INTEGER,
ifMtu Integer32,
ifSpeed Gauge32,
ifPhysAddress PhysAddress,
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ifAdminStatus INTEGER,
ifOperStatus INTEGER,
ifLastChange TimeTicks,
ifInOctets Counter32,
ifInUcastPkts Counter32,
ifInNUcastPkts Counter32,
ifInDiscards Counter32,
ifInErrors Counter32,
ifInUnknownProtos Counter32,
ifOutOctets Counter32,
ifOutUcastPkts Counter32,
ifOutNUcastPkts Counter32,
ifOutDiscards Counter32,
ifOutErrors Counter32,
ifOutQLen Gauge32,
ifSpecific OBJECT IDENTIFIER
}
ifIndex OBJECT-TYPE
SYNTAX Integer32
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 hardware interface."
::= { ifEntry 2 }
ifType OBJECT-TYPE
SYNTAX INTEGER {
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other(1), -- none of the following
regular1822(2),
hdh1822(3),
ddn-x25(4),
rfc877-x25(5),
ethernet-csmacd(6),
iso88023-csmacd(7),
iso88024-tokenBus(8),
iso88025-tokenRing(9),
iso88026-man(10),
starLan(11),
proteon-10Mbit(12),
proteon-80Mbit(13),
hyperchannel(14),
fddi(15),
lapb(16),
sdlc(17),
ds1(18), -- T-1
e1(19), -- european equiv. of T-1
basicISDN(20),
primaryISDN(21), -- proprietary serial
propPointToPointSerial(22),
ppp(23),
softwareLoopback(24),
eon(25), -- CLNP over IP [11]
ethernet-3Mbit(26),
nsip(27), -- XNS over IP
slip(28), -- generic SLIP
ultra(29), -- ULTRA technologies
ds3(30), -- T-3
sip(31), -- SMDS
frame-relay(32)
}
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The type of interface."
::= { ifEntry 3 }
ifMtu OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The size of the largest datagram which can be
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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. 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 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."
::= { ifEntry 7 }
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ifOperStatus OBJECT-TYPE
SYNTAX INTEGER {
up(1), -- ready to pass packets
down(2),
testing(3) -- in some test mode
}
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."
::= { 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-layer protocol, which were not
addressed to a multicast or broadcast address at
this sub-layer."
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::= { ifEntry 11 }
ifInNUcastPkts OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of packets, delivered by this sub-
layer to a higher-layer protocol, which were
addressed to a multicast or broadcast address at
this sub-layer."
::= { ifEntry 12 }
ifInDiscards OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of inbound packets which were chosen
to be discarded even though no errors had been
detected to prevent their being deliverable to a
higher-layer protocol. One possible reason for
discarding such a packet could be to free up
buffer space."
::= { ifEntry 13 }
ifInErrors OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of inbound packets that contained
errors preventing them from being deliverable to a
higher-layer protocol."
::= { ifEntry 14 }
ifInUnknownProtos OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of packets received via the interface
which were discarded because of an unknown or
unsupported protocol."
::= { ifEntry 15 }
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ifOutOctets OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The total number of octets transmitted out of the
interface, including framing characters."
::= { ifEntry 16 }
ifOutUcastPkts OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The total number of packets that higher-level
protocols requested be transmitted, and which were
not addressed to a multicast or broadcast address
at this sub-layer, including those that were
discarded or not sent."
::= { ifEntry 17 }
ifOutNUcastPkts OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
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."
::= { ifEntry 18 }
ifOutDiscards OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of outbound packets which were chosen
to be discarded even though no errors had been
detected to prevent their being transmitted. One
possible reason for discarding such a packet could
be to free up buffer space."
::= { ifEntry 19 }
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ifOutErrors OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of outbound packets that could not be
transmitted because of errors."
::= { ifEntry 20 }
ifOutQLen OBJECT-TYPE
SYNTAX Gauge32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The length of the output packet queue (in
packets)."
::= { ifEntry 21 }
ifSpecific OBJECT-TYPE
SYNTAX OBJECT IDENTIFIER
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A reference to MIB definitions specific to the
particular media being used to realize the
interface. For example, if the interface is
realized by an ethernet, then the value of this
object refers to a document defining objects
specific to ethernet. If this information is not
present, its value should be set to the OBJECT
IDENTIFIER { 0 0 }, which is a syntactically valid
object identifier, and any conformant
implementation of ASN.1 and BER must be able to
generate and recognize this value."
::= { ifEntry 22 }
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--
-- The Interface Stack Group
--
-- Implementation of this group is mandatory for all systems
ifStackTable OBJECT-TYPE
SYNTAX SEQUENCE OF IfStackEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The table containing information on the
relationships between the multiple sub-layers of
network interfaces. In particular, it contains
information on which sub-layers run 'on top of'
which other sub-layers. Each sub-layer
corresponds to a conceptual row in the ifTable."
::= { ifMIBObjects 1 }
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
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"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-write
STATUS current
DESCRIPTION
"The status of the relationship between two sub-
layers.
Changing the value of this object from "active" to
"notInService" or "destroy" will likely have
consequences up and down the interface stack.
Thus, write access to this object is likely to be
inappropriate for some types of interfaces, and
many implementations will choose not to support
write-access for any type of interface."
::= { ifStackEntry 3 }
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-- conformance information
ifConformance OBJECT IDENTIFIER ::= { ifMIB 2 }
ifGroups OBJECT IDENTIFIER ::= { ifConformance 1 }
ifCompliances OBJECT IDENTIFIER ::= { ifConformance 2 }
-- compliance statements
ifCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMPv2 entities
which have network interfaces."
MODULE -- this module
MANDATORY-GROUPS { ifGeneralGroup, ifStackGroup }
GROUP ifCharacterGroup
DESCRIPTION
"This group is mandatory only for those network
interfaces which are character-oriented or
packet-oriented."
GROUP ifPacketGroup
DESCRIPTION
"This group is mandatory only for those network
interfaces which are packet-oriented."
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)."
::= { ifCompliances 1 }
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-- units of conformance
ifGeneralGroup OBJECT-GROUP
OBJECTS { ifDescr, ifType, ifSpeed, ifPhysAddress,
ifAdminStatus, ifOperStatus, ifLastChange,
ifSpecific }
STATUS current
DESCRIPTION
"A collection of objects providing information
applicable to all network interfaces."
::= { ifGroups 1 }
ifCharacterGroup OBJECT-GROUP
OBJECTS { ifInOctets, ifOutOctets }
STATUS current
DESCRIPTION
"A collection of objects providing information
specific to packet-oriented or character-oriented
network interfaces."
::= { ifGroups 2 }
ifPacketGroup OBJECT-GROUP
OBJECTS { ifMtu, ifInUcastPkts, ifInNUcastPkts,
ifInDiscards, ifInErrors, ifInUnknownProtos,
ifOutUcastPkts, ifOutNUcastPkts, ifOutDiscards,
ifOutErrors, ifOutQLen }
STATUS current
DESCRIPTION
"A collection of objects providing information
specific to packet-oriented network interfaces."
::= { ifGroups 3 }
ifStackGroup OBJECT-GROUP
OBJECTS { ifStackStatus }
STATUS current
DESCRIPTION
"A collection of objects providing information on
the layering of MIB-II interfaces."
::= { ifGroups 4 }
END
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5. Acknowledgements
The proposals in this memo are the result of conversations and
discussions with many people, including at least the
following: Fred Baker, Ted Brunner, Chuck Davin, Jeremy
Greene, Marshall Rose, Kaj Tesink, and Dean Throop. However,
it does not necessarily represent any consensus among the
above-mentioned.
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6. References
[1] M.T. Rose and K. McCloghrie, Structure and Identification
of Management Information for TCP/IP-based internets,
Request for Comments 1155. (May, 1990).
[2] M. Rose and K. McCloghrie, Editors, Concise MIB
Definitions, RFC 1212, March 1991.
[3] K. McCloghrie and M.T. Rose, Management Information Base
for Network Management of TCP/IP-based internets - MIB-2,
Request for Comments 1213. (March, 1991).
[4] J.D. Case, M.S. Fedor, M.L. Schoffstall, and J.R. Davin,
Simple Network Management Protocol, Request for Comments
1157. (May, 1990).
[5] International Organization for Standardization,
Information processing systems - Open Systems
Interconnection - Specification of Abstract Syntax
Notation One (ASN.1), International Standard 8824,
(December, 1987).
[6] J. Postel, Internet Protocol, RFC791, September 1981.
[7] K. McCloghrie, Extensions to the Generic-Interface MIB,
RFC1229, May 1991.
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7. Security Considerations
Security issues are not discussed in this memo.
8. Authors' Address
Keith McCloghrie
Hughes LAN Systems
1225 Charleston Rd,
Mountain View, Ca 94043
415-966-7934
kzm@hls.com
Frank Kastenholz
FTP Software
2 High Street
North Andover, Mass. USA 01845
(508)685-4000
kasten@ftp.com
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Table of Contents
1 Introduction .......................................... 2
2 The SNMPv2 Network Management Framework ............... 3
2.1 Object Definitions .................................. 3
3 Experience with the Interfaces Group .................. 4
3.1 Areas of Clarification/Revision ..................... 4
3.1.1 Interface Numbering ............................... 4
3.1.2 Interface Sub-Layers .............................. 5
3.1.3 Virtual Circuits .................................. 6
3.1.4 Bit and Character Oriented Interfaces ............. 6
3.2 Clarifications/Revisions ............................ 6
3.2.1 Interface Numbering ............................... 7
3.2.2 Interface Sub-Layers .............................. 8
3.2.3 Virtual Circuits .................................. 9
3.2.4 Bit and Character Oriented Interfaces ............. 10
4 Definitions ........................................... 12
5 Acknowledgements ...................................... 25
6 References ............................................ 26
7 Security Considerations ............................... 27
8 Authors' Address ...................................... 27
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