Network Working Group SNMPv2 Working Group

Network Working Group SNMPv2 Working Group
Request for Comments: 1904 J. Case
Obsoletes: 1444 SNMP Research, Inc.
Category: Standards Track K. McCloghrie
Cisco Systems, Inc.
M. Rose
Dover Beach Consulting, Inc.
S. Waldbusser
International Network Services
January 1996

Conformance Statements for Version 2 of the
Simple Network Management Protocol (SNMPv2)

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
1.1 A Note on Terminology ...................................... 3
2. Definitions ................................................. 3
2.1 The OBJECT-GROUP macro ..................................... 3
2.2 The NOTIFICATION-GROUP macro ............................... 4
2.3 The MODULE-COMPLIANCE macro ................................ 5
2.4 The AGENT-CAPABILITIES macro ............................... 7
3. Mapping of the OBJECT-GROUP macro ........................... 9
3.1 Mapping of the OBJECTS clause .............................. 10
3.2 Mapping of the STATUS clause ............................... 10
3.3 Mapping of the DESCRIPTION clause .......................... 10
3.4 Mapping of the REFERENCE clause ............................ 10
3.5 Mapping of the OBJECT-GROUP value .......................... 10
3.6 Usage Example .............................................. 11
4. Mapping of the NOTIFICATION-GROUP macro ..................... 11
4.1 Mapping of the NOTIFICATIONS clause ........................ 11
4.2 Mapping of the STATUS clause ............................... 11
4.3 Mapping of the DESCRIPTION clause .......................... 12
4.4 Mapping of the REFERENCE clause ............................ 12
4.5 Mapping of the NOTIFICATION-GROUP value .................... 12
4.6 Usage Example .............................................. 12
5. Mapping of the MODULE-COMPLIANCE macro ...................... 12
5.1 Mapping of the STATUS clause ............................... 13

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5.2 Mapping of the DESCRIPTION clause .......................... 13
5.3 Mapping of the REFERENCE clause ............................ 13
5.4 Mapping of the MODULE clause ............................... 13
5.4.1 Mapping of the MANDATORY-GROUPS clause ................... 13
5.4.2 Mapping of the GROUP clause .............................. 14
5.4.3 Mapping of the OBJECT clause ............................. 14
5.4.3.1 Mapping of the SYNTAX clause ........................... 14
5.4.3.2 Mapping of the WRITE-SYNTAX clause ..................... 15
5.4.3.3 Mapping of the MIN-ACCESS clause ....................... 15
5.4.4 Mapping of the DESCRIPTION clause ........................ 15
5.5 Mapping of the MODULE-COMPLIANCE value ..................... 15
5.6 Usage Example .............................................. 16
6. Mapping of the AGENT-CAPABILITIES macro ..................... 16
6.1 Mapping of the PRODUCT-RELEASE clause ...................... 17
6.2 Mapping of the STATUS clause ............................... 17
6.3 Mapping of the DESCRIPTION clause .......................... 17
6.4 Mapping of the REFERENCE clause ............................ 17
6.5 Mapping of the SUPPORTS clause ............................. 18
6.5.1 Mapping of the INCLUDES clause ........................... 18
6.5.2 Mapping of the VARIATION clause .......................... 18
6.5.2.1 Mapping of the SYNTAX clause ........................... 18
6.5.2.2 Mapping of the WRITE-SYNTAX clause ..................... 18
6.5.2.3 Mapping of the ACCESS clause ........................... 19
6.5.2.4 Mapping of the CREATION-REQUIRES clause ................ 19
6.5.2.5 Mapping of the DEFVAL clause ........................... 20
6.5.2.6 Mapping of the DESCRIPTION clause ...................... 20
6.6 Mapping of the AGENT-CAPABILITIES value .................... 20
6.7 Usage Example .............................................. 20
7. Extending an Information Module ............................. 22
7.1 Conformance Groups ......................................... 22
7.2 Compliance Definitions ..................................... 22
7.3 Capabilities Definitions ................................... 22
8. Security Considerations ..................................... 23
9. Editor's Address ............................................ 23
10. Acknowledgements ........................................... 23
11. References ................................................. 24

1. Introduction

A management system contains: several (potentially many) nodes, each
with a processing entity, termed an agent, which has access to
management instrumentation; at least one management station; and, a
management protocol, used to convey management information between
the agents and management stations. Operations of the protocol are
carried out under an administrative framework which defines
authentication, authorization, access control, and privacy policies.

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Management stations execute management applications which monitor and
control managed elements. Managed elements are devices such as
hosts, routers, terminal servers, etc., which are monitored and
controlled via access to their management information.

Management information is viewed as a collection of managed objects,
residing in a virtual information store, termed the Management
Information Base (MIB). Collections of related objects are defined
in MIB modules. These modules are written using a subset of OSI's
Abstract Syntax Notation One (ASN.1) [1], termed the Structure of
Management Information (SMI) [2].

It may be useful to define the acceptable lower-bounds of
implementation, along with the actual level of implementation
achieved. It is the purpose of this document to define the notation
used for these purposes.

1.1. A Note on Terminology

For the purpose of exposition, the original Internet-standard Network
Management Framework, as described in RFCs 1155 (STD 16), 1157 (STD
15), and 1212 (STD 16), is termed the SNMP version 1 framework
(SNMPv1). The current framework is termed the SNMP version 2
framework (SNMPv2).

2. Definitions

SNMPv2-CONF DEFINITIONS ::= BEGIN

-- definitions for conformance groups

OBJECT-GROUP MACRO ::=
BEGIN
TYPE NOTATION ::=
ObjectsPart
"STATUS" Status
"DESCRIPTION" Text
ReferPart

VALUE NOTATION ::=
value(VALUE OBJECT IDENTIFIER)

ObjectsPart ::=
"OBJECTS" "{" Objects "}"
Objects ::=
Object
| Objects "," Object
Object ::=

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value(Name ObjectName)

Status ::=
"current"
| "deprecated"
| "obsolete"

ReferPart ::=
"REFERENCE" Text
| empty

-- uses the NVT ASCII character set
Text ::= """" string """"
END

-- more definitions for conformance groups

NOTIFICATION-GROUP MACRO ::=
BEGIN
TYPE NOTATION ::=
NotificationsPart
"STATUS" Status
"DESCRIPTION" Text
ReferPart

VALUE NOTATION ::=
value(VALUE OBJECT IDENTIFIER)

NotificationsPart ::=
"NOTIFICATIONS" "{" Notifications "}"
Notifications ::=
Notification
| Notifications "," Notification
Notification ::=
value(Name NotificationName)

Status ::=
"current"
| "deprecated"
| "obsolete"

ReferPart ::=
"REFERENCE" Text
| empty

-- uses the NVT ASCII character set
Text ::= """" string """"

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END

-- definitions for compliance statements

MODULE-COMPLIANCE MACRO ::=
BEGIN
TYPE NOTATION ::=
"STATUS" Status
"DESCRIPTION" Text
ReferPart
ModulePart

VALUE NOTATION ::=
value(VALUE OBJECT IDENTIFIER)

Status ::=
"current"
| "deprecated"
| "obsolete"

ReferPart ::=
"REFERENCE" Text
| empty

ModulePart ::=
Modules
| empty
Modules ::=
Module
| Modules Module
Module ::=
-- name of module --
"MODULE" ModuleName
MandatoryPart
CompliancePart

ModuleName ::=
modulereference ModuleIdentifier
-- must not be empty unless contained
-- in MIB Module
| empty
ModuleIdentifier ::=
value(ModuleID OBJECT IDENTIFIER)
| empty

MandatoryPart ::=
"MANDATORY-GROUPS" "{" Groups "}"

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| empty

Groups ::=
Group
| Groups "," Group
Group ::=
value(Group OBJECT IDENTIFIER)

CompliancePart ::=
Compliances
| empty

Compliances ::=
Compliance
| Compliances Compliance
Compliance ::=
ComplianceGroup
| Object

ComplianceGroup ::=
"GROUP" value(Name OBJECT IDENTIFIER)
"DESCRIPTION" Text

Object ::=
"OBJECT" value(Name ObjectName)
SyntaxPart
WriteSyntaxPart
AccessPart
"DESCRIPTION" Text

-- must be a refinement for object's SYNTAX clause
SyntaxPart ::=
"SYNTAX" type(SYNTAX)
| empty

-- must be a refinement for object's SYNTAX clause
WriteSyntaxPart ::=
"WRITE-SYNTAX" type(WriteSYNTAX)
| empty

AccessPart ::=
"MIN-ACCESS" Access
| empty
Access ::=
"not-accessible"
| "accessible-for-notify"
| "read-only"
| "read-write"

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| "read-create"

-- uses the NVT ASCII character set
Text ::= """" string """"
END

-- definitions for capabilities statements

AGENT-CAPABILITIES MACRO ::=
BEGIN
TYPE NOTATION ::=
"PRODUCT-RELEASE" Text
"STATUS" Status
"DESCRIPTION" Text
ReferPart
ModulePart

VALUE NOTATION ::=
value(VALUE OBJECT IDENTIFIER)

Status ::=
"current"
| "obsolete"

ReferPart ::=
"REFERENCE" Text
| empty

ModulePart ::=
Modules
| empty
Modules ::=
Module
| Modules Module
Module ::=
-- name of module --
"SUPPORTS" ModuleName
"INCLUDES" "{" Groups "}"
VariationPart

ModuleName ::=
identifier ModuleIdentifier
ModuleIdentifier ::=
value(ModuleID OBJECT IDENTIFIER)
| empty

Groups ::=

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Group
| Groups "," Group
Group ::=
value(Name OBJECT IDENTIFIER)

VariationPart ::=
Variations
| empty
Variations ::=
Variation
| Variations Variation

Variation ::=
ObjectVariation
| NotificationVariation

NotificationVariation ::=
"VARIATION" value(Name NotificationName)
AccessPart
"DESCRIPTION" Text

ObjectVariation ::=
"VARIATION" value(Name ObjectName)
SyntaxPart
WriteSyntaxPart
AccessPart
CreationPart
DefValPart
"DESCRIPTION" Text

-- must be a refinement for object's SYNTAX clause
SyntaxPart ::=
"SYNTAX" type(SYNTAX)
| empty

-- must be a refinement for object's SYNTAX clause
WriteSyntaxPart ::=
"WRITE-SYNTAX" type(WriteSYNTAX)
| empty

AccessPart ::=
"ACCESS" Access
| empty

Access ::=
"not-implemented"
-- only "not-implemented" for notifications
| "accessible-for-notify"

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| "read-only"
| "read-write"
| "read-create"
-- following is for backward-compatibility only
| "write-only"

CreationPart ::=
"CREATION-REQUIRES" "{" Cells "}"
| empty

Cells ::=
Cell
| Cells "," Cell

Cell ::=
value(Cell ObjectName)

DefValPart ::=
"DEFVAL" "{" value(Defval ObjectSyntax) "}"
| empty

-- uses the NVT ASCII character set
Text ::= """" string """"
END

END

3. Mapping of the OBJECT-GROUP macro

For conformance purposes, it is useful to define a collection of
related managed objects. The OBJECT-GROUP macro is used to define
each such collection of related objects. It should be noted that the
expansion of the OBJECT-GROUP macro is something which conceptually
happens during implementation and not during run-time.

To "implement" an object, a SNMPv2 entity acting in an agent role
must return a reasonably accurate value for management protocol
retrieval operations; similarly, if the object is writable, then in
response to a management protocol set operation, a SNMPv2 entity must
accordingly be able to reasonably influence the underlying managed
entity. If a SNMPv2 entity acting in an agent role can not implement
an object, the management protocol provides for the SNMPv2 entity to
return an exception or error, e.g, noSuchObject [4]. Under no
circumstances shall a SNMPv2 entity return a value for objects which
it does not implement -- it must always return the appropriate
exception or error, as described in the protocol specification [4].

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3.1. Mapping of the OBJECTS clause

The OBJECTS clause, which must be present, is used to name each
object contained in the conformance group. Each of the named objects
must be defined in the same information module as the OBJECT-GROUP
macro appears, and must have a MAX-ACCESS clause value of
"accessible-for-notify", "read-only", "read-write", or "read-create".

It is required that every object defined in an information module
with a MAX-ACCESS clause other than "not-accessible" be contained in
at least one object group. This avoids the common error of adding a
new object to an information module and forgetting to add the new
object to a group.

3.2. Mapping of the STATUS clause

The STATUS clause, which must be present, indicates whether this
definition is current or historic.

The values "current", and "obsolete" are self-explanatory. The
"deprecated" value indicates that the definition is obsolete, but
that an implementor may wish to support the group to foster
interoperability with older implementations.

3.3. Mapping of the DESCRIPTION clause

The DESCRIPTION clause, which must be present, contains a textual
definition of that group, along with a description of any relations
to other groups. Note that generic compliance requirements should
not be stated in this clause. However, implementation relationships
between this group and other groups may be defined in this clause.

3.4. Mapping of the REFERENCE clause

The REFERENCE clause, which need not be present, contains a textual
cross-reference to a group defined in some other information module.
This is useful when de-osifying a MIB module produced by some other
organization.

3.5. Mapping of the OBJECT-GROUP value

The value of an invocation of the OBJECT-GROUP macro is the name of
the group, which is an OBJECT IDENTIFIER, an administratively
assigned name.

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3.6. Usage Example

The SNMP Group [3] is described:

snmpGroup OBJECT-GROUP
OBJECTS { snmpInPkts,
snmpInBadVersions,
snmpInASNParseErrs,
snmpBadOperations,
snmpSilentDrops,
snmpProxyDrops,
snmpEnableAuthenTraps }
STATUS current
DESCRIPTION
"A collection of objects providing basic instrumentation and
control of an SNMPv2 entity."
::= { snmpMIBGroups 8 }

According to this invocation, the conformance group named

{ snmpMIBGroups 8 }

contains 7 objects.

4. Mapping of the NOTIFICATION-GROUP macro

For conformance purposes, it is useful to define a collection of
notifications. The NOTIFICATION-GROUP macro serves this purpose. It
should be noted that the expansion of the NOTIFICATION-GROUP macro is
something which conceptually happens during implementation and not
during run-time.

4.1. Mapping of the NOTIFICATIONS clause

The NOTIFICATIONS clause, which must be present, is used to name each
notification contained in the conformance group. Each of the named
notifications must be defined in the same information module as the
NOTIFICATION-GROUP macro appears.

4.2. Mapping of the STATUS clause

The STATUS clause, which must be present, indicates whether this
definition is current or historic.

The values "current", and "obsolete" are self-explanatory. The
"deprecated" value indicates that the definition is obsolete, but
that an implementor may wish to support the group to foster

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interoperability with older implementations.

4.3. Mapping of the DESCRIPTION clause

The DESCRIPTION clause, which must be present, contains a textual
definition of the group, along with a description of any relations to
other groups. Note that generic compliance requirements should not
be stated in this clause. However, implementation relationships
between this group and other groups may be defined in this clause.

4.4. Mapping of the REFERENCE clause

The REFERENCE clause, which need not be present, contains a textual
cross-reference to a group defined in some other information module.
This is useful when de-osifying a MIB module produced by some other
organization.

4.5. Mapping of the NOTIFICATION-GROUP value

The value of an invocation of the NOTIFICATION-GROUP macro is the
name of the group, which is an OBJECT IDENTIFIER, an administratively
assigned name.

4.6. Usage Example

The SNMP Basic Notifications Group [3] is described:

snmpBasicNotificationsGroup NOTIFICATION-GROUP
NOTIFICATIONS { coldStart, authenticationFailure }
STATUS current
DESCRIPTION
"The two notifications which an SNMPv2 entity is required to
implement."
::= { snmpMIBGroups 7 }

According to this invocation, the conformance group named

{ snmpMIBGroups 1 }

contains 2 notifications.

5. Mapping of the MODULE-COMPLIANCE macro

The MODULE-COMPLIANCE macro is used to convey a minimum set of
requirements with respect to implementation of one or more MIB
modules. It should be noted that the expansion of the MODULE-
COMPLIANCE macro is something which conceptually happens during
implementation and not during run-time.

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A requirement on all "standard" MIB modules is that a corresponding
MODULE-COMPLIANCE specification is also defined, either in the same
information module or in a companion information module.

5.1. Mapping of the STATUS clause

The STATUS clause, which must be present, indicates whether this
definition is current or historic.

The values "current", and "obsolete" are self-explanatory. The
"deprecated" value indicates that the specification is obsolete, but
that an implementor may wish to support that object to foster
interoperability with older implementations.

5.2. Mapping of the DESCRIPTION clause

The DESCRIPTION clause, which must be present, contains a textual
definition of this compliance statement and should embody any
information which would otherwise be communicated in any ASN.1
commentary annotations associated with the statement.

5.3. Mapping of the REFERENCE clause

The REFERENCE clause, which need not be present, contains a textual
cross-reference to a compliance statement defined in some other
information module.

5.4. Mapping of the MODULE clause

The MODULE clause, which must be present, is repeatedly used to name
each MIB module for which compliance requirements are being
specified. Each MIB module is named by its module name, and
optionally, by its associated OBJECT IDENTIFIER as well. The module
name can be omitted when the MODULE-COMPLIANCE invocation occurs
inside a MIB module, to refer to the encompassing MIB module.

5.4.1. Mapping of the MANDATORY-GROUPS clause

The MANDATORY-GROUPS clause, which need not be present, names the one
or more object or notification groups within the correspondent MIB
module which are unconditionally mandatory for implementation. If a
SNMPv2 entity acting in an agent role claims compliance to the MIB
module, then it must implement each and every object and notification
within each conformance group listed. That is, if a SNMPv2 entity
returns a noSuchObject exception in response to a management protocol
get operation [4] for any object within any mandatory conformance
group for every MIB view, or if the SNMPv2 entity cannot generate
each notification listed in any conformance group under the

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appropriate circumstances, then that SNMPv2 entity is not a
conformant implementation of the MIB module.

5.4.2. Mapping of the GROUP clause

The GROUP clause, which need not be present, is repeatedly used to
name each object and notification group which is conditionally
mandatory or unconditionally optional for compliance to the MIB
module. A group named in a GROUP clause must be absent from the
correspondent MANDATORY-GROUPS clause.

Conditionally mandatory groups include those which are mandatory only
if a particular protocol is implemented, or only if another group is
implemented. A GROUP clause's DESCRIPTION specifies the conditions
under which the group is conditionally mandatory.

A group which is named in neither a MANDATORY-GROUPS clause nor a
GROUP clause, is unconditionally optional for compliance to the MIB
module.

5.4.3. Mapping of the OBJECT clause

The OBJECT clause, which need not be present, is repeatedly used to
name each MIB object for which compliance has a refined requirement
with respect to the MIB module definition. The MIB object must be
present in one of the conformance groups named in the correspondent
MANDATORY-GROUPS clause or GROUP clauses.

By definition, each object specified in an OBJECT clause follows a
MODULE clause which names the information module in which that object
is defined. Therefore, the use of an IMPORTS statement, to specify
from where such objects are imported, is redundant and is not
required in an information module.

5.4.3.1. Mapping of the SYNTAX clause

The SYNTAX clause, which need not be present, is used to provide a
refined SYNTAX for the object named in the correspondent OBJECT
clause. Note that if this clause and a WRITE-SYNTAX clause are both
present, then this clause only applies when instances of the object
named in the correspondent OBJECT clause are read.

Consult Section 9 of [2] for more information on refined syntax.

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5.4.3.2. Mapping of the WRITE-SYNTAX clause

The WRITE-SYNTAX clause, which need not be present, is used to
provide a refined SYNTAX for the object named in the correspondent
OBJECT clause when instances of that object are written.

Consult Section 9 of [2] for more information on refined syntax.

5.4.3.3. Mapping of the MIN-ACCESS clause

The MIN-ACCESS clause, which need not be present, is used to define
the minimal level of access for the object named in the correspondent
OBJECT clause. If this clause is absent, the minimal level of access
is the same as the maximal level specified in the correspondent
invocation of the OBJECT-TYPE macro. If present, this clause must
not specify a greater level of access than is specified in the
correspondent invocation of the OBJECT-TYPE macro.

The level of access for certain types of objects is fixed according
to their syntax definition. These types include: conceptual tables
and rows, auxiliary objects, and objects with the syntax of
Counter32, Counter64 (and possibly, certain types of textual
conventions). A MIN-ACCESS clause should not be present for such
objects.

An implementation is compliant if the level of access it provides is
greater or equal to the minimal level in the MODULE-COMPLIANCE macro
and less or equal to the maximal level in the OBJECT-TYPE macro.

5.4.4. Mapping of the DESCRIPTION clause

The DESCRIPTION clause must be present for each use of the GROUP or
OBJECT clause. For an OBJECT clause, it contains a textual
description of the refined compliance requirement. For a GROUP
clause, it contains a textual description of the conditions under
which the group is conditionally mandatory or unconditionally
optional.

5.5. Mapping of the MODULE-COMPLIANCE value

The value of an invocation of the MODULE-COMPLIANCE macro is an
OBJECT IDENTIFIER. As such, this value may be authoritatively used
when referring to the compliance statement embodied by that
invocation of the macro.

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5.6. Usage Example

The compliance statement contained in the (hypothetical) XYZv2-MIB
might be:

xyzMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for XYZv2 entities which implement
the XYZv2 MIB."
MODULE -- compliance to the containing MIB module
MANDATORY-GROUPS { xyzSystemGroup,
xyzStatsGroup, xyzTrapGroup,
xyzSetGroup,
xyzBasicNotificationsGroup }

GROUP xyzV1Group
DESCRIPTION
"The xyzV1 group is mandatory only for those
XYZv2 entities which also implement XYZv1."
::= { xyzMIBCompliances 1 }

According to this invocation, to claim alignment with the compliance
statement named

{ xyzMIBCompliances 1 }

a system must implement the XYZv2-MIB's xyzSystemGroup,
xyzStatsGroup, xyzTrapGroup, and xyzSetGroup object conformance
groups, as well as the xyzBasicNotificationsGroup notifications
group. Furthermore, if the XYZv2 entity also implements XYZv1, then
it must also support the XYZv1Group group, if compliance is to be
claimed.

6. Mapping of the AGENT-CAPABILITIES macro

The AGENT-CAPABILITIES macro is used to convey a set of capabilities
present in a SNMPv2 entity acting in an agent role. It should be
noted that the expansion of the AGENT-CAPABILITIES macro is something
which conceptually happens during implementation and not during run-
time.

When a MIB module is written, it is divided into units of conformance
termed groups. If a SNMPv2 entity acting in an agent role claims to
implement a group, then it must implement each and every object
within that group. Of course, for whatever reason, a SNMPv2 entity
might implement only a subset of the groups within a MIB module. In
addition, the definition of some MIB objects leave some aspects of

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the definition to the discretion of an implementor.

Practical experience has demonstrated a need for concisely describing
the capabilities of an agent with respect to one or more MIB modules.
The AGENT-CAPABILITIES macro allows an agent implementor to describe
the precise level of support which an agent claims in regards to a
MIB group, and to bind that description to the value of an instance
of sysORID [3]. In particular, some objects may have restricted or
augmented syntax or access-levels.

If the AGENT-CAPABILITIES invocation is given to a management-station
implementor, then that implementor can build management applications
which optimize themselves when communicating with a particular agent.
For example, the management-station can maintain a database of these
invocations. When a management-station interacts with an agent, it
retrieves from the agent the values of all instances of sysORID [3].
Based on this, it consults the database to locate each entry matching
one of the retrieved values of sysORID. Using the located entries,
the management application can now optimize its behavior accordingly.

Note that the AGENT-CAPABILITIES macro specifies refinements or
variations with respect to OBJECT-TYPE and NOTIFICATION-TYPE macros
in MIB modules, NOT with respect to MODULE-COMPLIANCE macros in
compliance statements.

6.1. Mapping of the PRODUCT-RELEASE clause

The PRODUCT-RELEASE clause, which must be present, contains a textual
description of the product release which includes this set of
capabilities.

6.2. Mapping of the STATUS clause

The STATUS clause, which must be present, indicates whether this
definition is current ("current") or historic ("obsolete").

6.3. Mapping of the DESCRIPTION clause

The DESCRIPTION clause, which must be present, contains a textual
description of this set of capabilities.

6.4. Mapping of the REFERENCE clause

The REFERENCE clause, which need not be present, contains a textual
cross-reference to a capability statement defined in some other
information module.

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6.5. Mapping of the SUPPORTS clause

The SUPPORTS clause, which need not be present, is repeatedly used to
name each MIB module for which the agent claims a complete or partial
implementation. Each MIB module is named by its module name, and
optionally, by its associated OBJECT IDENTIFIER as well.

6.5.1. Mapping of the INCLUDES clause

The INCLUDES clause, which must be present for each use of the
SUPPORTS clause, is used to name each MIB group associated with the
SUPPORTS clause, which the agent claims to implement.

6.5.2. Mapping of the VARIATION clause

The VARIATION clause, which need not be present, is repeatedly used
to name each object or notification which the agent implements in
some variant or refined fashion with respect to the correspondent
invocation of the OBJECT-TYPE or NOTIFICATION-TYPE macro.

Note that the variation concept is meant for generic implementation
restrictions, e.g., if the variation for an object depends on the
values of other objects, then this should be noted in the appropriate
DESCRIPTION clause.

By definition, each object specified in a VARIATION clause follows a
SUPPORTS clause which names the information module in which that
object is defined. Therefore, the use of an IMPORTS statement, to
specify from where such objects are imported, is redundant and is not
required in an information module.

6.5.2.1. Mapping of the SYNTAX clause

The SYNTAX clause, which need not be present, is used to provide a
refined SYNTAX for the object named in the correspondent VARIATION
clause. Note that if this clause and a WRITE-SYNTAX clause are both
present, then this clause only applies when instances of the object
named in the correspondent VARIATION clause are read.

Consult Section 9 of [2] for more information on refined syntax.

6.5.2.2. Mapping of the WRITE-SYNTAX clause

The WRITE-SYNTAX clause, which need not be present, is used to
provide a refined SYNTAX for the object named in the correspondent
VARIATION clause when instances of that object are written.

Consult Section 9 of [2] for more information on refined syntax.

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6.5.2.3. Mapping of the ACCESS clause

The ACCESS clause, which need not be present, is used to indicate the
agent provides less than the maximal level of access to the object or
notification named in the correspondent VARIATION clause.

The only value applicable to notifications is "not-implemented".

The value "not-implemented" indicates the agent does not implement
the object or notification, and in the ordering of possible values is
equivalent to "not-accessible".

The value "write-only" is provided solely for backward compatibility,
and shall not be used for newly-defined object types. In the
ordering of possible values, "write-only" is less than "not-
accessible".

6.5.2.4. Mapping of the CREATION-REQUIRES clause

The CREATION-REQUIRES clause, which need not be present, is used to
name the columnar objects of a conceptual row to which values must be
explicitly assigned, by a management protocol set operation, before
the agent will allow the instance of the status column of that row to
be set to `active'. (Consult the definition of RowStatus [5].)

If the conceptual row does not have a status column (i.e., the
objects corresponding to the conceptual table were defined using the
mechanisms in [6,7]), then the CREATION-REQUIRES clause, which need
not be present, is used to name the columnar objects of a conceptual
row to which values must be explicitly assigned, by a management
protocol set operation, before the agent will create new instances of
objects in that row.

This clause must not present unless the object named in the
correspondent VARIATION clause is a conceptual row, i.e., has a
syntax which resolves to a SEQUENCE containing columnar objects. The
objects named in the value of this clause usually will refer to
columnar objects in that row. However, objects unrelated to the
conceptual row may also be specified.

All objects which are named in the CREATION-REQUIRES clause for a
conceptual row, and which are columnar objects of that row, must have
an access level of "read-create".

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6.5.2.5. Mapping of the DEFVAL clause

The DEFVAL clause, which need not be present, is used to provide a
refined DEFVAL value for the object named in the correspondent
VARIATION clause. The semantics of this value are identical to those
of the OBJECT-TYPE macro's DEFVAL clause.

6.5.2.6. Mapping of the DESCRIPTION clause

The DESCRIPTION clause, which must be present for each use of the
VARIATION clause, contains a textual description of the variant or
refined implementation of the object or notification.

6.6. Mapping of the AGENT-CAPABILITIES value

The value of an invocation of the AGENT-CAPABILITIES macro is an
OBJECT IDENTIFIER, which names the value of sysORID [3] for which
this capabilities statement is valid.

6.7. Usage Example

Consider how a capabilities statement for an agent might be
described:

exampleAgent AGENT-CAPABILITIES
PRODUCT-RELEASE "ACME Agent release 1.1 for 4BSD"
STATUS current
DESCRIPTION "ACME agent for 4BSD"

SUPPORTS SNMPv2-MIB
INCLUDES { systemGroup, snmpGroup, snmpSetGroup,
snmpBasicNotificationsGroup }

VARIATION coldStart
DESCRIPTION "A coldStart trap is generated on all
reboots."

SUPPORTS IF-MIB
INCLUDES { ifGeneralGroup, ifPacketGroup }

VARIATION ifAdminStatus
SYNTAX INTEGER { up(1), down(2) }
DESCRIPTION "Unable to set test mode on 4BSD"

VARIATION ifOperStatus
SYNTAX INTEGER { up(1), down(2) }
DESCRIPTION "Information limited on 4BSD"

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SUPPORTS IP-MIB
INCLUDES { ipGroup, icmpGroup }

VARIATION ipDefaultTTL
SYNTAX INTEGER (255..255)
DESCRIPTION "Hard-wired on 4BSD"

VARIATION ipInAddrErrors
ACCESS not-implemented
DESCRIPTION "Information not available on 4BSD"

VARIATION ipNetToMediaEntry
CREATION-REQUIRES { ipNetToMediaPhysAddress }
DESCRIPTION "Address mappings on 4BSD require
both protocol and media addresses"

SUPPORTS TCP-MIB
INCLUDES { tcpGroup }
VARIATION tcpConnState
ACCESS read-only
DESCRIPTION "Unable to set this on 4BSD"

SUPPORTS UDP-MIB
INCLUDES { udpGroup }

SUPPORTS EVAL-MIB
INCLUDES { functionsGroup, expressionsGroup }
VARIATION exprEntry
CREATION-REQUIRES { evalString }
DESCRIPTION "Conceptual row creation supported"

::= { acmeAgents 1 }

According to this invocation, an agent with a sysORID value of

{ acmeAgents 1 }

supports six MIB modules.

From SNMPv2-MIB, five conformance groups are supported.

From IF-MIB, the ifGeneralGroup and ifPacketGroup groups are
supported. However, the objects ifAdminStatus and ifOperStatus have
a restricted syntax.

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From IP-MIB, all objects in the ipGroup and icmpGroup are supported
except ipInAddrErrors, while ipDefaultTTL has a restricted range, and
when creating a new instance in the ipNetToMediaTable, the set-
request must create an instance of atPhysAddress.

From TCP-MIB, the tcpGroup is supported except that tcpConnState is
available only for reading.

From UDP-MIB, the udpGroup is fully supported.

From the EVAL-MIB, all the objects contained in the functionsGroup
and expressionsGroup conformance groups are supported, without
variation. In addition, creation of new instances in the expr table
is supported.

7. Extending an Information Module

As experience is gained with a published information module, it may
be desirable to revise that information module.

Section 10 of [2] defines the rules for extending an information
module. The remainder of this section defines how conformance
groups, compliance statements, and capabilities statements may be
extended.

7.1. Conformance Groups

If any non-editorial change is made to any clause of an object group
then the OBJECT IDENTIFIER value associated with that object group
must also be changed, along with its associated descriptor.

7.2. Compliance Definitions

If any non-editorial change is made to any clause of a compliance
definition, then the OBJECT IDENTIFIER value associated with that
compliance definition must also be changed, along with its associated
descriptor.

7.3. Capabilities Definitions

If any non-editorial change is made to any clause of a capabilities
definition, then the OBJECT IDENTIFIER value associated with that
capabilities definition must also be changed, along with its
associated descriptor.

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8. Security Considerations

Security issues are not discussed in this memo.

9. Editor's Address

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

Phone: +1 408 526 5260
EMail: [email protected]

10. Acknowledgements

This document is the result of significant work by the four major
contributors:

Jeffrey D. Case (SNMP Research, [email protected])
Keith McCloghrie (Cisco Systems, [email protected])
Marshall T. Rose (Dover Beach Consulting, [email protected])
Steven Waldbusser (International Network Services, [email protected])

In addition, the contributions of the SNMPv2 Working Group are
acknowledged. In particular, a special thanks is extended for the
contributions of:

Alexander I. Alten (Novell)
Dave Arneson (Cabletron)
Uri Blumenthal (IBM)
Doug Book (Chipcom)
Kim Curran (Bell-Northern Research)
Jim Galvin (Trusted Information Systems)
Maria Greene (Ascom Timeplex)
Iain Hanson (Digital)
Dave Harrington (Cabletron)
Nguyen Hien (IBM)
Jeff Johnson (Cisco Systems)
Michael Kornegay (Object Quest)
Deirdre Kostick (AT&T Bell Labs)
David Levi (SNMP Research)
Daniel Mahoney (Cabletron)
Bob Natale (ACE*COMM)
Brian O'Keefe (Hewlett Packard)
Andrew Pearson (SNMP Research)
Dave Perkins (Peer Networks)

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RFC 1904 Conformance Statements for SNMPv2 January 1996

Randy Presuhn (Peer Networks)
Aleksey Romanov (Quality Quorum)
Shawn Routhier (Epilogue)
Jon Saperia (BGS Systems)
Bob Stewart (Cisco Systems, [email protected]), chair
Kaj Tesink (Bellcore)
Glenn Waters (Bell-Northern Research)
Bert Wijnen (IBM)

11. References

[1] Information processing systems - Open Systems Interconnection -
Specification of Abstract Syntax Notation One (ASN.1),
International Organization for Standardization. International
Standard 8824, (December, 1987).

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

[3] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
S. Waldbusser, "Management Information Base for Version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC 1907,
January 1996.

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

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

[6] Rose, M., and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based internets", STD 16, RFC
1155, May 1990.

[7] Rose, M., and K. McCloghrie, "Concise MIB Definitions", STD 16,
RFC 1212, March 1991.

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