path: root/doc/rfc/rfc1444.txt

          Network Working Group                                  J. Case
          Request for Comments: 1444                 SNMP Research, Inc.
                                                           K. McCloghrie
                                                      Hughes LAN Systems
                                                                 M. Rose
                                            Dover Beach Consulting, Inc.
                                                           S. Waldbusser
                                              Carnegie Mellon University
                                                              April 1993


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


          Status of this Memo

          This RFC specifes an IAB standards track protocol for the
          Internet community, and requests discussion and suggestions
          for improvements.  Please refer to the current edition of the
          "IAB Official Protocol Standards" 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 ...............................    2
          2 Definitions ...........................................    3
          3.1 The OBJECT-GROUP macro ..............................    3
          3.2 The MODULE-COMPLIANCE macro .........................    4
          3.3 The AGENT-CAPABILITIES macro ........................    7
          3 Mapping of the OBJECT-GROUP macro .....................   10
          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 .....................   11
          3.5 Mapping of the OBJECT-GROUP value ...................   11
          3.6 Usage Example .......................................   12
          4 Mapping of the MODULE-COMPLIANCE macro ................   13
          4.1 Mapping of the STATUS clause ........................   13
          4.2 Mapping of the DESCRIPTION clause ...................   13
          4.3 Mapping of the REFERENCE clause .....................   13
          4.4 Mapping of the MODULE clause ........................   13
          4.4.1 Mapping of the MANDATORY-GROUPS clause ............   14
          4.4.2 Mapping of the GROUP clause .......................   14
          4.4.3 Mapping of the OBJECT clause ......................   14




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          4.4.3.1 Mapping of the SYNTAX clause ....................   15
          4.4.3.2 Mapping of the WRITE-SYNTAX clause ..............   15
          4.4.3.3 Mapping of the MIN-ACCESS clause ................   15
          4.4.3.4 Mapping of the DESCRIPTION clause ...............   16
          4.5 Mapping of the MODULE-COMPLIANCE value ..............   16
          4.6 Usage Example .......................................   17
          5 Mapping of the AGENT-CAPABILITIES macro ...............   19
          5.1 Mapping of the PRODUCT-RELEASE clause ...............   20
          5.2 Mapping of the STATUS clause ........................   20
          5.3 Mapping of the DESCRIPTION clause ...................   20
          5.4 Mapping of the REFERENCE clause .....................   20
          5.5 Mapping of the SUPPORTS clause ......................   20
          5.5.1 Mapping of the INCLUDES clause ....................   21
          5.5.2 Mapping of the VARIATION clause ...................   21
          5.5.2.1 Mapping of the SYNTAX clause ....................   21
          5.5.2.2 Mapping of the WRITE-SYNTAX clause ..............   21
          5.5.2.3 Mapping of the ACCESS clause ....................   22
          5.5.2.4 Mapping of the CREATION-REQUIRES clause .........   22
          5.5.2.5 Mapping of the DEFVAL clause ....................   23
          5.5.2.6 Mapping of the DESCRIPTION clause ...............   23
          5.6 Mapping of the AGENT-CAPABILITIES value .............   23
          5.7 Usage Example .......................................   24
          6 Extending an Information Module .......................   26
          6.1 Conformance Groups ..................................   26
          6.2 Compliance Definitions ..............................   26
          6.3 Capabilities Definitions ............................   26
          7 Acknowledgements ......................................   27
          8 References ............................................   31
          9 Security Considerations ...............................   32
          10 Authors' Addresses ...................................   32




















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          1.  Introduction

          A network 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 both authentication and
          authorization policies.

          Network management stations execute management applications
          which monitor and control network elements.  Network elements
          are devices such as hosts, routers, terminal servers, etc.,
          which are monitored and controlled through 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, 1157,
          and 1212, is termed the SNMP version 1 framework (SNMPv1).
          The current framework is termed the SNMP version 2 framework
          (SNMPv2).













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          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 ::=
                            value(Name ObjectName)

              Status ::=
                            "current"
                          | "obsolete"

              ReferPart ::=
                            "REFERENCE" Text
                          | empty

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














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          -- definitions for compliance statements

          MODULE-COMPLIANCE MACRO ::=
          BEGIN
              TYPE NOTATION ::=
                            "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 --
                            "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 "}"
                          | empty





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              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"
                          | "read-only"
                          | "read-write"





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                          | "read-create"

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













































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          -- definitions for capabilities statements

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

              VALUE NOTATION ::=
                            -- agent's sysObjectID [3] or snmpORID [4]
                            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 ::=
                            Group
                          | Groups "," Group
              Group ::=





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                            value(Name OBJECT IDENTIFIER)

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

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

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

              Cells ::=





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                            Cell
                          | Cells "," Cell

              Cell ::=
                            value(Cell ObjectName)

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

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


          END


































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          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 [6].  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 [6].


          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 "read-only", "read-write", or "read-create".


          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.


          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





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          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

          Consider how the system group from MIB-II [3] might be
          described:

          systemGroup OBJECT-GROUP
              OBJECTS     { sysDescr, sysObjectID, sysUpTime,
                            sysContact, sysName, sysLocation,
                            sysServices }
              STATUS  current
              DESCRIPTION
                      "The system group defines objects which are common
                      to all managed systems."
              ::= { mibIIGroups 1 }

          According to this invocation, the conformance group named

               { mibIIGroups 1 }

          contains 7 objects.






























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          4.  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.

          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.


          4.1.  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 that object is obsolete,
          but that an implementor may wish to support that object to
          foster interoperability with older implementations.


          4.2.  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.


          4.3.  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.


          4.4.  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





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          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.


          4.4.1.  Mapping of the MANDATORY-GROUPS clause

          The MANDATORY-GROUPS clause, which need not be present, names
          the one or more 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
          within each conformance group listed.  That is, if a SNMPv2
          entity returns a noSuchObject exception in response to a
          management protocol get operation [5] for any object within
          any mandatory conformance group for every MIB view, then that
          SNMPv2 entity is not a conformant implementation of the MIB
          module.


          4.4.2.  Mapping of the GROUP clause

          The GROUP clause which need not be present, is repeatedly used
          to name each MIB group which is conditionally mandatory or
          unconditionally optional for compliance to the MIB module.  A
          MIB 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 MIB group which is named in neither a MANDATORY-GROUPS
          clause nor a GROUP clause, is unconditionally optional for
          compliance to the MIB module.


          4.4.3.  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





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          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.


          4.4.3.1.  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 10 of [2] for more information on refined
          syntax.


          4.4.3.2.  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 10 of [2] for more information on refined
          syntax.


          4.4.3.3.  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 are:
          conceptual tables and rows, auxiliary objects, and objects
          with the syntax of Counter32, Counter64, or certain types of





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          textual conventions (e.g., RowStatus [6]).  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.


          4.4.3.4.  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.


          4.5.  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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          4.6.  Usage Example

          Consider how a compliance statement might be included at the
          end of the MIB-II document [3], assuming that conformance
          groups were defined therein:

          mibIICompliances
                         OBJECT IDENTIFIER ::= { mibIIConformance 1 }
          mibIIGroups    OBJECT IDENTIFIER ::= { mibIIConformance 2 }

          mibIICompliance MODULE-COMPLIANCE
              STATUS  current
              DESCRIPTION
                      "The compliance statement for SNMPv2 entities
                      residing on systems which implement the Internet
                      suite of protocols."
              MODULE  -- compliance to the containing MIB module
                  MANDATORY-GROUPS   { systemGroup, snmpGroup }

                  GROUP       interfacesGroup
                  DESCRIPTION
                      "The interfaces group is mandatory for systems
                      with network interfaces."

                  GROUP       ipGroup
                  DESCRIPTION
                      "The ip group is mandatory for systems which
                      implement IP."

                  GROUP       icmpGroup
                  DESCRIPTION
                      "The icmp group is mandatory for systems which
                      implement ICMP."

                  GROUP       tcpGroup
                  DESCRIPTION
                      "The tcp group is mandatory for systems which
                      implement TCP."
                      OBJECT      tcpConnState
                      MIN-ACCESS  read-only
                      DESCRIPTION
                          "A compliant system need not allow
                           write-access to this object."

                  GROUP       udpGroup





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                  DESCRIPTION
                      "The udp group is mandatory for systems which
                      implement UDP."

                  GROUP       egpGroup
                  DESCRIPTION
                      "The egp group is mandatory for systems which
                      implement EGP."

          ::= { mibIICompliances 1 }

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

               { mibIICompliances 1 }

          a system must implement RFC1213's systemGroup and snmpGroup
          conformance groups.  If the system implements any network
          interfaces, then RFC1213's interfacesGroup conformance group
          must be implemented.  Further, if the system implements any of
          the IP, ICMP, TCP, UDP, or EGP protocols, then the
          correspondent conformance group in RFC1213 must be
          implemented, if compliance is to be claimed.  Finally,
          although RFC1213 specifies that it makes "protocol sense" for
          the tcpConnState object to be writable, this specification
          allows the system to permit only read-only access and still
          claim compliance.























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          5.  Mapping of the AGENT-CAPABILITIES macro

          The AGENT-CAPABILITIES macro is used to convey the
          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 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 sysObjectID [3] associated
          with the agent, or to the value of an instance of the snmpORID
          object in the snmpORTable [4].  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 the agent's sysObjectID [3].  Based on
          this, it consults the database.  If an entry is found, then
          the management application can optimize its behavior
          accordingly.

          Note that this binding to sysObjectID may not always suffice
          to define all MIB objects to which an agent can provide
          access.  In particular, this situation occurs where the agent
          dynamically learns of the objects it supports.  In these
          cases, the snmpORID column of snmpORTable [4] contains
          information which should be used in addition to sysObjectID.






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


          5.1.  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
          agent.


          5.2.  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 that object is obsolete,
          but that an implementor may wish to support that object to
          foster interoperability with older implementations.


          5.3.  Mapping of the DESCRIPTION clause

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


          5.4.  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.


          5.5.  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.






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          5.5.1.  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 SUPPORT clause, which the agent claims to implement.


          5.5.2.  Mapping of the VARIATION clause

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


          5.5.2.1.  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 10 of [2] for more information on refined
          syntax.


          5.5.2.2.  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 10 of [2] for more information on refined
          syntax.








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          5.5.2.3.  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 named in the correspondent VARIATION
          clause.

          The value "not-implemented" indicates the agent does not
          implement the object, 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".


          5.5.2.4.  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 [6].)

          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 [7,8]), 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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          5.5.2.5.  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.


          5.5.2.6.  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.


          5.6.  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 sysObjectID [3]
          or snmpORID [4] for which this capabilities statement is
          valid.




























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          5.7.  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             RFC1213-MIB
                  INCLUDES         { systemGroup, interfacesGroup,
                                     atGroup, ipGroup, icmpGroup,
                                     tcpGroup, udpGroup, snmpGroup }

                  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"

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

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

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

                  VARIATION        ipRouteType
                      SYNTAX       INTEGER { direct(3), indirect(4) }
                      WRITE-SYNTAX INTEGER { invalid(2), direct(3),
                                             indirect(4) }
                      DESCRIPTION  "Information limited on 4BSD"

                  VARIATION        tcpConnState
                      ACCESS       read-only
                      DESCRIPTION  "Unable to set this on 4BSD"





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              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 sysObjectID (or
          snmpORID) value of

               { acmeAgents 1 }

          supports two MIB modules.

          From MIB-II, all conformance groups except the egpGroup
          conformance group are supported.  However, the object
          ipInAddrErrors is not implemented, whilst the objects

               ifAdminStatus
               ifOperStatus
               ipDefaultTTL
               ipRouteType

          have a restricted syntax, and the object

               tcpConnState

          is available only for reading.  Note that in the case of the
          object ipRouteType the set of values which may be read is
          different than the set of values which may be written.
          Finally, when creating a new instance in the atTable, the
          set-request must create an instance of atPhysAddress.

          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.











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          6.  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.


          6.1.  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.


          6.2.  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.


          6.3.  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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          7.  Acknowledgements

          The section on compliance statements is based, in part, on a
          conversation with James R. Davin in December, 1990.

          The section on capabilities statements is based, in part, on
          RFC 1303.

          Finally, the comments of the SNMP version 2 working group are
          gratefully acknowledged:

               Beth Adams, Network Management Forum
               Steve Alexander, INTERACTIVE Systems Corporation
               David Arneson, Cabletron Systems
               Toshiya Asaba
               Fred Baker, ACC
               Jim Barnes, Xylogics, Inc.
               Brian Bataille
               Andy Bierman, SynOptics Communications, Inc.
               Uri Blumenthal, IBM Corporation
               Fred Bohle, Interlink
               Jack Brown
               Theodore Brunner, Bellcore
               Stephen F. Bush, GE Information Services
               Jeffrey D. Case, University of Tennessee, Knoxville
               John Chang, IBM Corporation
               Szusin Chen, Sun Microsystems
               Robert Ching
               Chris Chiotasso, Ungermann-Bass
               Bobby A. Clay, NASA/Boeing
               John Cooke, Chipcom
               Tracy Cox, Bellcore
               Juan Cruz, Datability, Inc.
               David Cullerot, Cabletron Systems
               Cathy Cunningham, Microcom
               James R. (Chuck) Davin, Bellcore
               Michael Davis, Clearpoint
               Mike Davison, FiberCom
               Cynthia DellaTorre, MITRE
               Taso N. Devetzis, Bellcore
               Manual Diaz, DAVID Systems, Inc.
               Jon Dreyer, Sun Microsystems
               David Engel, Optical Data Systems
               Mike Erlinger, Lexcel
               Roger Fajman, NIH





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               Daniel Fauvarque, Sun Microsystems
               Karen Frisa, CMU
               Shari Galitzer, MITRE
               Shawn Gallagher, Digital Equipment Corporation
               Richard Graveman, Bellcore
               Maria Greene, Xyplex, Inc.
               Michel Guittet, Apple
               Robert Gutierrez, NASA
               Bill Hagerty, Cabletron Systems
               Gary W. Haney, Martin Marietta Energy Systems
               Patrick Hanil, Nokia Telecommunications
               Matt Hecht, SNMP Research, Inc.
               Edward A. Heiner, Jr., Synernetics Inc.
               Susan E. Hicks, Martin Marietta Energy Systems
               Geral Holzhauer, Apple
               John Hopprich, DAVID Systems, Inc.
               Jeff Hughes, Hewlett-Packard
               Robin Iddon, Axon Networks, Inc.
               David Itusak
               Kevin M. Jackson, Concord Communications, Inc.
               Ole J. Jacobsen, Interop Company
               Ronald Jacoby, Silicon Graphics, Inc.
               Satish Joshi, SynOptics Communications, Inc.
               Frank Kastenholz, FTP Software
               Mark Kepke, Hewlett-Packard
               Ken Key, SNMP Research, Inc.
               Zbiginew Kielczewski, Eicon
               Jongyeoi Kim
               Andrew Knutsen, The Santa Cruz Operation
               Michael L. Kornegay, VisiSoft
               Deirdre C. Kostik, Bellcore
               Cheryl Krupczak, Georgia Tech
               Mark S. Lewis, Telebit
               David Lin
               David Lindemulder, AT&T/NCR
               Ben Lisowski, Sprint
               David Liu, Bell-Northern Research
               John Lunny, The Wollongong Group
               Robert C. Lushbaugh Martin, Marietta Energy Systems
               Michael Luufer, BBN
               Carl Madison, Star-Tek, Inc.
               Keith McCloghrie, Hughes LAN Systems
               Evan McGinnis, 3Com Corporation
               Bill McKenzie, IBM Corporation
               Donna McMaster, SynOptics Communications, Inc.





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               John Medicke, IBM Corporation
               Doug Miller, Telebit
               Dave Minnich, FiberCom
               Mohammad Mirhakkak, MITRE
               Rohit Mital, Protools
               George Mouradian, AT&T Bell Labs
               Patrick Mullaney, Cabletron Systems
               Dan Myers, 3Com Corporation
               Rina Nathaniel, Rad Network Devices Ltd.
               Hien V. Nguyen, Sprint
               Mo Nikain
               Tom Nisbet
               William B. Norton, MERIT
               Steve Onishi, Wellfleet Communications, Inc.
               David T. Perkins, SynOptics Communications, Inc.
               Carl Powell, BBN
               Ilan Raab, SynOptics Communications, Inc.
               Richard Ramons, AT&T
               Venkat D. Rangan, Metric Network Systems, Inc.
               Louise Reingold, Sprint
               Sam Roberts, Farallon Computing, Inc.
               Kary Robertson, Concord Communications, Inc.
               Dan Romascanu, Lannet Data Communications Ltd.
               Marshall T. Rose, Dover Beach Consulting, Inc.
               Shawn A. Routhier, Epilogue Technology Corporation
               Chris Rozman
               Asaf Rubissa, Fibronics
               Jon Saperia, Digital Equipment Corporation
               Michael Sapich
               Mike Scanlon, Interlan
               Sam Schaen, MITRE
               John Seligson, Ultra Network Technologies
               Paul A. Serice, Corporation for Open Systems
               Chris Shaw, Banyan Systems
               Timon Sloane
               Robert Snyder, Cisco Systems
               Joo Young Song
               Roy Spitier, Sprint
               Einar Stefferud, Network Management Associates
               John Stephens, Cayman Systems, Inc.
               Robert L. Stewart, Xyplex, Inc. (chair)
               Kaj Tesink, Bellcore
               Dean Throop, Data General
               Ahmet Tuncay, France Telecom-CNET
               Maurice Turcotte, Racal Datacom





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               Warren Vik, INTERACTIVE Systems Corporation
               Yannis Viniotis
               Steven L. Waldbusser, Carnegie Mellon Universitty
               Timothy M. Walden, ACC
               Alice Wang, Sun Microsystems
               James Watt, Newbridge
               Luanne Waul, Timeplex
               Donald E. Westlake III, Digital Equipment Corporation
               Gerry White
               Bert Wijnen, IBM Corporation
               Peter Wilson, 3Com Corporation
               Steven Wong, Digital Equipment Corporation
               Randy Worzella, IBM Corporation
               Daniel Woycke, MITRE
               Honda Wu
               Jeff Yarnell, Protools
               Chris Young, Cabletron
               Kiho Yum, 3Com Corporation
































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          8.  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]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Structure of Management Information for version 2 of the
               Simple Network Management Protocol (SNMPv2)", RFC 1442,
               SNMP Research, Inc., Hughes LAN Systems, Dover Beach
               Consulting, Inc., Carnegie Mellon University, April 1993.

          [3]  McCloghrie, K., and Rose, M., "Management Information
               Base for Network Management of TCP/IP-based internets:
               MIB-II", STD 17, RFC 1213, March 1991.

          [4]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Management Information Base for version 2 of the Simple
               Network Management Protocol (SNMPv2)", RFC 1450, SNMP
               Research, Inc., Hughes LAN Systems, Dover Beach
               Consulting, Inc., Carnegie Mellon University, April 1993.

          [5]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Protocol Operations for version 2 of the Simple Network
               Management Protocol (SNMPv2)", RFC 1448, SNMP Research,
               Inc., Hughes LAN Systems, Dover Beach Consulting, Inc.,
               Carnegie Mellon University, April 1993.

          [6]  Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
               "Textual Conventions for version 2 of the the Simple
               Network Management Protocol (SNMPv2)", RFC 1443, SNMP
               Research, Inc., Hughes LAN Systems, Dover Beach
               Consulting, Inc., Carnegie Mellon University, April 1993.

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

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








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          9.  Security Considerations

          Security issues are not discussed in this memo.


          10.  Authors' Addresses

               Jeffrey D. Case
               SNMP Research, Inc.
               3001 Kimberlin Heights Rd.
               Knoxville, TN  37920-9716
               US

               Phone: +1 615 573 1434
               Email: case@snmp.com


               Keith McCloghrie
               Hughes LAN Systems
               1225 Charleston Road
               Mountain View, CA  94043
               US

               Phone: +1 415 966 7934
               Email: kzm@hls.com


               Marshall T. Rose
               Dover Beach Consulting, Inc.
               420 Whisman Court
               Mountain View, CA  94043-2186
               US

               Phone: +1 415 968 1052
               Email: mrose@dbc.mtview.ca.us

               Steven Waldbusser
               Carnegie Mellon University
               4910 Forbes Ave
               Pittsburgh, PA  15213
               US

               Phone: +1 412 268 6628
               Email: waldbusser@cmu.edu






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