rfc1215.txt

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Network Working Group                                   M. Rose, Editor
Request for Comments: 1215            Performance Systems International
                                                             March 1991


                    A Convention for Defining Traps
                         for use with the SNMP

Status of this Memo

   This memo suggests a straight-forward approach towards defining traps
   used with the SNMP.  Readers should note that the use of traps in the
   Internet-standard network management framework is controversial.  As
   such, this memo is being put forward for information purposes.
   Network management practitioners who employ traps are encouraged to
   make use of this document.  Practitioners who do not employ traps can
   safely ignore this document.

   This memo provides information for the Internet community.  It does
   not specify any standard.  Distribution of this memo is unlimited.

Table of Contents

   1. Historical Perspective ................................    1
   2. Defining Traps ........................................    2
   2.1 Mapping of the TRAP-TYPE macro .......................    3
   2.1.1 Mapping of the ENTERPRISE clause ...................    3
   2.1.2 Mapping of the VARIABLES clause ....................    4
   2.1.3 Mapping of the DESCRIPTION clause ..................    4
   2.1.4 Mapping of the REFERENCE clause ....................    4
   2.1.5 Mapping of the TRAP-TYPE value .....................    4
   2.2 Usage Examples .......................................    5
   2.2.1 Enterprise-specific Trap ...........................    5
   2.2.2 Generic-Traps for use with the SNMP ................    5
   3. Acknowledgements ......................................    7
   4. References ............................................    9
   5. Security Considerations................................    9
   6. Author's Address.......................................    9

1.  Historical Perspective

   As reported in RFC 1052, IAB Recommendations for the Development of
   Internet Network Management Standards [1], a two-prong strategy for
   network management of TCP/IP-based internets was undertaken.  In the
   short-term, the Simple Network Management Protocol (SNMP), defined in
   RFC 1067, was to be used to manage nodes in the Internet community.
   In the long-term, the use of the OSI network management framework was
   be examined.  Two documents were produced to define the management



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   information: RFC 1065, which defined the Structure of Management
   Information (SMI), and RFC 1066, which defined the Management
   Information Base (MIB).  Both of these documents were designed so as
   to be compatible with both the SNMP and the OSI network management
   framework.

   This strategy was quite successful in the short-term: Internet-based
   network management technology was fielded, by both the research and
   commercial communities, within a few months.  As a result of this,
   portions of the Internet community became network manageable in a
   timely fashion.

   As reported in RFC 1109, Report of the Second Ad Hoc Network
   Management Review Group [2], the requirements of the SNMP and the OSI
   network management frameworks were more different than anticipated.
   As such, the requirement for compatibility between the SMI/MIB and
   both frameworks was suspended.  This action permitted the operational
   network management framework, based on the SNMP, to respond to new
   operational needs in the Internet community by producing MIB-II.

   In May of 1990, the core documents were elevated to "Standard
   Protocols" with "Recommended" status.  As such, the Internet-standard
   network management framework consists of: Structure and
   Identification of Management Information for TCP/IP-based internets,
   RFC 1155 [3], which describes how managed objects contained in the
   MIB are defined; Management Information Base for Network Management
   of TCP/IP-based internets, which describes the managed objects
   contained in the MIB, RFC 1156 [4]; and, the Simple Network
   Management Protocol, RFC 1157 [5], which defines the protocol used to
   manage these objects.

2.  Defining Traps

   Due to its initial requirement to be protocol-independent, the
   Internet-standard SMI does not provide a means for defining traps.
   Instead, the SNMP defines a few standardized traps and provides a
   means for management enterprises to transmit enterprise-specific
   traps.

   However, with the introduction of experimental MIBs, some of which
   have a need to define experiment-specific traps, a convenient means
   of defining traps is desirable.  The TRAP-TYPE macro is suggested for
   this purpose:

          IMPORTS
              ObjectName
                  FROM RFC1155-SMI;




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          TRAP-TYPE MACRO ::=
          BEGIN
              TYPE NOTATION ::= "ENTERPRISE" value
                                    (enterprise OBJECT IDENTIFIER)
                                VarPart
                                DescrPart
                                ReferPart
              VALUE NOTATION ::= value (VALUE INTEGER)

              VarPart ::=
                         "VARIABLES" "{" VarTypes "}"
                              | empty
              VarTypes ::=
                         VarType | VarTypes "," VarType
              VarType ::=
                         value (vartype ObjectName)

              DescrPart ::=
                         "DESCRIPTION" value (description DisplayString)
                              | empty

              ReferPart ::=
                         "REFERENCE" value (reference DisplayString)
                              | empty

          END

   It must be emphasized however, that the use of traps is STRONGLY
   discouraged in the Internet-standard Network Management Framework.
   The TRAP-TYPE macro is intended to allow concise definitions of
   existing traps, not to spur the definition of new traps.

2.1.  Mapping of the TRAP-TYPE macro

   It should be noted that the expansion of the TRAP-TYPE macro is
   something which conceptually happens during implementation and not
   during run-time.

2.1.1.  Mapping of the ENTERPRISE clause

   The ENTERPRISE clause, which must be present, defines the management
   enterprise under whose registration authority this trap is defined
   (for a discussion on delegation of registration authority, see the
   SMI [3]).  This value is placed inside the enterprise field of the
   SNMP Trap-PDU.

   By convention, if the value of the ENTERPRISE clause is




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                snmp   OBJECT IDENTIFIER ::= { mib-2 11 }

   as defined in MIB-II [7], then instead of using this value, the value
   of sysObjectID is placed in the enterprise field of the SNMP Trap-
   PDU.  This provides a simple means of using the TRAP-TYPE macro to
   represent the existing standard SNMP traps; it is not intended to
   provide a means to define additional standard SNMP traps.

2.1.2.  Mapping of the VARIABLES clause

   The VARIABLES clause, which need not be present, defines the ordered
   sequence of MIB objects which are contained within every instance of
   the trap type.  Each variable is placed, in order, inside the
   variable-bindings field of the SNMP Trap-PDU.  Note that at the
   option of the agent, additional variables may follow in the
   variable-bindings field.

   However, if the value of the ENTERPRISE clause is

               snmp   OBJECT IDENTIFIER ::= { mib-2 11 }

   as defined in MIB-II [7], then the introduction of additional
   variables must not result in the serialized SNMP Message being larger
   than 484 octets.

2.1.3.  Mapping of the DESCRIPTION clause

   The DESCRIPTION clause, which need not be present, contains a textual
   definition of the trap type.  Note that in order to conform to the
   ASN.1 syntax, the entire value of this clause must be enclosed in
   double quotation marks, although the value may be multi-line.

   Further, note that if the MIB module does not contain a textual
   description of the trap elsewhere then the DESCRIPTION clause must be
   present.

2.1.4.  Mapping of the REFERENCE clause

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

2.1.5.  Mapping of the TRAP-TYPE value

   The value of an invocation of the TRAP-TYPE macro is the (integer)
   number which is uniquely assigned to the trap by the registration
   authority indicated by the ENTERPRISE clause.  This value is placed



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   inside the specific-trap field of the SNMP Trap-PDU, and the
   generic-trap field is set to "enterpriseSpecific(6)".

   By convention, if the value of the ENTERPRISE clause is

               snmp   OBJECT IDENTIFIER ::= { mib-2 11 }

   as defined in MIB-II [7], then the value of an invocation of the
   TRAP-TYPE macro is placed inside the generic-trap field of the SNMP
   Trap-PDU, and the specific-trap field is set to 0.  This provides a
   simple means of using the TRAP-TYPE macro to represent the existing
   standard SNMP traps; it is not intended to provide a means to define
   additional standard SNMP traps.

2.2.  Usage Examples

2.2.1.  Enterprise-specific Trap

   Consider a simple example of an enterprise-specific trap that is sent
   when a communication link failure is encountered:

          myEnterprise OBJECT IDENTIFIER ::= { enterprises 9999 }

          myLinkDown TRAP-TYPE