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rfc:rfc1908

Network Working Group SNMPv2 Working Group Request for Comments: 1908 J. Case Obsoletes: 1452 SNMP Research, Inc. Category: Standards Track K. McCloghrie

                                                   Cisco Systems, Inc.
                                                               M. Rose
                                          Dover Beach Consulting, Inc.
                                                         S. Waldbusser
                                        International Network Services
                                                          January 1996
         Coexistence between Version 1 and Version 2 of the
           Internet-standard Network Management Framework

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Table of Contents

 1. Introduction ................................................    2
 2. Management Information ......................................    2
 2.1 Object Definitions .........................................    3
 2.2 Trap Definitions ...........................................    5
 2.3 Compliance Statements ......................................    5
 2.4 Capabilities Statements ....................................    6
 3 Protocol Operations ..........................................    6
 3.1 Proxy Agent Behavior .......................................    6
 3.1.1 SNMPv2 -> SNMPv1 .........................................    7
 3.1.2 SNMPv1 -> SNMPv2 .........................................    7
 3.2 Bi-lingual Manager Behavior ................................    8
 4. Security Considerations .....................................    8
 5. Editor's Address ............................................    8
 6. Acknowledgements ............................................    8
 7. References ..................................................    9

SNMPv2 Working Group Standards Track [Page 1] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

1. Introduction

 The purpose of this document is to describe coexistence between
 version 2 of the Internet-standard Network Management Framework [1-
 6], termed the SNMP version 2 framework (SNMPv2), and the original
 Internet-standard Network Management Framework (SNMPv1), which
 consists of these three documents:
    STD 16, RFC 1155 [7] which defines the Structure of Management
    Information (SMI), the mechanisms used for describing and naming
    objects for the purpose of management.
    STD 16, RFC 1212 [8] which defines a more concise description
    mechanism, which is wholly consistent with the SMI.
    STD 15, RFC 1157 [9] which defines the Simple Network Management
    Protocol (SNMP), the protocol used for network access to managed
    objects.

2. Management Information

 The SNMPv2 approach towards describing collections of managed objects
 is nearly a proper superset of the approach defined in the Internet-
 standard Network Management Framework.  For example, both approaches
 use ASN.1 [10] as the basis for a formal descriptive notation.
 Indeed, one might note that the SNMPv2 approach largely codifies the
 existing practice for defining MIB modules, based on extensive
 experience with the current framework.
 The SNMPv2 documents which deal with information modules are:
   Structure of Management Information for SNMPv2 [1], which defines
   concise notations for describing information modules, managed
   objects and notifications;
   Textual Conventions for SNMPv2 [2], which defines a concise
   notation for describing textual conventions, and also defines some
   initial conventions; and,
   Conformance Statements for SNMPv2 [3], which defines concise
   notation for describing compliance and capabilities statements.
 The following sections consider the three areas:  MIB modules,
 compliance statements, and capabilities statements.
 MIB modules defined using the current framework may continue to be
 used with the SNMPv2 protocol.  However, for the MIB modules to
 conform to the SNMPv2 framework, the following changes are required:

SNMPv2 Working Group Standards Track [Page 2] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

2.1. Object Definitions

 In general, conversion of a MIB module does not require the
 deprecation of the objects contained therein.  Only if the semantics
 of an object truly changes should deprecation be performed.

(1) The IMPORTS statement must reference SNMPv2-SMI, instead of

   RFC1155-SMI and RFC-1212.

(2) The MODULE-IDENTITY macro must be invoked immediately after any

   IMPORTs statement.

(3) For any descriptor which contains the hyphen character, the hyphen

   character is removed.

(4) For any label for a named-number enumeration which contains the

   hyphen character, the hyphen character is removed.

(5) For any object with an integer-valued SYNTAX clause, in which the

   corresponding INTEGER does not have a range restriction (i.e., the
   INTEGER has neither a defined set of named-number enumerations nor
   an assignment of lower- and upper-bounds on its value), the object
   must have the value of its SYNTAX clause changed to Integer32.

(6) For any object with a SYNTAX clause value of an enumerated INTEGER,

   the hyphen character is removed from any named-number labels which
   contain the hyphen character.

(7) For any object with a SYNTAX clause value of Counter, the object

   must have the value of its SYNTAX clause changed to Counter32.

(8) For any object with a SYNTAX clause value of Gauge, the object must

   have the value of its SYNTAX clause changed to Gauge32.

(9) For all objects, the ACCESS clause must be replaced by a MAX-ACCESS

   clause.  The value of the MAX-ACCESS clause is the same as that of
   the ACCESS clause unless some other value makes "protocol sense" as
   the maximal level of access for the object.  In particular, object
   types for which instances can be explicitly created by a protocol
   set operation, will have a MAX-ACCESS clause of "read-create".  If
   the value of the ACCESS clause is "write-only", then the value of
   the MAX-ACCESS clause is "read-write", and the DESCRIPTION clause
   notes that reading this object will result implementation-specific
   results.

(10) For all objects, if the value of the STATUS clause is "mandatory",

   the value must be replaced with "current".

SNMPv2 Working Group Standards Track [Page 3] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

(11) For all objects, if the value of the STATUS clause is "optional",

   the value must be replaced with "obsolete".

(12) For any object not containing a DESCRIPTION clause, the object must

   have a DESCRIPTION clause defined.

(13) For any object corresponding to a conceptual row which does not

   have an INDEX clause, the object must have either an INDEX clause
   or an AUGMENTS clause defined.

(14) For any object with an INDEX clause that references an object with

   a syntax of NetworkAddress, the value of the STATUS clause of both
   objects is changed to "obsolete".

(15) For any object containing a DEFVAL clause with an OBJECT IDENTIFIER

   value which is expressed as a collection of sub-identifiers, change
   the value to reference a single ASN.1 identifier.

Other changes are desirable, but not necessary:

(1) Creation and deletion of conceptual rows is inconsistent using the

   current framework.  The SNMPv2 framework corrects this.  As such,
   if the MIB module undergoes review early in its lifetime, and it
   contains conceptual tables which allow creation and deletion of
   conceptual rows, then it may be worthwhile to deprecate the objects
   relating to those tables and replace them with objects defined
   using the new approach.

(2) For any object with a string-valued SYNTAX clause, in which the

   corresponding OCTET STRING does not have a size restriction (i.e.,
   the OCTET STRING has no assignment of lower- and upper-bounds on
   its length), one might consider defining the bounds for the size of
   the object.

(3) For all textual conventions informally defined in the MIB module,

   one might consider redefining those conventions using the TEXTUAL-
   CONVENTION macro.  Such a change would not necessitate deprecating
   objects previously defined using an informal textual convention.

(4) For any object which represents a measurement in some kind of

   units, one might consider adding a UNITS clause to the definition
   of that object.

(5) For any conceptual row which is an extension of another conceptual

   row, i.e., for which subordinate columnar objects both exist and
   are identified via the same semantics as the other conceptual row,
   one might consider using an AUGMENTS clause in place of the INDEX
   clause for the object corresponding to the conceptual row which is

SNMPv2 Working Group Standards Track [Page 4] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

   an extension.

Finally, when encountering common errors in SNMPv1 MIB modules:

(1) For any non-columnar object that is instanced as if it were

   immediately subordinate to a conceptual row, the value of the
   STATUS clause of that object is changed to "obsolete".

(2) For any conceptual row object that is not contained immediately

   subordinate to a conceptual table, the value of the STATUS clause
   of that object (and all subordinate objects) is changed to
   "obsolete".

2.2. Trap Definitions

 If a MIB module is changed to conform to the SNMPv2 framework, then
 each occurrence of the TRAP-TYPE macro must be changed to a
 corresponding invocation of the NOTIFICATION-TYPE macro:
 (1)  The IMPORTS statement must not reference RFC-1215.
 (2)  The ENTERPRISES clause must be removed.
 (3)  The VARIABLES clause must be renamed to the OBJECTS clause.
 (4)  The STATUS clause must be added.
 (5)  The value of an invocation of the NOTIFICATION-TYPE macro is an
      OBJECT IDENTIFIER, not an INTEGER, and must be changed accordingly.
      Specifically, if the value of the ENTERPRISE clause is not 'snmp'
      then the value of the invocation is the value of the ENTERPRISE
      clause extended with two sub-identifiers, the first of which has
      the value 0, and the second has the value of the invocation of the
      TRAP-TYPE.

2.3. Compliance Statements

 For those information modules which are "standard", a corresponding
 invocation of the MODULE-COMPLIANCE macro must be included within the
 information module (or in a companion information module), and any
 commentary text in the information module which relates to compliance
 must be removed.  Typically this editing can occur when the
 information module undergoes review.

SNMPv2 Working Group Standards Track [Page 5] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

2.4. Capabilities Statements

 In the current framework, the informational document [11] uses the
 MODULE-CONFORMANCE macro to describe an agent's capabilities with
 respect to one or more MIB modules.  Converting such a description
 for use with the SNMPv2 framework requires these changes:
 (1)  Use the macro name AGENT-CAPABILITIES instead of MODULE-
      CONFORMANCE.
 (2)  The STATUS clause must be added.
 (3)  For all occurrences of the CREATION-REQUIRES clause, note the
      slight change in semantics, and omit this clause if appropriate.
 In order to ease the coexistence between SNMPv1 and SNMPv2, object
 groups defined in an SNMPv1 MIB module may be referenced by the
 INCLUDES clause of an invocation of the AGENT-CAPABILITIES macro:
 upon encountering a reference to an OBJECT IDENTIFIER subtree defined
 in an SNMPv1 MIB module, all leaf objects which are subordinate to
 the subtree and have a STATUS clause value of mandatory are deemed to
 be INCLUDEd.  (Note that this method is ambiguous when different
 revisions of a SNMPv1 MIB have different sets of mandatory objects
 under the same subtree; in such cases, the only solution is to
 rewrite the MIB using the SNMPv2 SMI in order to define the object
 groups unambiguously.)

3. Protocol Operations

 The SNMPv2 documents which deal with protocol operations are:
   Protocol Operations for SNMPv2 [4], which defines the syntax and
   semantics of the operations conveyed by the protocol; and,
   Transport Mappings for SNMPv2 [5], which defines how the protocol
   operations are carried over different transport services.
 The following section considers two areas:  the proxy behavior
 between a SNMPv2 entity and a SNMPv1 agent; and, the behavior of
 "bi-lingual" protocol entities acting in a manager role.

3.1. Proxy Agent Behavior

 To achieve coexistence at the protocol-level, a proxy mechanism may
 be used.  A SNMPv2 entity acting in an agent role may be implemented
 and configured to act in the role of a proxy agent.

SNMPv2 Working Group Standards Track [Page 6] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

3.1.1. SNMPv2 → SNMPv1

 When converting requests from a SNMPv2 entity acting in a manager
 role into requests sent to a SNMPv1 entity acting in an agent role:
 (1)  If a GetRequest-PDU, GetNextRequest-PDU, or SetRequest-PDU is
      received, then it is passed unaltered by the proxy agent.
 (2)  If a GetBulkRequest-PDU is received, the proxy agent sets the non-
      repeaters and max-repetitions fields to zero, and sets the tag of
      the PDU to GetNextRequest-PDU.

3.1.2. SNMPv1 → SNMPv2

 When converting responses received from a SNMPv1 entity acting in an
 agent role into responses sent to a SNMPv2 entity acting in a manager
 role:

(1) If a GetResponse-PDU is received, then it is passed unaltered by

   the proxy agent.  Note that even though a SNMPv2 entity will never
   generate a Response-PDU with a error-status field having a value of
   `noSuchName', `badValue', or `readOnly', the proxy agent must not
   change this field.  This allows the SNMPv2 entity acting in a
   manager role to interpret the response correctly.
   If a GetResponse-PDU is received with an error-status field having
   a value of `tooBig', the proxy agent will remove the contents of
   the variable-bindings field before propagating the response.  Note
   that even though a SNMPv2 entity will never generate a `tooBig' in
   response to a GetBulkRequest-PDU, the proxy agent must propagate
   such a response.

(2) If a Trap-PDU is received, then it is mapped into a SNMPv2-Trap-

   PDU.  This is done by prepending onto the variable-bindings field
   two new bindings:  sysUpTime.0 [6], which takes its value from the
   timestamp field of the Trap-PDU; and, snmpTrapOID.0 [6], which is
   calculated thusly:  if the value of generic-trap field is
   `enterpriseSpecific', then the value used is the concatenation of
   the enterprise field from the Trap-PDU with two additional sub-
   identifiers, `0', and the value of the specific-trap field;
   otherwise, the value of the corresponding trap defined in [6] is
   used.  (For example, if the value of the generic-trap field is
   `coldStart', then the coldStart trap [6] is used.)  Then, one new
   binding is appended onto the variable-bindings field:
   snmpTrapEnterprise.0 [6], which takes its value from the enterprise
   field of the Trap-PDU.  The destinations for the SNMPv2-Trap-PDU
   are determined in an implementation-dependent fashion by the proxy
   agent.

SNMPv2 Working Group Standards Track [Page 7] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

3.2. Bi-lingual Manager Behavior

 To achieve coexistence at the protocol-level, a protocol entity
 acting in a manager role might support both SNMPv1 and SNMPv2.  When
 a management application needs to contact a protocol entity acting in
 an agent role, the entity acting in a manager role consults a local
 database to select the correct management protocol to use.
 In order to provide transparency to management applications, the
 entity acting in a manager role must map operations as if it were
 acting as a proxy agent.

4. Security Considerations

 Security issues are not discussed in this memo.

5. Editor's Address

 Keith McCloghrie
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA  95134-1706
 US
 Phone: +1 408 526 5260
 EMail: kzm@cisco.com

6. Acknowledgements

 This document is the result of significant work by the four major
 contributors:
 Jeffrey D. Case (SNMP Research, case@snmp.com)
 Keith McCloghrie (Cisco Systems, kzm@cisco.com)
 Marshall T. Rose (Dover Beach Consulting, mrose@dbc.mtview.ca.us)
 Steven Waldbusser (International Network Services, stevew@uni.ins.com)
 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)

SNMPv2 Working Group Standards Track [Page 8] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

   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)
   Randy Presuhn (Peer Networks)
   Aleksey Romanov (Quality Quorum)
   Shawn Routhier (Epilogue)
   Jon Saperia (BGS Systems)
   Bob Stewart (Cisco Systems, bstewart@cisco.com), chair
   Kaj Tesink (Bellcore)
   Glenn Waters (Bell-Northern Research)
   Bert Wijnen (IBM)

7. References

[1] 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.

[2] 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.

[3] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and

   S. Waldbusser, "Conformance Statements for Version 2 of the Simple
   Network Management Protocol (SNMPv2)", RFC 1904, 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, "Transport Mappings for Version 2 of the Simple
   Network Management Protocol (SNMPv2)", RFC 1906, January 1996.

[6] 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.

SNMPv2 Working Group Standards Track [Page 9] RFC 1908 Coexistence between SNMPv1 and SNMPv2 January 1996

[7] Rose, M., and K. McCloghrie, "Structure and Identification of

   Management Information for TCP/IP-based internets", STD 16, RFC
   1155, May 1990.

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

   RFC 1212, March 1991.

[9] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network

   Management Protocol", STD 15, RFC 1157, SNMP Research, Performance
   Systems International, MIT Laboratory for Computer Science, May
   1990.

[10] Information processing systems - Open Systems Interconnection -

   Specification of Abstract Syntax Notation One (ASN.1),
   International Organization for Standardization.  International
   Standard 8824, (December, 1987).

[11] McCloghrie, K., and M. Rose, "A Convention for Describing SNMP-

   based Agents", RFC 1303, Hughes LAN Systems, Dover Beach
   Consulting, Inc., February 1992.

SNMPv2 Working Group Standards Track [Page 10]

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