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Internet Draft     Coexistence between SNMP versions         10 Feb 1999


INTERNET-DRAFT                                                  Rob Frye
                                                MCI Communications Corp.
                                                           David B. Levi
                                                     SNMP Research, Inc.
                                                       Shawn A. Routhier
                                                 Integrated Systems Inc.
                                                             Bert Wijnen
                                                IBM T.J. Watson Research
                                                             10 Feb 1999


        Coexistence between Version 1, Version 2, and Version 3
         of the Internet-standard Network Management Framework
                    <draft-ietf-snmpv3-coex-03.txt>


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

Copyright Notice

   Copyright (C) The Internet Society (1999). All Rights Reserved.













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Abstract

   The purpose of this document is to describe coexistence between
   version 3 of the Internet-standard Network Management Framework,
   (SNMPv3), version 2 of the Internet-standard Network Management
   Framework (SNMPv2), and the original Internet-standard Network
   Management Framework (SNMPv1).  This document obsoletes RFC 1908 [13]
   and RFC2089 [14].











































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   Table Of Contents


   1 Overview .....................................................    4
   1.1 SNMPv1 .....................................................    4
   1.2 SNMPv2 .....................................................    5
   1.3 SNMPv3 .....................................................    6
   1.4 SNMPv1 and SNMPv2 MIB Instrumentation ......................    6
   2 SMI and Management Information Mappings ......................    8
   2.1 Object Definitions .........................................    8
   2.2 Trap and Notification Definitions ..........................   10
   2.3 Compliance Statements ......................................   11
   2.4 Capabilities Statements ....................................   11
   3 Translating Notifications Parameters .........................   13
   3.1 Translating SNMPv1 Notification Parameters to SNMPv2  No-
        tification Parameters .....................................   14
   3.2 Translating SNMPv2 Notification Parameters to SNMPv1  No-
        tification Parameters .....................................   15
   4 Approaches to Coexistence in a Multi-lingual Network .........   18
   4.1 Multi-lingual implementations ..............................   18
   4.1.1 Command Generator ........................................   18
   4.1.2 Command Responder ........................................   18
   4.1.2.1 Handling Counter64 .....................................   19
   4.1.2.2 Mapping SNMPv2 Exceptions ..............................   20
   4.1.2.2.1 Mapping noSuchObject and noSuchInstance ..............   20
   4.1.2.2.2 Mapping endOfMibView .................................   21
   4.1.2.3 Processing An SNMPv1 GetRequest ........................   21
   4.1.2.4 Processing An SNMPv1 GetNextRequest ....................   22
   4.1.3 Notification Originator ..................................   23
   4.1.4 Notification Receiver ....................................   24
   4.2 Proxy Implementations ......................................   24
   4.3 Error Status Mappings ......................................   26
   5 Message Processing Models and Security Models ................   27
   5.1 Mappings ...................................................   27
   5.2 The SNMPv1 Message Processing Model ........................   27
   5.2.1 Processing An Incoming Request ...........................   28
   5.2.2 Generating An Outgoing Response ..........................   30
   5.2.3 Generating An Outgoing Notification ......................   30
   5.3 The SNMP Community MIB Module ..............................   31
   6 Intellectual Property ........................................   41
   7 Acknowledgments ..............................................   42
   8 Security Considerations ......................................   43
   9 References ...................................................   44
   10 Editor's Address ............................................   46
   A. Full Copyright Statement ....................................   47






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1.  Overview

   The purpose of this document is to describe coexistence between
   version 3 of the Internet-standard Network Management Framework,
   termed the SNMP version 3 framework (SNMPv3), version 2 of the
   Internet-standard Network Management Framework, termed the SNMP
   version 2 framework (SNMPv2), and the original Internet-standard
   Network Management Framework (SNMPv1).

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [15].

   There are four general aspects of coexistence described in this
   document.  Each of these is described in a separate section:

       -  Conversion of MIB documents between SMIv1 and SMIv2 formats is
          documented in section 2.

       -  Mapping of notification parameters is documented in section 3.

       -  Approaches to coexistence between entities which support the
          various versions of SNMP in a multi-lingual network is
          documented in section 4.  This section addresses the
          processing of protocol operations in multi-lingual
          implementations, as well as behaviour of proxy
          implementations.

       -  The SNMPv1 Message Processing Model and Community-Based
          Security Model, which provides mechanisms for adapting SNMPv1
          into the View-Based Access Control Model (VACM) [20], is
          documented in section 5 (this section also addresses the
          SNMPv2c Message Processing Model and Community-Based Security
          Model).



1.1.  SNMPv1

   SNMPv1 is defined by these documents:

       -  STD 16, RFC 1155 [1] which defines the Structure of Management
          Information (SMIv1), the mechanisms used for describing and
          naming objects for the purpose of management.

       -  STD 16, RFC 1212 [3] which defines a more concise description
          mechanism, which is wholly consistent with the SMIv1.





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       -  STD 15, RFC 1157 [2] which defines the Simple Network
          Management Protocol (SNMPv1), the protocol used for network
          access to managed objects.

       -  RFC 1215 [4] which defines a convention for defining Traps for
          use with the SMIv1.

   Note that throughout this document, the term 'SMIv1' is used.  This
   term generally refers to the information presented in RFC 1155, RFC
   1212, and RFC 1215.



1.2.  SNMPv2

   SNMPv2 is defined by these documents:

       -  RFC 1902 which defines Version 2 of the Structure of
          Management Information (SMIv2) [7].

       -  RFC 1903 which defines common MIB "Textual Conventions" [8].

       -  RFC 1904 which defines Conformance Statements and requirements
          for defining agent and manager capabilities [9].

       -  RFC 1905 which defines the Protocol Operations used in
          processing [10].

       -  RFC 1906 which defines the Transport Mappings used "on the
          wire" [11].

       -  RFC 1907 which defines the basic Management Information Base
          upon which other MIBs can be built [12].

   Note that SMIv2 as used throughout this document refers to the first
   three documents listed above (RFCs 1902, 1903, and 1904).

   The following document augments the definition of SNMPv2:

       -  RFC 1901 [6] is an Experimental definition for using SNMPv2
          PDUs within a community-based message wrapper.  This is
          referred to throughout this document as SNMPv2c.









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1.3.  SNMPv3

   SNMPv3 is defined by these documents:

       -  RFC 2271 which defines an Architecture for Describing SNMP
          Management Frameworks [16].

       -  RFC 2272 which defines Message Processing and Dispatching
          [17].

       -  RFC 2273 which defines various SNMP Applications [18].

       -  RFC 2274 which defines the User-based Security Model (USM),
          providing for both Authenticated and Private (encrypted) SNMP
          messages [19].

       -  RFC 2275 which defines the View-based Access Control Model
          (VACM), providing the ability to limit access to different MIB
          objects on a per-user basis [20].

   SNMPv3 also uses the SNMPv2 definitions of RFCs 1902 through 1907
   described above.



1.4.  SNMPv1 and SNMPv2 MIB Instrumentation

   In several places, this document refers to 'SNMPv1 MIB
   Instrumentation' and 'SNMPv2 MIB Instrumentation'.  These terms refer
   to the part of an SNMP agent which actually implements MIB objects,
   and which actually initiates generation of notifications.
   Differences between the two types of MIB instrumentation are:

       -  Error-status values generated.

       -  Generation of exception codes.

       -  Use of the Counter64 data type.

       -  The format of parameters provided when a notification is
          generated.

   SNMPv1 MIB instrumentation will generate SNMPv1 error-status values,
   will never generate exception codes nor use the Counter64 data type,
   and will provide SNMPv1 format parameters for generating
   notifications.  Note also that SNMPv1 MIB instrumentation will
   actually never generate a readOnly error (a noSuchName error would





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   always occur in the situation where one would expect a readOnly
   error).

   SNMPv2 MIB instrumentation will generate SNMPv2 error-status values,
   will generate exception codes, will use the Counter64 data type, and
   will provide SNMPv2 format parameters for generating notifications.
   Note that SNMPv2 MIB instrumentation will never generate readOnly,
   noSuchName, or badValue errors.

   Note that a particular multi-lingual implementation may choose to
   implement all MIB instrumentation as SNMPv2 MIB instrumentation.








































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2.  SMI and Management Information Mappings

   The SMIv2 approach towards describing collections of managed objects
   is nearly a proper superset of the approach defined in the SMIv1.
   For example, both approaches use an adapted subset of ASN.1 (1988)
   [11] as the basis for a formal descriptive notation.  Indeed, one
   might note that the SMIv2 approach largely codifies the existing
   practice for defining MIB modules, based on extensive experience with
   the SMIv1.

   The following sections consider the three areas:  MIB modules,
   compliance statements, and capabilities statements.

   MIB modules defined using the SMIv1 may continue to be used with
   protocol versions which use SNMPv2 PDUs.  However, for the MIB
   modules to conform to the SMIv2, the following changes SHALL be made:


2.1.  Object Definitions

   In general, conversion of a MIB module does not require the
   deprecation of the objects contained therein.  If the semantics of an
   object truly changes, the object SHALL be deprecated, otherwise
   deprecation is not required.

(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 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.

(4)  For any object with a SYNTAX clause value of Counter, the object
     MUST have the value of its SYNTAX clause changed to Counter32.

(5)  For any object with a SYNTAX clause value of Gauge, the object MUST
     have the value of its SYNTAX clause changed to Gauge32.

(6)  For all objects, the ACCESS clause MUST be replaced by a MAX-ACCESS
     clause.  The value of the MAX-ACCESS clause SHALL be 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





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     particular, object types for which instances can be explicitly
     created by a protocol set operation, SHALL 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 MUST be "read-
     write", and the DESCRIPTION clause SHALL note that reading this
     object will result in implementation-specific results.

(7)  For all objects, if the value of the STATUS clause is "mandatory",
     the value MUST be replaced with "current".

(8)  For all objects, if the value of the STATUS clause is "optional",
     the value MUST be replaced with "obsolete".

(9)  For any object not containing a DESCRIPTION clause, the object MUST
     have a DESCRIPTION clause defined.

(10) 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.

(11) 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 MUST be changed to "obsolete".

(12) For any object containing a DEFVAL clause with an OBJECT IDENTIFIER
     value which is expressed as a collection of sub-identifiers, the
     value MUST be changed to reference a single ASN.1 identifier.  This
     may require defining a series of new objects in order to define the
     single ASN.1 identifier.

   Other changes are desirable, but not necessary:

(1)  Creation and deletion of conceptual rows is inconsistent using the
     SMIv1.  The SMIv2 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
     the objects relating to those tables MAY be deprecated and replaced
     with objects defined using the new approach.  The new approach can
     be found in section 7 of RFC1902 [7], and the RowStatus and
     StorageType TEXTUAL-CONVENTIONs are described in section 2 of
     RFC1903 [8].

(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), the bounds for the size of the object SHOULD be
     defined.





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(3)  All textual conventions informally defined in the MIB module SHOULD
     be redefined 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, a UNITS clause SHOULD be added 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,
     an AUGMENTS clause SHOULD be used in place of the INDEX clause for
     the object corresponding to the conceptual row which is an
     extension.

   Finally, to avoid common errors in SMIv1 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 MUST be 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) MUST be changed to
     "obsolete".



2.2.  Trap and Notification Definitions

   If a MIB module is changed to conform to the SMIv2, 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 [4], and MUST
     reference SNMPv2-SMI instead.

(2)  The ENTERPRISE clause MUST be removed.

(3)  The VARIABLES clause MUST be renamed to the OBJECTS clause.

(4)  The STATUS clause MUST be added, with a value of 'current'.

(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'





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     then the value of the invocation SHALL be 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.

(6)  The DESCRIPTION clause MUST be added, if not already present.

(7)  One or more NOTIFICATION-GROUPs SHOULD be defined, and related
     notifications SHOULD be collected into those groups.



2.3.  Compliance Statements

   For those information modules which are "standard", a corresponding
   invocation of the MODULE-COMPLIANCE macro and related OBJECT-GROUP
   macros 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 SHOULD be removed.
   Typically this editing can occur when the information module
   undergoes review.



2.4.  Capabilities Statements

   In the SMIv1, RFC1303 [5] 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 SMIv2
   requires these changes:

(1)  The macro name AGENT-CAPABILITIES SHOULD be used instead of MODULE-
     CONFORMANCE.

(2)  The STATUS clause SHOULD be added, with a value of 'current'.

(3)  All occurrences of the CREATION-REQUIRES clause SHOULD either be
     omitted if appropriate, or be changed such that the semantics are
     consistent with RFC1904 [9].

   In order to ease coexistence, object groups defined in an SMIv1
   compliant 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 SMIv1 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 an





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   SMIv1 MIB have different sets of mandatory objects under the same
   subtree; in such cases, the only solution is to rewrite the MIB using
   the SMIv2 in order to define the object groups unambiguously.)
















































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3.  Translating Notifications Parameters

   This section describes how parameters used for generating
   notifications are translated between the format used for SNMPv1
   notification protocol operations and the format used for SNMPv2
   notification protocol operations.  The parameters used to generate a
   notification are called 'notification parameters'.  The format of
   parameters used for SNMPv1 notification protocol operations is
   refered to in this document as 'SNMPv1 notification parameters.'  The
   format of parameters used for SNMPv2 notification protocol operations
   is refered to in this document as 'SNMPv2 notification parameters.'

   The SMI version used to define a notification will usually determine
   which type of notification parameters are provided by MIB
   instrumentation when a notification is generated.

   The situations where notification parameters MUST be translated are:

       -  When MIB instrumentation in an entity generates a set of
          notification parameters in a particular format, and the
          configuration of the entity indicates that the notification
          must be sent using an SNMP message version that requires the
          other format for notification parameters.

       -  When a proxy receives a notification that was sent using an
          SNMP message version that requires one format of notification
          parameters, and must forward the notification using an SNMP
          message version that requires the other format of notification
          parameters.

   In addition, it MAY be desirable to translate notification parameters
   in a notification receiver application in order to present
   notifications to the end user in a consistent format.

   Note that for the purposes of this section, the set of notification
   parameters is independent of whether the notification is to be sent
   as a trap or an inform.

   SNMPv1 notification parameters consist of:

       -  An enterprise parameter (OBJECT IDENTIFIER).

       -  An agent-addr parameter (NetworkAddress).

       -  A generic-trap parameter (INTEGER).






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       -  A specific-trap parameter (INTEGER).

       -  A time-stamp parameter (TimeTicks).

       -  A list of variable-bindings (VarBindList).

   SNMPv2 notification parameters consist of:

       -  A sysUpTime parameter (TimeTicks).  This appears in the first
          variable-binding in an SNMPv2-Trap-PDU or InformRequest-PDU.

       -  An snmpTrapOID parameter (OBJECT IDENTIFIER).  This appears in
          the second variable-binding in an SNMPv2-Trap-PDU or
          InformRequest-PDU.

       -  A list of variable-bindings (VarBindList).  This refers to all
          but the first two variable-bindings in an SNMPv2-Trap-PDU or
          InformRequest-PDU.



3.1.  Translating SNMPv1 Notification Parameters to SNMPv2 Notification
Parameters

   The following procedure describes how to translate SNMPv1
   notification parameters into SNMPv2 notification parameters:

(1)  The SNMPv2 sysUpTime parameter SHALL be taken directly from the
     SNMPv1 time-stamp parameter.

(2)  If the SNMPv1 generic-trap parameter is 'enterpriseSpecific(6)',
     the SNMPv2 snmpTrapOID parameter SHALL be the concatentation of the
     SNMPv1 enterprise parameter and two additional sub-identifiers,
     '0', and the SNMPv1 specific-trap parameter.

















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(3)  If the SNMPv1 generic-trap parameter is not
     'enterpriseSpecific(6)', the SNMPv2 snmpTrapOID parameter SHALL be
     the corresponding trap as defined in section 2 of RFC1907 [12]:

            generic-trap parameter   snmpTrapOID.0
            ======================   =============
            0                        1.3.6.1.6.3.1.1.5.1 (coldStart)
            1                        1.3.6.1.6.3.1.1.5.2 (warmStart)
            2                        1.3.6.1.6.3.1.1.5.3 (linkDown)
            3                        1.3.6.1.6.3.1.1.5.4 (linkUp)
            4                        1.3.6.1.6.3.1.1.5.5 (authenticationFailure)
            5                        1.3.6.1.6.3.1.1.5.6 (egpNeighborLoss)


(4)  The SNMPv2 variable-bindings SHALL be the SNMPv1 variable-bindings.
     In addition, if the translation is being performed by a proxy in
     order to forward a received trap, three additional variable-
     bindings will be appended, if these three additional variable-
     bindings do not already exist in the SNMPv1 variable-bindings.  The
     name portion of the first variable binding SHALL contain
     snmpTrapAddress.0, and the value SHALL contain the SNMPv1 agent-
     addr parameter.  The name portion of the second variable binding
     SHALL contain snmpTrapCommunity.0, and the value SHALL contain the
     value of the community-string field from the received SNMPv1
     message which contained the SNMPv1 Trap-PDU.  The name portion of
     the third variable binding SHALL contain snmpTrapEnterprise.0 [12],
     and the value SHALL be the SNMPv1 enterprise parameter.



3.2.  Translating SNMPv2 Notification Parameters to SNMPv1 Notification
Parameters

   The following procedure describes how to translate SNMPv2
   notification parameters into SNMPv1 notification parameters:

(1)  The SNMPv1 enterprise parameter SHALL be determined as follows:

       -  If the SNMPv2 snmpTrapOID parameter is one of the standard
          traps as defined in RFC1907 [12], then the SNMPv1 enterprise
          parameter SHALL be set to the value of the variable-binding in
          the SNMPv2 variable-bindings whose name is
          snmpTrapEnterprise.0 if that variable-binding exists.  If it
          does not exist, the SNMPv1 enterprise parameter SHALL be set
          to the value 'snmpTraps' as defined in RFC1907 [12].






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       -  If the SNMPv2 snmpTrapOID parameter is not one of the standard
          traps as defined in RFC1907 [12], then the SNMPv1 enterprise
          parameter SHALL be set to the SNMPv2 snmpTrapOID parameter as
          follows:

           -  If the next-to-last sub-identifier of the snmpTrapOID is
              zero, then the SMIv1 enterprise SHALL be the SMIv2
              snmpTrapOID with the last 2 sub-identifiers removed,
              otherwise

           -  If the next-to-last sub-identifier of the snmpTrapOID is
              non-zero, then the SMIv1 enterprise SHALL be the SMIv2
              snmpTrapOID with the last sub-identifier removed.

(2)  The SNMPv1 agent-addr parameter SHALL be determined based on the
     situation in which the translation occurs.

       -  If the translation occurs within a notification originator
          application, and the notification is to be sent over IP, the
          SNMPv1 agent-addr parameter SHALL be set to the IP address of
          the SNMP entity in which the notification originator resides.
          If the notification is to be sent over some other transport,
          the SNMPv1 agent-addr parameter SHALL be set to 0.0.0.0.

       -  If the translation occurs within a proxy application, the
          proxy must attempt to determine the original source of the
          notification.  If the SNMPv2 variable-bindings contains a
          variable binding whose name is snmpTrapAddress.0, the agent-
          addr parameter SHALL be set to the value of that variable
          binding.  Otherwise, Otherwise, the SNMPv1 agent-addr
          parameter SHALL be set to 0.0.0.0.

(3)  If the SNMPv2 snmpTrapOID parameter is one of the standard traps as
     defined in RFC1907 [12], the SNMPv1 generic-trap parameter SHALL be
     set as follows:

            snmpTrapOID.0 parameter               generic-trap
            ===============================       ============
            1.3.6.1.6.3.1.1.5.1 (coldStart)                  0
            1.3.6.1.6.3.1.1.5.2 (warmStart)                  1
            1.3.6.1.6.3.1.1.5.3 (linkDown)                   2
            1.3.6.1.6.3.1.1.5.4 (linkUp)                     3
            1.3.6.1.6.3.1.1.5.5 (authenticationFailure)      4
            1.3.6.1.6.3.1.1.5.6 (egpNeighborLoss)            5

    Otherwise, the SNMPv1 generic-trap parameter SHALL be set to 6.





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(4)  If the SNMPv2 snmpTrapOID parameter is one of the standard traps as
     defined in RFC1907 [12], the SNMPv1 specific-trap parameter SHALL
     be set to zero.  Otherwise, the SNMPv1 specific-trap parameter
     SHALL be set to the last sub-identifier of the SNMPv2 snmpTrapOID
     parameter.

(5)  The SNMPv1 time-stamp parameter SHALL be taken directly from the
     SNMPv2 sysUpTime parameter.

(6)  The SNMPv1 variable-bindings SHALL be the SNMPv2 variable-bindings
     with the following exceptions:

       -  Any variable-binding whose type is Counter64 which exists in
          the SNMPv2 variable-bindings SHALL be removed.





































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4.  Approaches to Coexistence in a Multi-lingual Network

   There are two basic approaches to coexistence in a multi-lingual
   network, multi-lingual implementations and proxy implementations.
   Multi-lingual implementations allow elements in a network to
   communicate with each other using an SNMP version which both elements
   support.  This allows a multi-lingual implementation to communicate
   with any mono-lingual implementation, regardless of the SNMP version
   supported by the mono-lingual implementation.

   Proxy implementations provide a mechanism for translating between
   SNMP versions using a third party network element.  This allows
   network elements which support only a single, but different, SNMP
   version to communicate with each other.  Proxy implementations are
   also useful for securing communications over an insecure link between
   two locally secure networks.


4.1.  Multi-lingual implementations

   This approach requires an entity to support multiple SNMP message
   versions.  Typically this means supporting SNMPv1, SNMPv2c, and
   SNMPv3 message versions.  The behaviour of various types of SNMP
   applications which support multiple message versions is described in
   the following sections.  This approach allows entities which support
   multiple SNMP message versions to coexist with and communicate with
   entities which support only a single SNMP message version.



4.1.1.  Command Generator

   A command generator must select an appropriate message version when
   sending requests to another entity.  One way to achieve this is to
   consult a local database to select the appropriate message version.

   In addition, a command generator should 'downgrade' GetBulk requests
   to GetNext requests when selecting SNMPv1 as the message version for
   an outgoing request.



4.1.2.  Command Responder

   A command responder must be able to deal with MIB instrumentation
   that is written using both the SNMPv1 and SNMPv2.  There are three
   aspects to dealing with this.  A command responder must:





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       -  Deal correctly with SNMPv2 MIB instrumentation that returns a
          Counter64 value while processing an SNMPv1 message,

       -  Deal correctly with SNMPv2 MIB instrumentation that returns
          one of the three exception values while processing an SNMPv1
          message, and

       -  Map SNMPv2 error codes returned from SNMPv2 MIB
          instrumentation into SNMPv1 error code when processing an
          SNMPv1 message.

   Note that SNMPv1 error codes can be used without any change when
   processing SNMPv2c or SNMPv3 messages.

   The following sections describe the behaviour of a command responder
   application which supports multiple SNMP message versions, and which
   has access to some combination of SNMPv1 and SNMPv2 MIB
   instrumentation.



4.1.2.1.  Handling Counter64

   The SMIv2 [7] defines one new syntax that is incompatible with SMIv1.
   This syntax is Counter64.  All other syntaxes defined by SMIv2 are
   compatible with SMIv1.

   The impact on multi-lingual command responders is that they MUST NOT
   ever return a variable binding containing a Counter64 value in a
   response to a request that was received using the SNMPv1 message
   version.

   Multi-lingual command responders SHALL take the approach that object
   instances whose type is Counter64 are implicitly excluded from view
   when processing an SNMPv1 message.  So:

       -  On an SNMPv1 GET request, an error-status of noSuchName SHALL
          be returned, and the error-index SHALL be set to the variable
          binding that caused this error.

       -  On an SNMPv1 GetNext request, any object instance which
          contains a syntax of Counter64 shall be skipped, and the next
          object instance that follows the one with a syntax of
          Counter64 SHALL be fetched.  This step may need to be repeated
          several times in order to find an object whose syntax is not
          Counter64.





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       -  Any SET request that has a variable binding with a Counter64
          value must have come from a SNMPv2 manager, and so it should
          not cause a problem.  However, if an object with SYNTAX of
          Counter64 is received in an SNMPv1 SET packet, it SHALL result
          in an ASN.1 parse error since Counter64 is not valid in the
          SNMPv1 protocol. When an ASN.1 parse error occurs, the counter
          snmpInASNParseErrs SHALL be incremented and no response is
          returned.


4.1.2.2.  Mapping SNMPv2 Exceptions

   SNMPv2 provides a feature called exceptions, which allow an SNMPv2
   Response PDU to return as much management information as possible,
   even when an error occurs.  However, SNMPv1 does not support
   exceptions, and so an SNMPv1 Response PDU cannot return any
   management information, and can only return an error-status and
   error-index value.

   When an SNMPv1 request is received, a command responder MUST check
   any variable bindings returned from SNMPv2 MIB instrumentation for
   exception values, and convert these exception values into SNMPv1
   error codes.

   The type of exception that can be returned from MIB instrumentation
   and the action taken depends on the type of SNMP request.

       -  For a GetRequest, a noSuchObject or noSuchInstance exception
          may be returned.

       -  For a GetNextRequest, an endOfMibView exception may be
          returned.

       -  No exceptions will be returned for a SetRequest, and a
          GetBulkRequest should only be received in an SNMPv2c or SNMPv3
          message, so these request types may be ignored when mapping
          exceptions.



4.1.2.2.1.  Mapping noSuchObject and noSuchInstance

   A noSuchObject or noSuchInstance exception generated by SNMPv2 MIB
   instrumentation indicates that the requested object instance can not
   be returned.  The SNMPv1 error code for this condition is noSuchName,
   and so the error-status field of the response PDU SHALL be set to
   noSuchName.  Also, the error-index field SHALL be set to the index of





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   the variable binding for which an exception occurred, and the
   variable binding list from the original request SHALL be returned
   with the response PDU.

   Note that when a response contains multiple exceptions, it is an
   implementation choice as to which variable binding the error-index
   should reference.



4.1.2.2.2.  Mapping endOfMibView

   When SNMPv2 MIB instrumentation returns a variable binding containing
   an endOfMibView exception, it indicates that there are no object
   instances available which lexicographically follow the object in the
   request. In an SNMPv1 agent, this condition normally results in a
   noSuchName error, and so the error-status field of the response PDU
   SHALL be set to noSuchName. Also, the error-index field SHALL be set
   to the index of the variable binding for which an exception occurred,
   and the variable binding list from the original request SHALL be
   returned with the response PDU.

   Note that when a response contains multiple exceptions, it is an
   implementation choice as to which variable binding the error-index
   should reference.



4.1.2.3.  Processing An SNMPv1 GetRequest

   When processing an SNMPv1 GetRequest, the following procedures MUST
   be followed when calling SNMPv2 MIB instrumentation.

   When such MIB instrumentation returns response data using SNMPv2
   syntax and error-status values, then:

(1)  If the error-status is anything other than noError,

       -  The error status SHALL be translated to an SNMPv1 error-status
          using the table in section 4.3, "Error Status Mappings".

       -  The error-index SHALL be set to the position (in the original
          request) of the variable binding that caused the error-status.

       -  The variable binding list of the response PDU SHALL be made
          exactly the same as the variable binding list that was
          received in the original request.





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(2)  If the error-status is noError, the variable bindings SHALL be
     checked for any SNMPv2 exception (noSuchObject or noSuchInstance)
     or an SNMPv2 syntax that is unknown to SNMPv1 (Counter64).  If
     there are any such variable bindings, one of those variable
     bindings SHALL be selected (it is an implementation choice as to
     which is selected), and:

       -  The error-status SHALL be set to noSuchName,

       -  The error-index SHALL be set to the position (in the variable
          binding list of the original request) of the selected variable
          binding, and

       -  The variable binding list of the response PDU SHALL be exactly
          the same as the variable binding list that was received in the
          original request.

(3)  If there are no such variable bindings, then:

       -  The error-status SHALL be set to noError,

       -  The error-index SHALL be set to zero, and

       -  The variable binding list of the response SHALL be composed
          from the data as it is returned by the MIB instrumentation.



4.1.2.4.  Processing An SNMPv1 GetNextRequest

   When processing an SNMPv1 GetNextRequest, the following procedures
   MUST be followed when SNMPv2 MIB instrumentation is called as part of
   processing the request.  There may be repetitive calls to (possibly
   different pieces of) MIB instrumentation to try to find the first
   object which lexicographically follows each of the objects in the
   request.  This is implementation specific.  These procedures are
   followed only for data returned from SNMPv2 MIB instrumentation.
   Data returned from SNMPv1 MIB instrumentation may be treated in the
   normal manner for an SNMPv1 request.

   First, if the MIB instrumentation returns an error-status of anything
   other than noError:

(1)  The error status SHALL be translated to an SNMPv1 error-status
     using the table in section 4.3, "Error Status Mappings".






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(2)  The error-index SHALL be set to the position (in the original
     request) of the variable binding that caused the error-status.

(3)  The variable binding list of the response PDU SHALL be exactly the
     same as the variable binding list that was received in the original
     request.

   Otherwise, if the MIB instrumentation returns an error-status of
   noError:

(1)  Any variable bindings containing an SNMPv2 syntax of Counter64
     SHALL be considered to be not in view, and the MIB instrumentation
     SHALL be called as often as is required until either a value other
     than Counter64 is returned, or an error occurs.

(2)  If there is any variable binding that contains an SNMPv2 exception
     endOfMibView (there may be more than one, it is an implementation
     decision as to which is chosen):

       -  The error-status SHALL be set to noSuchName,

       -  The error-index SHALL be set to the position (in the variable
          binding list of the original request) of the variable binding
          that returned such an SNMPv2 exception, and

       -  The variable binding list of the response PDU SHALL be exactly
          the same as the variable binding list that was received in the
          original request.

(3)  If there are no such variable bindings, then:

       -  The error-status SHALL be set to noError,

       -  The error-index SHALL be set to zero, and

       -  The variable binding list of the response SHALL be composed
          from the data as it is returned by the MIB instrumentation.



4.1.3.  Notification Originator

   A notification originator must be able to translate between SNMPv1
   notifications parameters and SNMPv2 notification parameters in order
   to send a notification using a particular SNMP message version.  If
   MIB instrumentation presents a notification using SNMPv1 notification
   parameters, and configuration information specifies that





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   notifications be sent using SNMPv2c or SNMPv3, the notification
   parameters must be translated to SNMPv2 notification parameters.
   Likewise, if MIB instrumentation presents a notification using SNMPv2
   notification parameters, and configuration information specifies that
   notifications be sent using SNMPv1, the notification parameters must
   be translated to SNMPv1 notification parameters.

   When a notification originator generates a notification, using
   parameters obtained from the SNMP-TARGET-MIB and SNMP-NOTIFICATION-
   MIB, if the SNMP version used to generate the notification is SNMPv1,
   the PDU type used will always be a TrapPDU, regardless of whether the
   value of snmpNotifyType is trap(1) or inform(2).

   Note also that access control and notification filtering are
   performed in the usual manner for notifications, regardless of the
   SNMP message version to be used when sending a notification.  The
   parameters for performing access control are found in the usual
   manner (i.e. from inspecting the SNMP-TARGET-MIB and SNMP-
   NOTIFICATION-MIB).  In particular, when generating an SNMPv1 Trap, in
   order to perform the access check specified in [18], section 3.3,
   bullet (3), the notification originator may need to generate a value
   for snmpTrapOID.0 as described in section 3.1, bullets (2) and (3) of
   this document.  If the SNMPv1 notification parameters being used were
   previously translated from a set of SNMPv2 notification parameters,
   this value may already be known, in which case it need not be
   generated.


4.1.4.  Notification Receiver

   There are no special requirements of a notification receiver.
   However, an implementation may find it useful to allow a higher level
   application to request whether notifications should be delivered to a
   higher level application using SNMPv1 notification parameter or
   SNMPv2 notification parameters.  The notification receiver would then
   translate notification parameters when required in order to present a
   notification using the desired set of parameters.



4.2.  Proxy Implementations

   A proxy implementation may be used to enable communication between
   entities which support different SNMP message versions.  This is
   accomplished in a proxy forwarder application by performing
   translations on a PDU in the following situations:





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       -  If a GetBulkRequest-PDU is received and must be forwarded
          using the SNMPv1 message version, the proxy forwarder SHALL
          set the non-repeaters and max-repetitions fields to 0, and
          SHALL set the tag of the PDU to GetNextRequest-PDU.

       -  If a GetResponse-PDU is received whose error-status field has
          a value of 'tooBig', and the message will be forwarded using
          the SNMPv2c or SNMPv3 message version, the proxy forwarder
          SHALL remove the contents of the variable-bindings field
          before forwarding the response.

       -  If a GetResponse-PDU is received which contains variable-
          bindings of type Counter64 or which contain an SNMPv2
          exception code, and the message would be forwarded using the
          SNMPv1 message version, the proxy MUST generate an alternate
          response PDU consisting of the request-id and variable
          bindings from the original SNMPv1 request, containing a
          noSuchName error-status value, and containing an error-index
          value indicating the position of the variable-binding
          containing the Counter64 type or exception code.

       -  If a GetResponse-PDU is received which contains an SNMPv2
          error-status value of wrongValue, wrongEncoding, wrongType,
          wrongLength, inconsistentValue, noAccess, notWritable,
          noCreation, inconsistentName, resourceUnavailable,
          commitFailed, undoFailed, or authorizationError, the error-
          status value is modified using the mappings in section 4.3.

       -  If a Trap-PDU is received, and will be forwarded using the
          SNMPv2c or SNMPv3 message version, the proxy SHALL apply the
          translation rules described in section 3, and SHALL forward
          the notification as an SNMPv2-Trap-PDU.

       -  If an SNMPv2-Trap-PDU is received, and will be forwarded using
          the SNMPv1 message version, the proxy SHALL apply the
          translation rules described in section 3, and SHALL forward
          the notification as a Trap-PDU.

       -  If an InformRequest-PDU is received, any configuration
          information indicating that it would be forwarded using the
          SNMPv1 message version SHALL be ignored.  An InformRequest-PDU
          can only be forwarded using the SNMPv2c or SNMPv3 message
          version.

       -  In all other cases, the proxy SHALL forward a received PDU
          without change.





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   Note that when an SNMPv1 agent generates a message containing a
   Trap-PDU which is subsequently forwarded by one or more proxy
   forwarders using SNMP versions other than SNMPv1, the community
   string and agent-addr fields from the original message generated by
   the SNMPv1 agent will be preserved through the use of the
   snmpTrapAddress and snmpTrapCommunity objects.



4.3.  Error Status Mappings

   The following tables shows the mappings of SNMPv1 error-status values
   into SNMPv2 error-status values, and the mappings of SNMPv2 error-
   status values into SNMPv1 error-status values.

                          SNMPv1 error-status    SNMPv2 error-status
                          ===================    ===================
                          noError                noError
                          tooBig                 tooBig
                          noSuchName             noSuchName
                          badValue               badValue
                          genErr                 genErr


                          SNMPv2 error-status    SNMPv1 error-status
                          ===================    ===================
                          noError                noError
                          tooBig                 tooBig
                          genErr                 genErr
                          wrongValue             badValue
                          wrongEncoding          badValue
                          wrongType              badValue
                          wrongLength            badValue
                          inconsistentValue      badValue
                          noAccess               noSuchName
                          notWritable            noSuchName
                          noCreation             noSuchName
                          inconsistentName       noSuchName
                          resourceUnavailable    genErr
                          commitFailed           genErr
                          undoFailed             genErr
                          authorizationError     noSuchName









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5.  Message Processing Models and Security Models

   In order to adapt SNMPv1 (and SNMPv2c) into the SNMP architecture,
   the following models are defined in this document:

       -  The SNMPv1 Message Processing Model

       -  The SNMPv1 Community-Based Security Model

   The following models are also described in this document:

       -  The SNMPv2c Message Processing Model

       -  The SNMPv2c Community-Based Security Model

          In most respects, the SNMPv1 Message Processing Model and the
          SNMPv2c Message Processing Model are identical, and so these
          are not discussed independently in this document.  Differences
          between the two models are described as required.

          Similarly, the SNMPv1 Community-Based Security Model and the
          SNMPv2c Community-Based Security Model are nearly identical,
          and so are not discussed independently.  Differences between
          these two models are also described as required.


5.1.  Mappings

The SNMPv1 (and SNMPv2c) Message Processing Model and Security Model
require mappings between parameters used in SNMPv1 (and SNMPv2c)
messages, and the version independent parameters used in the SNMP
architecture [16].  The parameters which MUST be mapped consist of the
SNMPv1 (and SNMPv2c) community name, and the SNMP securityName and
contextEngineID/contextName pair.  A MIB module (the SNMP-COMMUNITY-MIB)
is provided in this document in order to perform these mappings.  This
MIB provides mappings in both directions, that is, a community name may
be mapped to a securityName, contextEngineID, and contextName, or the
combination of securityName, contextEngineID, and contextName may be
mapped to a community name.


5.2.  The SNMPv1 Message Processing Model

   The SNMPv1 Message Processing Model handles processing of SNMPv1
   messages.  The processing of messages is handled generally in the
   same manner as described in RFC1157 [2], with differences and
   clarifications as described in the following sections.  The





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   SnmpMessageProcessingModel value for SNMPv1 is 0 (the value for
   SNMPv2c is 1).



5.2.1.  Processing An Incoming Request

   In RFC1157 [2], section 4.1, item (3) for an entity which receives a
   message, states that various parameters are passed to the 'desired
   authentication scheme.'  The desired authentication scheme in this
   case is the SNMPv1 Community-Based Security Model, which will be
   called using the processIncomingMsg ASI.  The parameters passed to
   this ASI are:

       -  The messageProcessingModel, which will be 0 (or 1 for
          SNMPv2c).

       -  The maxMessageSize, which should be the maximum size of a
          message that the receiving entity can generate (since there is
          no such value in the received message).

       -  The securityParameters, which consist of the community string
          and the message's source and destination transport addresses.

       -  The securityModel, which will be 1 (or 2 for SNMPv2c).

       -  The securityLevel, which will be noAuthNoPriv.

       -  The wholeMsg and wholeMsgLength.

   The Community-Based Security Model will attempt to select a row in
   the snmpCommunityTable.  This is done by performing a search through
   the snmpCommunityTable in lexicographic order.  The first entry for
   which the following matching criteria are satisfied will be selected:

       -  The community string is equal to the snmpCommunityName value.

       -  If the snmpCommunityTransportTag is not an empty string, the
          transportDomain and transportAddress from which the message
          was received must match one of the entries in the
          snmpTargetAddrTable selected by the snmpCommunityTransportTag
          value.  If the snmpCommunityTransportTag is an empty string,
          it is ignored for the purpose of matching.

   If no such entry can be found, an authentication failure occurs as
   described in RFC1157 [2].





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   The parameters returned from the Community-Based Security Model are:

       -  The securityEngineID, which will always be the local value of
          snmpEngineID.0.

       -  The securityName.

       -  The scopedPDU.  Note that this parameter will actually consist
          of three values, the contextSnmpEngineID, the contextName, and
          the PDU.  These must be separate values, since the first two
          do not actually appear in the message.

       -  The maxSizeResponseScopedPDU.

       -  The securityStateReference.

   The appropriate SNMP application will then be called (depending on
   the value of the contextEngineID and the request type in the PDU)
   using the processPdu ASI.  The parameters passed to this ASI are:

       -  The messageProcessingModel, which will be 0 (or 1 for
          SNMPv2c).

       -  The securityModel, which will be 1 (or 2 for SNMPv2c).

       -  The securityName, which was returned from the call to
          processIncomingMsg.

       -  The securityLevel, which is noAuthNoPriv.

       -  The contextEngineID, which was returned as part of the
          ScopedPDU from the call to processIncomingMsg.

       -  The contextName, which was returned as part of the ScopedPDU
          from the call to processIncomingMsg.

       -  The pduVersion, which should indicate an SNMPv1 version PDU
          (if the message version was SNMPv2c, this would be an SNMPv2
          version PDU).

       -  The PDU, which was returned as part of the ScopedPDU from the
          call to processIncomingMsg.

       -  The maxSizeResponseScopedPDU which was returned from the call
          to processIncomingMsg.






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       -  The stateReference which was returned from the call to
          processIncomingMsg.

   The SNMP application should process the request as described
   previously in this document.  Note that access control is applied by
   an SNMPv3 command responder application as usual.  The parameters as
   passed to the processPdu ASI will be used in calls to the
   isAccessAllowed ASI.



5.2.2.  Generating An Outgoing Response

   There is no special processing required for generating an outgoing
   response.  However, the community string used in an outgoing response
   must be the same as the community string from the original request.
   The original community string MUST be present in the stateReference
   information of the original request.



5.2.3.  Generating An Outgoing Notification

   In a multi-lingual SNMP entity, the parameters used for generating
   notifications will be obtained by examining the SNMP-TARGET-MIB and
   SNMP-NOTIFICATION-MIB.  These parameters will be passed to the SNMPv1
   Message Processing Model using the sendPdu ASI.  The SNMPv1 Message
   Processing Model will attempt to locate an appropriate community
   string in the snmpCommunityTable based on the parameters passed to
   the sendPdu ASI.  This is done by performing a search through the
   snmpCommunityTable in lexicographic order.  The first entry for which
   the following matching criteria are satisfied will be selected:

       -  The securityName must be equal to the
          snmpCommunitySecurityName value.

       -  The contextEngineID must be equal to the
          snmpCommunityContextEngineID value.

       -  The contextName must be equal to the snmpCommunityContextName
          value.

       -  If the snmpCommunityTransportTag is not an empty string, the
          transportDomain and transportAddress must match one of the
          entries in the snmpTargetAddrTable selected by the
          snmpCommunityTransportTag value.  If the
          snmpCommunityTransportTag is an empty string, it is ignored





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          for the purpose of matching.

   If no such entry can be found, the notification is not sent.
   Otherwise, the community string used in the outgoing notification
   will be the value of the snmpCommunityName column of the selected
   row.




5.3.  The SNMP Community MIB Module

   The SNMP-COMMUNITY-MIB contains objects for mapping between community
   strings and version-independent SNMP message parameters.  In
   addition, this MIB provides a mechanism for performing source address
   validation on incoming requests, and for selecting community strings
   based on target addresses for outgoing notifications.  These two
   features are accomplished by providing a tag in the
   snmpCommunityTable which selects sets of entries in the
   snmpTargetAddrTable [18].  In addition, the SNMP-COMMUNITY-MIB
   augments the snmpTargetAddrTable with a transport address mask value
   and a maximum message size value.  These values are used only where
   explicitly stated.  In cases where the snmpTargetAddrTable is used
   without mention of these augmenting values, the augmenting values
   should be ignored.

   The mask value, snmpTargetAddrTMask, allows selected entries in the
   snmpTargetAddrTable to specify multiple addresses (rather than just a
   single address per entry).  This would typically be used to specify a
   subnet in an snmpTargetAddrTable rather than just a single address.
   The mask value is used to select which bits of a transport address
   must match bits of the corresponding instance of
   snmpTargetAddrTAddress, in order for the transport address to match a
   particular entry in the snmpTargetAddrTable.  The value of an
   instance of snmpTargetAddrTMask must always be an OCTET STRING whose
   length is either zero or the same as that of the corresponding
   instance of snmpTargetAddrTAddress.

   When checking whether a transport address matches an entry in the
   snmpTargetAddrTable, if the value of snmpTargetAddrTMask is a zero-
   length OCTET STRING, the mask value is ignored, and the value of
   snmpTargetAddrTAddress must exactly match a transport address.
   Otherwise, each bit of each octet in the snmpTargetAddrTMask value
   corresponds to the same bit of the same octet in the
   snmpTargetAddrTAddress value.  For bits that are set in the
   snmpTargetAddrTMask value (i.e. bits equal to 1), the corresponding
   bits in the snmpTargetAddrTAddress value must match the bits in a





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   transport address.  If all such bits match, the transport address is
   matched by that snmpTargetAddrTable entry.  Otherwise, the transport
   address is not matched.

   The maximum message size value, snmpTargetAddrMMS, is used to
   determine the maximum message size acceptable to another SNMP entity
   when the value cannot be determined from the protocol.

      SNMP-COMMUNITY-MIB DEFINITIONS ::= BEGIN

      IMPORTS
          IpAddress
              FROM RFC1155-SMI
          MODULE-IDENTITY,
          OBJECT-TYPE,
          Integer32,
              FROM SNMPv2-SMI
          RowStatus,
          TestAndIncr,
          StorageType
              FROM SNMPv2-TC
          SnmpAdminString
              FROM SNMP-FRAMEWORK-MIB
          SnmpTagValue
              FROM SNMP-TARGET-MIB
          MODULE-COMPLIANCE,
          OBJECT-GROUP
              FROM SNMPv2-CONF;

      snmpCommunityMIB MODULE-IDENTITY
          LAST-UPDATED "9805110000Z"            -- 11 May 1998, midnight
          ORGANIZATION "SNMPv3 Working Group"
          CONTACT-INFO "WG-email:   snmpv3@tis.com
                        Subscribe:  majordomo@tis.com
                                    In msg body:  subscribe snmpv3

                        Chair:      Russ Mundy
                                    Trusted Information Systems
                        postal:     3060 Washington Rd
                                    Glenwood MD 21738
                                    USA
                        email:      mundy@tis.com
                        phone:      +1-301-854-6889

                        Co-editor:  Rob Frye
                                    MCI Communications Corp.
                        Postal:     2100 Reston Parkway, Suite 600





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                                    Reston, VA 20191
                                    USA
                        E-mail:     Rob.Frye@mci.com
                        Phone:      +1 703 715 7225

                        Co-editor:  David B. Levi
                                    SNMP Research, Inc.
                        Postal:     3001 Kimberlin Heights Road
                                    Knoxville, TN 37920-9716
                        E-mail:     levi@snmp.com
                        Phone:      +1 423 573 1434

                        Co-editor:  Shawn A. Routhier
                                    Integrated Systems Inc.
                        Postal:     333 North Ave 4th Floor
                                    Wakefield, MA 01880
                        E-mail:     sar@epilogue.com
                        Phone:      +1 781 245 0804

                        Co-editor:  Bert Wijnen
                                    IBM T. J. Watson Research
                        postal:     Schagen 33
                                    3461 GL Linschoten
                                    Netherlands
                        email:      wijnen@vnet.ibm.com
                        phone:      +31-348-432-794
                       "

              DESCRIPTION
                  "This MIB module defines objects to help support coexistence
                   between SNMPv1, SNMPv2, and SNMPv3."
          ::= { snmpModules 18 }

      -- Administrative assignments ****************************************

      snmpCommunityMIBObjects     OBJECT IDENTIFIER ::= { snmpCommunityMIB 1 }
      snmpCommunityMIBConformance OBJECT IDENTIFIER ::= { snmpCommunityMIB 2 }

      --
      -- The snmpCommunityTable contains a database of community strings.
      -- This table provides mappings between community strings, and the
      -- parameters required for View-based Access Control.
      --

      snmpCommunityTable OBJECT-TYPE
          SYNTAX       SEQUENCE OF SnmpCommunityEntry
          MAX-ACCESS   not-accessible





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          STATUS       current
          DESCRIPTION
              "The table of community strings configured in the SNMP
               engine's Local Configuration Datastore (LCD)."
          ::= { snmpCommunityMIBObjects 1 }

      snmpCommunityEntry OBJECT-TYPE
          SYNTAX       SnmpCommunityEntry
          MAX-ACCESS   not-accessible
          STATUS       current
          DESCRIPTION
              "Information about a particular community string."
          INDEX       { IMPLIED snmpCommunityIndex }
          ::= { snmpCommunityTable 1 }

      SnmpCommunityEntry ::= SEQUENCE {
          snmpCommunityIndex               SnmpAdminString,
          snmpCommunityName                OCTET STRING,
          snmpCommunitySecurityName        SnmpAdminString,
          snmpCommunityContextEngineID     SnmpEngineID,
          snmpCommunityContextName         SnmpAdminString,
          snmpCommunityTransportTag        SnmpTagValue,
          snmpCommunityStorageType         StorageType,
          snmpCommunityStatus              RowStatus
      }

      snmpCommunityIndex OBJECT-TYPE
          SYNTAX      SnmpAdminString (SIZE(1..32))
          MAX-ACCESS  not-accessible
          STATUS      current
          DESCRIPTION
              "The unique index value of a row in this table."
          ::= { snmpCommunityEntry 1 }

      snmpCommunityName OBJECT-TYPE
          SYNTAX       OCTET STRING (SIZE(1..64))
          MAX-ACCESS   read-create
          STATUS       current
          DESCRIPTION
              "The community string for which a row in this table
               represents a configuration."
          ::= { snmpCommunityEntry 2 }

      snmpCommunitySecurityName OBJECT-TYPE
          SYNTAX       SnmpAdminString
          MAX-ACCESS   read-create
          STATUS       current





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          DESCRIPTION
              "A human readable string representing the corresponding
               value of snmpCommunityName in a Security Model
               independent format."
          ::= { snmpCommunityEntry 3 }

      snmpCommunityContextEngineID OBJECT-TYPE
          SYNTAX       SnmpEngineID
          MAX-ACCESS   read-create
          STATUS       current
          DESCRIPTION
              "The contextEngineID indicating the location of the
               context in which management information is accessed
               when using the community string specified by the
               corresponding instance of snmpCommunityName.

               The default value is the snmpEngineID of the entity in
               which this object is instantiated."
          ::= { snmpCommunityEntry 4 }

      snmpCommunityContextName OBJECT-TYPE
          SYNTAX       SnmpAdminString
          MAX-ACCESS   read-create
          STATUS       current
          DESCRIPTION
              "The context in which management information is accessed
               when using the community string specified by the corresponding
               instance of snmpCommunityName."
          DEFVAL      { ''H }   -- the empty string
          ::= { snmpCommunityEntry 5 }

      snmpCommunityTransportTag OBJECT-TYPE
          SYNTAX       SnmpTagValue
          MAX-ACCESS   read-create
          STATUS       current
          DESCRIPTION
              "This object specifies a set of transport endpoints
               from which an agent will accept management requests.
               If a management request containing this community
               is received on a transport endpoint other than the
               transport endpoints identified by this object, the
               request is deemed unauthentic.

               The transports identified by this object are specified
               in the snmpTargetAddrTable.  Entries in that table
               whose snmpTargetAddrTagList contains this tag value
               are identified.





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               If the value of this object has zero-length, transport
               endpoints are not checked when authenticating messages
               containing this community string."
          DEFVAL      { ''H }   -- the empty string
          ::= { snmpCommunityEntry 6 }

      snmpCommunityStorageType OBJECT-TYPE
          SYNTAX       StorageType
          MAX-ACCESS   read-create
          STATUS       current
          DESCRIPTION
              "The storage type for this conceptual row in the
               snmpCommunityTable.  Conceptual rows having the value
               'permanent' need not allow write-access to any
               columnar object in the row."
          ::= { snmpCommunityEntry 7 }

      snmpCommunityStatus OBJECT-TYPE
          SYNTAX       RowStatus
          MAX-ACCESS   read-create
          STATUS       current
          DESCRIPTION
              "The status of this conceptual row in the snmpCommunityTable.

               An entry in this table is not qualified for activation
               until instances of all corresponding columns have been
               initialized, either through default values, or through
               Set operations.  The snmpCommunityName and
               snmpCommunitySecurityName objects must be explicitly set."
          ::= { snmpCommunityEntry 8 }

      --
      -- The snmpTargetAddrExtTable augments the snmpTargetAddrTable with
      -- a transport address mask value and a maximum message size value.
      -- The transport address mask allows entries in the
      -- snmpTargetAddrTable to define a set of addresses instead of just
      -- a single address.  The maximum message size value allows the
      -- maximum message size of another SNMP entity to be configured
      -- for use in SNMPv1 (and SNMPv2c) transactions, where the message
      -- format does not specify a maximum message size.
      --

      snmpTargetAddrExtTable OBJECT-TYPE
          SYNTAX       SEQUENCE OF SnmpTargetAddrExtEntry
          MAX-ACCESS   not-accessible
          STATUS       current
          DESCRIPTION





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              "The table of mask and mms values associated with the
               snmpTargetAddrTable."
          ::= { snmpCommunityMIBObjects 2 }

      snmpTargetAddrExtEntry OBJECT-TYPE
          SYNTAX       SnmpTargetAddrExtEntry
          MAX-ACCESS   not-accessible
          STATUS       current
          DESCRIPTION
              "Information about a particular mask and mms value."
          AUGMENTS       { snmpTargetAddrEntry }
          ::= { snmpTargetAddrExtTable 1 }

      SnmpTargetAddrExtEntry ::= SEQUENCE {
          snmpTargetAddrTMask              OCTET STRING,
          snmpTargetAddrMMS                Integer32
      }

      snmpTargetAddrTMask OBJECT-TYPE
          SYNTAX      OCTET STRING (SIZE (0..255))
          MAX-ACCESS  read-create
          STATUS      current
          DESCRIPTION
              "The mask value associated with an entry in the
               snmpTargetAddrTable.  The value of this object must
               have the same length as the corresponding instance of
               snmpTargetAddrTAddress, or must have length 0."
          DEFVAL { ''H }
          ::= { snmpTargetAddrExtEntry 1 }

      snmpTargetAddrMMS OBJECT-TYPE
          SYNTAX      Integer32 (484..65535)
          MAX-ACCESS  read-create
          STATUS      current
          DESCRIPTION
              "The maximum message size value associated with an entry
               in the snmpTargetAddrTable."
          DEFVAL { 2048 }
          ::= { snmpTargetAddrExtEntry 2 }

      --
      -- The snmpTrapAddress and snmpTrapCommunity objects are included
      -- in notifications that are forwarded by a proxy, which were
      -- originally received as SNMPv1 Trap messages.
      --

      snmpTrapAddress OBJECT-TYPE





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          SYNTAX      IpAddress
          MAX-ACCESS  accessible-for-notify
          STATUS      current
          DESCRIPTION
              "The value of the agent-addr field of a Trap PDU which
               is forwarded by a proxy forwarder application using
               an SNMP version other than SNMPv1.  The value of this
               object SHOULD contain the value of the agent-addr field
               from the original Trap PDU as generated by an SNMPv1
               agent."
          ::= { snmpCommunityMIBObjects 3 }

      snmpTrapCommunity OBJECT-TYPE
          SYNTAX      OCTET STRING
          MAX-ACCESS  accessible-for-notify
          STATUS      current
          DESCRIPTION
              "The value of the community string field of an SNMPv1
               message containing a Trap PDU which is forwarded by a
               a proxy forwarder application using an SNMP version
               other than SNMPv1.  The value of this object SHOULD
               contain the value of the community string field from
               the original SNMPv1 message containing a Trap PDU as
               generated by an SNMPv1 agent."
          ::= { snmpCommunityMIBObjects 4 }

      -- Conformance Information *******************************************

      snmpCommunityMIBCompliances OBJECT IDENTIFIER
                                  ::= { snmpCommunityMIBConformance 1 }
      snmpCommunityMIBGroups      OBJECT IDENTIFIER
                                  ::= { snmpCommunityMIBConformance 2 }

      -- Compliance statements

      snmpCommunityMIBCompliance MODULE-COMPLIANCE
          STATUS       current
          DESCRIPTION
              "The compliance statement for SNMP engines which
               implement the SNMP-COMMUNITY-MIB."

          MODULE       -- this module
              MANDATORY-GROUPS { snmpCommunityGroup }

              OBJECT           snmpCommunityName
              MIN-ACCESS       read-only
              DESCRIPTION     "Write access is not required."





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              OBJECT           snmpCommunitySecurityName
              MIN-ACCESS       read-only
              DESCRIPTION     "Write access is not required."

              OBJECT           snmpCommunitySecurityLevel
              MIN-ACCESS       read-only
              DESCRIPTION     "Write access is not required."

              OBJECT           snmpCommunityContextEngineID
              MIN-ACCESS       read-only
              DESCRIPTION     "Write access is not required."

              OBJECT           snmpCommunityContextName
              MIN-ACCESS       read-only
              DESCRIPTION     "Write access is not required."

              OBJECT           snmpCommunityTransportTag
              MIN-ACCESS       read-only
              DESCRIPTION     "Write access is not required."

              OBJECT           snmpCommunityStorageType
              MIN-ACCESS       read-only
              DESCRIPTION     "Write access is not required."

              OBJECT           snmpCommunityStatus
              MIN-ACCESS       read-only
              DESCRIPTION     "Write access is not required."

          ::= { snmpCommunityMIBCompliances 1 }

      snmpCommunityGroup OBJECT-GROUP
          OBJECTS {
              snmpCommunityIndex,
              snmpCommunityName,
              snmpCommunitySecurityName,
              snmpCommunityContextEngineID,
              snmpCommunityContextName,
              snmpCommunityTransportTag,
              snmpCommunityStorageType,
              snmpCommunityStatus,
              snmpTargetAddrTMask,
              snmpTargetAddrMMS
          }
          STATUS       current
          DESCRIPTION
              "A collection of objects providing for configuration
               of community strings for SNMPv1 (and SNMPv2c) usage."





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          ::= { snmpCommunityMIBGroups 1 }

      END
















































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6.  Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.






























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7.  Acknowledgments

   This document is the result of the efforts of the SNMPv3 Working
   Group.  The design of the SNMP-COMMUNITY-MIB incorporates work done
   by the authors of SNMPv2*:

       Jeff Case (SNMP Research, Inc.)
       David Harrington (Cabletron Systems Inc.)
       David Levi (SNMP Research, Inc.)
       Brian O'Keefe (Hewlett Packard)
       Jon Saperia (BGS Systems Inc.)
       Steve Waldbusser (International Network Services)







































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8.  Security Considerations

   Although SNMPv1 and SNMPv2 do not provide any security, allowing
   community names to be mapped into securityName/contextName provides
   the ability to use view-based access control to limit the access of
   unsecured SNMPv1 and SNMPv2 operations.  In fact, it is important for
   network administrators to make use of this capability in order to
   avoid unauthorized access to MIB data that would otherwise be secure.

   Further, the SNMP-COMMUNITY-MIB has the potential to expose community
   strings which provide access to more information than that which is
   available using the usual 'public' community string.  For this
   reason, a security administrator may wish to limit accessibility to
   the SNMP-COMMUNITY-MIB, and in particular, to make it inaccessible
   when using the 'public' community string.

   When a proxy implementation translates messages between SNMPv1 (or
   SNMPv2c) and SNMPv3, there may be a loss of security.  For example,
   an SNMPv3 message received using authentication and privacy which is
   subsequently forwarded using SNMPv1 will lose the security benefits
   of using authentication and privacy.  Careful configuration of
   proxies is required to address such situations.  One approach to deal
   with such situations might be to use an encrypted tunnel.




























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9.  References

[1]  Rose, M. and K. McCloghrie, "Structure and Identification of
     Management Information for TCP/IP-based internets"", STD16, RFC
     1155, May 1990.

[2]  Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network
     Management Protocol", STD15, RFC 1157, SNMP Research, Performance
     Systems International, Performance Systems International, MIT
     Laboratory for Computer Science, May 1990.

[3]  McCloghrie, K., and M. Rose, Editors, "Concise MIB Definitions",
     STD 16, RFC 1212, Hughes LAN Systems, Performance Systems
     International, March 1991.

[4]  Rose, M. T., "A Convention for Defining Traps for use with the
     SNMP", RFC 1215, March 1991.

[5]  McCloghrie, K., and M. Rose, "A Convention for Describing SNMP-
     based Agents", RFC 1303, Hughes LAN Systems, Dover Beach
     Consulting, Inc., February 1992.

[6]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
     Waldbusser, "Introduction to Community-based SNMPv2", RFC1901, SNMP
     Research,Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc.,
     International Network Services, January 1996.

[7]  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)", RFC1902, SNMP
     Research,Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc.,
     International Network Services, January 1996.

[8]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
     Waldbusser, "Textual Conventions for Version 2 of the Simple
     Network Management Protocol (SNMPv2)", RFC1903, SNMP Research,Inc.,
     Cisco Systems, Inc., Dover Beach Consulting, Inc., International
     Network Services, January 1996.

[9]  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.

[10] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
     Waldbusser, "Protocol Operations for Version 2 of the Simple
     Network Management Protocol (SNMPv2)", RFC1905, SNMP Research,Inc.,
     Cisco Systems, Inc., Dover Beach Consulting, Inc., International





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     Network Services, January 1996.

[11] 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.

[12] 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)", RFC1907, SNMP
     Research,Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc.,
     International Network Services, January 1996.

[13] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and S.
     Waldbusser, "Coexistence between Version 1 and Version 2 of the
     Internet-standard Network Management Framework", RFC1908, SNMP
     Research,Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc.,
     International Network Services, January 1996.

[14] Levi, D., Wijnen, B., "Mapping SNMPv2 onto SNMPv1 within a bi-
     lingual SNMP agent", RFC2089, SNMP Research, Inc., IBM, January
     1997.

[15] Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997.

[16] The SNMPv3 Working Group, Harrington, D., Wijnen, B., "An
     Architecture for Describing SNMP Management Frameworks", draft-
     ietf-snmpv3-arch-05.txt, February 1999.

[17] The SNMPv3 Working Group, Case, J., Harrington, D., Wijnen, B.,
     "Message Processing and Dispatching for the Simple Network
     Management Protocol (SNMP)", draft-ietf-snmpv3-mpc-05.txt, February
     1999.

[18] The SNMPv3 Working Group, Levi, D., Meyer, P., Stewart, B., "SNMP
     Applications", draft-ietf-snmpv3-appl-v2-03.txt, February 1999.

[19] The SNMPv3 Working Group, Blumenthal, U., Wijnen, B., "The User-
     Based Security Model for Version 3 of the Simple Network Management
     Protocol (SNMP)", draft-ietf-snmpv3-usm-v2-05.txt, February 1999.

[20] The SNMPv3 Working Group, Wijnen, B., Presuhn, R., McCloghrie, K.,
     "View-based Access Control Model for the Simple Network Management
     Protocol (SNMP)", draft-ietf-snmpv3-vacm-04.txt, February 1999.







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10.  Editor's Address

     Rob Frye
     MCI Communications Corp.
     2100 Reston Parkway, Suite 600
     Reston, VA 20191
     U.S.A.
     Phone: +1 703 715 7225
     EMail: Rob.Frye@mci.com

     David B. Levi
     SNMP Research, Inc.
     3001 Kimberlin Heights Road
     Knoxville, TN 37920-9716
     U.S.A.
     Phone: +1 423 573 1434
     EMail: levi@snmp.com

     Shawn A. Routhier
     Integrated Systems Inc.
     333 North Ave 4th Floor
     Wakefield MA 01880
     U.S.A.
     Phone: + 1 781 245 0804
     EMail: sar@epilogue.com

     Bert Wijnen
     IBM T. J. Watson Research
     Schagen 33
     3461 GL Linschoten
     Netherlands
     Phone: +31 348 432 794
     EMail: wijnen@vnet.ibm.com


















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   A.  Full Copyright Statement

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the  purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


























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