





Network Working Group                                          J. Davin
Request for Comments: 1351          MIT Laboratory for Computer Science
                                                              J. Galvin
                                      Trusted Information Systems, Inc.
                                                          K. McCloghrie
                                               Hughes LAN Systems, Inc.
                                                              July 1992


                       SNMP Administrative Model

Status of this Memo

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

Table of Contents

   1.    Abstract  . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.    Introduction  . . . . . . . . . . . . . . . . . . . . . . .  2
   3.    Elements of the Model . . . . . . . . . . . . . . . . . . .  2
   3.1   SNMP Party  . . . . . . . . . . . . . . . . . . . . . . . .  2
   3.2   SNMP Protocol Entity  . . . . . . . . . . . . . . . . . . .  6
   3.3   SNMP Management Station . . . . . . . . . . . . . . . . . .  6
   3.4   SNMP Agent  . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.5   View Subtree  . . . . . . . . . . . . . . . . . . . . . . .  7
   3.6   MIB View  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.7   SNMP Management Communication . . . . . . . . . . . . . . .  8
   3.8   SNMP Authenticated Management Communication . . . . . . . .  9
   3.9   SNMP Private Management Communication   . . . . . . . . . .  9
   3.10  SNMP Management Communication Class . . . . . . . . . . . . 10
   3.11  SNMP Access Control Policy  . . . . . . . . . . . . . . . . 11
   3.12  SNMP Proxy Party  . . . . . . . . . . . . . . . . . . . . . 12
   3.13  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . 13
   3.13.1  Generating a Request  . . . . . . . . . . . . . . . . . . 13
   3.13.2  Processing a Received Communication . . . . . . . . . . . 15
   3.13.3  Generating a Response . . . . . . . . . . . . . . . . . . 17
   4.    Application of the Model  . . . . . . . . . . . . . . . . . 17
   4.1   Non-Secure Minimal Agent Configuration  . . . . . . . . . . 17
   4.2   Secure Minimal Agent Configuration  . . . . . . . . . . . . 20
   4.3   Proxy Configuration   . . . . . . . . . . . . . . . . . . . 21
   4.3.1   Foreign Proxy Configuration . . . . . . . . . . . . . . . 22
   4.3.2   Native Proxy Configuration  . . . . . . . . . . . . . . . 25
   4.4   Public Key Configuration  . . . . . . . . . . . . . . . . . 27
   4.5   MIB View Configurations . . . . . . . . . . . . . . . . . . 29



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   5.    Compatibility . . . . . . . . . . . . . . . . . . . . . . . 33
   6.    Security Considerations . . . . . . . . . . . . . . . . . . 33
   7.    References  . . . . . . . . . . . . . . . . . . . . . . . .
   8.    Authors' Addresses  . . . . . . . . . . . . . . . . . . . . 34

1.  Abstract

   This memo presents an elaboration of the SNMP administrative model
   set forth in [1]. This model provides a unified conceptual basis for
   administering SNMP protocol entities to support

     o authentication and integrity,

     o privacy,

     o access control, and

     o the cooperation of multiple protocol entities.

   Please send comments to the SNMP Security Developers mailing list
   (snmp-sec-dev@tis.com).

2.  Introduction

   This memo presents an elaboration of the SNMP administrative model
   set forth in [1]. It describes how the elaborated administrative
   model is applied to realize effective network management in a variety
   of configurations and environments.

   The model described here entails the use of distinct identities for
   peers that exchange SNMP messages. Thus, it represents a departure
   from the community-based administrative model set forth in [1]. By
   unambiguously identifying the source and intended recipient of each
   SNMP message, this new strategy improves upon the historical
   community scheme both by supporting a more convenient access control
   model and allowing for effective use of asymmetric (public key)
   security protocols in the future.

3.  Elements of the Model

3.1   SNMP Party

   A SNMP party  is a conceptual, virtual execution context whose
   operation is restricted (for security or other purposes) to an
   administratively defined subset of all possible operations of a
   particular SNMP protocol entity (see Section 3.2).  Whenever a SNMP
   protocol entity processes a SNMP message, it does so by acting as a
   SNMP party and is thereby restricted to the set of operations defined



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   for that party. The set of possible operations specified for a SNMP
   party may be overlapping or disjoint with respect to the sets of
   other SNMP parties; it may also be a proper or improper subset of all
   possible operations of the SNMP protocol entity.

   Architecturally, each SNMP party comprises

     o a single, unique party identity,

     o a single authentication protocol and associated
       parameters by which all protocol messages originated by
       the party are authenticated as to origin and integrity,

     o a single privacy protocol and associated parameters by
       which all protocol messages received by the party are
       protected from disclosure,

     o a single MIB view (see Section 3.6) to which all
       management operations performed by the party are
       applied, and

     o a logical network location at which the party executes,
       characterized by a transport protocol domain and
       transport addressing information.

   Conceptually, each SNMP party may be represented by an ASN.1 value
   with the following syntax:


      SnmpParty ::= SEQUENCE {
        partyIdentity
           OBJECT IDENTIFIER,
        partyTDomain
           OBJECT IDENTIFIER,
        partyTAddr
           OCTET STRING,
        partyProxyFor
           OBJECT IDENTIFIER,
        partyMaxMessageSize
           INTEGER,
        partyAuthProtocol
           OBJECT IDENTIFIER,
        partyAuthClock
           INTEGER,
        partyAuthLastMsg
           INTEGER,
        partyAuthNonce
           INTEGER,



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        partyAuthPrivate
           OCTET STRING,
        partyAuthPublic
           OCTET STRING,
        partyAuthLifetime
           INTEGER,
        partyPrivProtocol
           OBJECT IDENTIFIER,
        partyPrivPrivate
           OCTET STRING,
        partyPrivPublic
           OCTET STRING
      }


   For each SnmpParty value that represents a SNMP party, the following
   statements are true:

     o Its partyIdentity component is the party identity.

     o Its partyTDomain component is called the transport
       domain and indicates the kind of transport service by
       which the party receives network management traffic.
       An example of a transport domain is
       rfc1351Domain (SNMP over UDP, using SNMP
       parties).

     o Its partyTAddr component is called the transport
       addressing information and represents a transport
       service address by which the party receives network
       management traffic.

     o Its partyProxyFor component is called the proxied
       party  and represents the identity of a second SNMP
       party or other management entity with which
       interaction may be necessary to satisfy received
       management requests. In this context, the value
       noProxy signifies that the party responds to received
       management requests by entirely local mechanisms.

     o Its partyMaxMessageSize component is called the
       maximum message size and represents the length in
       octets of the largest SNMP message this party is
       prepared to accept.

     o Its partyAuthProtocol component is called the
       authentication protocol and identifies a protocol and a
       mechanism by which all messages generated by the party



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       are authenticated as to integrity and origin. In this
       context, the value noAuth signifies that messages
       generated by the party are not authenticated as to
       integrity and origin.

     o Its partyAuthClock component is called the
       authentication clock and represents a notion of the
       current time that is specific to the party. The
       significance of this component is specific to the
       authentication protocol.

     o Its partyAuthLastMsg component is called the
       last-timestamp and represents a notion of time
       associated with the most recent, authentic protocol
       message generated by the party. The significance of this
       component is specific to the authentication protocol.

     o Its partyAuthNonce component is called the nonce
       and represents a monotonically increasing integer
       associated with the most recent, authentic protocol
       message generated by the party. The significance of this
       component is specific to the authentication protocol.

     o Its partyAuthPrivate component is called the private
       authentication key and represents any secret value
       needed to support the authentication protocol. The
       significance of this component is specific to the
       authentication protocol.

     o Its partyAuthPublic component is called the public
       authentication key and represents any public value that
       may be needed to support the authentication protocol.
       The significance of this component is specific to the
       authentication protocol.

     o Its partyAuthLifetime component is called the
       lifetime and represents an administrative upper bound
       on acceptable delivery delay for protocol messages
       generated by the party. The significance of this
       component is specific to the authentication protocol.

     o Its partyPrivProtocol component is called the privacy
       protocol and identifies a protocol and a mechanism by
       which all protocol messages received by the party are
       protected from disclosure. In this context, the value
       noPriv signifies that messages received by the party are
       not protected from disclosure.




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     o Its partyPrivPrivate component is called the private
       privacy key and represents any secret value needed to
       support the privacy protocol. The significance of this
       component is specific to the privacy protocol.

     o Its partyPrivPublic component is called the public
       privacy key and represents any public value that may be
       needed to support the privacy protocol. The significance
       of this component is specific to the privacy protocol.

   If, for all SNMP parties realized by a SNMP protocol entity, the
   authentication protocol is noAuth and the privacy protocol is noPriv,
   then that protocol entity is called non-secure.

3.2   SNMP Protocol Entity

   A SNMP protocol entity is an actual process which performs network
   management operations by generating and/or responding to SNMP
   protocol messages in the manner specified in [1]. When a protocol
   entity is acting as a particular SNMP party (see Section 3.1), the
   operation of that entity must be restricted to the subset of all
   possible operations that is administratively defined for that party.

   By definition, the operation of a SNMP protocol entity requires no
   concurrency between processing of any single protocol message (by a
   particular SNMP party) and processing of any other protocol message
   (by a potentially different SNMP party). Accordingly, implementation
   of a SNMP protocol entity to support more than one party need not be
   multi-threaded. However, there may be situations where implementors
   may choose to use multi-threading.

   Architecturally, every SNMP entity maintains a local database that
   represents all SNMP parties known to it -- those whose operation is
   realized locally, those whose operation is realized by proxy
   interactions with remote parties or devices, and those whose
   operation is realized by remote entities. In addition, every SNMP
   protocol entity maintains a local database that represents an access
   control policy (see Section 3.11) that defines the access privileges
   accorded to known SNMP parties.

3.3   SNMP Management Station

   A SNMP management station is the operational role assumed by a SNMP
   party when it initiates SNMP management operations by the generation
   of appropriate SNMP protocol messages or when it receives and
   processes trap notifications.

   Sometimes, the term SNMP management station is applied to partial



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   implementations of the SNMP (in graphics workstations, for example)
   that focus upon this operational role. Such partial implementations
   may provide for convenient, local invocation of management services,
   but they may provide little or no support for performing SNMP
   management operations on behalf of remote protocol users.

3.4   SNMP Agent

   A SNMP agent is the operational role assumed by a SNMP party when it
   performs SNMP management operations in response to received SNMP
   protocol messages such as those generated by a SNMP management
   station (see Section 3.3).

   Sometimes, the term SNMP agent is applied to partial implementations
   of the SNMP (in embedded systems, for example) that focus upon this
   operational role. Such partial implementations provide for
   realization of SNMP management operations on behalf of remote users
   of management services, but they may provide little or no support for
   local invocation of such services.

3.5   View Subtree

   A view subtree is the set of all MIB object instances which have a
   common ASN.1 OBJECT IDENTIFIER prefix to their names. A view subtree
   is identified by the OBJECT IDENTIFIER value which is the longest
   OBJECT IDENTIFIER prefix common to all (potential) MIB object
   instances in that subtree.

3.6   MIB View

   A MIB view is a subset of the set of all instances of all object
   types defined according to the Internet-standard SMI [2] (i.e., of
   the universal set of all instances of all MIB objects), subject to
   the following constraints:

     o Each element of a MIB view is uniquely named by an
       ASN.1 OBJECT IDENTIFIER value. As such,
       identically named instances of a particular object type
       (e.g., in different agents) must be contained within
       different MIB views. That is, a particular object
       instance name resolves within a particular MIB view to
       at most one object instance.

     o Every MIB view is defined as a collection of view
       subtrees.






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3.7   SNMP Management Communication

   A SNMP management communication is a communication from one specified
   SNMP party to a second specified SNMP party about management
   information that is represented in the MIB view of the appropriate
   party. In particular, a SNMP management communication may be

     o a query by the originating party about information in
       the MIB view of the addressed party (e.g., getRequest
       and getNextRequest),

     o an indicative assertion to the addressed party about
       information in the MIB view of the originating party
       (e.g., getResponse or trapNotification), or

     o an imperative assertion by the originating party about
       information in the MIB view of the addressed party
       (e.g., setRequest).

   A management communication is represented by an ASN.1 value with the
   syntax


      SnmpMgmtCom ::= [1] IMPLICIT SEQUENCE {
        dstParty
           OBJECT IDENTIFIER,
        srcParty
           OBJECT IDENTIFIER,
        pdu
           PDUs
      }


   For each SnmpMgmtCom value that represents a SNMP management
   communication, the following statements are true:

     o Its dstParty component is called the destination and
       identifies the SNMP party to which the communication
       is directed.

     o Its srcParty component is called the source and
       identifies the SNMP party from which the
       communication is originated.

     o Its pdu component has the form and significance
       attributed to it in [1].





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3.8   SNMP Authenticated Management Communication

   A SNMP authenticated management communication is a SNMP management
   communication (see Section 3.7) for which the originating SNMP party
   is (possibly) reliably identified and for which the integrity of the
   transmission of the communication is (possibly) protected. An
   authenticated management communication is represented by an ASN.1
   value with the syntax


      SnmpAuthMsg ::= [1] IMPLICIT SEQUENCE {
        authInfo
           ANY, - defined by authentication protocol
        authData
           SnmpMgmtCom
      }


   For each SnmpAuthMsg value that represents a SNMP authenticated
   management communication, the following statements are true:

     o Its authInfo component is called the authentication
       information and represents information required in
       support of the authentication protocol used by the
       SNMP party originating the message. The detailed
       significance of the authentication information is specific
       to the authentication protocol in use; it has no effect on
       the application semantics of the communication other
       than its use by the authentication protocol in
       determining whether the communication is authentic or
       not.

     o Its authData component is called the authentication
       data and represents a SNMP management
       communication.

3.9   SNMP Private Management Communication

   A SNMP private management communication is a SNMP authenticated
   management communication (see Section 3.8) that is (possibly)
   protected from disclosure. A private management communication is
   represented by an ASN.1 value with the syntax









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      SnmpPrivMsg ::= [1] IMPLICIT SEQUENCE {
        privDst
           OBJECT IDENTIFIER,
        privData
           [1] IMPLICIT OCTET STRING
      }


   For each SnmpPrivMsg value that represents a SNMP private management
   communication, the following statements are true:

     o Its privDst component is called the privacy destination
       and identifies the SNMP party to which the
       communication is directed.

     o Its privData component is called the privacy data and
       represents the (possibly encrypted) serialization
       (according to the conventions of [3] and [1]) of a SNMP
       authenticated management communication (see
       Section 3.8).

3.10   SNMP Management Communication Class

   A SNMP management communication class corresponds to a specific SNMP
   PDU type defined in [1]. A management communication class is
   represented by an ASN.1 INTEGER value according to the type of the
   identifying PDU (see Table 1).

                  Get             1
                  GetNext         2
                  GetResponse     4
                  Set             8
                  Trap           16

         Table 1: Management Communication Classes

   The value by which a communication class is represented is computed
   as 2 raised to the value of the ASN.1 context-specific tag for the
   appropriate SNMP PDU.

   A set of management communication classes is represented by the ASN.1
   INTEGER value that is the sum of the representations of the
   communication classes in that set. The null set is represented by the
   value zero.







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3.11   SNMP Access Control Policy

   A SNMP access control policy is a specification of a local access
   policy in terms of the network management communication classes which
   are authorized between pairs of SNMP parties. Architecturally, such a
   specification comprises three parts:

     o the targets of SNMP access control - the SNMP parties
       that may perform management operations as requested
       by management communications received from other
       parties,

     o the subjects of SNMP access control - the SNMP parties
       that may request, by sending management
       communications to other parties, that management
       operations be performed, and

     o the policy that specifies the classes of SNMP
       management communications that a particular target is
       authorized to accept from a particular subject.

   Access to individual MIB object instances is determined implicitly
   since by definition each (target) SNMP party performs operations on
   exactly one MIB view. Thus, defining the permitted access of a
   (reliably) identified subject party to a particular target party
   effectively defines the access permitted by that subject to that
   target's MIB view and, accordingly, to particular MIB object
   instances.

   Conceptually, a SNMP access policy is represented by a collection of
   ASN.1 values with the following syntax:


      AclEntry ::= SEQUENCE {
        aclTarget
           OBJECT IDENTIFIER,
        aclSubject
           OBJECT IDENTIFIER,
        aclPrivileges
           INTEGER
      }


   For each such value that represents one part of a SNMP access policy,
   the following statements are true:






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     o Its aclTarget component is called the target and
       identifies the SNMP party to which the partial policy
       permits access.

     o Its aclSubject component is called the subject and
       identifies the SNMP party to which the partial policy
       grants privileges.

     o Its aclPrivileges component is called the privileges and
       represents a set of SNMP management communication
       classes that are authorized to be processed by the
       specified target party when received from the specified
       subject party.

3.12   SNMP Proxy Party

   A SNMP proxy party is a SNMP party that performs management
   operations by communicating with another, logically remote party.

   When communication between a logically remote party and a SNMP proxy
   party is via the SNMP (over any transport protocol), then the proxy
   party is called a SNMP native proxy party. Deployment of SNMP native
   proxy parties is a means whereby the processing or bandwidth costs of
   management may be amortized or shifted -- thereby facilitating the
   construction of large management systems.

   When communication between a logically remote party and a SNMP proxy
   party is not via the SNMP, then the proxy party is called a SNMP
   foreign proxy party. Deployment of foreign proxy parties is a means
   whereby otherwise unmanageable devices or portions of an internet may
   be managed via the SNMP.

   The transparency principle that defines the behavior of a SNMP party
   in general applies in particular to a SNMP proxy party:

       The manner in which one SNMP party processes
       SNMP protocol messages received from another
       SNMP party is entirely transparent to the latter.

   The transparency principle derives directly from the historical SNMP
   philosophy of divorcing architecture from implementation. To this
   dichotomy are attributable many of the most valuable benefits in both
   the information and distribution models of the management framework,
   and it is the architectural cornerstone upon which large management
   systems may be built. Consistent with this philosophy, although the
   implementation of SNMP proxy agents in certain environments may
   resemble that of a transport-layer bridge, this particular
   implementation strategy (or any other!) does not merit special



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   recognition either in the SNMP management architecture or in standard
   mechanisms for proxy administration.

   Implicit in the transparency principle is the requirement that the
   semantics of SNMP management operations are preserved between any two
   SNMP peers. In particular, the "as if simultaneous" semantics of a
   Set operation are extremely difficult to guarantee if its scope
   extends to management information resident at multiple network
   locations. For this reason, proxy configurations that admit Set
   operations that apply to information at multiple locations are
   discouraged, although such operations are not explicitly precluded by
   the architecture in those rare cases where they might be supported in
   a conformant way.

   Also implicit in the transparency principle is the requirement that,
   throughout its interaction with a proxy agent, a management station
   is supplied with no information about the nature or progress of the
   proxy mechanisms by which its requests are realized. That is, it
   should seem to the management station -- except for any distinction
   in underlying transport address -- as if it were interacting via SNMP
   directly with the proxied device. Thus, a timeout in the
   communication between a proxy agent and its proxied device should be
   represented as a timeout in the communication between the management
   station and the proxy agent. Similarly, an error response from a
   proxied device should -- as much as possible -- be represented by the
   corresponding error response in the interaction between the proxy
   agent and management station.

3.13   Procedures

   This section describes the procedures followed by a SNMP protocol
   entity in processing SNMP messages. These procedures are independent
   of the particular authentication and privacy protocols that may be in
   use.

3.13.1   Generating a Request

   This section describes the procedure followed by a SNMP protocol
   entity whenever either a management request or a trap notification is
   to be transmitted by a SNMP party.

    1. An ASN.1 SnmpMgmtCom value is constructed for
       which the srcParty component identifies the originating
       party, for which the dstParty component identifies the
       receiving party, and for which the other component
       represents the desired management operation.





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    2. The local database is consulted to determine the
       authentication protocol and other relevant information
       for the originating SNMP party.

    3. An ASN.1 SnmpAuthMsg value is constructed with
       the following properties:

        o Its authInfo component is constructed according
          to the authentication protocol specified for the
          originating party.

          In particular, if the authentication protocol for the
          originating SNMP party is identified as noAuth,
          then this component corresponds to the OCTET
          STRING value of zero length.

        o Its authData component is the constructed
          SnmpMgmtCom value.

    4. The local database is consulted to determine the privacy
       protocol and other relevant information for the receiving
       SNMP party.

    5. An ASN.1 SnmpPrivMsg value is constructed with the
       following properties:

        o Its privDst component identifies the receiving
          SNMP party.

        o Its privData component is the (possibly
          encrypted) serialization of the SnmpAuthMsg
          value according to the conventions of [3] and [1].

          In particular, if the privacy protocol for the
          receiving SNMP party is identified as noPriv, then
          the privData component is unencrypted.
          Otherwise, the privData component is processed
          according to the privacy protocol.

    6. The constructed SnmpPrivMsg value is serialized
       according to the conventions of [3] and [1].

    7. The serialized SnmpPrivMsg value is transmitted
       using the transport address and transport domain for
       the receiving SNMP party.






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3.13.2   Processing a Received Communication

   This section describes the procedure followed by a SNMP protocol
   entity whenever a management communication is received.

    1. If the received message is not the serialization (according
       to the conventions of [3] and [1]) of an ASN.1
       SnmpPrivMsg value, then that message is discarded
       without further processing.

    2. The local database is consulted for information about
       the receiving SNMP party identified by the privDst
       component of the SnmpPrivMsg value.

    3. If information about the receiving SNMP party is absent
       from the local database, or specifies a transport domain
       and address which indicates that the receiving party's
       operation is not realized by the local SNMP protocol
       entity, then the received message is discarded without
       further processing.

    4. An ASN.1 OCTET STRING value is constructed
       (possibly by decryption, according to the privacy
       protocol in use) from the privData component of said
       SnmpPrivMsg value.

       In particular, if the privacy protocol recorded for the
       party is noPriv, then the OCTET STRING value
       corresponds exactly to the privData component of the
       SnmpPrivMsg value.

    5. If the OCTET STRING value is not the serialization
       (according to the conventions of [3] and [1]) of an ASN.1
       SnmpAuthMsg value, then the received message is
       discarded without further processing.

    6. If the dstParty component of the authData
       component of the obtained SnmpAuthMsg value is
       not the same as the privDst component of the
       SnmpPrivMsg value, then the received message is
       discarded without further processing.

    7. The local database is consulted for information about
       the originating SNMP party identified by the srcParty
       component of the authData component of the
       SnmpAuthMsg value.





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    8. If information about the originating SNMP party is
       absent from the local database, then the received
       message is discarded without further processing.

    9. The obtained SnmpAuthMsg value is evaluated
       according to the authentication protocol and other
       relevant information associated with the originating
       SNMP party in the local database.

       In particular, if the authentication protocol is identified
       as noAuth, then the SnmpAuthMsg value is always
       evaluated as authentic.

   10. If the SnmpAuthMsg value is evaluated as
       unauthentic, then the received message is discarded
       without further processing, and an authentication failure
       is noted.

   11. The ASN.1 SnmpMgmtCom value is extracted from
       the authData component of the SnmpAuthMsg
       value.

   12. The local database is consulted for access privileges
       permitted by the local access policy to the originating
       SNMP party with respect to the receiving SNMP party.

   13. The management communication class is determined
       from the ASN.1 tag value associated with the
       SnmpMgmtCom value.

   14. If the management communication class of the received
       message is either 16 or 4 (i.e., Trap or GetResponse) and
       this class is not among the access privileges, then the
       received message is discarded without further processing.

   15. If the management communication class of the received
       message is not among the access privileges, then the
       received message is discarded without further processing
       after generation and transmission of a response message.
       This response message is directed to the originating
       SNMP party on behalf of the receiving SNMP party. Its
       var-bind-list and request-id components are identical
       to those of the received request. Its error-index
       component is zero and its error-status component is
       readOnly.

   16. If the proxied party associated with the receiving SNMP
       party in the local database is identified as noProxy,



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       then the management operation represented by the
       SnmpMgmtCom value is performed by the receiving
       SNMP protocol entity with respect to the MIB view
       identified with the receiving SNMP party according to
       the procedures set forth in [1].

   17. If the proxied party associated with the receiving SNMP
       party in the local database is not identified as noProxy,
       then the management operation represented by the
       SnmpMgmtCom value is performed through
       appropriate cooperation between the receiving SNMP
       party and the identified proxied party.

       In particular, if the transport domain associated with
       the identified proxied party in the local database is
       rfc1351Domain, then the operation requested by
       the received message is performed by the generation of a
       corresponding request to the proxied party on behalf of
       the receiving party. If the received message requires a
       response from the local SNMP protocol entity, then that
       response is subsequently generated from the response (if
       any) received from the proxied party corresponding to
       the newly generated request.

3.13.3   Generating a Response

   This section describes the procedure followed by a SNMP protocol
   entity whenever a response to a management request is generated.

   The procedure for generating a response to a SNMP management request
   is identical to the procedure for transmitting a request (see Section
   3.13.1), except for the derivation of the transport domain and
   address information.  In this case, the response is transmitted using
   the transport domain and address from which the corresponding request
   originated -- even if that is different from the transport
   information recorded in the local database.

4.  Application of the Model

   This section describes how the administrative model set forth above
   is applied to realize effective network management in a variety of
   configurations and environments. Several types of administrative
   configurations are identified, and an example of each is presented.

4.1   Non-Secure Minimal Agent Configuration

   This section presents an example configuration for a minimal, non-
   secure SNMP agent that interacts with one or more SNMP management



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   stations. Table 2 presents information about SNMP parties that is
   known both to the minimal agent and to the manager, while Table 3
   presents similarly common information about the local access policy.

   As represented in Table 2, the example agent party operates at UDP
   port 161 at IP address 1.2.3.4 using the party identity gracie; the
   example manager operates at UDP port 2001 at IP address 1.2.3.5 using
   the identity george. At minimum, a non-secure SNMP agent
   implementation must provide for administrative configuration (and
   non-volatile storage) of the identities and transport addresses of
   two SNMP parties: itself and a remote peer. Strictly speaking, other
   information about these two parties (including access policy
   information) need not be configurable.

   Suppose that the managing party george wishes to interrogate the
   agent named gracie by issuing a SNMP GetNext request message. The
   manager consults its local database of party information. Because the
   authentication protocol for the party george is recorded as noAuth,
   the GetNext request message generated by the manager is not

    Identity          gracie                george
                      (agent)               (manager)
    Domain            rfc1351Domain         rfc1351Domain
    Address           1.2.3.4, 161          1.2.3.5, 2001
    Proxied Party     noProxy               noProxy
    Auth Prot         noAuth                noAuth
    Auth Priv Key     ""                    ""
    Auth Pub Key      ""                    ""
    Auth Clock        0                     0
    Auth Last Msg     0                     0
    Auth Lifetime     0                     0
    Priv Prot         noPriv                noPriv
    Priv Priv Key     ""                    ""
    Priv Pub Key      ""                    ""

         Table 2: Party Information for Minimal Agent



              Target    Subject   Privileges
              gracie    george    3
              george    gracie    20

        Table 3: Access Information for Minimal Agent

   authenticated as to origin and integrity. Because, according to the
   manager's database, the privacy protocol for the party gracie is
   noPriv, the GetNext request message is not protected from disclosure.



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   Rather, it is simply assembled, serialized, and transmitted to the
   transport address (IP address 1.2.3.4, UDP port 161) associated in
   the manager's database with the party gracie.

   When the GetNext request message is received at the agent, the
   identity of the party to which it is directed (gracie) is extracted
   from the message, and the receiving protocol entity consults its
   local database of party information. Because the privacy protocol for
   the party gracie is recorded as noPriv, the received message is
   assumed not to be protected from disclosure. Similarly, the identity
   of the originating party (george) is extracted, and the local party
   database is consulted. Because the authentication protocol for the
   party george is recorded as noAuth, the received message is
   immediately accepted as authentic.

   The received message is fully processed only if the access policy
   database local to the agent authorizes GetNext request communications
   by the party george with respect to the agent party gracie. The
   access policy database presented as Table 3 authorizes such
   communications (as well as Get operations).

   When the received request is processed, a GetResponse message is
   generated with gracie as the source party and george, the party from
   which the request originated, as the destination party. Because the
   authentication protocol for gracie is recorded in the local party
   database as noAuth, the generated GetResponse message is not
   authenticated as to origin or integrity. Because, according to the
   local database, the privacy protocol for the party george is noPriv,
   the response message is not protected from disclosure. The response
   message is transmitted to the transport address from which the
   corresponding request originated -- without regard for the transport
   address associated with george in the local database.

   When the generated response is received by the manager, the identity
   of the party to which it is directed (george) is extracted from the
   message, and the manager consults its local database of party
   information. Because the privacy protocol for the party george is
   recorded as noPriv, the received response is assumed not to be
   protected from disclosure. Similarly, the identity of the originating
   party (gracie) is extracted, and the local party database is
   consulted. Because the authentication protocol for the party gracie
   is recorded as noAuth, the received response is immediately accepted
   as authentic.

   The received message is fully processed only if the access policy
   database local to the manager authorizes GetResponse communications
   by the party gracie with respect to the manager party george. The
   access policy database presented as Table 3 authorizes such response



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   messages (as well as Trap messages).

4.2   Secure Minimal Agent Configuration

   This section presents an example configuration for a secure, minimal
   SNMP agent that interacts with a single SNMP management station.
   Table 4 presents information about SNMP parties that is known both to
   the minimal agent and to the manager, while Table 5 presents
   similarly common information about the local access policy.

   The interaction of manager and agent in this configuration is very
   similar to that sketched above for the non-secure minimal agent --
   except that all protocol messages are authenticated as to origin and
   integrity and protected from disclosure. This example requires
   encryption in order to support distribution of secret keys via the
   SNMP itself. A more elaborate example comprising an additional pair
   of SNMP parties could support the exchange of non-secret information
   in authenticated messages without incurring the cost of encryption.

   An actual secure agent configuration may require SNMP parties for
   which the authentication and privacy protocols are noAuth and noPriv,
   respectively, in order to support clock synchronization (see [4]).
   For clarity, these additional parties are not represented in this
   example.

     Identity          ollie                stan
                       (agent)              (manager)
     Domain            rfc1351Domain        rfc1351Domain
     Address           1.2.3.4, 161         1.2.3.5, 2001
     Proxied Party     noProxy              noProxy
     Auth Prot         md5AuthProtocol      md5AuthProtocol
     Auth Priv Key     "0123456789ABCDEF"   "GHIJKL0123456789"
     Auth Pub Key      ""                   ""
     Auth Clock        0                    0
     Auth Last Msg     0                    0
     Auth Lifetime     500                  500
     Priv Prot         desPrivProtocol      desPrivProtocol
     Priv Priv Key     "MNOPQR0123456789"   "STUVWX0123456789"
     Priv Pub Key      ""                   ""

      Table 4: Party Information for Secure Minimal Agent


               Target   Subject   Privileges
               ollie    stan      3
               stan     ollie     20

      Table 5: Access Information for Secure Minimal Agent



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   As represented in Table 4, the example agent party operates at UDP
   port 161 at IP address 1.2.3.4 using the party identity ollie; the
   example manager operates at UDP port 2001 at IP address 1.2.3.5 using
   the identity stan. At minimum, a secure SNMP agent implementation
   must provide for administrative configuration (and non-volatile
   storage) of relevant information about two SNMP parties: itself and a
   remote peer. Both ollie and stan authenticate all messages that they
   generate by using the SNMP authentication protocol md5AuthProtocol
   and their distinct, private authentication keys. Although these
   private authentication key values ("0123456789ABCDEF" and
   "GHIJKL0123456789") are presented here for expository purposes,
   knowledge of private authentication keys is not normally afforded to
   human beings and is confined to those portions of the protocol
   implementation that require it.

   When using the md5AuthProtocol, the public authentication key for
   each SNMP party is never used in authentication and verification of
   SNMP exchanges. Also, because the md5AuthProtocol is symmetric in
   character, the private authentication key for each party must be
   known to another SNMP party with which authenticated communication is
   desired. In contrast, asymmetric (public key) authentication
   protocols would not depend upon sharing of a private key for their
   operation.

   All protocol messages originated by the party stan are encrypted on
   transmission using the desPrivProtocol privacy protocol and the
   private key "STUVWX0123456789"; they are decrypted upon reception
   according to the same protocol and key. Similarly, all messages
   originated by the party ollie are encrypted on transmission using the
   desPrivProtocol protocol and private privacy key "MNOPQR0123456789";
   they are correspondingly decrypted on reception. As with
   authentication keys, knowledge of private privacy keys is not
   normally afforded to human beings and is confined to those portions
   of the protocol implementation that require it.

4.3   Proxy Configuration

   This section presents examples of SNMP proxy configurations.  On one
   hand, foreign proxy configurations provide the capability to manage
   non-SNMP devices. On the other hand, native proxy configurations
   allow an administrator to shift the computational burden of rich
   management functionality away from network devices whose primary task
   is not management.  To the extent that SNMP proxy agents function as
   points of aggregation for management information, proxy
   configurations may also reduce the bandwidth requirements of large-
   scale management activities.

   The example configurations in this section are simplified for



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   clarity: actual configurations may require additional parties in
   order to support clock synchronization and distribution of secrets.

4.3.1   Foreign Proxy Configuration

   This section presents an example configuration by which a SNMP
   management station may manage network elements that do not themselves
   support the SNMP. This configuration centers on a SNMP proxy agent
   that realizes SNMP management operations by interacting with a non-
   SNMP device using a proprietary protocol.

   Table 6 presents information about SNMP parties that is recorded in
   the local database of the SNMP proxy agent.  Table 7 presents
   information about SNMP parties that is recorded in the local database
   of the SNMP management station. Table 8 presents information about
   the access policy specified by the local administration.

   As represented in Table 6, the proxy agent party operates at UDP port
   161 at IP address 1.2.3.5 using the party identity moe; the example
   manager operates at UDP port 2002 at IP address 1.2.3.4 using the
   identity larry. Both larry and moe authenticate all messages that
   they generate by using the protocol md5AuthProtocol and their
   distinct, private authentication keys. Although these private
   authentication key values ("0123456789ABCDEF" and

   Identity        larry               moe                 curly
                   (manager)           (proxy)             (proxied)
   Domain          rfc1351Domain       rfc1351Domain       acmeMgmtPrtcl
   Address         1.2.3.4, 2002       1.2.3.5, 161        0x98765432
   Proxied Party   noProxy             curly               noProxy
   Auth Prot       md5AuthProtocol     md5AuthProtocol     noAuth
   Auth Priv Key   "0123456789ABCDEF"  "GHIJKL0123456789"  ""
   Auth Pub Key    ""                  ""                  ""
   Auth Clock      0                   0                   0
   Auth Last Msg   0                   0                   0
   Auth Lifetime   500                 500                 0
   Priv Prot       noPriv              noPriv              noPriv
   Priv Priv Key   ""                  ""                  ""
   Priv Pub Key    ""                  ""                  ""

         Table 6: Party Information for Proxy Agent










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     Identity        larry               moe
                     (manager)           (proxy)
     Domain          rfc1351Domain       rfc1351Domain
     Address         1.2.3.4, 2002       1.2.3.5, 161
     Proxied Party   noProxy             noProxy
     Auth Prot       md5AuthProtocol     md5AuthProtocol
     Auth Priv Key   "0123456789ABCDEF"  "GHIJKL0123456789"
     Auth Pub Key    ""                  ""
     Auth Clock      0                   0
     Auth Last Msg   0                   0
     Auth Lifetime   500                 500
     Priv Prot       noPriv              noPriv
     Priv Priv Key   ""                  ""
     Priv Pub Key    ""                  ""

       Table 7: Party Information for Management Station



               Target   Subject   Privileges
               moe      larry     3
               larry    moe       20

         Table 8: Access Information for Foreign Proxy

   "GHIJKL0123456789") are presented here for expository purposes,
   knowledge of private keys is not normally afforded to human beings
   and is confined to those portions of the protocol implementation that
   require it.

   Although all SNMP agents that use cryptographic keys in their
   communication with other protocol entities will almost certainly
   engage in private SNMP exchanges to distribute those keys, in order
   to simplify this example, neither the management station nor the
   proxy agent sends or receives private SNMP communications. Thus, the
   privacy protocol for each of them is recorded as noPriv.

   The party curly does not send or receive SNMP protocol messages;
   rather, all communication with that party proceeds via a hypothetical
   proprietary protocol identified by the value acmeMgmtPrtcl. Because
   the party curly does not participate in the SNMP, many of the
   attributes recorded for that party in a local database are ignored.

   In order to interrogate the proprietary device associated with the
   party curly, the management station larry constructs a SNMP GetNext
   request and transmits it to the party moe operating (see Table 7) at
   UDP port 161, and IP address 1.2.3.5. This request is authenticated
   using the private authentication key "0123456789ABCDEF."



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   When that request is received by the party moe, the originator of the
   message is verified as being the party larry by using local knowledge
   (see Table 6) of the private authentication key "0123456789ABCDEF."
   Because party larry is authorized to issue GetNext requests with
   respect to party moe by the relevant access control policy (Table 8),
   the request is accepted. Because the local database records the
   proxied party for party moe as curly, the request is satisfied by its
   translation into appropriate operations of the acmeMgmtPrtcl directed
   at party curly. These new operations are transmitted to the party
   curly at the address 0x98765432 in the acmeMgmtPrtcl domain.

   When and if the proprietary protocol exchange between the proxy agent
   and the proprietary device concludes, a SNMP GetResponse management
   operation is constructed by the SNMP party moe to relay the results
   to party larry. This response communication is authenticated as to
   origin and integrity using the authentication protocol
   md5AuthProtocol and private authentication key "GHIJKL0123456789"
   specified for transmissions from party moe. It is then transmitted to
   the SNMP party larry operating at the management station at IP
   address 1.2.3.4 and UDP port 2002 (the source address for the
   corresponding request).

   When this response is received by the party larry, the originator of
   the message is verified as being the party moe by using local
   knowledge (see Table 7) of the private authentication key
   "GHIJKL0123456789." Because party moe is authorized to issue
   GetResponse communications with respect to party larry by the
   relevant access control policy (Table 8), the response is accepted,
   and the interrogation of the proprietary device is complete.

   It is especially useful to observe that the database of SNMP parties
   recorded at the proxy agent (Table 6) need be neither static nor
   configured exclusively by the management station.  For instance,
   suppose that, in this example, the acmeMgmtPrtcl was a proprietary,
   MAC-layer mechanism for managing stations attached to a local area
   network. In such an environment, the SNMP party moe would reside at a
   SNMP proxy agent attached to such a LAN and could, by participating
   in the LAN protocols, detect the attachment and disconnection of
   various stations on the LAN. In this scenario, the SNMP proxy agent
   could easily adjust its local database of SNMP parties to support
   indirect management of the LAN stations by the SNMP management
   station. For each new LAN station detected, the SNMP proxy agent
   would add to its database both an entry analogous to that for party
   curly (representing the new LAN station itself) and an entry
   analogous to that for party moe (representing a proxy for that new
   station in the SNMP domain).

   By using the SNMP to interrogate the database of parties held locally



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   by the SNMP proxy agent, a SNMP management station can discover and
   interact with new stations as they are attached to the LAN.

4.3.2   Native Proxy Configuration

   This section presents an example configuration that supports SNMP
   native proxy operations -- indirect interaction between a SNMP agent
   and a management station that is mediated by a second SNMP (proxy)
   agent.

   This example configuration is similar to that presented in the
   discussion of SNMP foreign proxy above. In this example, however, the
   party associated with the identity curly receives messages via the
   SNMP, and, accordingly interacts with the SNMP proxy agent moe using
   authenticated SNMP communications.

   Table 9 presents information about SNMP parties that is recorded in
   the local database of the SNMP proxy agent.  Table 7 presents
   information about SNMP parties that is recorded in the local database
   of the SNMP management station. Table 10 presents information about
   the access policy specified by the local administration.

   As represented in Table 9, the proxy party operates at UDP port 161
   at IP address 1.2.3.5 using the party identity moe;

  Identity       larry              moe                curly
                 (manager)          (proxy)            (proxied)
  Domain         rfc1351Domain      rfc1351Domain      rfc1351Domain
  Address        1.2.3.4, 2002      1.2.3.5, 161       1.2.3.6, 16
  Proxied Party  noProxy            curly              noProxy
  Auth Prot      md5AuthProtocol    md5AuthProtocol    md5AuthProtocol
  Auth Priv Key  "0123456789ABCDEF" "GHIJKL0123456789" "MNOPQR0123456789"
  Auth Pub Key   ""                 ""                 ""
  Auth Clock     0                  0                  0
  Auth Last Msg  0                  0                  0
  Auth Lifetime  500                500                500
  Priv Prot      noPriv             noPriv             noPriv
  Priv Priv Key  ""                 ""                 ""
  Priv Pub Key   ""                 ""                 ""

         Table 9: Party Information for Proxy Agent










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               Target   Subject   Privileges
               moe      larry     3
               larry    moe       20
               curly    moe       3
               moe      curly     20

         Table 10: Access Information for Native Proxy

   the example manager operates at UDP port 2002 at IP address 1.2.3.4
   using the identity larry; the proxied party operates at UDP port 161
   at IP address 1.2.3.6 using the party identity curly. Messages
   generated by all three SNMP parties are authenticated as to origin
   and integrity by using the authentication protocol md5AuthProtocol
   and distinct, private authentication keys. Although these private key
   values ("0123456789ABCDEF," "GHIJKL0123456789," and
   "MNOPQR0123456789") are presented here for expository purposes,
   knowledge of private keys is not normally afforded to human beings
   and is confined to those portions of the protocol implementation that
   require it.

   In order to interrogate the proxied device associated with the party
   curly, the management station larry constructs a SNMP GetNext request
   and transmits it to the party moe operating (see Table 7) at UDP port
   161 and IP address 1.2.3.5. This request is authenticated using the
   private authentication key "0123456789ABCDEF."

   When that request is received by the party moe, the originator of the
   message is verified as being the party larry by using local knowledge
   (see Table 9) of the private authentication key "0123456789ABCDEF."
   Because party larry is authorized to issue GetNext (and Get) requests
   with respect to party moe by the relevant access control policy
   (Table 10), the request is accepted. Because the local database
   records the proxied party for party moe as curly, the request is
   satisfied by its translation into a corresponding SNMP GetNext
   request directed from party moe to party curly. This new
   communication is authenticated using the private authentication key
   "GHIJKL0123456789" and transmitted to party curly at the IP address
   1.2.3.6.

   When this new request is received by the party curly, the originator
   of the message is verified as being the party moe by using local
   knowledge (see Table 9) of the private authentication key
   "GHIJKL0123456789." Because party moe is authorized to issue GetNext
   (and Get) requests with respect to party curly by the relevant access
   control policy (Table 10), the request is accepted. Because the local
   database records the proxied party for party curly as noProxy, the
   GetNext request is satisfied by local mechanisms. A SNMP GetResponse
   message representing the results of the query is then generated by



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   party curly. This response communication is authenticated as to
   origin and integrity using the private authentication key
   "MNOPQR0123456789" and transmitted to party moe at IP address 1.2.3.5
   (the source address for the corresponding request).

   When this response is received by party moe, the originator of the
   message is verified as being the party curly by using local knowledge
   (see Table 9) of the private authentication key "MNOPQR0123456789."
   Because party curly is authorized to issue GetResponse communications
   with respect to party moe by the relevant access control policy
   (Table 10), the response is not rejected. Instead, it is translated
   into a response to the original GetNext request from party larry.
   This response is authenticated as to origin and integrity using the
   private authentication key "GHIJKL0123456789" and is transmitted to
   the party larry at IP address 1.2.3.4 (the source address for the
   original request).

   When this response is received by the party larry, the originator of
   the message is verified as being the party moe by using local
   knowledge (see Table 7) of the private authentication key
   "GHIJKL0123456789." Because party moe is authorized to issue
   GetResponse communications with respect to party larry by the
   relevant access control policy (Table 10), the response is accepted,
   and the interrogation is complete.

4.4   Public Key Configuration

   This section presents an example configuration predicated upon a
   hypothetical security protocol. This hypothetical protocol would be
   based on asymmetric (public key) cryptography as a means for
   providing data origin authentication (but not protection against
   disclosure). This example illustrates the consistency of the
   administrative model with public key technology, and the extension of
   the example to support protection against disclosure should be
   apparent.
















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    Identity          ollie                      stan
                      (agent)                    (manager)
    Domain            rfc1351Domain              rfc1351Domain
    Address           1.2.3.4, 161               1.2.3.5, 2004
    Proxied Party     noProxy                    noProxy
    Auth Prot         pkAuthProtocol             pkAuthProtocol
    Auth Priv Key     "0123456789ABCDEF"         ""
    Auth Pub Key      ""                         "ghijkl0123456789"
    Auth Clock        0                          0
    Auth Last Msg     0                          0
    Auth Lifetime     500                        500
    Priv Prot         noPriv                     noPriv
    Priv Priv Key     ""                         ""
    Priv Pub Key      ""                         ""

       Table 11: Party Information for Public Key Agent

   The example configuration comprises a single SNMP agent that
   interacts with a single SNMP management station.  Tables 11 and 12
   present information about SNMP parties that is by the agent and
   manager, respectively, while Table 5 presents information about the
   local access policy that is known to both manager and agent.

   As represented in Table 11, the example agent party operates at UDP
   port 161 at IP address 1.2.3.4 using the party identity ollie; the
   example manager operates at UDP port 2004 at IP address 1.2.3.5 using
   the identity stan. Both ollie and stan authenticate all messages that
   they generate as to origin and integrity by using the hypothetical
   SNMP authentication protocol pkAuthProtocol and their distinct,
   private

    Identity          ollie                  stan
                      (agent)                (manager)
    Domain            rfc1351Domain          rfc1351Domain
    Address           1.2.3.4, 161           1.2.3.5, 2004
    Proxied Party     noProxy                noProxy
    Auth Prot         pkAuthProtocol         pkAuthProtocol
    Auth Priv Key     ""                     "GHIJKL0123456789"
    Auth Pub Key      "0123456789abcdef"     ""
    Auth Clock        0                      0
    Auth Last Msg     0                      0
    Auth Lifetime     500                    500
    Priv Prot         noPriv                 noPriv
    Priv Priv Key     ""                     ""
    Priv Pub Key      ""                     ""

   Table 12:  Party Information for Public Key Management
              Station



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   authentication keys. Although these private authentication key values
   ("0123456789ABCDEF" and "GHIJKL0123456789") are presented here for
   expository purposes, knowledge of private keys is not normally
   afforded to human beings and is confined to those portions of the
   protocol implementation that require it.

   In most respects, the interaction between manager and agent in this
   configuration is almost identical to that in the example of the
   minimal, secure SNMP agent described above. The most significant
   difference is that neither SNMP party in the public key configuration
   has knowledge of the private key by which the other party
   authenticates its transmissions. Instead, for each received
   authenticated SNMP communication, the identity of the originator is
   verified by applying an asymmetric cryptographic algorithm to the
   received message together with the public authentication key for the
   originating party. Thus, in this configuration, the agent knows the
   manager's public key ("ghijkl0123456789") but not its private key
   ("GHIJKL0123456789"); similarly, the manager knows the agent's public
   key ("0123456789abcdef") but not its private key
   ("0123456789ABCDEF").

   For simplicity, privacy protocols are not addressed in this example
   configuration, although their use would be necessary to the secure,
   automated distribution of secret keys.

4.5   MIB View Configurations

   This section describes a convention for the definition of MIB views
   and, using that convention, presents example configurations of MIB
   views for SNMP parties.

   A MIB view is defined by a collection of view subtrees (see Section
   3.6), and any MIB view may be represented in this way. Because MIB
   view definitions may, in certain cases, comprise a very large number
   of view subtrees, a convention for abbreviating MIB view definitions
   is desirable.

   The convention adopted in [5] supports abbreviation of MIB view
   definitions in terms of families of view subtrees that are either
   included in or excluded from the definition of the relevant MIB view.
   By this convention, a table locally maintained by each SNMP entity
   defines the MIB view associated with each SNMP party realized by that
   entity.  Each entry in the table represents a family of view subtrees
   that (according to the status of that entry) is either included in or
   excluded from the MIB view of some SNMP party. Each table entry
   represents a subtree family as a pairing of an OBJECT IDENTIFIER
   value (called the family name) together with a bitstring value
   (called the family mask). The family mask indicates which



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   subidentifiers of the associated family name are significant to the
   definition of the represented subtree family. For each possible MIB
   object instance, that instance belongs to the view subtree family
   represented by a particular table entry if

     o the OBJECT IDENTIFIER name of that MIB
       object instance comprises at least as many subidentifiers
       as does the family name for said table entry, and

     o each subidentifier in the name of said MIB object
       instance matches the corresponding subidentifier of the
       relevant family name whenever the corresponding bit of
       the associated family mask is non-zero.

   The appearance of a MIB object instance in the MIB view for a
   particular SNMP party is related to the membership of that instance
   in the subtree families associated with that party in local table
   entries:

     o If a MIB object instance belongs to none of the relevant
       subtree families, then that instance is not in the MIB
       view for the relevant SNMP party.

     o If a MIB object instance belongs to the subtree family
       represented by exactly one of the relevant table entries,
       then that instance is included in, or excluded from, the
       relevant MIB view according to the status of that entry.

     o If a MIB object instance belongs to the subtree families
       represented by more than one of the relevant table
       entries, then that instance is included in, or excluded
       from, the relevant MIB view according to the status of
       the single such table entry for which, first, the associated
       family name comprises the greatest number of
       subidentifiers, and, second, the associated family name is
       lexicographically greatest.

   The subtree family represented by a table entry for which the
   associated family mask is all ones corresponds to the single view
   subtree identified by the family name for that entry.  Because the
   convention of [5] provides for implicit extension of family mask
   values with ones, the subtree family represented by a table entry
   with a family mask of zero length always corresponds to a single view
   subtree.







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     Party Identity  Status     Family Name    Family Mask
     lucy            include    internet       ""h

         Table 13: View Definition for Minimal Agent

   Using this convention for abbreviating MIB view definitions, some of
   the most common definitions of MIB views may be conveniently
   expressed. For example, Table 13 illustrates the MIB view definitions
   required for a minimal SNMP entity that locally realizes a single
   SNMP party for which the associated MIB view embraces all instances
   of all MIB objects defined within the internet network management
   framework.  The represented table has a single entry. The SNMP party
   (lucy) for which that entry defines the MIB view is identified in the
   first column. The status of that entry (include) signifies that any
   MIB object instance belonging to the subtree family represented by
   that entry may appear in the MIB view for party lucy. The family name
   for that entry is internet, and the zero-length family mask value
   signifies that the relevant subtree family corresponds to the single
   view subtree rooted at that node.

   Another example of MIB view definition (see Table 14) is that of a
   SNMP protocol entity that locally realizes multiple SNMP parties with
   distinct MIB views. The MIB view associated with the party lucy
   comprises all instances of all MIB objects defined within the
   internet network management framework, except those pertaining to the
   administration of SNMP parties. In contrast, the MIB view attributed
   to the party ricky contains only MIB object instances defined in the
   system group of the internet-standard MIB together with those object
   instances by which SNMP parties are administered.

   A more complicated example of MIB view configuration illustrates the
   abbreviation of related collections of view subtrees by view subtree
   families (see Table 15). In this


     Party Identity  Status     Family Name    Family Mask
     lucy            include    internet       ""h
     lucy            exclude    snmpParties    ""h
     ricky           include    system         ""h
     ricky           include    snmpParties    ""h

         Table 14: View Definition for Multiple Parties

   example, the MIB view associated with party lucy includes all object
   instances in the system group of the internet-standard MIB together
   with some information related to the second network interface
   attached to the managed device. However, this interface-related
   information does not include the speed of the interface. The family



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   mask value "FFA0"h in the second table entry signifies that a MIB
   object instance belongs to the relevant subtree family if the initial
   prefix of its name places it within the ifEntry portion of the
   registration hierarchy and if the eleventh subidentifier of its name
   is 2. The MIB object instance representing the speed of the second
   network interface belongs to the subtree families represented by both
   the second and third entries of the table, but that particular
   instance is excluded from the MIB view for party lucy because the
   lexicographically greater of the relevant family names appears in the
   table entry with status exclude.

   The MIB view for party ricky is also defined in this example.  The
   MIB view attributed to the party ricky includes all object instances
   in the icmp group of the internet-standard MIB, together with all
   information relevant to the fifth network interface attached to the
   managed device. In addition, the MIB view attributed to party ricky
   includes the number of octets received on the fourth attached network
   interface.

   While, as suggested by the examples above, a wide range of MIB view
   configurations are efficiently supported by the abbreviated
   representation of [5], prudent MIB design can sometimes further
   reduce the size and complexity of the most


    Party Identity  Status     Family Name        Family Mask
    lucy            include    system             ""h
    lucy            include    { ifEntry 0 2 }    "FFA0"h
    lucy            exclude    { ifSpeed 2 }      ""h
    ricky           include    icmp               ""h
    ricky           include    { ifEntry 0 5 }    "FFA0"h
    ricky           include    { ifInOctets 4 }   ""h

          Table 15: More Elaborate View Definitions

   likely MIB view definitions. On one hand, it is critical that
   mechanisms for MIB view configuration impose no absolute constraints
   either upon the access policies of local administrations or upon the
   structure of MIB namespaces; on the other hand, where the most common
   access policies are known, the configuration costs of realizing those
   policies may be slightly reduced by assigning to distinct portions of
   the registration hierarchy those MIB objects for which local policies
   most frequently require distinct treatment. The relegation in [5] of
   certain objects to a distinct arc in the MIB namespace is an example
   of this kind of optimization.






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5.  Compatibility

   Ideally, all SNMP management stations and agents would communicate
   exclusively using the secure facilities described in this memo. In
   reality, many SNMP agents may implement only the insecure SNMP
   mechanisms described in [1] for some time to come.

   New SNMP agent implementations should never implement both the
   insecure mechanisms of [1] and the facilities described here. Rather,
   consistent with the SNMP philosophy, the burden of supporting both
   sorts of communication should fall entirely upon managers. Perhaps
   the best way to realize both old and new modes of communication is by
   the use of a SNMP proxy agent deployed locally on the same system
   with a management station implementation. The management station
   implementation itself operates exclusively by using the newer, secure
   modes of communication, and the local proxy agent translates the
   requests of the manager into older, insecure modes as needed.

   It should be noted that proxy agent implementations may require
   additional information beyond that described in this memo in order to
   accomplish the requisite translation tasks implicit in the definition
   of the proxy function. This information could easily be retrieved
   from a filestore.

6.  Security Considerations

   It is important to note that, in the example configuration for native
   proxy operations presented in this memo, the use of symmetric
   cryptography does not securely prevent direct communication between
   the SNMP management station and the proxied SNMP agent.

   While secure isolation of the management station and the proxied
   agent can, according to the administrative model set forth in this
   memo, be realized using symmetric cryptography, the required
   configuration is more complex and is not described in this memo.
   Rather, it is recommended that native proxy configurations that
   require secure isolation of management station from proxied agent be
   implemented using security protocols based on asymmetric (or "public
   key") cryptography. However, no SNMP security protocols based on
   asymmetric cryptography are currently defined.

   In order to participate in the administrative model set forth in this
   memo, SNMP implementations must support local, non-volatile storage
   of the local party database. Accordingly, every attempt has been made
   to minimize the amount of non-volatile storage required.






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7.  References

   [1] Case, J., M. Fedor, M. Schoffstall, and J. Davin, The Simple
       Network Management Protocol", RFC 1157, University of Tennessee
       at Knoxville, Performance Systems International, Performance
       Systems International, and the MIT Laboratory for Computer
       Science, May 1990.  (Obsoletes RFC 1098.)

   [2] Rose, M., and K. McCloghrie, "Structure and Identification of
       Management Information for TCP/IP based internets", RFC 1155,
       Performance Systems International, Hughes LAN Systems, May 1990.
       (Obsoletes RFC 1065.)

   [3] Information Processing -- Open Systems Interconnection --
       Specification of Basic Encoding Rules for Abstract Syntax
       Notation One (ASN.1), International Organization for
       Standardization/International Electrotechnical Institute, 1987,
       International Standard 8825.

   [4] Galvin, J., McCloghrie, K., and J. Davin, "SNMP Security
       Protocols", RFC 1352, Trusted Information Systems, Inc., Hughes
       LAN Systems, Inc., MIT Laboratory for Computer Science, July
       1992.

   [5] McCloghrie, K., Davin, J., and J. Galvin, "Definitions of Managed
       Objects for Administration of SNMP Parties", RFC 1353, Hughes LAN
       Systems, Inc., MIT Laboratory for Computer Science, Trusted
       Information Systems, Inc., July 1992.

8.  Authors' Addresses

       James R. Davin
       MIT Laboratory for Computer Science
       545 Technology Square
       Cambridge, MA 02139

       Phone:  (617) 253-6020
       EMail:  jrd@ptt.lcs.mit.edu


       James M. Galvin
       Trusted Information Systems, Inc.
       3060 Washington Road, Route 97
       Glenwood, MD 21738

       Phone:  (301) 854-6889
       EMail:  galvin@tis.com




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

       Phone:  (415) 966-7934
       EMail:  kzm@hls.com












































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