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RFC 1592

 
 
 

Simple Network Management Protocol Distributed Protocol Interface Version 2.0

Part 3 of 3, p. 33 to 54
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3.3  CONSTANTS AND VALUES

   This section describes the constants that have been defined for this
   version of the SNMP DPI Protocol.

3.3.1  PROTOCOL VERSION AND RELEASE VALUES

     +-----------------------------------------------------------------+
     | Table 15. Protocol version and release values                   |
     +--------------------------------+--------------------------------+
     | FIELD                          | VALUE                          |
     +--------------------------------+--------------------------------+
     | protocol major version         | 2 (SNMP DPI protocol)          |
     +--------------------------------+--------------------------------+
     | protocol minor version         | 2 (version 2)                  |
     +--------------------------------+--------------------------------+
     | protocol release               | 0 (release 0)                  |
     +--------------------------------+--------------------------------+

   Previous versions of this protocol exist and should preferably be
   supported by an agent:

     o   version 1, release 0, described in [7]

   Previous internal versions of this protocol exist and may or may not
   be supported by an agent:

     o   version 1, release 1, experimental within IBM.
     o   version 1, release 2, experimental within BNR.

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3.3.2  PACKET TYPE VALUES

     +-----------------------------------------------------------------+
     | Table 16. Valid values for the packet type field                |
     +-------+---------------------------------------------------------+
     | VALUE | PACKET TYPE                                             |
     +-------+---------------------------------------------------------+
     | 1     | SNMP_DPI_GET                                            |
     +-------+---------------------------------------------------------+
     | 2     | SNMP_DPI_GETNEXT                                        |
     +-------+---------------------------------------------------------+
     | 3     | SNMP_DPI_SET                                            |
     +-------+---------------------------------------------------------+
     | 4     | SNMP_DPI_TRAP                                           |
     +-------+---------------------------------------------------------+
     | 5     | SNMP_DPI_RESPONSE                                       |
     +-------+---------------------------------------------------------+
     | 6     | SNMP_DPI_REGISTER                                       |
     +-------+---------------------------------------------------------+
     | 7     | SNMP_DPI_UNREGISTER                                     |
     +-------+---------------------------------------------------------+
     | 8     | SNMP_DPI_OPEN                                           |
     +-------+---------------------------------------------------------+
     | 9     | SNMP_DPI_CLOSE                                          |
     +-------+---------------------------------------------------------+
     | 10    | SNMP_DPI_COMMIT                                         |
     +-------+---------------------------------------------------------+
     | 11    | SNMP_DPI_UNDO                                           |
     +-------+---------------------------------------------------------+
     | 12    | SNMP_DPI_GETBULK                                        |
     +-------+---------------------------------------------------------+
     | 13    | SNMP_DPI_TRAPV2 (not yet used)                          |
     +-------+---------------------------------------------------------+
     | 14    | SNMP_DPI_INFORM (not yet used)                          |
     +-------+---------------------------------------------------------+
     | 15    | SNMP_DPI_ARE_YOU_THERE                                  |
     +-------+---------------------------------------------------------+

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3.3.3  VARIABLE TYPE VALUES

     +-----------------------------------------------------------------+
     | Table 17. Valid values for the Value Type field                 |
     +-------+---------------------------------------------------------+
     | VALUE | VALUE TYPE                                              |
     +-------+---------------------------------------------------------+
     | 129   | SNMP_TYPE_Integer32                                     |
     +-------+---------------------------------------------------------+
     | 2     | SNMP_TYPE_OCTET_STRING                                  |
     +-------+---------------------------------------------------------+
     | 3     | SNMP_TYPE_OBJECT_IDENTIFIER                             |
     +-------+---------------------------------------------------------+
     | 4     | SNMP_TYPE_NULL (empty, no value)                        |
     +-------+---------------------------------------------------------+
     | 5     | SNMP_TYPE_IpAddress                                     |
     +-------+---------------------------------------------------------+
     | 134   | SNMP_TYPE_Counter32                                     |
     +-------+---------------------------------------------------------+
     | 135   | SNMP_TYPE_Gauge32                                       |
     +-------+---------------------------------------------------------+
     | 136   | SNMP_TYPE_TimeTicks (1/100ths seconds)                  |
     +-------+---------------------------------------------------------+
     | 9     | SNMP_TYPE_DisplayString                                 |
     +-------+---------------------------------------------------------+
     | 10    | SNMP_TYPE_BIT_STRING                                    |
     +-------+---------------------------------------------------------+
     | 11    | SNMP_TYPE_NsapAddress                                   |
     +-------+---------------------------------------------------------+
     | 140   | SNMP_TYPE_UInteger32                                    |
     +-------+---------------------------------------------------------+
     | 13    | SNMP_TYPE_Counter64                                     |
     +-------+---------------------------------------------------------+
     | 14    | SNMP_TYPE_Opaque                                        |
     +-------+---------------------------------------------------------+
     | 15    | SNMP_TYPE_noSuchObject                                  |
     +-------+---------------------------------------------------------+
     | 16    | SNMP_TYPE_noSuchInstance                                |
     +-------+---------------------------------------------------------+
     | 17    | SNMP_TYPE_endOfMibView                                  |
     +-------+---------------------------------------------------------+

     Notes:

     1.  A 32-bit integer value has its base base type ORed with 128.
     2.  DisplayString is a textual convention.  An SNMP PDU shows a
         type of OCTET_STRING for the value.  An agent can handle such
         an object as DisplayString if the object is included in some

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         form of a compiled MIB for the agent.  If not, the agent passes
         the value as an OCTET_STRING.

3.3.4  VALUE REPRESENTATION

   Values in the DPI packets are represented as follows:

     o   32-bit integers are 4-byte elements in network byte order, MSB
         (most significant byte) first, LSB (least significant byte)
         last.  Example: '00000001'h represents 1.
     o   64-bit integers are 8-byte elements in network byte order, MSB
         first, LSB last.
         Example: '0000000100000001'h represents 4,294,967,297.
     o   Object Identifiers are NULL terminated strings in the selected
         character set, representing the OID in ASN.1 dotted notation.
         The length includes the terminating NULL.
         Example ASCII: '312e332e362e312e322e312e312e312e3000'h
         represents "1.3.6.1.2.1.1.1.0" which is sysDescr.0.
         Example EBCDIC: 'f14bf34bf64bf14bf24bf14bf14bf14bf000'h
         represents "1.3.6.1.2.1.1.1.0" which is sysDescr.0.
     o   DisplayStrings are in the selected character set.  The length
         specifies the length of the string.
         Example ASCII: '6162630d0a'h represents "abc\r\n", no NULL.
         Example EBCDIC: '8182830d25'h represents "abc\r\n", no NULL.
     o   IpAddress, NsapAddress and Opaque are implicit OCTET_STRING, so
         they are octets (e.g. IpAddress in network byte order).
     o   NULL has a zero length for the value, no value data.
     o   noSuchObject, noSuchInstance and endOfMibView are implicit NULL
         and represented as such.
     o   BIT_STRING is an OCTET_STRING of the form uubbbb...bb, where
         the first octet (uu) is 0x00-0x07 and indicates the number of
         unused bits in the last octet (bb). The bb octets represent the
         bit string itself, where bit zero (0) comes first and so on.

3.3.5  CHARACTER SET SELECTION

   In the DPI OPEN packet, the sub-agent can specify the character set
   to be used for the representation of:

     o   group and instance ID in the DPI REGISTER, UNREGISTER, GET,
         GETNEXT, GETBULK, SET, UNDO, COMMIT, RESPONSE and TRAP packets.
     o   sub-agent ID and sub-agent Description in DPI OPEN packet.
     o   Object Identifiers in the value field for a value of type
         SNMP_TYPE_OBJECT_IDENTIFIER.
     o   DisplayString in the value field for a value of type
         SNMP_TYPE_DPI_DisplayString.

   The choice is the native character set or the ASCII character set.

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   The native set is the set native to the platform where the agent
   runs.  If the native set is ASCII, then character set selection is a
   moot point.  On non-ASCII based platforms, the agent must convert
   between native and ASCII if the native character set is chosen.

3.3.6  ERROR CODE VALUES FOR SNMP DPI RESPONSE PACKETS

   When the RESPONSE packet is a response to a GET, GETNEXT, GETBULK,
   SET, COMMIT, or UNDO, then the error code can have one of the
   following values:

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     +-----------------------------------------------------------------+
     | Table 18. Valid SNMP_ERROR values for RESPONSE error code       |
     +-------+---------------------------------------------------------+
     | VALUE | ERROR CODE                                              |
     +-------+---------------------------------------------------------+
     | 0     | SNMP_ERROR_noError                                      |
     +-------+---------------------------------------------------------+
     | 1     | SNMP_ERROR_tooBig                                       |
     +-------+---------------------------------------------------------+
     | 2     | SNMP_ERROR_noSuchName (SNMPv1, do not use)              |
     +-------+---------------------------------------------------------+
     | 3     | SNMP_ERROR_badValue (SNMPv1, do not use)                |
     +-------+---------------------------------------------------------+
     | 4     | SNMP_ERROR_readOnly (SNMPv1 do not use)                 |
     +-------+---------------------------------------------------------+
     | 5     | SNMP_ERROR_genErr                                       |
     +-------+---------------------------------------------------------+
     | 6     | SNMP_ERROR_noAccess                                     |
     +-------+---------------------------------------------------------+
     | 7     | SNMP_ERROR_wrongType                                    |
     +-------+---------------------------------------------------------+
     | 8     | SNMP_ERROR_wrongLength                                  |
     +-------+---------------------------------------------------------+
     | 9     | SNMP_ERROR_wrongEncoding                                |
     +-------+---------------------------------------------------------+
     | 10    | SNMP_ERROR_wrongValue                                   |
     +-------+---------------------------------------------------------+
     | 11    | SNMP_ERROR_noCreation                                   |
     +-------+---------------------------------------------------------+
     | 12    | SNMP_ERROR_inconsistentValue                            |
     +-------+---------------------------------------------------------+
     | 13    | SNMP_ERROR_resourceUnavailable                          |
     +-------+---------------------------------------------------------+
     | 14    | SNMP_ERROR_commitFailed                                 |
     +-------+---------------------------------------------------------+
     | 15    | SNMP_ERROR_undoFailed                                   |
     +-------+---------------------------------------------------------+
     | 16    | SNMP_ERROR_authorizationError                           |
     +-------+---------------------------------------------------------+
     | 17    | SNMP_ERROR_notWritable                                  |
     +-------+---------------------------------------------------------+
     | 18    | SNMP_ERROR_inconsistentName                             |
     +-------+---------------------------------------------------------+

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   When the RESPONSE packet is a response to an OPEN, REGISTER or
   UNREGISTER, then the error code can have one of the following values:

     +-----------------------------------------------------------------+
     | Table 19. Valid SNMP_ERROR_DPI values for RESPONSE error code   |
     +-------+---------------------------------------------------------+
     | VALUE | ERROR CODE                                              |
     +-------+---------------------------------------------------------+
     | 0     | SNMP_ERROR_DPI_noError                                  |
     +-------+---------------------------------------------------------+
     | 101   | SNMP_ERROR_DPI_otherError                               |
     +-------+---------------------------------------------------------+
     | 102   | SNMP_ERROR_DPI_notFound                                 |
     +-------+---------------------------------------------------------+
     | 103   | SNMP_ERROR_DPI_alreadyRegistered                        |
     +-------+---------------------------------------------------------+
     | 104   | SNMP_ERROR_DPI_higherPriorityRegistered                 |
     +-------+---------------------------------------------------------+
     | 105   | SNMP_ERROR_DPI_mustOpenFirst                            |
     +-------+---------------------------------------------------------+
     | 106   | SNMP_ERROR_DPI_notAuthorized                            |
     +-------+---------------------------------------------------------+
     | 107   | SNMP_ERROR_DPI_viewSelectionNotSupported                |
     +-------+---------------------------------------------------------+
     | 108   | SNMP_ERROR_DPI_getBulkSelectionNotSupported             |
     +-------+---------------------------------------------------------+
     | 109   | SNMP_ERROR_DPI_duplicateSubAgentIdentifier              |
     +-------+---------------------------------------------------------+
     | 110   | SNMP_ERROR_DPI_invalidDisplayString                     |
     +-------+---------------------------------------------------------+
     | 111   | SNMP_ERROR_DPI_characterSetSelectionNotSupported        |
     +-------+---------------------------------------------------------+

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3.3.7  UNREGISTER REASON CODES

   The following are valid reason codes in an UNREGISTER packet.

     +-----------------------------------------------------------------+
     | Table 20. Valid UNREGISTER reason codes                         |
     +-------+---------------------------------------------------------+
     | VALUE | REASON CODE                                             |
     +-------+---------------------------------------------------------+
     | 1     | SNMP_UNREGISTER_otherReason                             |
     +-------+---------------------------------------------------------+
     | 2     | SNMP_UNREGISTER_goingDown                               |
     +-------+---------------------------------------------------------+
     | 3     | SNMP_UNREGISTER_justUnregister                          |
     +-------+---------------------------------------------------------+
     | 4     | SNMP_UNREGISTER_newRegistration                         |
     +-------+---------------------------------------------------------+
     | 5     | SNMP_UNREGISTER_higherPriorityRegistered                |
     +-------+---------------------------------------------------------+
     | 6     | SNMP_UNREGISTER_byManager                               |
     +-------+---------------------------------------------------------+
     | 7     | SNMP_UNREGISTER_timeout                                 |
     +-------+---------------------------------------------------------+

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3.3.8  CLOSE REASON CODES

   The following are valid reason codes in a CLOSE packet.

     +-----------------------------------------------------------------+
     | Table 21. Valid CLOSE reason codes                              |
     +-------+---------------------------------------------------------+
     | VALUE | REASON CODE                                             |
     +-------+---------------------------------------------------------+
     | 1     | SNMP_CLOSE_otherReason                                  |
     +-------+---------------------------------------------------------+
     | 2     | SNMP_CLOSE_goingDown                                    |
     +-------+---------------------------------------------------------+
     | 3     | SNMP_CLOSE_unsupportedVersion                           |
     +-------+---------------------------------------------------------+
     | 4     | SNMP_CLOSE_protocolError                                |
     +-------+---------------------------------------------------------+
     | 5     | SNMP_CLOSE_authenticationFailure                        |
     +-------+---------------------------------------------------------+
     | 6     | SNMP_CLOSE_byManager                                    |
     +-------+---------------------------------------------------------+
     | 7     | SNMP_CLOSE_timeout                                      |
     +-------+---------------------------------------------------------+
     | 8     | SNMP_CLOSE_openError                                    |
     +-------+---------------------------------------------------------+

4.  DPI 2.0 MIB DEFINITION

     DPI20-MIB DEFINITIONS ::= BEGIN

     -- Objects in this MIB are implemented in the local SNMP agent.

        IMPORTS
                MODULE-IDENTITY, OBJECT-TYPE, snmpModules, enterprises
                        FROM SNMPv2-SMI

        ibm      OBJECT IDENTIFIER ::= { enterprises 2 }
        ibmDPI   OBJECT IDENTIFIER ::= { ibm 2 }
        dpi20MIB OBJECT IDENTIFIER ::= { ibmDPI 1 }

     -- dpi20MIB MODULE-IDENTITY
     --   LAST-UPDATED "9401210000Z"
     --   ORGANIZATION "IBM Research - T.J. Watson Research Center"
     --   CONTACT-INFO "           Bert Wijnen
     --                 Postal:    IBM International Operations
     --                            Watsonweg 2
     --                            1423 ND Uithoorn
     --                            The Netherlands

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     --                 Tel:       +31 2975 53316
     --                 Fax:       +31 2975 62468
     --                 E-mail:    wijnen@vnet.ibm.com"
     --   DESCRIPTION "MIB module describing DPI objects."
     --   ::= { snmpModules x }

        dpiPort  OBJECT IDENTIFIER ::= { dpi20MIB 1 }

        dpiPortForTCP   OBJECT-TYPE
                SYNTAX  INTEGER (0..65535)
                ACCESS  read-only
                STATUS  mandatory
                DESCRIPTION "The TCP port number on which the agent
                             listens for DPI connections. A zero value
                             means the agent has no DPI TCP port."
                ::= { dpiPort 1 }

        dpiPortForUDP   OBJECT-TYPE
                SYNTAX  INTEGER (0..65535)
                ACCESS  read-only
                STATUS  mandatory
                DESCRIPTION "The UDP port number on which the agent
                             listens for DPI packets. A zero value
                             means the agent has no DPI UDP port."
                ::= { dpiPort 2 }
     END

5.  SUBAGENT CONSIDERATIONS

   When implementing a sub-agent, it is strongly recommended to use the
   DPI version 2 approach (SNMPv2 based).  This means:

     o   Use SNMPv2 error codes only (even though we have definitions
         for the old SNMPv1 error codes).
     o   Do implement SET, COMMIT, UNDO processing properly.
     o   For GET requests, use the SNMPv2 approach and pass back
         noSuchInstance or noSuchObject value if such is the case.
         Continue to process all remaining varBinds in this case.
     o   For GETNEXT, use the SNMPv2 approach and pass back endOfMibView
         value if such is the case.  Continue to process all remaining
         varBinds in this case.
     o   When you are processing a request from the agent (GET, GETNEXT,
         GETBULK, SET, COMMIT, UNDO) you are supposed to respond within
         the timeout period (which you can specify in the OPEN and
         REGISTER packets). If you fail to respond within that timeout
         period, the agent will most probably close your DPI connection
         and then discard your RESPONSE packet if it comes in later.  If
         you can detect that the response is not going to make it in

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         time, then you might decide to abort the request and return an
         SNMP_ERROR_genErr in the RESPONSE.
     o   If you have a UDP "connected" sub-agent, or one that uses
         another unreliable protocol, you may want to issue an SNMP DPI
         ARE_YOU_THERE request once in a while to ensure that the agent
         is still alive and still knows about you.
     o   When you are running on an EBCDIC based machine, and you use
         the (default) native character set, then all OID strings (as
         used for things like group ID, instance ID, Enterprise ID,
         sub-agent ID) and also all variable values of type
         OBJECT_IDENTIFIER or DisplayString will be passed to you in
         EBCDIC format.  When you return a response, you should then
         also use EBCDIC FORMAT.
     o   When you are running on an EBCDIC based machine, and you use
         the ASCII character set (specified in DPI OPEN), then all OID
         strings (as used for things like group ID, instance ID,
         Enterprise ID, sub-agent ID) and also all variable values of
         type OBJECT_IDENTIFIER or DisplayString will be passed to you
         in ASCII format.  When you return a response, you should then
         also use ASCII FORMAT.
     o   When you are running on an ASCII machine, then the character
         set selection for you basically is moot.  Except maybe when you
         connect to an EBCDIC based agent, in which case you may want to
         specify in the DPI OPEN packet that you want to use ASCII
         character set. After that, all this is transparent to you and
         the burden of conversion is on the EBCDIC based agent.
     o   Please realize that DisplayString is only a textual convention.
         In the SNMP PDU (SNMP packet), the type is just an
         OCTET_STRING, and from that it is not clear if this is a
         DisplayString or any arbitrary data.  This means that the agent
         can only know about an object being a DisplayString if the
         object is included in some sort of a compiled MIB.  If it is,
         then the agent will use SNMP_TYPE_DisplayString in the type
         field of the varBind in a DPI SET packet.  When you send a
         DisplayString in a RESPONSE packet, the agent will handle it as
         such (e.g. translate EBCDIC to ASCII if needed).

5.1  DPI API

   The primary goal of this document is to specify the SNMP DPI, a
   protocol by which sub-agents can exchange SNMP related information
   with an agent. On top of this protocol, one can imagine one or
   possibly many Application Programming Interfaces, but those are not
   addressed in this document.

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   However, in order to provide an environment that is more or less
   platform independent, we strongly suggest to also define a DPI API.
   We have a sample DPI API available, see 9, "Sample Sources for
   Anonymous FTP" for a place to obtain that sample DPI API.

5.2  OVERVIEW OF REQUEST PROCESSING

5.2.1  GET PROCESSING

   A GET request is the easiest to process.  The DPI GET packet holds
   one or more varBinds that the sub-agent has taken responsibility for.

   If the sub-agent encounters an error while processing the request, it
   creates a DPI RESPONSE packet with an appropriate error indication in
   the error_code field and sets the error_index to the position of the
   varBind at which the error occurs (first varBind is index 1, second
   varBind is index 2, and so on).  No name/type/length/value
   information needs to be provided in the packet, because by
   definition, the varBind information is the same as in the request to
   which this is a response, and the agent still has that information.

   If there are no errors, then the sub-agent creates a DPI RESPONSE
   packet in which the error_code is set to SNMP_ERROR_noError (zero)
   and error_index is set to zero.  The packet must also include the
   name/type/length/value of each varBind requested.  When you get a
   request for a non-existing object or a non-existing instance of an
   object, then you must return a NULL value with a type of
   SNMP_TYPE_noSuchObject or SNMP_TYPE_noSuchInstance respectively.

   These two values are not considered errors, so the error_code and
   error_index should be zero.

   The DPI RESPONSE packet is then sent back to the agent.

5.2.2  SET PROCESSING

   Processing a DPI SET request is more difficult than a DPI GET
   request.  In the case of a DPI SET packet, additional information is
   available in the packet, namely the value type, value length and
   value to be set.

   If the sub-agent encounters an error while processing the request, it
   creates a DPI RESPONSE packet with an appropriate error indication in
   the error_code field and an error_index listing the position of the
   varBind at which the error occurs (first varBind is index 1, second
   varBind is index 2, and so on).  No name/type/length/value
   information needs to provided in the packet, because by definition,
   the varBind information is the same as in the request to which this

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   is a response, and the agent still has that information.

   If there are no errors, then the sub-agent creates a DPI RESPONSE
   packet in which the error_code is set to SNMP_ERROR_noError (zero)
   and error_index is set to zero.  No name/type/length/value
   information is needed; by definition the RESPONSE to a SET should
   contain exactly the same varBind data as the data present in the
   request, so the agent can use the values it already has.  (This
   suggests that the agent must keep state information, and that is
   indeed the case.  It needs to do that anyway in order to be able to
   later pass the data with a DPI COMMIT or DPI UNDO packet).  The sub-
   agent must have allocated the required resources and prepared itself
   for the SET.  It does not yet effectuate the set, that will be done
   at COMMIT time.

   The sub-agent sends a DPI RESPONSE packet (indicating success or
   failure for the preparation phase) back to the agent.

   The agent will then issue a SET request for all other varBinds in the
   same original SNMP request it received.  This may be to the same or
   to one or more different sub-agents.  Once all SET requests have
   returned a "no error" condition, the agent starts sending DPI COMMIT
   packets to the sub-agent(s).  If any SET request returns an error,
   then the agent sends DPI UNDO packets to those sub-agents that
   indicated successful processing of the SET preparation phase.

   When the sub-agent receives the DPI COMMIT packet, again all the
   varBind information will be available in the packet.  The sub-agent
   can now effectuate the SET request.

   If the sub-agent encounters an error while processing the COMMIT
   request, it creates a DPI RESPONSE packet with value
   SNMP_ERROR_commitFailed in the error_code field and an error_index
   that lists at which varBind the error occurs (first varBind is index
   1 and so on).  No name/type/length/value information is needed.  The
   fact that a commitFailed error exists does not mean that this error
   should be returned easily.  A sub-agent should do all that is
   possible to make a COMMIT succeed.

   If there are no errors, and the SET/COMMIT has been effectuated with
   success, then the sub-agent creates a DPI RESPONSE packet in which
   the error_code is set to SNMP_ERROR_noError (zero) and error_index is
   set to zero.  No name/type/length/value information is needed.

   So far we have discussed a SET, COMMIT sequence.  That happens if all
   goes well.  However, after a successful SET, the sub-agent may
   receive a DPI UNDO packet.  The sub-agent must now undo any
   preparations it made during the SET processing (like free allocated

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   memory and such).  Even after a COMMIT, a sub-agent may still receive
   a DPI UNDO packet.  This is the case if some other sub-agent could
   not complete a COMMIT request.  Because of the SNMP-requirement that
   all varBinds in a single SNMP SET request must be changed "as if
   simultaneous", all committed changes must be undone if any of the
   COMMIT requests fail.  In this case the sub-agent must try and undo
   the committed SET operation.

   If the sub-agent encounters an error while processing the UNDO
   request, it creates a DPI RESPONSE packet with value
   SNMP_ERROR_undoFailed in the error_code field and an error_index that
   lists at which varBind the error occurs (first varBind is index 1 and
   so on).  No name/type/length/value information is needed.  The fact
   that an undoFailed error exists does not mean that this error should
   be returned easily.  A sub-agent should do all that is possible to
   make an UNDO succeed.

   If there are no errors, and the UNDO has been effectuated with
   success, then the sub-agent creates a DPI RESPONSE packet in which
   the error_code is set to SNMP_ERROR_noError (zero) and error_index is
   set to zero.  No name/type/length/value information is needed.

5.2.3  GETNEXT PROCESSING

   GETNEXT requests are a bit more complicated to process than a GET.
   The DPI GETNEXT packet contains the object(s) on which the GETNEXT
   operation must be performed.  The semantics of the operation are that
   the sub-agent is to return the name/type/length/value of the next
   variable it supports whose (ASN.1) name lexicographically follows the
   one passed in the group ID (sub-tree) and instance ID.

   In this case, the instance ID may not be present (NULL) implying that
   the NEXT object must be the first instance of the first object in the
   sub-tree that was registered.

   It is important to realize that a given sub-agent may support several
   discontiguous sections of the MIB tree.  In such a situation it would
   be incorrect to jump from one section to another.  This problem is
   correctly handled by examining the group ID in the DPI packet.  This
   group ID represents the "reason" why the sub-agent is being called.
   It holds the prefix of the tree that the sub-agent had indicated it
   supported (registered).

   If the next variable supported by the sub-agent does not begin with
   that prefix, the sub-agent must return the same object instance as in
   the request (e.g. group ID and instance ID) with a value of
   SNMP_TYPE_endOfMibView (implied NULL value).  This endOfMibView is
   not considered an error, so the error_code and error_index should be

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   zero.  If required, the SNMP agent will call upon the sub-agent
   again, but pass it a different group ID (prefix).  This is
   illustrated in the discussion below.

   Assume there are two sub-agents.  The first sub-agent registers two
   distinct sections of the tree, A and C.  In reality, the sub-agent
   supports variables A.1 and A.2, but it correctly registers the
   minimal prefix required to uniquely identify the variable class it
   supports.

   The second sub-agent registers a different section, B, which appears
   between the two sections registered by the first agent.

   If a management station begins dumping the MIB, starting from A, the
   following sequence of queries of the form get-next(group ID, instance
   ID) would be performed:

       Sub-agent 1 gets called:
              get-next(A,none) = A.1
              get-next(A,1)    = A.2
              get-next(A,2)    = endOfMibView

       Sub-agent 2 is then called:
              get-next(B,none) = B.1
              get-next(B,1)    = endOfMibView

       Sub-agent 1 gets called again:
              get-next(C,none) = C.1

5.2.4  GETBULK PROCESSING

   You can ask the agent to translate GETBULK requests into multiple
   GETNEXT requests.  This is basically the default and it is specified
   in the DPI REGISTER packet.  In principle, we expect the majority of
   DPI sub-agents to run on the same machine as the agent (or otherwise,
   on the same physical network), so repetitive GETNEXT requests stay
   local and in general should not be a problem.

   If experience tells us different, the sub-agent can tell the agent to
   pass on a DPI GETBULK packet.

   When a GETBULK request is received, the sub-agent must process the
   request and send a RESPONSE that sends back as many varBinds as
   requested by the request, as long as they fit with in the buffers.

   The GETBULK requires similar processing as a GETNEXT with regard to
   endOfMibView handling.

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5.2.5  OPEN REQUEST

   As the very first step, a DPI sub-agent must open a "connection" with
   the agent.  To do so, it must send a DPI OPEN packet in which these
   things must be specified:

     o   The max timeout value in seconds.  The agent is requested to
         wait this long for a response to any request for an object
         being handled by this sub-agent.  The agent may have an
         absolute maximum timeout value which will be used if the
         sub-agent asks for too big a timeout value.  A value of zero
         can be used to indicate that the agent's own default timeout
         value should be used.  A sub-agent is advised to use a
         reasonably short interval of a few seconds or so.  If a
         specific sub-tree needs a (much) longer time, then a specific
         REGISTER can be done for that sub-tree with a longer timeout
         value.
     o   The maximum number of varBinds that the sub-agent is prepared
         to handle per DPI packet.  Specifying 1 would result in DPI
         version 1 behavior of one varBind per DPI packet that the agent
         sends to the sub-agent.
     o   The character set you want to use. By default (value 0) this is
         the native character set of the machine (platform) where the
         agent runs.
         Since the sub-agent and agent normally run on the same system
         or platform, you want to use the native character set (which on
         many platforms is ASCII anyway).
         If your platform is EBCDIC based, then using the native
         character set of EBCDIC makes it easy to recognize the string
         representations of the fields like group ID, instance ID, etc.

         At the same time, the agent will translate the value from ASCII
         NVT to EBCDIC (and vice versa) for objects that it knows (from
         a compiled MIB) to have a textual convention of DisplayString.
         Be aware that this fact cannot be determined from the SNMP PDU
         encoding because in the PDU the object is only known to be an
         OCTET_STRING.
         If your sub-agent runs on an ASCII based platform and the agent
         runs on an EBCDIC based platform (or the other way around),
         then you can specify that you want to use the ASCII character
         set, and so you both know how to handle the string-based data.
         Beware that not all agents need to support other than native
         character set selection.  See 5, "Subagent Considerations"
         and 3.3.5, "Character set selection" for more information on
         character set usage.
     o   The sub-agent ID.  This an ASN.1 Object Identifier that
         uniquely identifies the sub-agent.  This OID is represented as
         a null terminated string using the selected character set.

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         Example: "1.3.5.1.2.3.4.5".
     o   The sub-agent Description.  This is a DisplayString describing
         the sub-agent.  This is a character string using the selected
         character set.  Example: "DPI sample sub-agent version 2.0"

   Once a sub-agent has sent a DPI OPEN packet to an agent, it should
   expect a DPI RESPONSE packet that informs the sub-agent about the
   result of the request.  The packet ID of the RESPONSE packet should
   be the same as that of the OPEN request to which the RESPONSE packet
   is the response.  See Table 19 for a list of valid DPI RESPONSE error
   codes that may be expected.  If you receive an error RESPONSE on the
   OPEN packet, then you will also receive a DPI CLOSE packet with an
   SNMP_CLOSE_openError code, and then the agent closes the
   "connection".

   If the OPEN is accepted, then the next step is to REGISTER one or
   more MIB sub-trees.

5.2.6  CLOSE REQUEST

   When a sub-agent is finished and wants to terminate it should first
   UNREGISTER its sub-trees and then close the "connection" with the
   agent.  To do so, it must send a DPI CLOSE packet in which it
   specifies a reason for the closing.  See Table 21 for a list of valid
   CLOSE reason codes.  You should not expect a response to the CLOSE
   request.

   A sub-agent should also be prepared to handle an incoming DPI CLOSE
   packet from the agent.  Again, the packet will contain a reason code
   for the CLOSE request.  A sub-agent need not send a response to a
   CLOSE request. The agent just assumes that the sub-agent will handle
   it appropriately.  The close takes place, no matter what the sub-
   agent does with it.

5.2.7  REGISTER REQUEST

   Before a sub-agent will receive any requests for MIB variables it
   must first register the variables or sub-tree it supports with the
   SNMP agent.  The sub-agent must specify a number of things in the
   REGISTER request:

     o   The sub-tree to be registered.  This is a null terminated
         string in the selected character set.  The sub-tree must have a
         trailing dot (example: "1.3.6.1.2.3.4.5.").
     o   The requested priority for the registration, one of:
         -1  Request for best available priority.
         0   Request for next better available priority than highest
             priority currently registered for this sub-tree.

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         NNN Any other positive value requests that specific priority if
             available or the first worse priority that is available.
     o   The max timeout value in seconds.  The agent is requested to
         wait this long for a response to any request for an object in
         this sub-tree.  The agent may have an absolute maximum timeout
         value which will be used if the sub-agents asks for too big a
         timeout value.  A value of zero can be used to indicate that
         the DPI OPEN value should be used for timeout.
     o   A specification if the sub-agent wants to do view selection.
         If it does, then the community name (from SNMPv1 packets) will
         be passed in the DPI GET, GETNEXT, SET packets).
     o   A specification if the sub-agent wants to receive GETBULK
         packets or if it just prefers that the agent converts a GETBULK
         into multiple GETNEXT requests.

   Once a sub-agent has sent a DPI REGISTER packet to the agent, it
   should expect a DPI RESPONSE packet that informs the sub-agent about
   the result of the request.  The packet ID of the RESPONSE packet
   should be the same as that of the REGISTER packet to which the
   RESPONSE packet is the response.  If the response indicates success,
   then the error_index field in the RESPONSE packet contains the
   priority that the agent assigned to the sub-tree registration.  See
   Table 19 for a list of valid DPI RESPONSE error codes that may be
   expected.

5.2.8  UNREGISTER REQUEST

   A sub-agent may unregister a previously registered sub-tree.  The
   sub-agent must specify a few things in the UNREGISTER request:

     o   The sub-tree to be unregistered.  This is a null terminated
         string in the selected character set.  The sub-tree must have a
         trailing dot (example: "1.3.6.1.2.3.4.5.").
     o   The reason for the unregister.  See Table 20 for a
         list of valid reason codes.

   Once a sub-agent has sent a DPI UNREGISTER packet to the agent, it
   should expect a DPI RESPONSE packet that informs the sub-agent about
   the result of the request.  The packet ID of the RESPONSE packet
   should be the same as that of the REGISTER packet to which the
   RESPONSE packet is the response.  See Table 19 for a list of valid
   DPI RESPONSE error codes that may be expected.

   A sub-agent should also be prepared to handle incoming DPI UNREGISTER
   packets from the agent.  Again, the DPI packet will contain a reason
   code for the UNREGISTER.  A sub-agent need not send a response to an
   UNREGISTER request.  The agent just assumes that the sub-agent will
   handle it appropriately.  The registration is removed, no matter what

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   the sub-agent returns.

5.2.9  TRAP REQUEST

   A sub-agent can request that the SNMP agent generates a trap for it.
   The sub-agent must provide the desired values for the generic and
   specific parameters of the trap.  It may optionally provide a set of
   one or more name/type/length/value tuples that will be included in
   the trap packet.  Also, it may optionally specify an Enterprise ID
   (Object Identifier) for the trap to be generated.  If a NULL value is
   specified for the Enterprise ID, then the agent will use the sub-
   agent Identifier (from the DPI OPEN packet) as the Enterprise ID to
   be sent with the trap.

5.2.10  ARE_YOU_THERE REQUEST

   A sub-agent can send an ARE_YOU_THERE packet to the agent.  This may
   be useful to do if you have a DPI "connection" over an unreliable
   transport protocol (like UDP).

   If the "connection" is in a healthy state, the agent responds with a
   RESPONSE packet with SNMP_ERROR_DPI_noError.

   If the "connection" is not in a healthy state, the agent may respond
   with a RESPONSE packet with an error indication, but the agent might
   not react at all, so you would timeout while waiting for a response.

5.2.11  HOW TO QUERY THE DPI PORT.

   The DPI API implementations are encouraged to provide a facility that
   helps DPI sub-agent programmers to dynamically find the port that the
   agent is using for the TCP and/or UDP DPI port(s).  A suggested name
   for such a function is: query_DPI_port().

6.  REFERENCES

   [1] Case, J., Fedor, M., Schoffstall M., and J. Davin, "Simple
       Network Management Protocol (SNMP)", STD 15, RFC 1157, SNMP
       Research, Performance Systems International, MIT Laboratory for
       Computer Science, May 1990.

   [2] Information processing systems - Open Systems Interconnection,
       "Specification of Abstract Syntax Notation One (ASN.1)",
       International Organization for Standardization, International
       Standard 8824, December 1987.

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   [3] Information processing systems - Open Systems Interconnection,
       "Specification of Basic Encoding Rules for Abstract Syntax
       Notation One (ASN.1)", International Organization for
       Standardization, International Standard 8825, December 1987.

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

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

   [6] Rose, M., "SNMP MUX Protocol and MIB", RFC 1227, Performance
       Systems International, RFC 1227, May 1991.

   [7] Carpenter G., and B. Wijnen, "SNMP-DPI, Simple Network Management
       Protocol Distributed Program Interface", RFC 1228, International
       Business Machines, Inc., May 1991.

   [8] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "SNMPv2
       RFCs (RFC 1441 through RFC 1452)", SNMP Research Inc, Hughes LAN
       Systems, Dover Beach Consulting Inc, Carnegie Mellon University,
       Trusted Information Systems, April 1993.

   [9] International Business Machines, Inc., TCP/IP for VM:
       Programmer's Reference, SC31-6084-0, 1990.

  [10] International Business Machines, Inc., Virtual Machine System
       Facilities for Programming, Release 6, SC24-5288-01, 1988.

7.  SECURITY CONSIDERATIONS

   Security issues are not discussed in this memo.

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8.  AUTHORS' ADDRESSES

   Bert Wijnen
   IBM International Operations
   Watsonweg 2
   1423 ND Uithoorn
   The Netherlands

   Phone: +31-2975-53316
   Fax:   +31-2975-62468
   EMail: wijnen@vnet.ibm.com


   Geoffrey C. Carpenter
   IBM T.J. Watson Research Center
   P.O. Box 218
   Yorktown Heights, NY 10598
   USA

   Phone: +1-914-945-1970
   EMail: gcc@watson.ibm.com


   Kim Curran
   Bell Northern Research Ltd.
   P.O. Box 3511 Station C
   Ottawa, Ontario K1Y 4HY
   Canada

   Phone: +1-613-763-5283
   EMail: kcurran@bnr.ca


   Aditya Sehgal
   Bell Northern Research Ltd.
   P. O. Box 3511 Station C
   Ottawa, Ontario K1Y 4HY
   Canada

   Phone: +1-613-763-8821
   EMail: asehgal@bnr.ca

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   Glen Waters
   Bell Northern Research Ltd.
   P.O. Box 3511 Station C
   Ottawa, Ontario K1Y 4HY
   Canada

   Phone: +1-613-763-3933
   EMail: gwaters@bnr.ca

9.  SAMPLE SOURCES FOR ANONYMOUS FTP

   An implementation sample of a DPI API (as used at the agent and sub-
   agent side) plus sample sub-agent code and documentation are
   available for anonymous FTP from:

          software.watson.ibm.com  (129.34.139.5)

   To obtain the source, perform the following steps:

          ftp software.watson.ibm.com
          user:     anonymous
          password: your_e-mail_address
          cd /public/dpi
          get README
          binary
          get dpi_api.tar (or compressed dpi_api.tar.Z)
          quit