GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc1592

Network Working Group B. Wijnen Request for Comments: 1592 G. Carpenter Obsoletes: 1228 T.J. Watson Research Center, IBM Corp. Category: Experimental K. Curran

                                                             A. Sehgal
                                                             G. Waters
                                          Bell Northern Research, Ltd.
                                                            March 1994
                 Simple Network Management Protocol
                   Distributed Protocol Interface
                            Version 2.0

Status of this Memo

 This memo defines an Experimental Protocol for the Internet
 community.  This memo does not specify an Internet standard of any
 kind.  Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Table of Contents

   1. INTRODUCTION  . . . . . . . . . . . . . . . . . . . . . . . .  2
   1.1  Motivation  . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.2  Summary of Changes  . . . . . . . . . . . . . . . . . . . .  4
   2. THEORY OF OPERATION . . . . . . . . . . . . . . . . . . . . .  5
   2.1  Connection Establishment and Termination  . . . . . . . . .  5
   2.2  Registration  . . . . . . . . . . . . . . . . . . . . . . .  6
   2.3  Normal Operation  . . . . . . . . . . . . . . . . . . . . .  6
   2.4  DPI Architecture  . . . . . . . . . . . . . . . . . . . . .  6
   3. SNMP DPI PROTOCOL . . . . . . . . . . . . . . . . . . . . .   10
   3.1  Connection Establishment  . . . . . . . . . . . . . . . .   10
   3.1.1  SNMP PDU to GET the Agent's DPI port  . . . . . . . . .   11
   3.1.2  SNMP PDU Containing the RESPONSE to the GET   . . . . .   13
   3.2  SNMP DPI Packet Formats   . . . . . . . . . . . . . . . .   15
   3.2.1  DPI Packet Header   . . . . . . . . . . . . . . . . . .   15
   3.2.2  OPEN  . . . . . . . . . . . . . . . . . . . . . . . . .   16
   3.2.3  CLOSE   . . . . . . . . . . . . . . . . . . . . . . . .   18
   3.2.4  ARE_YOU_THERE   . . . . . . . . . . . . . . . . . . . .   19
   3.2.5  REGISTER  . . . . . . . . . . . . . . . . . . . . . . .   20
   3.2.6  UNREGISTER  . . . . . . . . . . . . . . . . . . . . . .   22
   3.2.7  GET   . . . . . . . . . . . . . . . . . . . . . . . . .   23
   3.2.8  GETNEXT   . . . . . . . . . . . . . . . . . . . . . . .   24
   3.2.9  GETBULK   . . . . . . . . . . . . . . . . . . . . . . .   25
   3.2.10  SET, COMMIT and UNDO   . . . . . . . . . . . . . . . .   26
   3.2.11  RESPONSE   . . . . . . . . . . . . . . . . . . . . . .   29
   3.2.12  TRAP   . . . . . . . . . . . . . . . . . . . . . . . .   31
   3.3  Constants and Values  . . . . . . . . . . . . . . . . . .   33

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 1] RFC 1592 SNMP-DPI March 1994

   3.3.1  Protocol Version and Release Values   . . . . . . . . .   33
   3.3.2  Packet Type Values  . . . . . . . . . . . . . . . . . .   34
   3.3.3  Variable Type Values  . . . . . . . . . . . . . . . . .   35
   3.3.4  Value Representation  . . . . . . . . . . . . . . . . .   36
   3.3.5  Character set selection   . . . . . . . . . . . . . . .   36
   3.3.6  Error Code Values for SNMP DPI RESPONSE packets   . . .   37
   3.3.7  UNREGISTER Reason Codes   . . . . . . . . . . . . . . .   40
   3.3.8  CLOSE Reason Codes  . . . . . . . . . . . . . . . . . .   41
   4. DPI 2.0 MIB DEFINITION  . . . . . . . . . . . . . . . . . .   41
   5. SUBAGENT CONSIDERATIONS . . . . . . . . . . . . . . . . . .   42
   5.1  DPI API   . . . . . . . . . . . . . . . . . . . . . . . .   43
   5.2  Overview of Request Processing  . . . . . . . . . . . . .   44
   5.2.1  GET Processing  . . . . . . . . . . . . . . . . . . . .   44
   5.2.2  SET Processing  . . . . . . . . . . . . . . . . . . . .   44
   5.2.3  GETNEXT Processing  . . . . . . . . . . . . . . . . . .   46
   5.2.4  GETBULK Processing  . . . . . . . . . . . . . . . . . .   47
   5.2.5  OPEN Request  . . . . . . . . . . . . . . . . . . . . .   48
   5.2.6  CLOSE Request   . . . . . . . . . . . . . . . . . . . .   49
   5.2.7  REGISTER Request  . . . . . . . . . . . . . . . . . . .   49
   5.2.8  UNREGISTER Request  . . . . . . . . . . . . . . . . . .   50
   5.2.9  TRAP Request  . . . . . . . . . . . . . . . . . . . . .   51
   5.2.10  ARE_YOU_THERE request  . . . . . . . . . . . . . . . .   51
   5.2.11  How to query the DPI port.   . . . . . . . . . . . . .   51
   6. REFERENCES  . . . . . . . . . . . . . . . . . . . . . . . .   51
   7. SECURITY CONSIDERATIONS . . . . . . . . . . . . . . . . . .   52
   8. AUTHORS' ADDRESSES  . . . . . . . . . . . . . . . . . . . .   53
   9. SAMPLE SOURCES FOR ANONYMOUS FTP  . . . . . . . . . . . . .   54

1. INTRODUCTION

 This RFC describes version 2.0 of a protocol that International
 Business Machines Corporation (IBM) has been implementing in most of
 its SNMP agents to allow dynamic extension of supported MIBs.  Bell
 Northern Research (BNR) has also implemented a version of this
 protocol in some of its SNMP agents for the same reason.
 The Simple Network Management Protocol (SNMP [1]) Distributed
 Protocol Interface (DPI) is an extension to SNMP agents that permits
 end-users to dynamically add, delete or replace management variables
 in the local Management Information Base without requiring
 recompilation of the SNMP agent.  This is achieved by writing a so-
 called sub-agent that communicates with the agent via the SNMP-DPI.
 For the author of a sub-agent, the SNMP-DPI eliminates the need to
 know the details of ASN.1 [2] or SNMP PDU (Protocol Data Unit)
 encoding/decoding [1, 3].
 Versions 1.0 and 1.1 of this protocol have been in use within IBM

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 2] RFC 1592 SNMP-DPI March 1994

 since 1989 and is included in the SNMP agents for VM, MVS and OS/2.
 Version 1.2 of this protocol has been in use within BNR since 1992.

1.1 MOTIVATION

 The Simple Network Management Protocol [1] defines a protocol that
 permits operations on a collection of variables.  This set of
 variables is called the Management Information Base (MIB) and a core
 set of variables has previously been defined [4, 5]; however, the
 design of the MIB makes provision for extension of this core set.
 Thus, an enterprise or individual can define variables of their own
 which represent information of use to them.  An example of a
 potentially interesting variable which is not in the core MIB would
 be CPU utilization (percent busy).  Unfortunately, conventional SNMP
 agent implementations provide no means for an end-user to make
 available new variables.
 Besides this, today there are many MIBs that people want to implement
 on a system.  Without a capability for sub-agents, this requires all
 the MIBs to be implemented in one big monolithic agent, which is in
 many cases undesirable.
 The SNMP DPI addresses these issues by providing a light-weight
 mechanism by which a process can register the existence of a MIB
 variable or a MIB sub-tree with the SNMP agent.  Requests for the
 variable(s) that are received by the SNMP agent are passed to the
 process acting as a sub-agent.  The sub-agent then returns an
 appropriate answer to the SNMP agent.  The SNMP agent eventually
 packages an SNMP response packet and sends the answer back to the
 remote network management station that initiated the request.
 Remote network management stations have no knowledge that the SNMP
 agent calls on other processes to obtain an answer.  As far as they
 can tell, there is only one network management application (agent)
 running on the host.
 At the San Diego IETF (March 1992) a BOF was held on multiplexing
 SNMP agent's requirements.  Both the SMUX [6] and DPI [7] protocols
 were discussed, as well as other unpublished approaches.  There was
 also discussion regarding a need for a standard for multiplexing SNMP
 agents or sub-agent support.  At the end of the BOF, however, there
 was not enough support for defining a standard.  This was due, at
 least partially, to a few well known SNMP authors who stated that the
 proxy and party support for SNMPv2 (SMP at the time) would solve the
 problem.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 3] RFC 1592 SNMP-DPI March 1994

 Nevertheless, questions continue to be raised about sub-agent support
 (both in SNMP and SNMP2 mail lists) in spite of both SNMPv2 [8] being
 on the standard's track and SMUX being changed to a historic RFC.
 Furthermore, within IBM and BNR we continue to see a substantial and
 expanding use of the DPI protocol.  with positive results.
 Therefore, we believe that there is a place for a sub-agent protocol
 and we again offer this new version as an experimental protocol.  We
 encourage people to try it and send us feedback.  Depending on that
 feedback, we may decide to try to get onto the standards track at a
 later time.
 During discussions about sub-agent interfaces at the San Diego BOF it
 also became clear that we should reduce the focus on the API for the
 sub-agent programmers.  This RFC, therefore, specifies only the
 protocol to distribute SNMP requests from the main SNMP agent to the
 sub-agents.  Programmers can build one or more Programming APIs on
 top of that protocol as needed, and sample API code is available from
 the authors of this document.

1.2 SUMMARY OF CHANGES

 The following changes have been made since the initial definition of
 SNMP-DPI [7].  Some of these resulted from comparing the SMUX [6] and
 DPI [7] protocols.
   o   Documentation changes to cleanup and be more specific in some
       areas.  Among other things, this includes:
  1. Defining that integers are in network byte order
  2. Defining the character set used for strings
  3. Defining how DisplayStrings are handled.
  4. Including DPI20 MIB definition.
   o   Removal of the Programming API from the document.
   o   Addition of new DPI packet types:
  1. SNMP_DPI_OPEN for a sub-agent to open a "connection" with

the DPI SNMP capable agent. The sub-agent must now

           identify itself and optionally provide a "password" for the
           connection.
       -   SNMP_DPI_CLOSE for the agent or sub-agent to close the
           connection in a graceful way.
       -   SNMP_DPI_ARE_YOU_THERE for the sub-agent to verify that the
           agent still knows about the sub-agent.
       -   SNMP_DPI_UNREGISTER for the agent or sub-agent to terminate
           the registration of a MIB variable or MIB sub-tree.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 4] RFC 1592 SNMP-DPI March 1994

  1. SNMP_DPI_COMMIT which instructs the sub-agent to actually

commit a previous SNMP_DPI_SET request. This, together

           with the UNDO, allows DPI sub-agents to be compliant with
           SNMP in the sense that we can now handle the "as if
           simultaneous" requirement.
       -   SNMP_DPI_UNDO which instructs the sub-agent to UNDO a SET
           or COMMIT if such is needed.
   o   Changes to DPI packets:
  1. Multiple varBinds can now be exchanged in one DPI packet

(for GET, GETNEXT, SET, TRAP). The sub-agent can specify

           the maximum it wants to handle per packet.
       -   The packet headers now contain a packet-ID (similar to SNMP
           request ID in SNMP PDU).  This allows to match RESPONSE
           packets to REQUESTS, which is important for UDP based
           DPI-connections.
       -   The SNMP_DPI_REGISTER packet has new fields for time_out
           and for requested priority.
       -   The SNMP_DPI_TRAP packet allows to specify an enterprise
           OID.  In addition, the generic and specific trap types are
           now 4 octets, so that we can pass the types correctly.
       -   In general, the packets have a more consistent layout.
   o   The agent now sends a RESPONSE to a REGISTER request
   o   Addition of SNMPv2 error codes and value types.

2. THEORY OF OPERATION

2.1 CONNECTION ESTABLISHMENT AND TERMINATION

 Communication between the SNMP Agent and its clients (sub-agents)
 takes place via a communication mechanism.  The communication type
 can be either a logical stream connection (via TCP, for instance) or
 an unreliable datagram connection (UDP, for instance).  It should be
 noted that other stream oriented transport communication mechanisms
 can also be used.  For example, the VM SNMP agent allows DPI
 connections over IUCV (Inter-User Communications Vehicle) [9, 10].
 Other than the connection establishment procedure, the protocol used
 is identical in these environments.
 In Unix the number of processes is limited by the number of file-
 descriptors that can be opened.  Since each TCP socket represents a
 file-descriptor, restricting SNMP-DPI protocol to TCP only
 connections would limit the number of sub-agents an agent could
 support.  As a result, the some SNMP-DPI agents support both TCP and
 UDP socket type communication mechanisms for the SNMP-DPI protocol.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 5] RFC 1592 SNMP-DPI March 1994

 Please note that in the following portion of this text the SNMP-DPI
 agent is referred simply as the agent.
 Once the transport connection has been set up, the sub-agent must
 also initialize the logical connection with the agent.  To do so it
 issues an OPEN request to the agent in which the sub-agent uniquely
 identifies itself and passes some other parameters to the agent, such
 as, the maximum number of varBinds per interaction it is prepared to
 handle, and the timeout the agent should use when waiting for a
 response from the sub-agent.
 When the sub-agent prepares to stop or cease operations, it first
 issues a CLOSE to shut down the logical connection with the agent,
 and then closes the transport connection.

2.2 REGISTRATION

 A sub-agent supports a collection of MIB variables or object
 identifiers (object IDs) that constitute its MIB (sub)tree.  Each of
 these object IDs consists of a group ID and an instance ID.  The
 group ID is the root of the sub-agent's MIB tree that it supports and
 the point of registration to the agent's MIB tree.  The instance ID
 is the piece of the Object Identifier that follows the group ID
 (registration point), so it is not an instance in the terms of the
 SNMP definition of an instance.
 Regardless of the transport mechanism used, after establishing a
 connection to the agent, the sub-agent registers a branch (group ID)
 to the Agent's MIB tree.  With the registration request, the sub-
 agent passes some parameters, such as, requested priority and a
 timeout value for this specific sub-tree.
 The agent sends back a response to indicate success or failure of the
 registration request.

2.3 NORMAL OPERATION

 Once the sub-agent has set up both the physical and logical
 connection to the agent, and once it has successfully registered the
 sub-tree(s) of the MIB(s) that it supports, it waits for requests
 from the SNMP agent or generates traps as required.

2.4 DPI ARCHITECTURE

 These are the requests that can be initiated by the SNMP agent:
     GET, GETNEXT, GETBULK, SET, COMMIT, UNDO, UNREGISTER, and CLOSE.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 6] RFC 1592 SNMP-DPI March 1994

 The first four of these correspond directly to SNMP requests that a
 network management station can make (By default a GETBULK request
 will be translated into multiple GETNEXT requests by the agent, but a
 sub-agent may request that the GETBULK be passed to it).  The COMMIT,
 UNDO, UNREGISTER, ARE_YOU_THERE and CLOSE requests are specific
 SNMP-DPI requests.  The sub-agent normally responds to a request with
 a RESPONSE packet.  The CLOSE request is an exception for which the
 sub-agent only closes the physical connection.
 These are the requests that can be initiated by a sub-agent:
     OPEN, REGISTER, TRAP, UNREGISTER, ARE_YOU_THERE and CLOSE.
 The agent responds to OPEN, REGISTER, UNREGISTER and ARE_YOU_THERE
 with a RESPONSE packet.  The TRAP packet is just accepted and
 forwarded by the agent without returning any information to the sub-
 agent.  The CLOSE packet is also just accepted by the agent upon
 which it closes the physical connection.
 See Figure 1 for an overview of the DPI packet flow.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 7] RFC 1592 SNMP-DPI March 1994

  1. ——————————————————————
  • ———————————*

| |

   |  SNMP Network                   |
   |  Management Station             |
   |                                 |
   |---------------------------------|
   |  SNMP Protocol                  |
   *---------------------------------*
         A      | Get         A
         |      | GetNext     |  GetResponse
    Trap |      | GetBulk     |
         |      | Set         |
         |      V             |
   *------------------------------*             *-------------------*
   |     SNMP Protocol            |             |   DPI Interface   |
   |------------------------------|  Response   |    *--------------|
   |                       |      |<----------->|    |              |
   |                       |      |             |    |              |
   |    SNMP Agent         |      |             |    |              |
   |                       |      | Get,GetNext |    |              |
   |                       |      | (GetBulk)   |    |   Client     |
   |                       |      | Set,Commit  |    |              |
   |     A     *-----------+->    |  Undo       |    |              |
   |     |     | Get/Set   |      |------------>|    |     or       |
   | Trap|     | info      |      |             |    |              |
   |     |     |           | SNMP |             |    |              |
   |-----+-----+-------*   |      |  trap       |    |   SNMP       |
   |     |     V       |   | DPI  |<------------|    |   Sub-Agent  |
   |                   |   |      |             |    |              |
   | Statically Linked |   |      |             |    |              |
   | Instrumentation   |   |      |             |    |              |
   |   (like MIB II)   |   |      |             |    |              |
   |                   |   |      |   close     |    |              |
   |       A           |   |      | unregister  |    |              |
   |-------+-----------|   |      |<----------->|    |              |
   |       V           |   |      |             |    |              |
   |                   |   |      |             |    |              |
   |                   |   |      | AreYouThere |    |              |
   | TCP/IP layers     |   |      |    open     |    |              |
   | Kernel            |   |      |  register   |    |              |
   |                   |   |      |<------------|    |              |
   *------------------------------*             *-------------------*
  1. ——————————————————————

Figure 1. SNMP DPI overview

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 8] RFC 1592 SNMP-DPI March 1994

   Remarks for Figure 1:
   o   The SNMP agent communicates with the SNMP manager via the
       standard SNMP protocol.
   o   The SNMP agent communicates with some statically linked-in
       instrumentation (potentially for the MIB II), which in turn
       talks to the TCP/IP layers and kernel (operating system) in an
       implementation-dependent manner.
   o   An SNMP sub-agent, running as a separate process (potentially
       on another machine), can set up a connection with the agent.
       The sub-agent has an option to communicate with the SNMP agent
       through UDP or TCP sockets, or even through other mechanisms.
   o   Once the connection is established, the sub-agent issues a DPI
       OPEN and one or more REGISTER requests to register one or more
       MIB sub-trees with the SNMP agent.
   o   The SNMP agent responds to DPI OPEN and REGISTER requests with
       a RESPONSE packet, indicating success or failure.
   o   The SNMP agent will decode SNMP packets.
       If such a packet contains a Get or GetNext request for an
       object in a sub-tree registered by a sub-agent, it sends a
       corresponding DPI packet to the sub-agent.
       If the request is for a GetBulk, then the agent translates it
       into multiple DPI GETNEXT packets and sends those to the
       sub-agent.  However, the sub-agent can request (in the REGISTER
       packet) that a GETBULK be passed to the sub-agent.
       If the request is for a Set, then the agent uses a 2-phase
       commit scheme and sends the sub-agent a sequence of SET/COMMIT,
       SET/UNDO or SET/COMMIT/UNDO DPI packets.
   o   The SNMP sub-agent sends responses back via a RESPONSE packet.
   o   The SNMP agent then encodes the reply into an SNMP packet and
       sends it back to the requesting SNMP manager.
   o   If the sub-agent wants to report an important state change, it
       sends a DPI TRAP packet to the SNMP agent which will encode it
       into an SNMP trap packet and send it to the manager(s).
   o   If the sub-agent wants to stop operations, it sends a DPI
       UNREGISTER and a DPI CLOSE packet to the agent.  The agent
       sends a response to an UNREGISTER request.
   o   There is no RESPONSE to a CLOSE, the agent just closes the DPI
       connection.  A CLOSE implies an UNREGISTER for all
       registrations that exist for the DPI connection being CLOSED.
   o   An agent can send DPI UNREGISTER (if a higher priority
       registration comes in or for other reasons) to the sub-agent,
       the sub-agent then responds with a DPI RESPONSE packet.
   o   An agent can also (for whatever reason) send a DPI CLOSE to
       indicate it is terminating the DPI connection.
   o   A sub-agent can send an ARE_YOU_THERE to verify that the
       "connection" is still open. If so, the agent sends a RESPONSE
       with no error, otherwise, it may send a RESPONSE with an error

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 9] RFC 1592 SNMP-DPI March 1994

       indication, or not react at all.

3. SNMP DPI PROTOCOL

 This section describes the actual protocol used between the SNMP
 agent and sub-agents.

3.1 CONNECTION ESTABLISHMENT

 In a TCP/IP environment, the SNMP agent listens on an arbitrary
 TCP/UDP port for a connection request from a sub-agent.  It is
 important to realize that a well-known port is not used: every
 invocation of the SNMP agent will potentially result in a different
 TCP/UDP port being used.
 A sub-agent needs to determine this port number to establish a
 connection.  The sub-agent learns the port number from the agent by
 sending it one conventional SNMP get-request PDU.  The port numbers
 are maintained by the SNMP agent as the objects whose identifiers
 are:
      1.3.6.1.4.1.2.2.1.1.0    dpiPort.0       (old DPI 1.x form)
      1.3.6.1.4.1.2.2.1.1.1.0  dpiPortForTCP.0
      1.3.6.1.4.1.2.2.1.1.2.0  dpiPortForUDP.0
 These variables are registered under the IBM enterprise-specific
 tree.  See 4, "DPI 2.0 MIB definition" for more information.  The
 SNMP agent replies with a conventional SNMP response PDU that
 contains the port number to be used.  This response is examined by
 the sub-agent and the port number is extracted.  The sub-agent then
 establishes the connection to the specified port.
 On the surface, this procedure appears to mean that the sub-agent
 must be able to create and parse SNMP packets, but this is not the
 case.  A DPI Application Programming Interface (API) normally
 provides a library routine, query_DPI_port(), which can be used to
 generate and parse the required SNMP packets.  This very small
 routine (under 100 lines of C), does not greatly increase the size of
 any sub-agent.
 NOTE: Since this RFC does not define an API, the actual code of and
 interface to a query_DPI_port() type of function depends on the
 implementation.
 For completeness, byte-by-byte descriptions of the packets to be
 generated by an SNMP DPI API routine query_DPI_port() are provided
 below.  This is probably of little interest to most readers and
 reading the source of a query_DPI_port() function provides much of

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 10] RFC 1592 SNMP-DPI March 1994

 the same information.

3.1.1 SNMP PDU TO GET THE AGENT'S DPI PORT

 As noted, before a TCP/UDP connection to the SNMP agent can be made,
 the sub-agent must learn which port that the agent is listening on.
 To do so, it can issue an SNMP GET for the variable dpiPortForTCP.0
 (1.3.6.1.4.1.2.2.1.1.1.0) or variable dpiPortForUDP.0
 (1.3.6.1.4.1.2.2.1.1.2.0).
 The SNMP PDU can be constructed as shown below.  This PDU must be
 sent to UDP port 161 on the host where the agent runs (probably the
 same host where the sub-agent runs).
 The (SNMPv1) packet shown below is for the TCP port.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 11] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 1 (Page 1 of 2). SNMP GET PDU for dpiPortForTCP.0         |
   +---------------+----------------+--------------------------------+
   | OFFSET        | VALUE          | FIELD                          |
   +---------------+----------------+--------------------------------+
   | 0             | 0x30           | ASN.1 header                   |
   +---------------+----------------+--------------------------------+
   | 1             | 37 + len       | PDU_length, see formula below  |
   +---------------+----------------+--------------------------------+
   | 2             | 0x02 0x01 0x00 | SNMP version:                  |
   |               |                | (integer,length=1,value=0)     |
   +---------------+----------------+--------------------------------+
   | 5             | 0x04           | community name (string)        |
   +---------------+----------------+--------------------------------+
   | 6             | len            | length of community name       |
   +---------------+----------------+--------------------------------+
   | 7             | community name | varies                         |
   +---------------+----------------+--------------------------------+
   | 7 + len       | 0xa0 0x1c      | SNMP GET request:              |
   |               |                | request_type=0xa0,length=0x1c  |
   +---------------+----------------+--------------------------------+
   | 7 + len + 2   | 0x02 0x01 0x01 | SNMP request ID:               |
   |               |                | integer,length=1,ID=1          |
   +---------------+----------------+--------------------------------+
   | 7 + len + 5   | 0x02 0x01 0x00 | SNMP error status:             |
   |               |                | integer,length=1,error=0       |
   +---------------+----------------+--------------------------------+
   | 7 + len + 8   | 0x02 0x01 0x00 | SNMP index:                    |
   |               |                | integer,length=1,index=0       |
   +---------------+----------------+--------------------------------+
   | 7 + len + 11  | 0x30 0x11      | varBind list, length=0x11      |
   +---------------+----------------+--------------------------------+
   | 7 + len + 13  | 0x30 0x0f      | varBind, length=0x0f           |
   +---------------+----------------+--------------------------------+
   | 7 + len + 15  | 0x06 0x0b      | Object ID, length=0x0b         |
   +---------------+----------------+--------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 12] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 1 (Page 2 of 2). SNMP GET PDU for dpiPortForTCP.0         |
   +---------------+----------------+--------------------------------+
   | OFFSET        | VALUE          | FIELD                          |
   +---------------+----------------+--------------------------------+
   | 7 + len + 17  | 0x2b 0x06 0x01 | Object-ID:                     |
   |               | 0x04 0x01 0x02 | 1.3.6.1.4.1.2.2.1.1.1          |
   |               | 0x02 0x01 0x01 | Object-instance: 0             |
   |               | 0x01 0x00      |                                |
   +---------------+----------------+--------------------------------+
   | 7 + len + 28  | 0x05 0x00      | null value, length=0           |
   +---------------+----------------+--------------------------------+
   | NOTE:  Formula to calculate "PDU_length":                       |
   |                                                                 |
   |   PDU_length =  length of version field and string tag (4 bytes)|
   |              +  length of community length field (1 byte)       |
   |              +  length of community name (depends...)           |
   |              +  length of SNMP GET request (32 bytes)           |
   |                                                                 |
   |              =  37 + length of community name                   |
   +-----------------------------------------------------------------+

3.1.2 SNMP PDU CONTAINING THE RESPONSE TO THE GET

 Assuming that no errors occurred, the port is returned in the last
 few octets of the received packet.  In the simple case, where the
 port number will be between 1024 and 16,385, the format of the packet
 is shown below.
 Note: In practice, the port number can be any positive number in the
 range from 1 through 65,535.  A port number of 0 means that the agent
 does not have a dpiPort defined for the requested protocol.  So the
 actual port value maybe in the last 1, 2 or 3 octets.  The sample
 implementation code shows how to handle the response to cover all
 those cases, including error conditions.
 Note: The (SNMPv1) packet shown below is for the TCP port.
   +-----------------------------------------------------------------+
   | Table 2 (Page 1 of 3). SNMP RESPONSE PDU for dpiPortForTCP.0    |
   +---------------+----------------+--------------------------------+
   | OFFSET        | VALUE          | FIELD                          |
   +---------------+----------------+--------------------------------+
   | 0             | 0x30           | ASN.1 header                   |
   +---------------+----------------+--------------------------------+
   | 1             | 39 + len       | length, see formula below      |
   +---------------+----------------+--------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 13] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 2 (Page 2 of 3). SNMP RESPONSE PDU for dpiPortForTCP.0    |
   +---------------+----------------+--------------------------------+
   | OFFSET        | VALUE          | FIELD                          |
   +---------------+----------------+--------------------------------+
   | 2             | 0x02 0x01 0x00 | version                        |
   |               |                | (integer,length=1,value=0)     |
   +---------------+----------------+--------------------------------+
   | 5             | 0x04           | community name (string)        |
   +---------------+----------------+--------------------------------+
   | 6             | len            | length of community name       |
   +---------------+----------------+--------------------------------+
   | 7             | community name |                                |
   +---------------+----------------+--------------------------------+
   | 7 + len       | 0xa2 0x1e      | SNMP RESPONSE:                 |
   |               |                | request_type=0xa2,length=0x1e  |
   +---------------+----------------+--------------------------------+
   | 7 + len + 2   | 0x02 0x01 0x01 | SNMP request ID:               |
   |               |                | integer,length=1,ID=1          |
   +---------------+----------------+--------------------------------+
   | 7 + len + 5   | 0x02 0x01 0x00 | SNMP error status:             |
   |               |                | integer,length=1,error=0       |
   +---------------+----------------+--------------------------------+
   | 7 + len + 8   | 0x02 0x01 0x00 | SNMP index:                    |
   |               |                | integer,length=1,index=0       |
   +---------------+----------------+--------------------------------+
   | 7 + len + 11  | 0x30 0x13      | varBind list, length=0x13      |
   +---------------+----------------+--------------------------------+
   | 7 + len + 13  | 0x30 0x11      | varBind, length=0x11           |
   +---------------+----------------+--------------------------------+
   | 7 + len + 15  | 0x06 0x0b      | Object ID, length=0x0b         |
   +---------------+----------------+--------------------------------+
   | 7 + len + 17  | 0x2b 0x06 0x01 | Object-ID:                     |
   |               | 0x04 0x01 0x02 | 1.3.6.1.4.1.2.2.1.1.1          |
   |               | 0x02 0x01 0x01 | Object-instance: 0             |
   |               | 0x01 0x00      |                                |
   +---------------+----------------+--------------------------------+
   | 7 + len + 28  | 0x02 0x02      | integer, length=2              |
   +---------------+----------------+--------------------------------+
   | 7 + len + 30  | MSB LSB        | port number (MSB, LSB)         |
   +---------------+----------------+--------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 14] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 2 (Page 3 of 3). SNMP RESPONSE PDU for dpiPortForTCP.0    |
   +---------------+----------------+--------------------------------+
   | NOTE:  Formula to calculate "PDU_length":                       |
   |                                                                 |
   |   PDU_length =  length of version field and string tag (4 bytes)|
   |              +  length of community length field (1 byte)       |
   |              +  length of community name (depends...)           |
   |              +  length of SNMP RESPONSE (34 bytes)              |
   |                                                                 |
   |              =  39 + length of community name                   |
   +-----------------------------------------------------------------+

3.2 SNMP DPI PACKET FORMATS

 Each request to, or response from, the agent or sub-agent is
 constructed as a "packet" and is written to the stream.
 Each packet is prefaced with the length of the data remaining in the
 packet.  The length is stored in network byte order, the most
 significant byte (MSB) first, least significant byte (LSB) last.  If
 we consider a stream connection (like TCP), the receiving side will
 read the packet by doing something similar to:
        unsigned char len_bfr[2];
        unsigned char *bfr;
        int len;
        read(fd,len_bfr,2);
        len = len_bfr[0] * 256 + len_bfr[1];
        bfr = malloc(len);
        read(fd,bfr,len);
 Note: The above example makes no provisions for error handling or a
 read returning less than the requested amount of data,and it is not
 intended to be used literally.

3.2.1 DPI PACKET HEADER

 The first part of every packet identifies the application protocol
 being used as well as some version information.  The protocol major
 version is intended to indicate, in broad terms, what version of the
 protocol is used.  The protocol minor version is intended to identify
 major incompatible versions of the protocol.  The protocol release is
 intended to indicate incremental modifications to the protocol.  The
 constants that are valid for these fields are defined in Table 15.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 15] RFC 1592 SNMP-DPI March 1994

 The next field, present in all packets, is the packet ID.  It
 contains packet identification that can help an agent or sub-agent
 match responses with request.  This is useful with UDP connections
 over which packets can be lost.  The packet ID is a monotonically
 increasing unsigned 16-bit integer which wraps at its maximum value.
 The next field, present in all packets, is the packet type.  It
 indicates what kind of packet we're dealing with (OPEN, REGISTER,
 GET, GETNEXT, GETBULK, SET, COMMIT, UNDO, TRAP, RESPONSE, UNREGISTER,
 or CLOSE).  The permitted values for this field are defined in Table
 16.
   +-----------------------------------------------------------------+
   | Table 3. SNMP DPI packet header.  Present in all packets.       |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type                                        |
   +------------+----------------------------------------------------+
 From this point onwards, the contents of the packet are defined by
 the protocol being used.  The remainder of this section describes:
   o   Layout of packets for the SNMP DPI protocol, version 2.0.
   o   Constants as defined with this version of the protocol.

3.2.2 OPEN

 In order for a sub-agent to communicate with a DPI capable SNMP
 agent, it must first send an SNMP DPI OPEN request to the agent to
 setup the "connection" with that agent.
 Such a packet contains the standard SNMP DPI header plus OPEN
 specific data.  This data consists of:

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 16] RFC 1592 SNMP-DPI March 1994

   o   a timeout value (in seconds).
       This is a requested timeout value to be used for all requests
       for objects for which there is no timeout value specified for
       the sub-tree under which the object is registered.  If you
       specify a zero timeout value, then the agent will use its own
       default timeout value.  If you want a larger value than the
       default value, then you can specify it here. However, the agent
       may have a maximum value that you can never exceed. If you do
       ask for a larger timeout than that maximum, the agent will set
       it at the maximum it accepts.
   o   the maximum number of varBinds per DPI packet that the
       sub-agent is prepared to handle.
   o   Selected character set to be used for the representation of the
       OBJECT ID strings and DisplayStrings.
       The choices are the native character set (0) or the ASCII
       character set (1).  See 3.3.5, "Character set selection"
       for more information in character set selection.
       An agent may choose to support only the native character set.
   o   null terminated sub-agent ID, which is a unique ASN.1 OBJECT
       identifier, so in dotted ASN.1 notation.  This string is
       represented in the selected character set.
   o   null terminated sub-agent description, which is a DisplayString
       describing the sub-agent.  This string is represented in the
       selected character set.  This may be the null-string if there
       is no description.
   o   optionally a password that the agent uses to validate the
       sub-agent.  It depends on the agent implementation if a
       password is required.  If no password is passed, the length
       must be specified as zero.
 The sub-agent must expect a response indicating success or failure.
 See Table 19 for the valid codes in a DPI RESPONSE to a DPI OPEN
 request.
 If the error_code in the RESPONSE is not SNMP_ERROR_DPI_noError, then
 the agent closes the connection.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 17] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 4. Layout SNMP DPI OPEN packet                            |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_OPEN                        |
   +------------+----------------------------------------------------+
   | 8          | requested overall timeout (seconds, MSB to LSB)    |
   +------------+----------------------------------------------------+
   | 10         | max varBinds per DPI packet (MSB to LSB)           |
   +------------+----------------------------------------------------+
   | 12         | Selected character set (0=Native, 1=ASCII)         |
   +------------+----------------------------------------------------+
   | 13         | null terminated sub-agent ID (OID)                 |
   +------------+----------------------------------------------------+
   | 13+L1      | null terminated sub-agent Description              |
   +------------+----------------------------------------------------+
   | 13+L2      | password length (zero if no password, MSB to LSB)  |
   +------------+----------------------------------------------------+
   | 15+L2      | password (if any)                                  |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   L1 = strlen(sub-agent ID) + 1                               |
   | o   L2 = L1 + strlen(sub-agent Description) + 1                 |
   | o   OID and Description strings use selected character set      |
   +-----------------------------------------------------------------+

3.2.3 CLOSE

 In order for a sub-agent to close the "connection" with the DPI
 capable SNMP agent, it must send an SNMP DPI CLOSE request to the
 agent.  The agent will not send a response, but closes the physical
 connection and implicitly unregisters any sub-trees related to the
 connection.
 An agent may also send to the sub-agent an SNMP DPI CLOSE packet that
 contains the standard SNMP DPI header plus CLOSE specific data.  This

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 18] RFC 1592 SNMP-DPI March 1994

 data consists of:
   o   a reason code for closing.  See Table 21 for a list
       of valid reason codes.
   +-----------------------------------------------------------------+
   | Table 5. Layout SNMP DPI CLOSE packet                           |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_CLOSE                       |
   +------------+----------------------------------------------------+
   | 8          | reason code (1 octet)                              |
   +------------+----------------------------------------------------+

3.2.4 ARE_YOU_THERE

 An ARE_YOU_THERE packet allows a sub-agent to determine if it still
 has a DPI connection with the agent.  This packet is necessary
 because a sub-agent passively awaits requests from an agent and
 normally will not detect problems with an agent connection in a
 timely manner.  (In contrast, an agent becomes aware of any sub-agent
 connection problem in a timely manner because it sets a timeout when
 sending request).
 A sub-agent can send a SNMP DPI ARE_YOU_THERE packet to an agent
 which will then return a RESPONSE with a zero error code and a a zero
 error index if the connection is healthy.  Otherwise, the agent may
 return a RESPONSE with an error indication.  If the connection is
 broken, the sub-agent will see no response at all.
 An ARE_YOU_THERE packet contains the standard SNMP DPI header with no
 additional data.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 19] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 6. Layout SNMP DPI ARE_YOU_THERE packet                   |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_ARE_YOU_THERE               |
   +------------+----------------------------------------------------+

3.2.5 REGISTER

 In order to register a branch in the MIB tree, an SNMP sub-agent
 sends an SNMP DPI REGISTER packet to the agent.
 Such a packet contains the standard SNMP DPI header plus REGISTER
 specific data.  This data consists of:
   o   a requested priority.
       There are 2 special values, namely minus one (-1, requests best
       available priority) and zero (0, requests next better priority
       than the highest priority in use).  Any other value requests a
       specific priority or the next best priority if already in use).
       The lower the number, the better the priority.  An agent will
       send requests to only the one sub-agent that has registered
       with the best priority.  The agent returns the actual priority
       assigned in the RESPONSE packet in the error_index field.
   o   a requested timeout.
       If a zero value is specified, then the agent uses the timeout
       value specified in the DPI OPEN request.
       If you want a shorter or longer timeout value for this specific
       sub-tree, then you specify it here.  The agent has a maximum
       timeout it will allow in this field.  The agent will use this
       value (or its maximum) to await a response to requests for this
       sub-tree.
   o   an indication as to whether the sub-agent wishes to handle MIB
       view selection (SNMPv1 community string authentication)
       in subsequent GET, GETNEXT or SET, COMMIT, UNDO requests.  Not
       all DPI capable agents need to support this feature, but they
       must at least recognize this indication and give an appropriate

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 20] RFC 1592 SNMP-DPI March 1994

       response if they do not support it.
   o   an indication as to whether the sub-agent wishes to handle the
       GETBULK itself.  If not, then the agent will translate a
       GETBULK into multiple GETNEXT requests.
       Not all DPI capable agents need to support this feature.  They
       may opt to always translate a GETBULK into multiple GETNEXT
       requests.  In this case the agent will send the appropriate
       RESPONSE to indicate this.
   o   the group ID (sub-tree) to be registered (with trailing dot).
       The group ID is represented in the selected character set as
       specified in DPI OPEN packet.
 The agent will respond with an SNMP DPI RESPONSE packet indicating
 registration error or success.  The packet ID of the response will be
 the same as that for the REGISTER request to which this is a
 response.
 The group ID will be the same as that specified in the REGISTER
 request.  There will be no instance returned (e.g. NULL string for
 instance ID).  The value will be an SNMP_TYPE_NULL value with a zero
 length.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 21] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 7. Layout SNMP DPI REGISTER packet                        |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_REGISTER                    |
   +------------+----------------------------------------------------+
   | 8          | requested priority (MSB to LSB)                    |
   +------------+----------------------------------------------------+
   | 12         | timeout in seconds (MSB to LSB)                    |
   +------------+----------------------------------------------------+
   | 14         | view selection (0 = you (agent) do, 1 = I do)      |
   +------------+----------------------------------------------------+
   | 15         | getbulk selection (0=use GetNext, 1=use GetBulk)   |
   +------------+----------------------------------------------------+
   | 16         | null terminated group ID (with trailing dot)       |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   group ID string uses selected character set                 |
   +-----------------------------------------------------------------+

3.2.6 UNREGISTER

 In order to unregister a branch in the MIB tree, an SNMP sub-agent
 sends an SNMP DPI UNREGISTER packet to the agent.
 Such a packet contains the standard SNMP DPI header plus UNREGISTER
 specific data: a null terminated string (represented in the selected
 character set) representing the group ID in ASN.1 dotted notation and
 an indication as to the reason for the unregister (see table 14).
 The agent will respond with an SNMP DPI RESPONSE packet indicating
 error or success.  The packet ID of the response will be the same as
 that for the UNREGISTER request to which this is a response.
 The group ID will be the same as that specified in the UNREGISTER
 request.  There will be no instance returned (e.g. NULL string for

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 22] RFC 1592 SNMP-DPI March 1994

 instance ID).  The value will be an SNMP_TYPE_NULL value with a zero
 length.
   +-----------------------------------------------------------------+
   | Table 8. Layout SNMP DPI UNREGISTER packet                      |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_UNREGISTER                  |
   +------------+----------------------------------------------------+
   | 8          | reason code                                        |
   +------------+----------------------------------------------------+
   | 9          | null terminated group ID (with trailing dot)       |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   group ID string uses selected character set                 |
   +-----------------------------------------------------------------+

3.2.7 GET

 When the SNMP agent receives a PDU containing an SNMP GET request for
 a variable that resides in a sub-tree registered by a sub-agent, it
 passes an SNMP DPI GET packet to the sub-agent.
 Such a packet contains the standard SNMP DPI header plus GET specific
 data:
   o   the community name used in the SNMP PDU.  The length is zero
       unless view handling was selected by the sub-agent.  The length
       is also zero if the SNMP PDU was not in SNMPv1 format.
   o   per varBind two null terminated strings (in the selected
       character set) representing the group and instance ID in ASN.1
       dotted notation.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 23] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 9. Layout SNMP DPI GET packet                             |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_GET                         |
   +------------+----------------------------------------------------+
   | 8          | community name length (MSB to LSB)                 |
   +------------+----------------------------------------------------+
   | 10         | community name (if any)                            |
   +------------+----------------------------------------------------+
   | 10+L1      | null terminated group ID (with trailing dot)       |
   +------------+----------------------------------------------------+
   | 10+L2      | null terminated instance ID (no trailing dot)      |
   +------------+----------------------------------------------------+
   | 10+L3      | optionally more varBinds (group/instance ID pairs) |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   L1 = length of community name                               |
   | o   L2 = L1 +  strlen(group ID) + 1                             |
   | o   L3 = L2 +  strlen(instance ID) + 1                          |
   | o   group and instance ID strings use selected character set    |
   +-----------------------------------------------------------------+

3.2.8 GETNEXT

 When the SNMP agent receives a PDU containing an SNMP GETNEXT request
 for a variable for which a sub-agent may be authoritative, it passes
 an SNMP DPI GETNEXT packet to the sub-agent.
 Such a packet contains the standard SNMP DPI header plus GETNEXT
 specific data:
   o   the community name used in the SNMP PDU.  The length is zero
       unless view handling was selected by the sub-agent.  The length
       is also zero if the SNMP PDU was not in SNMPv1 format.
   o   per varBind two null terminated strings (in the selected

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 24] RFC 1592 SNMP-DPI March 1994

       character set) representing the group and instance ID in ASN.1
       dotted notation.
   +-----------------------------------------------------------------+
   | Table 10. Layout SNMP DPI GETNEXT packet                        |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_GETNEXT                     |
   +------------+----------------------------------------------------+
   | 8          | community name length (MSB to LSB)                 |
   +------------+----------------------------------------------------+
   | 10         | community name                                     |
   +------------+----------------------------------------------------+
   | 10+L1      | null terminated group ID (with trailing dot)       |
   +------------+----------------------------------------------------+
   | 10+L2      | null terminated instance ID (no trailing dot)      |
   +------------+----------------------------------------------------+
   | 10+L3      | optionally more varBinds (group/instance ID pairs) |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   L1 = length of community name                               |
   | o   L2 = L1 +  strlen(group ID) + 1                             |
   | o   L3 = L2 +  strlen(instance ID) + 1                          |
   | o   group and instance ID strings use selected character set    |
   +-----------------------------------------------------------------+

3.2.9 GETBULK

 When the SNMP agent receives a PDU containing an SNMP GETBULK request
 that includes variables for which a sub-agent may be authoritative,
 it checks if the sub-agent wants to handle the GETBULK itself (as
 specified at registration time).  If so, it sends an SNMP DPI GETBULK
 packet to the sub-agent.
 Such a packet contains the standard SNMP DPI header plus GETBULK
 specific data:

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 25] RFC 1592 SNMP-DPI March 1994

   o   non-repeaters
   o   max repetitions
   o   per varBind two null terminated strings (in the selected
       character set) representing the group and instance ID in ASN.1
       dotted notation.
   +-----------------------------------------------------------------+
   | Table 11. Layout SNMP DPI GETBULK packet                        |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_GETBULK                     |
   +------------+----------------------------------------------------+
   | 8          | non-repeaters (4 octets, MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 12         | max-repetitions (4 octets, MSB to LSB)             |
   +------------+----------------------------------------------------+
   | 16         | null terminated group ID (with trailing dot)       |
   +------------+----------------------------------------------------+
   | 16+L1      | null terminated instance ID (no trailing dot)      |
   +------------+----------------------------------------------------+
   | 16+L2      | optionally more varBinds (group/instance ID pairs) |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   L1 = strlen(group ID) + 1                                   |
   | o   L2 = L1 +  strlen(instance ID) + 1                          |
   | o   group and instance ID strings use selected character set    |
   +-----------------------------------------------------------------+

3.2.10 SET, COMMIT AND UNDO

 When the SNMP agent receives a PDU containing an SNMP SET request for
 a variable that is in a sub-tree registered by a sub-agent, it passes
 one of 3 sequences of SNMP DPI packets to the sub-agent:

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 26] RFC 1592 SNMP-DPI March 1994

   o   SET, COMMIT
       This is the normal sequence.  The SET request is the first
       phase.  The sub-agent must verify that the SET request is valid
       and that the resources needed are available.  The COMMIT
       request comes next.  The sub-agent must now effectuate the SET
       request.
   o   SET, UNDO
       If an SNMP packet has a SET request for multiple varBinds that
       reside in different sub-trees, then the agent first sends a SET
       to all sub-agents.  If any sub-agent returns an error on the
       SET, then the agent sends UNDO to those sub-agents that
       returned no error on the SET, meaning the SET is being
       canceled.
   o   SET, COMMIT, UNDO
       In the very rare circumstance where all sub-agents have
       responded error-free to a SET and where one of them fails to
       perform the COMMIT, then the agent sends an UNDO to all
       involved sub-agents (also those who completed COMMIT).
       Sub-agents should try, to the best of their ability, to never
       let a commit fail and to undo an already committed set if asked
       to do so.
 Such packets contain the standard SNMP DPI header plus SET specific
 data:
   o   the community name used in the SNMP PDU.  The length is zero
       unless view handling was selected by the sub-agent.  The length
       is also zero if the SNMP PDU was not in SNMPv1 format.
   o   per varBind:
  1. two null terminated strings (in the selected character set)

representing the group and instance ID in ASN.1 dotted

           notation.
       -   the type, value length and value to be set.
       The permitted types for the type field are defined in Table 17.
       See 3.3.4, "Value Representation" for information on how the
       value data is represented in the packet value field.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 27] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 12. Layout SNMP DPI SET, COMMIT, UNDO packet              |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_SET/COMMIT/UNDO             |
   +------------+----------------------------------------------------+
   | 8          | community name length (MSB to LSB)                 |
   +------------+----------------------------------------------------+
   | 10         | community name                                     |
   +------------+----------------------------------------------------+
   | 10+L1      | null terminated group ID (with trailing dot)       |
   +------------+----------------------------------------------------+
   | 10+L2      | null terminated instance ID (no trailing dot)      |
   +------------+----------------------------------------------------+
   | 10+L3      | SNMP Variable Type Value                           |
   +------------+----------------------------------------------------+
   | 10+L3+1    | Length of value (2 octets, MSB to LSB)             |
   +------------+----------------------------------------------------+
   | 10+L3+3    | Value                                              |
   +------------+----------------------------------------------------+
   | 10+L4      | optionally more varBinds (sequences of group ID,   |
   |            | instance ID, Type, Length and Value)               |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   L1 = length of community name                               |
   | o   L2 = L1 + strlen(group ID) + 1                              |
   | o   L3 = L2 + strlen(instance ID) + 1                           |
   | o   L4 = L3 + 3 + length of value                               |
   | o   group and instance ID strings use selected character set    |
   | o   OID and DisplayString values use selected character set     |
   | o   Integer values are in network byte order                    |
   +-----------------------------------------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 28] RFC 1592 SNMP-DPI March 1994

3.2.11 RESPONSE

 An SNMP sub-agent must respond to a GET, GETNEXT, GETBULK, SET,
 COMMIT, UNDO or UNREGISTER request that it has received from the
 agent (unless it fails or has a bug ;-)).  To do so, it sends an SNMP
 DPI RESPONSE packet to the agent.
 Such a packet contains the standard SNMP DPI header plus RESPONSE
 specific data:
   o   an error_code,
   o   an error_index,
   o   plus for a successful GET, GETNEXT, or GETBULK, the
       name/type/length/value tuple(s) representing the returned
       object(s).  For each varBind this is described as:
  1. two null terminated strings (in the selected character set)

representing the group and instance ID in ASN.1 dotted

           notation.
       -   the type, value length and value of the object that is
           returned.
       The permitted types for the type field are defined in Table 17.
       See 3.3.4, "Value Representation" for information on how the
       value data is represented in the packet value field.
 For an unsuccessful GET, GETNEXT or GETBULK, the sub-agent does not
 need to return any name/type/length/value tuple(s), 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.
 The group ID and the packet ID must always be the same as the
 corresponding fields in request PDU which has prompted the RESPONSE.
 If the response is to a SET, COMMIT or UNDO request, there is no need
 to return any varBind information, 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 the response is to a REGISTER or UNREGISTER, no variable
 (instance) is being returned, so the instance ID is the NULL string
 (one 0x00 byte).  In the response to a REGISTER request indicating
 success, the error index contains the priority assigned by the agent.
 If the response is to an OPEN, ARE_YOU_THERE or CLOSE, no varBind
 data will be passed, so no group ID, instance ID or value data. The
 packet will only include the header, the error code and the error

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 29] RFC 1592 SNMP-DPI March 1994

 index.
   +-----------------------------------------------------------------+
   | Table 13. Layout SNMP DPI RESPONSE packet                       |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type = SNMP_DPI_RESPONSE                    |
   +------------+----------------------------------------------------+
   | 8          | error code (1 octet)                               |
   +------------+----------------------------------------------------+
   | 9          | error index (4 octets, MSB to LSB)                 |
   +------------+----------------------------------------------------+
   | 15         | null terminated group ID (with trailing dot)       |
   +------------+----------------------------------------------------+
   | 15+L1      | null terminated instance ID (no trailing dot)      |
   +------------+----------------------------------------------------+
   | 15+L2      | SNMP Variable Type Value                           |
   +------------+----------------------------------------------------+
   | 15+L2+1    | Length of value (MSB to LSB)                       |
   +------------+----------------------------------------------------+
   | 15+L2+3    | Value                                              |
   +------------+----------------------------------------------------+
   | 15+L3      | optionally more varBinds (sequences of group ID,   |
   |            | instance ID, Type, Length and Value)               |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   L1 = strlen(group ID) + 1                                   |
   | o   L2 = L1 + strlen(instance ID) + 1                           |
   | o   L3 = L2 + 3 + length of value                               |
   | o   group and instance ID strings use selected character set    |
   | o   OID and DisplayString values use selected character set     |
   | o   Integer values are in network byte order                    |
   +-----------------------------------------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 30] RFC 1592 SNMP-DPI March 1994

3.2.12 TRAP

 An SNMP sub-agent can request the agent to generate an SNMPv1 or
 SNMPv2 TRAP (depending on the trap destinations defined at the agent)
 by sending an SNMP DPI TRAP packet to the agent.
 Such a packet contains the standard SNMP DPI header plus TRAP
 specific data:
   o   the generic and specific trap codes
   o   optionally a null terminated string (in the selected character
       set) representing the enterprise ID in ASN.1 dotted notation.
       This enterprise ID will be sent with the TRAP.  If the null
       string is passed, then the agent uses the sub-agent Identifier
       (OID as passed with the DPI OPEN packet) as the Enterprise ID.
   o   optionally a set of one or more name/type/length/value tuples.
       representing varBinds to be sent with the trap.  Each varBind
       consists of:
  1. two null terminated strings (in the selected character set)

representing the group and instance ID in ASN.1 dotted

           notation.
       -   the type, value length and value of the object that is
           returned.
       The permitted types for the type field are defined in Table 17.
       See 3.3.4, "Value Representation" for information on how the
       value data is represented in the packet value field.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 31] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | Table 14. Layout SNMP DPI TRAP packet                           |
   +------------+----------------------------------------------------+
   | OFFSET     | FIELD                                              |
   +------------+----------------------------------------------------+
   | 0          | packet length to follow (MSB to LSB)               |
   +------------+----------------------------------------------------+
   | 2          | protocol major version                             |
   +------------+----------------------------------------------------+
   | 3          | protocol minor version                             |
   +------------+----------------------------------------------------+
   | 4          | protocol release                                   |
   +------------+----------------------------------------------------+
   | 5          | packet id (MSB to LSB)                             |
   +------------+----------------------------------------------------+
   | 7          | packet type - SNMP_DPI_TRAP                        |
   +------------+----------------------------------------------------+
   | 8          | SNMP generic trap code                             |
   +------------+----------------------------------------------------+
   | 12         | SNMP specific trap code                            |
   +------------+----------------------------------------------------+
   | 14         | null terminated enterprise ID (no trailing dot)    |
   +------------+----------------------------------------------------+
   | 14+L1      | null terminated group ID (with trailing dot)       |
   +------------+----------------------------------------------------+
   | 14+L2      | null terminated instance ID (no trailing dot)      |
   +------------+----------------------------------------------------+
   | 14+L3      | SNMP Variable Type Value                           |
   +------------+----------------------------------------------------+
   | 14+L3+1    | Length of value (MSB to LSB)                       |
   +------------+----------------------------------------------------+
   | 14+L3+3    | Value                                              |
   +------------+----------------------------------------------------+
   | 14+L4      | optionally more varBinds (sequences of group ID,   |
   |            | instance ID, Type, Length and Value)               |
   +------------+----------------------------------------------------+
   | NOTE:                                                           |
   |                                                                 |
   | o   L1 = strlen(enterprise ID) + 1                              |
   | o   L2 = L1 + strlen(group ID) + 1                              |
   | o   L3 = L1 + L2 + strlen(instance ID) + 1                      |
   | o   L4 = L1 + L2 + L3 + 3 + length of Value                     |
   | o   enterprise, group and instance ID strings use selected      |
   |     character set                                               |
   | o   OID and DisplayString values use selected character set     |
   | o   Integer values are in network byte order                    |
   +-----------------------------------------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 32] RFC 1592 SNMP-DPI March 1994

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.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 33] RFC 1592 SNMP-DPI March 1994

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                                  |
   +-------+---------------------------------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 34] RFC 1592 SNMP-DPI March 1994

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

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 35] RFC 1592 SNMP-DPI March 1994

       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.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 36] RFC 1592 SNMP-DPI March 1994

 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:

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 37] RFC 1592 SNMP-DPI March 1994

   +-----------------------------------------------------------------+
   | 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                             |
   +-------+---------------------------------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 38] RFC 1592 SNMP-DPI March 1994

 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        |
   +-------+---------------------------------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 39] RFC 1592 SNMP-DPI March 1994

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                                 |
   +-------+---------------------------------------------------------+

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 40] RFC 1592 SNMP-DPI March 1994

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
  1. - 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 }
  1. - dpi20MIB MODULE-IDENTITY
  2. - LAST-UPDATED "9401210000Z"
  3. - ORGANIZATION "IBM Research - T.J. Watson Research Center"
  4. - CONTACT-INFO " Bert Wijnen
  5. - Postal: IBM International Operations
  6. - Watsonweg 2
  7. - 1423 ND Uithoorn
  8. - The Netherlands

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 41] RFC 1592 SNMP-DPI March 1994

  1. - Tel: +31 2975 53316
  2. - Fax: +31 2975 62468
  3. - E-mail: wijnen@vnet.ibm.com"
  4. - DESCRIPTION "MIB module describing DPI objects."
  5. - ::= { 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

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 42] RFC 1592 SNMP-DPI March 1994

       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.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 43] RFC 1592 SNMP-DPI March 1994

 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

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 44] RFC 1592 SNMP-DPI March 1994

 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

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 45] RFC 1592 SNMP-DPI March 1994

 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

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 46] RFC 1592 SNMP-DPI March 1994

 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.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 47] RFC 1592 SNMP-DPI March 1994

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.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 48] RFC 1592 SNMP-DPI March 1994

       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.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 49] RFC 1592 SNMP-DPI March 1994

       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

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 50] RFC 1592 SNMP-DPI March 1994

 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.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 51] RFC 1592 SNMP-DPI March 1994

 [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.

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 52] RFC 1592 SNMP-DPI March 1994

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

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 53] RFC 1592 SNMP-DPI March 1994

 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

Wijnen, Carpenter, Curran, Sehgal & Waters [Page 54]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1592.txt · Last modified: 1994/03/02 19:55 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki