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Versions: 00 01 02 03 RFC 2257

                   Agent Extensibility (AgentX) Protocol
                                 Version 1

                    <draft-ietf-agentx-ext-pro-03.txt>

                               Mike Daniele
                       Digital Equipment Corporation
                            daniele@zk3.dec.com

                                Bert Wijnen
                  T.J. Watson Research Center, IBM Corp.
                            wijnen@vnet.ibm.com

                          Dale Francisco (editor)
                            Cisco Systems, Inc.
                            dfrancis@cisco.com



Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

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

   To learn the current status of any Internet-Draft, please check the
   "1id-abstracts.txt" listing contained in the Internet-Drafts
   Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net
   (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
   Rim).















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   1 Introduction......................................................5

   2 The SNMP Framework................................................5
     2.1 A Note on Terminology.........................................5

   3 Extending the MIB.................................................6
     3.1 Motivation for AgentX.........................................6

   4 AgentX Framework..................................................7
     4.1 AgentX Roles..................................................8
     4.2 Applicability.................................................9
     4.3 Design Features of AgentX....................................10
     4.4 Non-Goals....................................................11

   5 AgentX Encodings.................................................12
     5.1 Object Identifier............................................12
     5.2 SearchRange..................................................14
     5.3 Octet String.................................................16
     5.4 Value Representation.........................................17

   6 Protocol Definitions.............................................19
     6.1 AgentX PDU Header............................................19
       6.1.1 Context..................................................22
     6.2 AgentX PDUs..................................................23
       6.2.1 The agentx-Open-PDU......................................23
       6.2.2 The agentx-Close-PDU.....................................24
       6.2.3 The agentx-Register-PDU..................................26
       6.2.4 The agentx-Unregister-PDU................................29
       6.2.5 The agentx-Get-PDU.......................................31
       6.2.6 The agentx-GetNext-PDU...................................32
       6.2.7 The agentx-GetBulk-PDU...................................34
       6.2.8 The agentx-TestSet-PDU...................................35
       6.2.9 The agentx-CommitSet, -UndoSet, -CleanupSet
             PDUs.....................................................36
       6.2.10 The agentx-Notify-PDU...................................37
       6.2.11 The agentx-Ping-PDU.....................................38
       6.2.12 The agentx-IndexAllocate-PDU............................39
       6.2.13 The agentx-IndexDeallocate-PDU..........................40
       6.2.14 The agentx-AddAgentCaps-PDU.............................41
       6.2.15 The agentx-RemoveAgentCaps-PDU..........................43
       6.2.16 The agentx-Response-PDU.................................44

   7 Elements of Procedure............................................46
     7.1 Processing AgentX Administrative Messages....................46
       7.1.1 Processing the agentx-Open-PDU...........................47
       7.1.2 Processing the agentx-IndexAllocate-PDU..................48
       7.1.3 Using the agentx-IndexAllocate-PDU.......................49
       7.1.4 Processing the agentx-IndexDeallocate-PDU................51
       7.1.5 Processing the agentx-Register-PDU.......................52
         7.1.5.1 Handling Duplicate OID Ranges........................54
       7.1.6 Processing the agentx-Unregister-PDU.....................54



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       7.1.7 Processing the agentx-AddAgentCaps-PDU...................55
       7.1.8 Processing the agentx-RemoveAgentCaps-PDU................56
       7.1.9 Processing the agentx-Close-PDU..........................56
       7.1.10 Detecting Connection Loss...............................57
       7.1.11 Processing the agentx-Notify-PDU........................57
       7.1.12 Processing the agentx-Ping-PDU..........................58
     7.2 Processing Received SNMP Protocol Messages...................58
       7.2.1 Dispatching AgentX PDUs..................................59
         7.2.1.1 agentx-Get-PDU.......................................61
         7.2.1.2 agentx-GetNext-PDU...................................62
         7.2.1.3 agentx-GetBulk-PDU...................................62
         7.2.1.4 agentx-TestSet-PDU...................................63
         7.2.1.5 Dispatch.............................................64
       7.2.2 Subagent Processing of agentx-Get, GetNext,
             GetBulk-PDUs.............................................64
         7.2.2.1 Subagent Processing of the agentx-Get-PDU............64
         7.2.2.2 Subagent Processing of the
                 agentx-GetNext-PDU...................................65
         7.2.2.3 Subagent Processing of the
                 agentx-GetBulk-PDU...................................65
       7.2.3 Subagent Processing of agentx-TestSet,
             -CommitSet, -UndoSet, -CleanupSet-PDUs...................67
         7.2.3.1 Subagent Processing of the
                 agentx-TestSet-PDU...................................67
         7.2.3.2 Subagent Processing of the
                 agentx-CommitSet-PDU.................................68
         7.2.3.3 Subagent Processing of the
                 agentx-UndoSet-PDU...................................68
         7.2.3.4 Subagent Processing of the
                 agentx-CleanupSet-PDU................................69
       7.2.4 Master Agent Processing of AgentX Responses..............69
         7.2.4.1 Common Processing of All AgentX Response
                 PDUs.................................................69
         7.2.4.2 Processing of Responses to agentx-Get-PDUs...........69
         7.2.4.3 Processing of Responses to
                 agentx-GetNext-PDU and agentx-GetBulk-PDU............70
         7.2.4.4 Processing of Responses to
                 agentx-TestSet-PDUs..................................71
         7.2.4.5 Processing of Responses to
                 agentx-CommitSet-PDUs................................71
         7.2.4.6 Processing of Responses to
                 agentx-UndoSet-PDUs..................................72
       7.2.5 Sending the SNMP Response-PDU............................72
       7.2.6 MIB Views................................................72
     7.3 State Transitions............................................73
       7.3.1 Set Transaction States...................................73
       7.3.2 Transport Connection States..............................75
       7.3.3 Session States...........................................76

   8 Transport Mappings...............................................77
     8.1 AgentX over TCP..............................................77



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       8.1.1 Well-known Values........................................77
       8.1.2 Operation................................................77
     8.2 AgentX over UNIX-domain Sockets..............................77
       8.2.1 Well-known Values........................................78
       8.2.2 Operation................................................78

   9 Security Considerations..........................................78

   10 Acknowledgements................................................79

   11 Authors' and Editor's Addresses.................................80

   12 References......................................................80









































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1.  Introduction

   This memo defines a standardized framework for extensible SNMP
   agents.  It defines processing entities called master agents
   and subagents, a protocol (AgentX) used to communicate between
   them, and the elements of procedure by which the extensible agent
   processes SNMP protocol messages.


2.  The SNMP Framework

   A management system contains:  several (potentially many) nodes,
   each with a processing entity, termed an agent, which has access to
   management instrumentation; at least one management station; and, a
   management protocol, used to convey management information between
   the agents and management stations.  Operations of the protocol are
   carried out under an administrative framework which defines
   authentication, authorization, access control, and privacy
   policies.

   Management stations execute management applications which monitor
   and control managed elements.  Managed elements are devices such as
   hosts, routers, terminal servers, etc., which are monitored and
   controlled via access to their management information.

   Management information is viewed as a collection of managed objects,
   residing in a virtual information store, termed the Management
   Information Base (MIB).  Collections of related objects are defined
   in MIB modules.  These modules are written using a subset of OSI's
   Abstract Syntax Notation One (ASN.1) [1], termed the Structure of
   Management Information (SMI) (see RFC 1902 [2]).

2.1.  A Note on Terminology

   The term "variable" refers to an instance of a non-aggregate
   object type defined according to the conventions set forth in the
   SMI (RFC 1902, [2]) or the textual conventions based on the SMI
   (RFC 1903 [3]).  The term "variable binding" normally refers to
   the pairing of the name of a variable and its associated value.
   However, if certain kinds of exceptional conditions occur during
   processing of a retrieval request, a variable binding will pair a
   name and an indication of that exception.

   A variable-binding list is a simple list of variable bindings.

   The name of a variable is an OBJECT IDENTIFIER, which is the
   concatenation of the OBJECT IDENTIFIER of the corresponding object
   type together with an OBJECT IDENTIFIER fragment identifying the
   instance.  The OBJECT IDENTIFIER of the corresponding object-type is
   called the OBJECT IDENTIFIER prefix of the variable.
   For the purpose of exposition, the original Internet-standard



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   Network Management Framework, as described in RFCs 1155 (STD 16),
   1157 (STD 15), and 1212 (STD 16), is termed the SNMP version 1
   framework (SNMPv1).  The current framework, as described in RFCs
   1902-1908, is termed the SNMP version 2 framework (SNMPv2).


3.  Extending the MIB

   New MIB modules that extend the Internet-standard MIB are
   continuously being defined by various IETF working groups.  It is
   also common for enterprises or individuals to create or extend
   enterprise-specific or experimental MIBs.

   As a result, managed devices are frequently complex collections of
   manageable components that have been independently installed on a
   managed node.  Each component provides instrumentation for the
   managed objects defined in the MIB module(s) it implements.

   Neither the SNMP version 1 or version 2 framework addresses how
   managed objects may be dynamically added to or removed from the
   agent view within a particular managed node.

3.1.  Motivation for AgentX

   This very real need to dynamically extend the management objects
   within a node has given rise to a variety of "extensible agents",
   which typically comprise

      - a "master" agent that is available on the standard transport
        address and that accepts SNMP protocol messages

      - a set of "subagents" that each contain management
        instrumentation

      - a protocol that operates between the master agent and subagents,
        permitting subagents to "connect" to the master agent, and the
        master agent to multiplex received SNMP protocol messages
        amongst the subagents.

      - a set of tools to aid subagent development, and a runtime (API)
        environment that hides much of the protocol operation between a
        subagent and the master agent.

   The wide deployment of extensible SNMP agents, coupled with the
   lack of Internet standards in this area, makes it difficult to field
   SNMP-manageable applications.  A vendor may have to support several
   different subagent environments (APIs) in order to support different
   target platforms.

   It can also become quite cumbersome to configure subagents and
   (possibly multiple) master agents on a particular managed node.



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   Specifying a standard protocol for agent extensibility (AgentX)
   provides the technical foundation required to solve both of
   these problems.  Independently developed AgentX-capable master
   agents and subagents will be able to interoperate at the protocol
   level.  Vendors can continue to differentiate their products
   in all other respects.


4.  AgentX Framework

   Within the SNMP framework, a managed node contains a processing
   entity, called an agent, which has access to management
   information.

   Within the AgentX framework, an agent is further defined to
   consist of

      - a single processing entity called the master agent, which sends
        and receives SNMP protocol messages in an agent role (as
        specified by the SNMP version 1 and version 2 framework
        documents) but typically has little or no direct access to
        management information.

      - 0 or more processing entities called subagents, which are
        "shielded" from the SNMP protocol messages processed by the
        master agent, but which have access to management information.

   The master and subagent entities communicate via AgentX protocol
   messages, as specified in this memo.  Other interfaces (if any) on
   these entities, and their associated protocols, are outside the
   scope of this document.  While some of the AgentX protocol messages
   appear similar in syntax and semantics to the SNMP, bear in mind
   that AgentX is not SNMP.

   The internal operations of AgentX are invisible to an SNMP entity
   operating in a manager role.  From a manager's point of view, an
   extensible agent behaves exactly as would a non-extensible
   (monolithic) agent that has access to the same management
   instrumentation.

   This transparency to managers is a fundamental requirement of
   AgentX, and is what differentiates AgentX subagents from SNMP proxy
   agents.











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4.1.  AgentX Roles

   An entity acting in a master agent role performs the following
   functions:

      - Accepts AgentX session establishment requests from subagents.

      - Accepts registration of MIB regions by subagents.

      - Sends and accepts SNMP protocol messages on the agent's
        specified transport addresses.

      - Implements the agent role Elements of Procedure specified
        for the administrative framework applicable to the SNMP
        protocol message, except where they specify performing
        management operations.  (The application of MIB views, and
        the access control policy for the managed node, are
        implemented by the master agent.)

      - Provides instrumentation for the MIB objects defined in RFC
        1907 [5], and for any MIB objects relevant to any
        administrative framework it supports.

      - Sends and receives AgentX protocol messages to access
        management information, based on the current registry of MIB
        regions.

      - Forwards notifications on behalf of subagents.

   An entity acting in a subagent role performs the following functions:

      - Initiates an AgentX session with the master agent.

      - Registers MIB regions with the master agent.

      - Instantiates managed objects.

      - Binds OIDs within its registered MIB regions to actual
        variables.

      - Performs management operations on variables.

      - Initiates notifications.











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4.2  Applicability

   It is intended that this draft specify the smallest amount of
   required behavior necessary to achieve the largest benefit,
   that is, to cover a very large number of possible MIB
   implementations and configurations with minimum complexity and low
   "cost of entry".

   This section discusses several typical usage scenarios.

   1) Subagents implement separate MIB modules--for example,
      subagent A implements "mib-2", subagent b implements
      "host-resources".

      It is anticipated that this will be the most common subagent
      configuration.

   2) Subagents implement rows in a "simple table".  A simple table
      is one in which row creation is not specified, and for which
      the MIB does not define an object that counts entries in the
      table.  Examples of simple tables are rdbmsDbTable, udpTable,
      and hrSWRunTable.

      This is the most commonly defined type of MIB table, and
      probably represents the next most typical configuration
      that AgentX would support.

   3) Subagents share MIBs along non-row partitions.  Subagents
      register "chunks" of the MIB that represent multiple rows,
      due to the nature of the MIB's index structure.  Examples
      include registering ipNetToMediaEntry.n, where n represents
      the ifIndex value for an interface implemented by the subagent,
      and tcpConnEntry.a.b.c.d, where a.b.c.d represents an IP
      address on an interface implemented by the subagent.

   AgentX supports these three common configurations, and all
   permutations of them, completely.  The consensus is that they
   comprise a very large majority of current and likely future uses
   of multi-vendor extensible agent configurations.

   4) Subagents implement rows in "complex tables".  Complex tables
      here are defined as tables permitting row creation, or whose
      MIB also defines an object that counts entries in the table.
      Examples include the MIB-2 ifTable (due to ifNumber), and the
      RMON historyControlTable.

   The subagent that implements such a counter object (like
   ifNumber) must go beyond AgentX to correctly implement it.
   This is an implementation issue (and most new MIB designs
   no longer include such objects).




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   To implement row creation in such tables, at least one AgentX
   subagent must register at a point "higher" in the OID tree
   than an individual row (per AgentX's dispatching procedure).
   Again, this is an implementation issue.

   Scenarios in this category were thought to occur somewhat
   rarely in configurations where subagents are independently
   implemented by different vendors.  The focus of a standard
   protocol, however, must be in just those areas where multi-
   vendor interoperability must be assured.

   Note that it would be inefficient (due to AgentX registration
   overhead) to share a table among AgentX subagents if the table
   contains very dynamic instances, and each subagent registers fully
   qualified instances.  ipRouteTable could be an example of such a
   table in some environments.



4.3.  Design Features of AgentX

   The primary features of the design described in this memo are

   1) A general architectural division of labor between master
      agent and subagent: The master agent is MIB ignorant and
      SNMP omniscient, while the subagent is SNMP ignorant and
      MIB omniscient.  That is, master agents, exclusively, are
      concerned with SNMP protocol operations and the translations
      to and from AgentX protocol operations needed to carry them
      out; subagents are exclusively concerned with management
      instrumentation; and neither should intrude on the other's
      territory.

   2) A standard protocol and "rules of engagement" to enable
      interoperability between management instrumentation and
      extensible agents.

   3) Mechanisms for independently developed subagents to
      integrate into the extensible agent on a particular
      managed node in such a way that they need not be aware
      of any other existing subagents.

   4) A simple, deterministic registry and dispatching algorithm.
      For a given extensible agent configuration, there is a single
      subagent who is "authoritative" for any particular region of
      the MIB (where "region" may extend from an entire MIB down
      to a single object-instance).

   5) Performance considerations.  It is likely that the master
      agent and all subagents will reside on the same host, and
      in such cases AgentX is more a form of inter-process



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      communication than a traditional communications protocol.
      Some of the design decisions made with this in mind include:

         - 32-bit alignment of data within PDUs

         - Native byte-order encoding by subagents

         - Large AgentX PDU payload sizes.
4.4  Non-Goals

   1) Subagent-to-subagent communication.  This is out of scope,
      due to the security ramifications and complexity involved.

   2) Subagent access (via the master agent) to MIB variables.
      This is not addressed, since various other mechanisms
      are available and it was not a fundamental requirement.

   3) The ability to accommodate every conceivable extensible
      agent configuration option. This was the most contentious
      aspect in the drafting of this protocol.  In essence,
      certain features currently available in some commercial
      extensible agent products are not included in AgentX.
      Although useful or even vital in some implementation
      strategies, the rough consensus was that these features
      were not appropriate for an Internet Standard, or not
      typically required for independently developed subagents
      to coexist.  The set of supported extensible agent
      configurations is described above, in Section 4.2.

   Some possible future version of the AgentX protocol may provide
   coverage for one or more of these "non-goals" or for new goals
   that might be identified after greater deployment experience.






















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5.  AgentX Encodings

   AgentX PDUs consist of a common header, followed by PDU-specific
   data of variable length.  Unlike SNMP PDUs, AgentX PDUs are not
   encoded using the BER (as specified in ISO 8824 [1]), but are
   transmitted as a contiguous byte stream.  The data within this
   stream is organized to provide natural alignment with respect to
   the start of the PDU, permitting direct (integer) access by the
   processing entities.

   The first four fields in the header are single-byte values.
   A bit (NETWORK_BYTE_ORDER) in the third field (h.flags) is
   used to indicate the byte ordering of all multi-byte integer
   values in the PDU, including those which follow in the header
   itself.  This is described in more detail in Section 6.1,
   "AgentX PDU Header", below.

   PDUs are depicted in this memo using the following convention
   (where byte 1 is the first transmitted byte):

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  byte 1       |  byte 2       |  byte 3       |  byte 4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  byte 5       |  byte 6       |  byte 7       |  byte 8       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...

   Fields marked "<reserved>" are reserved for future use and must be
   zero-filled.

5.1.  Object Identifier

   An object identifier is encoded as a 4-byte header, followed by a
   variable number of contiguous 4-byte fields representing
   sub-identifiers.  This representation (termed Object Identifier) is
   as follows:


   Object Identifier

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  n_subid      |  prefix       |  include      |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       sub-identifier #1                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       sub-identifier #n_subid                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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   Object Identifier header fields:

      n_subid

         The number (0-128) of sub-identifiers in the object
         identifier.  An ordered list of "n_subid" 4-byte
         sub-identifiers follows the 4-byte header.

      prefix

         An unsigned value used to reduce the length of object
         identifier encodings.  A non-zero value "x" is interpreted as
         the first sub-identifier after "internet" (1.3.6.1), and
         indicates an implicit prefix "internet.x" to the actual
         sub-identifiers encoded in the Object Identifier.  For
         example, a prefix field value 2 indicates an implicit prefix
         "1.3.6.1.2".  A value of 0 in the prefix field indicates there
         is no prefix to the sub-identifiers.

      include

         Used only when the Object Identifier is the start of a
         SearchRange, as described in section 5.2.


   A null Object Identifier consists of the 4-byte header with all
   bytes set to 0.



























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   Examples:

   sysDescr.0 (1.3.6.1.2.1.1.1.0)

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 4             | 2             | 0             | 0             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   1.2.3.4

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 4             | 0             | 0             | 0             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 2                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 3                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 4                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.2.  SearchRange

   A SearchRange consists of two Object Identifiers.  In its
   communication with a subagent, the master agent uses a SearchRange
   to identify a requested variable binding, and, in GetNext and
   GetBulk operations, to set an upper bound on the names of managed
   object instances the subagent may send in reply.

   The first Object Identifier in a SearchRange (called the starting
   OID) indicates the beginning of the range.  It is frequently (but
   not necessarily) the name of a requested variable binding.

   The "include" field in this OID's header is a boolean value
   (0 or 1) indicating whether or not the starting OID is included in
   the range.

   The second object identifier indicates the non-inclusive end of
   the range, and its "include" field is always 0.




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   Example:  To indicate a search range from 1.3.6.1.2.1.25.2
   (inclusive) to 1.3.6.1.2.1.25.2.1 (exclusive), the SearchRange would
   be

   (start)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 3             | 2             | 1             |       0       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 25                                                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 2                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (end)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 4             | 2             | 0             |       0       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 25                                                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 2                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   A SearchRangeList is a contiguous list of SearchRanges.

























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5.3.  Octet String

   An octet string is represented by a contiguous series of bytes,
   beginning with a 4-byte integer whose value is the number of octets
   in the octet string, followed by the octets themselves.  This
   representation is termed an Octet String.  If the last octet does
   not end on a 4-byte offset from the start of the Octet String,
   padding bytes are appended to achieve alignment of following data.
   This padding must be added even if the Octet String is the last item
   in the PDU.  Padding bytes must be zero filled.

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Octet String Length (L)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet L - 1  |  Octet L      |       Padding (as required)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   A null Octet String consists of a 4-byte length field set to 0.
































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5.4.  Value Representation

   Variable bindings may be encoded within the variable-length portion
   of some PDUs.  The representation of a variable binding (termed a
   VarBind) consists of a 2-byte type field, a name (Object
   Identifier), and the actual value data.

   VarBind

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          v.type               |          <reserved>           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (v.name)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  n_subid      |  prefix       |      0        |       0       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       sub-identifier #1                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       sub-identifier #n_subid                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (v.data)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       data                                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       data                                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






















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   VarBind fields:

   v.type

         Indicates the variable binding's syntax, and must be one of
         the following values:

                     Integer                  (2),
                     Octet String             (4),
                     Null                     (5),
                     Object Identifier        (6),
                     IpAddress               (64),
                     Counter32               (65),
                     Gauge32                 (66),
                     TimeTicks               (67),
                     Opaque                  (68),
                     Counter64               (70),
                     noSuchObject           (128),
                     noSuchInstance         (129),
                     endOfMibView           (130)

   v.name

         The Object Identifier which names the variable.

   v.data

         The actual value, encoded as follows:

          - Integer, Counter32, Gauge32, and TimeTicks are encoded as
            4 contiguous bytes.  If the NETWORK_BYTE_ORDER bit is set
            in h.flags, the bytes are ordered most significant to least
            significant, otherwise they are ordered least significant
            to most significant.

          - Counter64 is encoded as 8 contiguous bytes.  If the
            NETWORK_BYTE_ORDER bit is set in h.flags, the bytes are
            ordered most significant to least significant, otherwise
            they are ordered least significant to most significant.

          - Object Identifiers are encoded as described in section
            5.1, Object Identifier.

          - IpAddress, Opaque, and Octet String are all octet strings
            and are encoded as described in section 5.3, Octet String.

            Value data always follows v.name whenever v.type is one
            of the above types.  These data bytes are present even if
            they will not be used (as, for example, in certain types
            of index allocation).




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          - Null, noSuchObject, noSuchInstance, and endOfMibView do not
            contain any encoded value.  Value data never follows
            v.name in these cases.

         Note that the VarBind itself does not contain the value size.
         That information is implied for the fixed-length types, and
         explicitly contained in the encodings of variable-length types
         (Object Identifier and Octet String).

   A VarBindList is a contiguous list of VarBinds.  Within a
   VarBindList, a particular VarBind is identified by an index value.
   The first VarBind in a VarBindList has index value 1, the second
   has index value 2, and so on.


6.  Protocol Definitions

6.1.  AgentX PDU Header

   The AgentX PDU header is a fixed-format, 20-octet structure:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   h.version   |    h.type     |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.packetID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   An AgentX PDU header contains the following fields:

      h.version

         The version of the AgentX protocol (1 for this draft).

      h.type

         The PDU type; one of the following values:

              agentx-Open-PDU             (1),
              agentx-Close-PDU            (2),
              agentx-Register-PDU         (3),
              agentx-Unregister-PDU       (4),
              agentx-Get-PDU              (5),
              agentx-GetNext-PDU          (6),
              agentx-GetBulk-PDU          (7),
              agentx-TestSet-PDU          (8),



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              agentx-CommitSet-PDU        (9),
              agentx-UndoSet-PDU         (10),
              agentx-CleanupSet-PDU      (11),
              agentx-Notify-PDU          (12),
              agentx-Ping-PDU            (13),
              agentx-IndexAllocate-PDU   (14),
              agentx-IndexDeallocate-PDU (15),
              agentx-AddAgentCaps-PDU    (16),
              agentx-RemoveAgentCaps-PDU (17),
              agentx-Response-PDU        (18)

      h.flags

         A bitmask, with bit 0 the least significant bit.  The bit
         definitions are as follows:

                 Bit             Definition
                 ---             ----------
                 0               INSTANCE_REGISTRATION
                 1               NEW_INDEX
                 2               ANY_INDEX
                 3               NON_DEFAULT_CONTEXT
                 4               NETWORK_BYTE_ORDER
                 5-7             (reserved)

         The NETWORK_BYTE_ORDER bit applies to all multi-byte
         integer values in the entire AgentX packet, including
         the remaining header fields.  If set, then network byte
         order (most significant byte first; "big endian") is
         used.  If not set, then least significant byte first
         ("little endian") is used.

         The NETWORK_BYTE_ORDER bit applies to all AgentX PDUs.

         The NON_DEFAULT_CONTEXT bit is used only in the AgentX PDUs
         described in section 6.1.1.

         The NEW_INDEX and ANY_INDEX bits are used only within the
         agentx-IndexAllocate-, and -IndexDeallocate-PDUs.

         The INSTANCE_REGISTRATION bit is used only within the
         agentx-Register-PDU.



      h.sessionID

         The session ID uniquely identifies a session over
         which AgentX PDUs are exchanged between a subagent and
         the master agent.  The session ID has no significance
         and no defined value in the agentx-Open-PDU sent by a



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         subagent to open a session with the master agent; in
         this case, the master agent will assign a unique
         sessionID that it will pass back in the corresponding
         agentx-Response-PDU.  From that point on, that same
         sessionID will appear in every AgentX PDU exchanged
         over that session between the master and the subagent.
         A subagent may establish multiple AgentX sessions by
         sending multiple agentx-Open-PDUs to the master agent.

         In master agents that support multiple transport
         protocols, the sessionID should be globally unique
         rather than unique just to a particular transport.


      h.transactionID

         The transaction ID uniquely identifies, for a given
         session, the single SNMP management request (and single
         SNMP PDU) with which an AgentX PDU is associated.  If
         a single SNMP management request results in multiple
         AgentX PDUs being sent by the master agent with the same
         sessionID, each of these AgentX PDUs must contain the
         same transaction ID; conversely, AgentX PDUs sent during
         a particular session, that result from distinct SNMP
         management requests, must have distinct transaction IDs
        (within the limits of the 32-bit field).

         Note that the transaction ID is not the same as the SNMP
         PDU's request-id (as described in section 4.1 of RFC
         1905 [4]), nor can it be, since a master agent might
         receive SNMP requests with the same request-ids from
         different managers.

         The transaction ID has no significance and no defined
         value in AgentX administrative PDUs, i.e., AgentX
         PDUs that are not associated with an SNMP management
         request.

      h.packetID

         A packet ID generated by the sender for all AgentX PDUs
         except the agentx-Response-PDU. In an agentx-Response-PDU,
         the packet ID must be the same as that in the received
         AgentX PDU to which it is a response.  A master agent
         might use this field to associate subagent response PDUs
         with their corresponding request PDUs.  A subagent might
         use this field to correlate responses to multiple
         (batched) registrations.






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      h.payload_length

         The size in octets of the PDU contents, excluding the
         20-byte header.  As a result of the encoding schemes
         and PDU layouts, this value will always be either 0,
         or a multiple of 4.

6.1.1.  Context

   In the SNMPv1 or v2c frameworks, the community string may be used as
   an index into a local repository of configuration information that
   may include community profiles or more complex context information.
   Future versions of the SNMP will likely formalize this notion of
   "context".

   AgentX provides a mechanism for transmitting a context specification
   within relevant PDUs, but does not place any constraints on the
   content of that specification.

   An optional context field may be present in the agentx-Register-,
   UnRegister-, AddAgentCaps-, RemoveAgentCaps-, Get-, GetNext-,
   GetBulk-, IndexAllocate-, IndexDeallocate-, Notify-, TestSet-,
   and Ping- PDUs.

   If the NON_DEFAULT_CONTEXT bit in the AgentX header field h.flags is
   clear, then there is no context field in the PDU, and the operation
   refers to the default context.

   If the NON_DEFAULT_CONTEXT bit is set, then a context field
   immediately follows the AgentX header, and the operation refers
   to that specific context.  The context is represented as an Octet
   String.  There are no constraints on its length or contents.

   Thus, all of these AgentX PDUs (that is, those listed immediately
   above) refer to, or "indicate" a context, which is either the
   default context, or a non-default context explicitly named in the
   PDU.

















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6.2.  AgentX PDUs

6.2.1.  The agentx-Open-PDU

   An agentx-Open-PDU is generated by a subagent to request
   establishment of an AgentX session with the master agent.

   (AgentX header)

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (1)   |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  o.timeout    |                     <reserved>                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (o.id)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  n_subid      |  prefix       |       0       |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             subidentifier #1                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             subidentifier #n_subid                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (o.descr)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Octet String Length (L)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet L - 1  |  Octet L      |       Padding (as required)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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   An agentx-Open-PDU contains the following fields:

      o.timeout

         The length of time, in seconds, that a master agent should
         allow to elapse after dispatching a message to a subagent
         before it regards the subagent as not responding.  This is a
         subagent-wide default value that may be overridden by values
         associated with specific registered MIB regions.  The default
         value of 0 indicates that no subagent-wide value is
         requested.

      o.id

         An Object Identifier that identifies the subagent.  Subagents
         that do not support such an notion may send a null Object
         Identifier.

      o.descr

         An Octet String containing a DisplayString describing the
         subagent.


6.2.2.  The agentx-Close-PDU

   An agentx-Close-PDU issued by either a subagent or the master
   agent terminates an AgentX session.

   (AgentX header)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (2)   |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  c.reason     |                     <reserved>                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+









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   An agentx-Close-PDU contains the following field:

      c.reason

         An enumerated value that gives the reason that the master
         agent or subagent closed the AgentX session.  This field may
         take one of the following values:

            reasonOther(1)
               None of the following reasons

            reasonParseError(2)
               Too many AgentX parse errors from peer

            reasonProtocolError(3)
               Too many AgentX protocol errors from peer

            reasonTimeouts(4)
               Too many timeouts waiting for peer

            reasonShutdown(5)
               Sending entity is shutting down

            reasonByManager(6)
               Due to Set operation; this reason code can
               be used only by the master agent, in response
               to an SNMP management request.



























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6.2.3.  The agentx-Register-PDU

   An agentx-Register-PDU is generated by a subagent for each region of
   the MIB variable naming tree (within one or more contexts) that it
   wishes to support.

    (AgentX header)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (3)   |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (r.context) (OPTIONAL)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  r.timeout    |  r.priority   | r.range_subid |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (r.region)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |      0        |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #n_subid                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (r.upper_bound)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             optional upper-bound sub-identifier               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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   An agentx-Register-PDU contains the following fields:

      r.context

         An optional non-default context.

      r.timeout

         The length of time, in seconds, that a master agent should
         allow to elapse after dispatching a message to a subagent
         before it regards the subagent as not responding.  r.timeout
         applies only to messages that concern MIB objects within
         r.region.  It overrides both the subagent-wide value (if any)
         indicated when the AgentX session with the master agent was
         established, and the master agent's default timeout.  The
         default value for r.timeout is 0 (no override).

      r.priority

         A value between 1 and 255, used to achieve a desired
         configuration when different subagents register identical or
         overlapping regions.  Subagents with no particular knowledge
         of priority should register with the default value of 255
         (lowest priority).

         In the master agent's dispatching algorithm, smaller
         values of r.priority take precedence over larger values,
         as described in section 7.1.5.1.

      r.region

         An Object Identifier that, in conjunction with r.range_subid,
         indicates a region of the MIB that a subagent wishes to
         support.  It may be a fully-qualified instance name, a partial
         instance name, a MIB table, an entire MIB, or ranges of any of
         these.

         The choice of what to register is implementation-specific;
         this memo does not specify permissible values.  Standard
         practice however is for a subagent to register at the
         highest level of the naming tree that makes sense.
         Registration of fully-qualified instances is typically done
         only when a subagent can perform management operations only
         on particular rows of a conceptual table.

         If r.region is in fact a fully qualified instance name, the
         INSTANCE_REGISTRATION bit in h.flags must be set, otherwise it
         must be cleared.  The master agent may save this information
         to optimize subsequent operational dispatching.





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      r.range_subid

         Permits specifying a range in place of one of r.region's
         sub-identifiers.  If this value is 0, no range is specified.
         Otherwise the "r.range_subid"-th sub-identifier in
         r.region is a range lower bound, and the range upper
         bound sub-identifier (r.upper_bound) immediately follows
         r.region.

         This permits registering a conceptual row with a single
         PDU.  For example, the following PDU would register row
         7 of the RFC 1573 ifTable (1.3.6.1.2.1.2.2.1.1-22.7):

   (AgentX header)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (3)   |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   r.timeout   |  r.priority   | 5             |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (r.region)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 6             |  2            |  0            |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 2                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 2                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 1                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 7                                                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (r.upper_bound)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 22                                                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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6.2.4.  The agentx-Unregister-PDU

   The agentx-Unregister-PDU is sent by a subagent to remove a
   previously registered MIB region from the master agent's OID space.

   (AgentX header)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (4)   |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (u.context) OPTIONAL
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Octet String Length (L)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet L - 1  |  Octet L      |       Padding (as required)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          <reserved>           | u.range_subid |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (u.region)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  n_subid      |  prefix       |      0        |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             sub-identifier #1                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             sub-identifier #n_subid                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (u.upper_bound)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             optional upper-bound sub-identifier               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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   An agentx-Unregister-PDU contains the following fields:

      u.context

         An optional non-default context.

      u.region

         Indicates a previously-registered region of the MIB that a
         subagent no longer wishes to support.












































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6.2.5.  The agentx-Get-PDU

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (5)   |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (g.context) OPTIONAL
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (g.sr)

    (start 1)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |  include      |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #n_subid                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (end 1)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | 0             | 0             | 0             |       0       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    (start n)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |  include      |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...



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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #n_subid                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (end n)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | 0             | 0             | 0             |       0       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   An agentx-Get-PDU contains the following fields:

      g.context

         An optional non-default context.

      g.sr

         A SearchRangeList containing the requested variables for this
         subagent.


6.2.6.  The agentx-GetNext-PDU

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (6)   |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (g.context) OPTIONAL
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (g.sr)





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    (start 1)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |  include      |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #n_subid                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (end 1)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |      0        |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #n_subid                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...

    (start n)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |  include      |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #n_subid                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (end n)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |      0        |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #n_subid                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...









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6.2.7.  The agentx-GetBulk-PDU

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (7)   |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (g.context) OPTIONAL
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             g.non_repeaters   |     g.max_repetitions         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (g.sr)
    ...






















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6.2.8.  The agentx-TestSet-PDU

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (8)   |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (t.context) OPTIONAL
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (t.vb)

    (VarBind 1)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          v.type               |        <reserved>             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |      0        |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       sub-identifier #1                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       sub-identifier #n_subid                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       data                                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       data                                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...







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    (VarBind n)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          v.type               |        <reserved>             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |      0        |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       sub-identifier #1                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       sub-identifier #n_subid                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       data                                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       data                                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   An agentx-TestSet-PDU contains the following fields:

      t.context

         An optional non-default context.

      t.vb

         A VarBindList containing the requested VarBinds for
         this subagent.


6.2.9.  The agentx-CommitSet, -UndoSet, -CleanupSet PDUs

   These PDUs consist of the AgentX header only.

   The agentx-CommitSet-, -UndoSet-, and -Cleanup-PDUs are
   used in processing an SNMP SetRequest operation.
















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6.2.10.  The agentx-Notify-PDU

   An agentx-Notify-PDU is sent by a subagent to cause the master agent
   to forward a notification.

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (12)  |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (n.context) OPTIONAL
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (n.vb)
    ...


   An agentx-Notify-PDU contains the following fields:

      n.context

         An optional non-default context.

      n.vb

         A VarBindList whose contents define the actual PDU to be
         sent.  This memo places the following restrictions on its
         contents:

             - If the subagent supplies sysUpTime.0, it must be
               present as the first varbind.

             - snmpTrapOID.0 must be present, as the second
               varbind if sysUpTime.0 was supplied, as the
               first if it was not.



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6.2.11  The agentx-Ping-PDU

   The agentx-Ping-PDU is sent by a subagent to the master agent to
   monitor the master agent's ability to receive and send AgentX
   PDUs over their AgentX session.

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (13)  |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (p.context) OPTIONAL
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   An agentx-Ping-PDU may contain the following field:

      p.context

         An optional non-default context.

   Using p.context a subagent can retrieve the sysUpTime value
   for a specific context, if required.
















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6.2.12.  The agentx-IndexAllocate-PDU

   An agentx-IndexAllocate-PDU is sent by a subagent to request
   allocation of a value for specific index objects.  Refer to section
   7.1.3 (Using the agentx-IndexAllocate-PDU) for suggested usage.

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (14)  |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (i.context) OPTIONAL
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (i.vb)
    ...


   An agentx-IndexAllocate-PDU contains the following fields:

      i.context

         An optional non-default context.

      i.vb

         A VarBindList containing the index names and values requested
         for allocation.










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6.2.13.  The agentx-IndexDeallocate-PDU

   An agentx-IndexDeallocate-PDU is sent by a subagent to release
   previously allocated index values.

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (15)  |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (i.context) OPTIONAL
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Padding (as required)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (i.vb)
    ...


   An agentx-IndexDeallocate-PDU contains the following fields:

      i.context

         An optional non-default context.

      i.vb

         A VarBindList containing the index names and values to be
         released.











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6.2.14.  The agentx-AddAgentCaps-PDU

   An agentx-AddAgentCaps-PDU is generated by a subagent to inform the
   master agent of its agent capabilities.

    (AgentX header)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | h.version (1) |  h.type (16)  |    h.flags    |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          h.sessionID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.transactionID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           h.packetID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        h.payload_length                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (a.context) (OPTIONAL)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Optional Padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (a.id)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  n_subid      |  prefix       |      0        |  <reserved>   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #1                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             sub-identifier #n_subid                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    (a.descr)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Octet String Length (L)                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Octet L - 1  |  Octet L      |       Optional Padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   An agentx-AddAgentCaps-PDU contains the following fields:

      a.context

         An optional non-default context.

      a.id

         An Object Identifier containing the value of an invocation of
         the AGENT-CAPABILITIES macro, which the master agent exports
         as a value of sysORID for the indicated context.  (Recall that
         the value of an invocation of an AGENT-CAPABILITIES macro is
         an object identifier that describes a precise level of support
         with respect to implemented MIB modules.  A more complete
         discussion of the AGENT-CAPABILITIES macro and related sysORID
         values can be found in section 6 of RFC 1904 [10].)

      a.descr

         An Octet String containing a DisplayString to be used as the
         value of sysORDescr corresponding to the sysORID value above.

































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6.2.15.  The agentx-RemoveAgentCaps-PDU

   An agentx-RemoveAgentCaps-PDU is generated by a subagent to request
   that the master agent stop exporting a particular value of sysORID.
   This value must have previously been advertised by the subagent in
   an agentx-AddAgentCaps-PDU.

   (AgentX header)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (17)  |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (a.context) (OPTIONAL)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Octet String Length (L)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet 1      |  Octet 2      |   Octet 3     |   Octet 4     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Octet L - 1  |  Octet L      |       Optional Padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   (a.id)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  n_subid      |  prefix       |       0       |   <reserved>  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             sub-identifier #1                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             sub-identifier #n_subid                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+













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   An agentx-RemoveAgentCaps-PDU contains the following fields:

      a.context

         An optional non-default context.

      a.id

         An ObjectIdentifier containing the value of sysORID that
         should no longer be exported.


6.2.16.  The agentx-Response-PDU

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | h.version (1) |  h.type (18)  |    h.flags    |  <reserved>   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          h.sessionID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.transactionID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           h.packetID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        h.payload_length                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        res.sysUpTime                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             res.error         |     res.index                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...


   An agentx-Response-PDU contains the following fields:

      h.sessionID

         If this is a response to a agentx-Open-PDU, then it
         contains the new and unique sessionID (as assigned by
         the master agent) for this session.

         Otherwise it must be identical to the h.sessionID
         value in the PDU to which this PDU is a response.

      h.transactionID

         Must be identical to the h.transactionID value in the PDU to
         which this PDU is a response.

         In an agentx response PDU from the master agent to the



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         subagent, the value of h.transactionID has no significance
         and can be ignored by the subagent.

      h.packetID

         Must be identical to the h.packetID value in the PDU to
         which this PDU is a response.

      res.sysUpTime

         This field contains the current value of sysUpTime for
         the indicated context.  It is relevant only in agentx
         response PDUs sent from the master agent to a subagent in
         response to the following agentx PDUs:

               agentx-Open-PDU               (1),
               agentx-Close-PDU              (2),
               agentx-Register-PDU           (3),
               agentx-Unregister-PDU         (4),
               agentx-Ping-PDU              (13),
               agentx-IndexAllocate-PDU     (14),
               agentx-IndexDeallocate-PDU   (15),
               agentx-AddAgentCaps-PDU      (16),
               agentx-RemoveAgentCaps-PDU   (17)

         In an agentx response PDU from the subagent to the master
         agent, the value of res.sysUpTime has no significance and
         is ignored by the master agent.

      res.error

         Indicates error status (including `noError').  Values are
         limited to those defined for errors in the SNMPv2 SMI (RFC
         1905 [4]), and the following AgentX-specific values:

                openFailed                 (256),
                notOpen                    (257),
                indexWrongType             (258),
                indexAlreadyAllocated      (259),
                indexNoneAvailable         (260),
                indexNotAllocated          (261),
                unsupportedContext         (262),
                duplicateRegistration      (263),
                unknownRegistration        (264),
                unknownAgentCaps           (265)


      res.index

         In error cases, this is the index of the failed variable
         binding within a received request PDU.  (Note: As explained in



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         section 5.4, Value Representation, the index values of
         variable bindings within a variable binding list are 1-based.)
   Other data may follow these latter two fields, depending on
   which AgentX PDU is being responded to.  These data are
   specified in the subsequent elements of procedure.


7.  Elements of Procedure

   This section describes the actions of protocol entities (master
   agents and subagents) implementing the AgentX protocol.  Note,
   however, that it is not intended to constrain the internal
   architecture of any conformant implementation.

   Specific error conditions and associated actions are described in
   various places.  Other error conditions not specifically mentioned
   fall into one of two categories, "parse" errors and "protocol"
   errors.

   A parse error occurs when a receiving entity cannot decode the PDU.
   For instance, a VarBind contains an unknown type, or a PDU contains
   a malformed Object Identifier.

   A protocol error occurs when a receiving entity can parse a PDU, but
   the resulting data is unspecified.  For instance, an
   agentx-Response-PDU is successfully parsed, but contains an unknown
   res.error value.

   An implementation may choose either to ignore such messages, or to
   close the session on which they are received, using the appropriate
   reason code as defined in the agentx-Close-PDU.

   The actions of AgentX protocol entities can be broadly categorized
   under two headings, each of which is described separately:

      (1) processing AgentX administrative messages (e.g., connection
          requests from a subagent to a master agent); and

      (2) processing SNMP messages (e.g., the coordinated actions of a
          master agent and one or more subagents in processing a
          received SNMP Get-PDU).

7.1.  Processing AgentX Administrative Messages

   This subsection describes the actions of AgentX protocol entities
   in processing AgentX administrative messages.  Such messages
   include those involved in establishing and terminating an AgentX
   session between a subagent and a master agent, those by which a
   subagent requests allocation of instance index values, and those
   by which a subagent communicates to a master agent which MIB
   regions it supports.



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7.1.1.  Processing the agentx-Open-PDU

   When the master agent receives an agentx-Open-PDU, it processes
   it as follows:

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the indicated context.

   2) If the master agent is unable to open an AgentX session for
      any reason, it may refuse the session establishment request,
      sending in reply the agentx-Response-PDU, with res.error
      field set to `openFailed'.

   3) Otherwise:  The master agent assigns a sessionID to the new
      session and puts the value in the h.sessionID field of the
      agentx-Response-PDU.  This value must be unique among all
      existing open sessions.

   4) The master agent retains session-specific information
      from the PDU for this subagent:

       - The NETWORK_BYTE_ORDER value in h.flags is retained.
         All subsequent AgentX protocol operations initiated by
         the master agent for this session must use this byte
         ordering and set this bit accordingly.

         The subagent typically sets this bit to correspond to
         its native byte ordering, and typically does not vary
         byte ordering for an initiated session.  The master
         agent must be able to decode each PDU according to its
         h.flag NETWORK_BYTE_ORDER bit, but does not need to
         toggle its retained value for the session if the
         subagent varies its byte ordering.

       - The o.timeout value is used in calculating timeout
         conditions for this subagent.

       - The o.id and o.descr fields are used for informational
         purposes.  (Such purposes are implementation-specific
         for now, and may be used in a possible future standard
         AgentX MIB.)

   5) The agentx-Response-PDU is sent with the res.error field
      set to `noError'.

   At this point, an AgentX session is considered established between
   the master agent and the subagent.  An AgentX session is a distinct
   channel for the exchange of AgentX protocol messages between a
   master agent and one subagent, qualified by the session-specific
   attributes listed in 4) above.  AgentX session establishment is



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   initiated by the subagent.  An AgentX session can be terminated
   by either the master agent or the subagent.

7.1.2.  Processing the agentx-IndexAllocate-PDU

   When the master agent receives an agentx-IndexAllocate-PDU, it
   processes it as follows:

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the default context.

   2) If h.sessionID does not correspond to a currently established
      session with this subagent, the agentx-Response-PDU is sent
      in reply with res.error set to `notOpen'.

   3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
      supports only a default context, the agentx-Response-PDU is
      returned with res.error set to `unsupportedContext', and the
      requested allocation fails.  Otherwise: The value of
      res.sysUpTime is set to the value of sysUpTime.0 for the
      indicated context.

   4) Each VarBind in the VarBindList is processed until either all
      are successful, or one fails.  If any VarBind fails, the
      agentx-Response-PDU is sent in reply containing the original
      VarBindList, with res.index set to indicate the failed VarBind,
      and with res.error set as described subsequently.  All other
      VarBinds are ignored; no index values are allocated.

      VarBinds are processed as follows:

      - v.name is the name of the index for which a value is to be
        allocated.

      - v.type is the syntax of the index object.

      - v.data indicates the specific index value requested.
        If the NEW_INDEX or the ANY_INDEX bit is set, the actual
        value in v.data is ignored and an appropriate index value
        is generated.

      a) If there are no currently allocated index values for v.name
         in the indicated context, and v.type does not correspond to
         a valid index type value, the VarBind fails and res.error
         is set to `indexWrongType'.

      b) If there are currently allocated index values for v.name
         in the indicated context, but the syntax of those values
         does not match v.type, the VarBind fails and res.error is
         set to `indexWrongType'.




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      c) Otherwise, if both the NEW_INDEX and ANY_INDEX bits are
         clear, allocation of a specific index value is being
         requested.  If the requested index is already allocated
         for v.name in the indicated context, the VarBind fails
         and res.error is set to `indexAlreadyAllocated'.

      d) Otherwise, if the NEW_INDEX bit is set, the master agent
         should generate the next available index value for v.name
         in the indicated context, with the constraint that this
         value must not have been allocated (even if subsequently
         released) to any subagent since the last re-initialization
         of the master agent.  If no such value can be generated,
         the VarBind fails and res.error is set to `indexNoneAvailable'.

      e) Otherwise, if the ANY_INDEX bit is set, the master agent
         should generate an index value for v.name in the
         indicated context, with the constraint that this value is
         not currently allocated to any subagent.  If no such value
         can be generated, then the VarBind fails and res.error is
         set to `indexNoneAvailable'.

   5) If all VarBinds are processed successfully, the
      agentx-Response-PDU is sent in reply with res.error set to
      `noError'.  A VarBindList is included that is identical to the
      one sent in the agentx-IndexAllocate-PDU, except that VarBinds
      requesting a NEW_INDEX or ANY_INDEX value are generated with an
      appropriate value.

7.1.3.  Using the agentx-IndexAllocate-PDU

   Index allocation is a service provided by an AgentX master agent.
   It provides generic support for sharing MIB conceptual tables among
   subagents who are assumed to have no knowledge of each other.

   Each subagent sharing a table should first request allocation of
   index values, then use those index values to qualify MIB regions in
   its subsequent registrations.

   The master agent maintains a database of index objects (OIDs), and,
   for each index, the values that have been allocated for it.  It is
   unaware of what MIB variables (if any) the index objects represent.

   By convention, subagents use the MIB variable listed in the INDEX
   clause as the index object for which values must be allocated.  For
   tables indexed by multiple variables, values may be allocated for
   each index (although this is frequently unnecessary; see example 2
   below).  The subagent may request allocation of

        - a specific index value
        - an index value that is not currently allocated
        - an index value that has never been allocated



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   The last two alternatives reflect the uniqueness and constancy
   requirements present in many MIB specifications for arbitrary
   integer indexes (e.g., ifIndex in the IF MIB (RFC 1573 [11]),
   snmpFddiSMTIndex in the FDDI MIB (RFC 1285 [12]), or
   sysApplInstallPkgIndex in the Application MIB [13]).  The need for
   subagents to share tables using such indexes is the main motivation
   for index allocation in AgentX.

   Example 1:

      A subagent implements an interface, and wishes to register a
      single row of the RFC 1573 ifTable.  It requests an allocation
      for the index object "ifIndex", for a value that has never been
      allocated (since ifIndex values must be unique).  The master agent
      returns the value "7".

      The subagent now attempts to register row 7 of ifTable, by
      specifying a MIB region in the agentx-Register-PDU of
      1.3.6.1.2.1.2.2.1.[1-22].7.  If the registration succeeds, no
      further processing is required.  The master agent will dispatch
      to this subagent correctly.

      But the registration may fail.  Index allocation and MIB region
      registration are not coupled in the master agent.  Some other
      subagent may have already registered ifTable row 7 without first
      having requested allocation of the index.  The current state of
      index allocations is not considered when processing registration
      requests, and the current registry is not considered when
      processing index allocation requests.  If subagents follow the
      model of "first request allocation of an index, then register the
      corresponding region", then a successful index allocation request
      gives a subagent a good hint (but no guarantee) of what it should
      be able to register.

      If the registration failed, the subagent should request allocation
      of a new index i, and attempt to register ifTable.[1-22].i, until
      successful.

   Example 2:

      This same subagent wishes to register ipNetToMediaTable rows
      corresponding to its interface (ifIndex i).  Due to structure of
      this table, no further index allocation need be done.  The
      subagent can register the MIB region ipNetToMediaTable.[1-4].i,
      It is claiming responsibility for all rows of the table whose
      value of ipNetToMediaIfIndex is i.

   Example 3:

      A network device consists of a set of processors, each of which
      accepts network connections for a unique set of IP addresses.



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      Further, each processor contains a subagent that implements
      tcpConnTable.  In order to represent tcpConnTable for the entire
      managed device, the subagents need to share tcpConnTable.

      In this case, no index allocation need be done at all.  Each
      subagent can register a MIB region of tcpConnTable.[1-5].a.b.c.d,
      where a.b.c.d represents an unique IP address of the individual
      processor.

      Each subagent is claiming responsibility for the region of
      tcpConnTable where the value of tcpConnLocalAddress is a.b.c.d.

7.1.4   Processing the agentx-IndexDeallocate-PDU

   When the master agent receives an agentx-IndexDeallocate-PDU, it
   processes it as follows:

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the default context.

   2) If h.sessionID does not correspond to a currently
      established session with this subagent, the
      agentx-Response-PDU is sent in reply with res.error set
      to `notOpen'.

   3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
      supports only a default context, the agentx-Response-PDU is
      returned with res.error set to `unsupportedContext', and the
      requested allocation fails.  Otherwise: The value of
      res.sysUpTime is set to the value of sysUpTime.0 for the
      indicated context.

   4) Each VarBind in the VarBindList is processed until either all
      are successful, or one fails.  If any VarBind fails, the
      agentx-Response-PDU is sent in reply, containing the original
      VarBindList, with res.index set to indicate the failed VarBind,
      and with res.error set as described subsequently.  All other
      VarBinds are ignored; no index values are released.

      VarBinds are processed as follows:

      - v.name is the name of the index for which a value is to be
        released

      - v.type is the syntax of the index object

      - v.data indicates the specific index value to be released.
        The NEW_INDEX and ANY_INDEX bits are ignored.

      a) If the index value for the named index is not currently
         allocated to this subagent, the VarBind fails and res.error



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         is set to `indexNotAllocated'.

   5) If all VarBinds are processed successfully, res.error is
      set to `noError' and the agentx-Response-PDU is sent.
      A VarBindList is included which is identical to the one
      sent in the agentx-IndexDeallocate-PDU.

      All released index values are now available, and may be
      used in response to subsequent allocation requests for
      ANY_INDEX values for the particular index.

7.1.5.  Processing the agentx-Register-PDU

   When the master agent receives an agentx-Register-PDU, it processes
   it as follows:

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the default context.

   2) If h.sessionID does not correspond to a currently
      established session with this subagent, the
      agentx-Response-PDU is sent in reply with res.error set
      to `notOpen'.

   3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
      supports only a default context, the agentx-Response-PDU is
      returned with res.error set to `unsupportedContext', and the
      requested allocation fails.  Otherwise:  The value of
      res.sysUpTime is set to the value of sysUpTime.0 for the
      indicated context.

      Note: Non-default contexts might be added on the fly by
            the master agent, or the master agent might require
            such non-default contexts to be pre-configured.
            The choice is implementation-specific.

   4) Characterize the request.

      If r.region (or any of its set of Object Identifiers, if r.range
      is non-zero) is exactly the same as any currently registered
      value of r.region (or any of its set of Object Identifiers),
      this registration is termed a duplicate region.

      If r.region (or any of its set of Object Identifiers, if r.range
      is non-zero) is a subtree of, or contains, any currently
      registered value of r.region (or any of its set of
      Object Identifiers), this registration is termed an overlapping
      region.

      If the NON_DEFAULT_CONTEXT bit is set, this region is to be
      logically registered within the context indicated by r.context.



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      Otherwise this region is to be logically registered within the
      default context.

      A registration that would result in a duplicate region with the
      same priority and within the same context as that of a current
      registration is termed a duplicate registration.

   5) Otherwise, if this is a duplicate registration, the
      agentx-Response-PDU is returned with res.error set to
      `duplicateRegistration', and the requested registration fails.

   6) Otherwise, the agentx-Response-PDU is returned with res.error
      set to `noError'.

      The master agent adds this region to its registered OID space for
      the indicated context, to be considered during the dispatching
      phase for subsequently received SNMP protocol messages.

      Note: The following algorithm describes maintaining a set of
      OID ranges derived from "splitting" registered regions.  The
      algorithm for operational dispatching is also stated in terms of
      these OID ranges.

      These OID ranges are a useful explanatory device, but are not
      required for a correct implementation.

       - If r.region (R1) is a subtree of a currently registered
         region (R2), split R2 into 3 new regions (R2a, R2b, and R2c)
         such that R2b is an exact duplicate of R1.  Now remove R2 and
         add R1, R2a, R2b, and R2c to the master agent's
         lexicographically ordered set of ranges (the registered OID
         space).  Note: Though newly-added ranges R1 and R2b are
         identical in terms of the MIB objects they contain, they are
         registered by different subagents, possibly at different
         priorities.

         For instance, if subagent S2 registered "ip" (R2 is
         1.3.6.1.2.1.4) and subagent S1 subsequently registered
         "ipNetToMediaTable" (R1 is 1.3.6.1.2.1.4.22), the resulting
         set of registered regions would be:

   1.3.6.1.2.1.4    up to but not including 1.3.6.1.2.1.4.22     (by S2)
   1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23     (by S2)
   1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23     (by S1)
   1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5        (by S2)

       - If r.region (R1) overlaps one or more currently registered
         regions, then for each overlapped region (R2) split R1 into 3
         new ranges (R1a, R1b, R1c) such that R1b is an exact
         duplicate of R2.  Add R1b and R2 into the lexicographically
         ordered set of regions.  Apply (5) above iteratively to R1a and



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         R1c (since they may overlap, or be subtrees of, other regions).

         For instance, given the currently registered regions in the
         example above, if subagent S3 now registers mib-2 (R1 is
         1.3.6.1.2.1) the resulting set of regions would be:

   1.3.6.1.2.1      up to but not including 1.3.6.1.2.1.4        (by S3)
   1.3.6.1.2.1.4    up to but not including 1.3.6.1.2.1.4.22     (by S2)
   1.3.6.1.2.1.4    up to but not including 1.3.6.1.2.1.4.22     (by S3)
   1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23     (by S2)
   1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23     (by S1)
   1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23     (by S3)
   1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5        (by S2)
   1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5        (by S3)
   1.3.6.1.2.1.5    up to but not including 1.3.6.1.2.2          (by S3)

   Note that at registration time a region may be split into multiple
   OID ranges due to pre-existing registrations, or as a result of any
   subsequent registration.  This region splitting is transparent to
   subagents.  Hence the master agent must always be able to associate
   any OID range with the information contained in its original
   agentx-Register-PDU.


7.1.5.1.  Handling Duplicate OID Ranges

   As a result of this registration algorithm there are likely to be
   duplicate OID ranges (regions of identical MIB objects registered to
   different subagents) in the master agent's registered OID space.
   Whenever the master agent's dispatching algorithm (see 7.2.1,
   Dispatching AgentX PDUs) selects a duplicate OID range, the
   determination of which one to use proceeds as follows:

      1) Choose the one whose original agentx-Register-PDU
         r.region contained the most subids, i.e., the most specific
         r.region.  Note: The presence or absence of a range subid
         has no bearing on how "specific" one object identifier is
         compared to another.

      2) If still ambiguous, there were duplicate regions.  Choose the
         one whose original agentx-Register-PDU specified the smaller
         value of r.priority.

7.1.6.  Processing the agentx-Unregister-PDU

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the default context.

   2) If h.sessionID does not correspond to a currently
      established session with this subagent, the
      agentx-Response-PDU is sent in reply with res.error set



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      to `notOpen'.

   3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
      supports only a default context, the agentx-Response-PDU is
      returned with res.error set to `unsupportedContext', and the
      requested allocation fails.  Otherwise:  The value of
      res.sysUpTime is set to the value of sysUpTime.0 for the
      indicated context.

   4) If u.region and the indicated context do not match an existing
      registration made during this session, the agentx-Response-PDU
      is returned with res.error set to `unknownRegistration'.

   5) Otherwise, the agentx-Response-PDU is sent in reply with res.error
      set to `noError', and the previous registration is removed:

      - The master agent removes u.region from its registered OID space
        within the indicated context.  If the original region had been
        split, all such related regions are removed.





        For instance, given the example registry above, if subagent S2
        unregisters "ip", the resulting registry would be:

   1.3.6.1.2.1      up to but not including 1.3.6.1.2.1.4        (by S3)
   1.3.6.1.2.1.4    up to but not including 1.3.6.1.2.1.4.22     (by S3)
   1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23     (by S1)
   1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23     (by S3)
   1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5        (by S3)
   1.3.6.1.2.1.5    up to but not including 1.3.6.1.2.2          (by S3)


7.1.7.  Processing the agentx-AddAgentCaps-PDU

   When the master agent receives an agentx-AddAgentCaps-PDU,
   it processes it as follows:

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the default context.

   2) If h.sessionID does not correspond to a currently
      established session with this subagent, the
      agentx-Response-PDU is sent in reply with res.error set
      to `notOpen'.

   3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
      supports only a default context, the agentx-Response-PDU is
      returned with res.error set to `unsupportedContext', and the



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      requested allocation fails.  Otherwise:  The value of
      res.sysUpTime is set to the value of sysUpTime.0 for the
      indicated context.

   4) Otherwise, the master agent adds the subagent's capabilities
      information to the sysORTable for the indicated context.  An
      agentx-Response-PDU is sent in reply with res.error set to
      `noError'.

7.1.8.  Processing the agentx-RemoveAgentCaps-PDU

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the default context.

   2) If h.sessionID does not correspond to a currently
      established session with this subagent, the
      agentx-Response-PDU is sent in reply with res.error set
      to `notOpen'.

   3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
      supports only a default context, the agentx-Response-PDU is
      returned with res.error set to `unsupportedContext', and the
      requested allocation fails.  Otherwise:  The value of
      res.sysUpTime is set to the value of sysUpTime.0 for the
      indicated context.

   4) If the combination of a.id and the optional a.context does not
      represent a sysORTable entry that was added by this subagent,
      during this session, the agentx-Response-PDU is returned with
      res.error set to `unknownAgentCaps'.

   5) Otherwise the master agent deletes the corresponding sysORTable
      entry and sends in reply the agentx-Response-PDU, with res.error
      set to `noError'.

7.1.9.  Processing the agentx-Close-PDU

   When the master agent receives an agentx-Close-PDU, it processes it
   as follows:

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the default context.

   2) If h.sessionID does not correspond to a currently
      established session with this subagent, the
      agentx-Response-PDU is sent in reply with res.error set
      to `notOpen'.

   3) Otherwise, the master agent closes the AgentX session
      as described below.  No agentx-Response-PDU is sent.




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      - All MIB regions that have been registered during this session
        are unregistered, as described in 7.1.6.

      - All index values allocated during this session are freed, as
        described in section 7.1.4.

      - All sysORID values that were registered during this session
        are removed, as described in section 7.1.8.

   The master agent does not maintain state for closed sessions.
   If a subagent wishes to re-establish a session after receiving
   an agentx-Close-PDU, it needs to re-register MIB regions, agent
   capabilities, etc.

7.1.10.  Detecting Connection Loss

   If a master agent is able to detect (from the underlying transport)
   that a subagent cannot receive AgentX PDUs, it should close all
   affected AgentX sessions as described in 7.1.9, step 3).

7.1.11.  Processing the agentx-Notify-PDU

   A subagent sending SNMPv1 trap information must map this into
   (minimally) a value of snmpTrapOID.0, as described in 3.1.2 of
   RFC 1908 [8].

   The master agent processes the agentx-Notify-PDU as follows:

   1) If h.sessionID does not correspond to a currently
      established session with this subagent, an
      agentx-Response-PDU is sent in reply with res.error set
      to `notOpen', and res.sysUpTime set to the value of
      sysUpTime.0 for the indicated context.

   2) The VarBindList is parsed.  If it does not contain a value for
      sysUpTime.0, the master agent supplies the current value of
      sysUpTime.0 for the indicated context.  If the next VarBind
      (either the first or second VarBind; see section 6.2.10.1)
      is not snmpTrapOID.0, the master agent ceases further processing
      of the notification.

   3) Notifications are sent according to the implementation-specific
      configuration of the master agent.

      If SNMPv1 Trap PDUs are generated, the recommended mapping is as
      described in RFC 2089 [9].

      Except in the case of a `notOpen' error as described in
      (1) above, no agentx-Response-PDU is sent to the subagent
      when the master agent finishes processing the notification.




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7.1.12.  Processing the agentx-Ping-PDU

   When the master agent receives an agentx-Ping-PDU, it processes it
   as follows:

   1) An agentx-Response-PDU is created and res.sysUpTime is set to
      the value of sysUpTime.0 for the default context.

   2) If h.sessionID does not correspond to a currently
      established session with this subagent, the
      agentx-Response-PDU is sent in reply with res.error set
      to `notOpen'.

   3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
      supports only a default context, the agentx-Response-PDU is
      returned with res.error set to `unsupportedContext'.
      Otherwise:  The value of res.sysUpTime is set to the value
      of sysUpTime.0 for the indicated context.

   4) The agentx-Response-PDU is sent, with res.error set to
      `noError'.

   If a subagent does not receive a response to its pings, or if it
   is able to detect (from the underlying transport) that the
   master agent is not able to receive AgentX messages, then it
   eventually must initiate a new AgentX session, re-register its
   regions, etc.

7.2.  Processing Received SNMP Protocol Messages

   When an SNMP GetRequest, GetNextRequest, GetBulkRequest, or
   SetRequest protocol message is received by the master agent, the
   master agent applies its access control policy.

   In particular, for SNMPv1 or SNMPv2c PDUs, the master agent
   applies the Elements of Procedure defined in section 4.1 of RFC
   1157 [6] that apply to receiving entities.  (For other versions
   of SNMP, the master agent applies the access control policy
   defined in the Elements of Procedure for those versions.)

   In the SNMPv1 or v2c frameworks, the master agent uses the community
   string as an index into a local repository of configuration
   information that may include community profiles or more complex
   context information.

   If application of the access control policy results in a valid SNMP
   request PDU, then an SNMP Response-PDU is constructed from
   information gathered in the exchange of AgentX PDUs between the
   master agent and one or more subagents.  Upon receipt and initial
   validation of an SNMP request PDU, a master agent uses the
   procedures described below to dispatch AgentX PDUs to the proper



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   subagents, marshal the subagent responses, and construct an SNMP
   response PDU.

7.2.1.  Dispatching AgentX PDUs

   Upon receipt and initial validation of an SNMP request PDU, a master
   agent uses the procedures described below to dispatch AgentX PDUs to
   the proper subagents.

   Note: In the following procedures, an object identifier is said to
   be "contained" within an OID range when both of the following
   are true:

       - The object identifier does not lexicographically precede
         the range.

       - The object identifier lexicographically precedes the end
         of the range.

   General Rules of Procedure

   While processing a particular SNMP request, the master agent may
   send one or more AgentX PDUs to one or more subagents.  The
   following rules of procedure apply in general to the AgentX master
   agent. PDU-specific rules are listed in the applicable sections.

   1) Honoring the registry

      Because AgentX supports overlapping registrations, it is
      possible for the master agent to obtain a value for a requested
      varbind from within multiple registered MIB regions.

      The master agent must ensure that the value (or exception)
      actually returned in the SNMP response PDU is taken from the
      authoritative region (as defined in section 7.1.5.1).

   2) GetNext and GetBulk Processing

      The master agent may choose to send agentx-Get-PDUs while
      servicing an SNMP GetNextRequest-PDU.  The master agent may
      choose to send agentx-Get-PDUs or agentx-GetNext-PDUs while
      servicing an SNMP GetBulkRequest-PDU.  One possible reason for
      this would be if the current iteration has targeted
      instance-level registrations.

      The master agent may or may not choose to "scope" the possible
      instances returned by a subagent through the use of the ending
      OID in the SearchRange.  A typical usage of this field would be
      to encode the ending OID with the registered MIB region that is
      the first lexicographical successor to the target OID range,
      and that was not registered by the target subagent.



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      Regardless of this choice, rule (1) must be obeyed.

      The master agent may require multiple request-response
      iterations on the same subagent session, to determine the
      final value of all requested variables.

      All AgentX PDUs sent on the session while processing a given
      SNMP request must contain identical values of transactionID.
      Each different SNMP request processed by the master agent must
      present a unique value of transactionID (within the limits of
      the 32-bit field) to the session.

   3) Number and order of variables sent per AgentX PDU

      For Get/GetNext/GetBulk operations, at any stage of the
      possibly iterative process, the master agent may need to
      dispatch several SearchRanges to a particular subagent
      session.  The master agent may send one, some, or all
      of the SearchRanges in a single AgentX PDU.

      The master agent must ensure that the correct contents
      and ordering of the VarBindList in the SNMP Response-PDU
      are maintained.

      The following rules govern the number of VarBinds in a
      given AgentX PDU:

         a) The subagent must support processing of AgentX PDUs
            with multiple VarBinds.

         b) When processing an SNMP Set request, the master agent
            must send all of the VarBinds applicable to a particular
            subagent session in a single Test/Set transaction.

         c) When processing an SNMP Get, GetNext, or GetBulk request,
            the master agent may send a single AgentX PDU to the
            subagent with all applicable VarBinds, or multiple
            PDUs with single VarBinds, or something in between
            those extremes. The determination of which method to
            use in a particular case is implementation-specific.

   4) Timeout Values

      The master agent chooses a timeout value for each MIB region
      being queried, which is

         a) the value specified during registration of the MIB region,
            if it was non-zero

         b) otherwise, the value specified during establishment of
            the session in which this region was subsequently



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            registered, if that value was non-zero.

         c) otherwise, the master agent's default value

      When an AgentX PDU that references multiple MIB regions is
      dispatched, the timeout value used for the PDU is the maximum
      value of the timeouts so determined for each of the referenced
      MIB regions.

   5) Context

      If the master agent has determined that a specific non-default
      context is associated with the request PDU, that context is
      encoded into the AgentX PDU's context field and the
      NON_DEFAULT_CONTEXT bit is set in h.flags.

      Otherwise, no context Octet String is added to the PDU, and the
      NON_DEFAULT_CONTEXT bit is cleared.

7.2.1.1.  agentx-Get-PDU

   Each variable binding in the SNMP request PDU is processed as
   follows:

   (1) Identify the target OID range.

       Within a lexicographically ordered set of OID ranges, valid for
       the indicated context, locate the region that contains the
       binding's name.

   (2) If no such OID range exists the variable binding is not
       processed further, and its value is set to `noSuchObject'.

   (3) Identify the subagent session in which this region was
       registered, termed the target session.

   (4) If this is the first variable binding to be dispatched over
       the target session in a request-response exchange entailed
       in the processing of this management request:

       - Create an agentx-Get-PDU for this session, with the header
         fields initialized as described above (see 6.1 AgentX PDU
         Header).

   (5) Add a SearchRange to the end of the target session's PDU
       for this variable binding.

        - The variable binding's name is encoded into the starting OID.

        - The ending OID is encoded as null.




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7.2.1.2.  agentx-GetNext-PDU

   Each variable binding in the SNMP request PDU is processed as
   follows:

   (1) Identify the target OID range.

       Within a lexicographically ordered set of OID ranges, valid for
       the indicated context, locate

        a) the OID range that contains the variable binding's name and
           is not a fully qualified instance, or

        b) the OID range that is the first lexicographical successor to
           the variable binding's name.

   (2) If no such OID range exists the variable binding is not processed
       further, and its value is set to `endOfMibView'.

   (3) Identify the subagent session in which this region was
       registered, termed the target session.

   (4) If this is the first variable binding to be dispatched over the
       target session in a request-response exchange entailed in the
       processing of this management request:

       - Create an agentx-GetNext-PDU for the session, with
         the header fields initialized as described above (see 6.1
         AgentX PDU Header).

   (5) Add a SearchRange to the end of the target session's
       agentx-GetNext-PDU for this variable binding.

        - if (1a) applies, the variable binding's name is encoded
          into the starting OID, and the OID's "include" field
          is set to 0.

        - if (1b) applies, the target OID is encoded into the starting
          OID, and its "include" field is set to 1.

7.2.1.3.  agentx-GetBulk-PDU

   (Note: The outline of the following procedure is based closely on
   section 4.2.3, "The GetBulkRequest-PDU" of RFC 1905 [4].  Please
   refer to it for details on the format of the SNMP GetBulkRequest-PDU
   itself.)

   Each variable binding in the request PDU is processed as follows:

   (1) Identify the target OID range and target session, exactly as
       described for the agentx-GetNext-PDU (see 7.2.1.2).



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   (2) If this is the first variable binding to be dispatched over the
       target session in a request-response exchange entailed in the
       processing of this management request:

       - Create an agentx-GetBulk-PDU for the session, with
         the header fields initialized as described above (see 6.1
         AgentX PDU Header).

   (3) Add a SearchRange to the end of the target session's
       agentx-GetBulk-PDU for this variable binding, as described
       for the agentx-GetNext-PDU.  If the variable binding was
       a non-repeater in the original request PDU, it must be a
       non-repeater in the agentx-GetBulk-PDU.

   The value of g.max_repetitions in the agentx-GetBulk-PDU may be less
   than (but not greater than) the value in the original request PDU.

   The master agent may make such alterations due to simple sanity
   checking, optimizations for the current iteration based on the
   registry, the maximum possible size of a potential Response-PDU,
   known constraints of the AgentX transport, or any other
   implementation-specific constraint.

7.2.1.4.  agentx-TestSet-PDU

   AgentX employs test-commit-undo-cleanup phases
   to achieve "as if simultaneous" semantics of the SNMP SetRequest-PDU
   within the extensible agent.  The initial phase involves
   the agentx-TestSet-PDU.

   Each variable binding in the request PDU is processed in order, as
   follows:

   (1) Identify the target OID range.

       Within a lexicographically ordered set of OID ranges, valid for
       the indicated context, locate the range that contains the
       variable binding's name.

   (2) If no such OID range exists, this variable binding fails with an
       error of `notWritable'.  Processing is complete for this
       request.

   (3) Identify the single subagent responsible for this OID range,
       termed the target subagent, and the applicable session,
       termed the target session.

   (4) If this is the first variable binding to be dispatched over
       the target session in a request-response exchange entailed
       in the processing of this management request:



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       - create an agentx-TestSet-PDU for the session, with the
         header fields initialized as described above (see 6.1
         AgentX PDU Header).

   (5) Add a VarBind to the end of the target session's PDU
       for this variable binding, as described in section 5.4.

    Note that all VarBinds applicable to a given session must be
    sent in a single agentx-TestSet-PDU.

7.2.1.5.  Dispatch

   A timeout value is calculated for each PDU to be sent, which is the
   maximum value of the timeouts determined for each of the PDU's
   SearchRanges (as described above in 7.2.1 Dispatching AgentX PDUs,
   item 4). Each pending PDU is mapped (via its h.sessionID value) to a
   particular transport domain/endpoint, as described in section 8
   (Transport Mappings).

7.2.2.  Subagent Processing of agentx-Get, GetNext, GetBulk-PDUs

   A conformant AgentX subagent must support the agentx-Get, -GetNext,
   and -GetBulk PDUs, and must support multiple variables being supplied
   in each PDU.

   When a subagent receives an agentx-Get-, GetNext-, or GetBulk-PDU, it
   performs the indicated management operations and returns an
   agentx-Response-PDU.

   The agentx-Response-PDU header fields are identical to the received
   request PDU except that, at the start of processing, the subagent
   initializes h.type to Response, res.error to `noError',
   res.index to 0, and the VarBindList to null.

   Each SearchRange in the request PDU's SearchRangeList is processed as
   described below, and a VarBind is added in the corresponding
   location of the agentx-Response-PDU's  VarbindList.  If processing
   should fail for any reason not described below, res.error is set to
   `genErr', res.index to the index of the failed SearchRange,
   the VarBindList is reset to null, and this agentx-Response-PDU is
   returned to the master agent.


7.2.2.1.  Subagent Processing of the agentx-Get-PDU

   Upon the subagent's receipt of an agentx-Get-PDU, each SearchRange
   in the request is processed as follows:

   (1) The starting OID is copied to v.name.




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   (2) If the starting OID exactly matches the name of a
       variable instantiated by this subagent within the indicated
       context and session, v.type and v.data are encoded to represent
       the variable's syntax and value, as described in section 5.4,
       Value Representation.

   (3) Otherwise, if the starting OID does not match the object
       identifier prefix of any variable instantiated within the
       indicated context and session, the VarBind is set to
       `noSuchObject', in the manner described in section 5.4,
       Value Representation.

   (4) Otherwise, the VarBind is set to `noSuchInstance'
       in the manner described in section 5.4, Value Representation.

7.2.2.2.  Subagent Processing of the agentx-GetNext-PDU

   Upon the subagent's receipt of an agentx-GetNext-PDU, each
   SearchRange in the request is processed as follows:

   (1) The subagent searches for a variable within the
       lexicographically ordered list of variable names for all
       variables it instantiates (without regard to registration of
       regions) within the indicated context and session, for which
       the following are all true:

       - if the "include" field of the starting OID is 0, the
         variable's name is the closest lexicographical successor to
         the starting OID.

       - if the "include" field of the starting OID is 1, the
         variable's name is either equal to, or the closest
         lexicographical successor to, the starting OID.

       - If the ending OID is not null, the variable's name
         lexicographically precedes the ending OID.

       If all of these conditions are met, v.name is set to the
       located variable's name.  v.type and v.data are encoded to
       represent the variable's syntax and value, as described in
       section 5.4, Value Representation.

   (2) If no such variable exists, v.name is set to the starting OID,
       and the VarBind is set to `endOfMibView', in the manner described
       in section 5.4, Value Representation.

7.2.2.3.  Subagent Processing of the agentx-GetBulk-PDU

   A maximum of N + (M * R) VarBinds are returned, where

      N equals g.non_repeaters,



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      M equals g.max_repetitions, and

      R is (number of SearchRanges in the GetBulk request) - N.

   The first N SearchRanges are processed exactly as for the
   agentx-GetNext-PDU.

   If M and R are both non-zero, the remaining R SearchRanges are
   processed iteratively to produce potentially many VarBinds.  For
   each iteration i, such that i is greater than zero and less than or
   equal to M, and for each repeated SearchRange s, such that s is
   greater than zero and less than or equal to R, the
   (N+((i-1)*R)+s)-th VarBind is added to the agentx-Response-PDU
   as follows:

      1) The subagent searches for a variable within the
         lexicographically ordered list of variable names for all
         variables it instantiates (without regard to registration of
         regions) within the indicated context and session, for which
         the following are all true:

          - The variable's name is the (i)-th lexicographical successor
            to the (N+s)-th requested OID.

            (Note that if i is 0 and the "include" field is 1, the
            variable's name may be equivalent to, or the first
            lexicographical successor to, the (N+s)-th requested OID.)

          - If the ending OID is not null, the variable's name
            lexicographically precedes the ending OID.

         If all of these conditions are met, v.name is set to the
         located variable's name.  v.type and v.data are
         encoded to represent the variable's syntax and value, as
         described in section 5.4, Value Representation.


      2) If no such variable exists, the VarBind is set to
         `endOfMibView' as described in section 5.4, Value
         Representation.  v.name is set to v.name of the
         (N+((i-2)*R)+s)-th VarBind unless i is currently 1, in which
         case it is set to the value of the starting OID in the (N+s)-th
         SearchRange.

   Note that further iterative processing should stop if

        - For any iteration i, all s values of v.type are
          `endOfMibView'.

        - An AgentX transport constraint or other
          implementation-specific constraint is reached.



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7.2.3.  Subagent Processing of agentx-TestSet, -CommitSet, -UndoSet,
        -CleanupSet-PDUs

   A conformant AgentX subagent must support the agentx-TestSet,
   -CommitSet, -UndoSet, and -CleanupSet PDUs, and must support multiple
   variables being supplied in each PDU.

   These four PDUs are used to collectively perform the indicated
   management operation.  An agentx-Response-PDU is sent in reply to
   each of the PDUs, to inform the master agent of the state of the
   operation.

   The agentx-Response-PDU header fields are identical to the received
   request PDU except that, at the start of processing, the subagent
   initializes h.type to Response, res.error to `noError', and
   res.index to 0.

   These Response-PDUs do not contain a VarBindList.


7.2.3.1.  Subagent Processing of the agentx-TestSet-PDU

   Upon the subagent's receipt of an agentx-TestSet-PDU, each VarBind
   in the PDU is validated until they are all successful, or until one
   fails, as described in section 4.2.5 of RFC 1905 [4]. The subagent
   validates variables with respect to the context and session
   indicated in the testSet-PDU.

   If each VarBind is successful, the subagent has a further
   responsibility to ensure the availability of all resources (memory,
   write access, etc.) required for successfully carrying out a
   subsequent agentx-CommitSet operation.  If this cannot be guaranteed,
   the subagent should set res.error to `resourceUnavailable'.

   As a result of this validation step, an agentx-Response-PDU
   is sent in reply whose res.error field is set to one of the
   following (SNMPv2 SMI) values:

            noError                    (0),
            genErr                     (5),
            noAccess                   (6),
            wrongType                  (7),
            wrongLength                (8),
            wrongEncoding              (9),
            wrongValue                (10),
            noCreation                (11),
            inconsistentValue         (12),
            resourceUnavailable       (13),
            notWritable               (17),
            inconsistentName          (18)




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   If this value is not `noError', the res.index field must be
   set to the index of the VarBind for which validation failed.

   Implementation of rigorous validation code may be one of the
   most demanding aspects of subagent development.  Implementors
   are strongly encouraged to do this right, so as to avoid if at
   all possible the extensible agent's having to return `commitFailed'
   or `undoFailed' during subsequent processing.


7.2.3.2.  Subagent Processing of the agentx-CommitSet-PDU

   The agentx-CommitSet-PDU indicates that the subagent should actually
   perform (as described in the post-validation sections of 4.2.5 of
   RFC 1905 [4]) the management operation indicated by the previous
   TestSet-PDU.
   After carrying out the management operation, the subagent sends in
   reply an agentx-Response-PDU whose res.error field is set to one of
   the following (SNMPv2 SMI) values:

            noError                    (0),
            commitFailed              (14)

   If this value is `commitFailed', the res.index field must be
   set to the index of the VarBind for which the operation failed.
   Otherwise res.index is set to 0.

7.2.3.3.  Subagent Processing of the agentx-UndoSet-PDU

   The agentx-UndoSet-PDU indicates that the subagent should undo
   the management operation requested in a preceding CommitSet-PDU.
   The undo process is as described in section 4.2.5 of RFC 1905
   [4].

   After carrying out the undo process, the subagent sends in reply an
   agentx-Response-PDU whose res.index field is set to 0, and whose
   res.error field is set to one of the following (SNMPv2 SMI) values:

            noError                    (0),
            undoFailed                (15)

   If this value is `undoFailed', the res.index field must be
   set to the index of the VarBind for which the operation failed.
   Otherwise res.index is set to 0.

   This PDU also signals the end of processing of the management
   operation initiated by the previous TestSet-PDU.  The subagent
   should release resources, etc. as described in section 7.2.3.4.






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7.2.3.4.  Subagent Processing of the agentx-CleanupSet-PDU

   The agentx-CleanupSet-PDU signals the end of processing of the
   management operation requested in the previous TestSet-PDU.  This
   is an indication to the subagent that it may now release any
   resources it may have reserved in order to carry out the management
   request.

   No response is sent by the subagent.


7.2.4.  Master Agent Processing of AgentX Responses

   The master agent now marshals all subagent AgentX response PDUs and
   builds an SNMP response PDU.  In the next several subsections, the
   initial processing of all subagent AgentX response PDUs is
   described, followed by descriptions of subsequent processing
   for each specific subagent Response.

7.2.4.1.  Common Processing of All AgentX Response PDUs

   1) If a subagent does not respond within the timeout interval for
      this dispatch, it is treated as if the subagent had returned
      `genErr' and processed as described below.

      A timeout may be due to a variety of reasons, and does
      not necessarily denote a failed or malfunctioning
      subagent.  As such, the master agent's response to a
      subagent timeout is implementation-specific, but with the
      following constraint:

         A subagent that times out on three consecutive requests
         is considered unable to respond, and the master agent
         must close the AgentX session as described in
         7.1.9, step (2).

   2) Otherwise, the h.packetID, h.sessionID, and h.transactionID
      fields of the AgentX response PDU are used to correlate subagent
      responses.  If the response does not pertain to this SNMP
      operation, it is ignored.

   3) Otherwise, the responses are processed jointly to form the SNMP
      response PDU.

7.2.4.2.  Processing of Responses to agentx-Get-PDUs

   After common processing of the subagent's response to an
   agentx-Get-PDU (see 7.2.4.1 above), processing continues with
   the following steps:

   1)  For any received AgentX response PDU, if res.error is not



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       `noError', the SNMP response PDU's error code is set to this
       value, and its error index to the index of the variable binding
       corresponding to the failed VarBind in the subagent's
       AgentX response PDU.

       All other AgentX response PDUs received due to processing this
       SNMP request are ignored.  Processing is complete; the SNMP
       Response PDU is ready to be sent (see section 7.2.5, Sending
       the SNMP Response-PDU).

   2)  Otherwise, the content of each VarBind in the AgentX response PDU
       is used to update the corresponding variable binding in the SNMP
       Response-PDU.

7.2.4.3.  Processing of Responses to agentx-GetNext-PDU and
          agentx-GetBulk-PDU

   After common processing of the subagent's response to an
   agentx-GetNext-PDU or agentx-GetBulk-PDU (see 7.2.4.1 above),
   processing continues with the following steps:

   1)  For any received AgentX response PDU, if res.error is not
       `noError', the SNMP response PDU's error code is set to this
       value, and its error index to the index of the VarBind
       corresponding to the failed VarBind in the subagent's
       AgentX response PDU.

       All other AgentX response PDUs received due to processing this
       SNMP request are ignored.  Processing is complete; the SNMP
       response PDU is ready to be sent (see section 7.2.5, Sending
       the SNMP Response PDU).

   2)  Otherwise, the content of each VarBind in the AgentX response
       PDU is used to update the corresponding VarBind in the SNMP
       response PDU.

   After all expected AgentX response PDUs have been processed, if
   any VarBinds still contain the value `endOfMibView' in their
   v.type fields, processing must continue:

   3)  A new iteration of AgentX request dispatching is initiated
       (as described in section 7.2.1.1), in which only those
       VarBinds whose v.type is `endOfMibView' are processed.

   4)  For each such VarBind, a target OID range is identified
       which is the lexicographical successor to the target OID
       range for this VarBind on the last iteration.  The target
       subagent is the one that registered the target OID range.
       The target session is the one in which the target OID range
       was registered.




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       If an agentx-GetNext- or GetBulk-PDU is being dispatched,
       the starting OID in the SearchRanges is set to the target
       OID range, and its "include" field is set to 1.

   5)  The value of transactionID must be identical to the value
       used during the previous iteration.

   6)  The AgentX PDUs are sent to the subagent(s), and the responses
       are received and processed according to the steps described in
       section 7.2.4.

   7)  This process continues iteratively until a complete SNMP
       Response-PDU has been built, or until there remain no
       target OID range lexicographical successors.

7.2.4.4.  Processing of Responses to agentx-TestSet-PDUs

   After common processing of the subagent's response to an
   agentx-TestSet-PDU (see 7.2.4.1 above), processing continues with
   the further exchange of AgentX PDUs.  The value of h.transactionID
   in the agentx-CommitSet, -UndoSet, and -CleanupSet-PDUs must be
   identical to the value sent in the testSet-PDU.

   The state transitions and PDU sequences are depicted in section 7.3.

   1)  If any target subagent's response is not `noError', all other
       agentx-Response-PDUs received due to processing this SNMP
       request are ignored.

       An agentx-CleanupSet-PDU is sent to each target subagent that has
       been sent a agentx-TestSet-PDU.

       Processing is complete; the SNMP response PDU is constructed as
       described below in 7.2.4.6, step (2).

   2)  Otherwise an agentx-CommitSet-PDU is sent to each target
       subagent.

7.2.4.5.  Processing of Responses to agentx-CommitSet-PDUs

   After common processing of the subagent's response to an
   agentx-CommitSet-PDU (see 7.2.4.1 above), processing continues with
   the following steps:

   1)  If any response is not `noError', all other
       agentx-Response-PDUs received due to processing this SNMP
       request are ignored.

       An agentx-UndoSet-PDU is sent to each target subagent that has
       been sent a agentx-CommitSet-PDU.  All other subagents are sent a
       agentx-CleanupSet-PDU.



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   2)  Otherwise an agentx-CleanupSet-PDU is sent to each target
       subagent.  Processing is complete; the SNMP response PDU is
       constructed as described below in 7.2.4.6, step (2).

7.2.4.6.  Processing of Responses to agentx-UndoSet-PDUs

   After common processing of the subagent's response to an
   agentx-UndoSet-PDU (see 7.2.4.1 above), processing continues with the
   following steps:

   1)  If any response is not `noError' the SNMP response
       PDU's error code is set to this value, and its error index to the
       index of the VarBind corresponding to the failed VarBind
       in the agentx-TestSet-PDU.

       Otherwise the SNMP response PDU's error code is set to `noError'
       and its error index to 0.

7.2.5.  Sending the SNMP Response-PDU

   Once the processing described in sections 7.2.1 - 7.2.4 is
   complete, there is an SNMP response PDU available.  The master agent
   now implements the Elements of Procedure for the applicable version
   of the SNMP protocol in order to encapsulate the PDU into a message,
   and transmit it to the originator of the SNMP management request.
   Note that this may involve altering the PDU contents (for instance,
   to replace the original VarBinds if an error condition is
   to be returned).

   The response PDU may also be altered in order to support the SNMP
   version 1 framework.  In such cases the required mapping is that
   defined in RFC 2089 [9].  (Note in particular that the rules for
   handling Counter64 syntax may require re-sending AgentX GetBulk
   or GetNext PDUs until a VarBind of suitable syntax is returned.)


7.2.6.  MIB Views

   AgentX subagents are not aware of MIB views, since view information
   is not contained in AgentX PDUs.

   As stated above, the descriptions of procedures in section 7 of this
   memo are not intended to constrain the internal architecture of any
   conformant implementation.  In particular, the master agent
   procedures described in sections 7.2.1 and 7.2.4 may be altered so
   as to optimize AgentX exchanges when implementing MIB views.

   Such optimizations are beyond the scope of this memo.  But note that
   section 7.2.3 defines subagent behavior in such a way that alteration
   of SearchRanges may be used in such optimizations.



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7.3.  State Transitions

   State diagrams are presented from the master agent's perspective
   for transport connection and session establishment, and from the
   subagent's perspective for Set transaction processing.

7.3.1.  Set Transaction States

   The following table presents, from the subagent's perspective,
   the state transitions involved in Set transaction processing:

                                       STATE
            +----------------+--------------+---------+--------+--------
            |       A        |      B       |   C     |   D    |   E
            |   (Initial     |    TestOK    | Commit  | Test   | Commit
            |     State)     |              |  OK     | Fail   |  Fail
            |                |              |         |        |
    EVENT   |                |              |         |        |
   ---------+----------------+--------------+---------+--------+--------
            | 7.2.3.1        |              |         |        |
   Receive  | All varbinds   |              |         |        |
   TestSet  | OK?            |      X       |    X    |   X    |    X
   PDU      |   Yes ->B      |              |         |        |
            |   No  ->D      |              |         |        |
   ---------+----------------+--------------+---------+--------+--------
            |                |  7.2.3.2     |         |        |
   Receive  |                |  NoError?    |         |        |
   Commit-  |       X        |   Yes ->C    |    X    |   X    |    X
   Set PDU  |                |   No  ->E    |         |        |
   ---------+----------------+--------------+---------+--------+--------
   Receive  |                |              | 7.2.3.3 |        |7.2.4.5
   UndoSet  |       X        |       X      | ->done  |   X    | ->done
   PDU      |                |              |         |        |
   ---------+----------------+--------------+---------+--------+--------
   Receive  |                |  7.2.4.4     | 7.2.3.4 |7.2.4.4 |
   Cleanup- |       X        |   ->done     | ->done  | ->done |   X
   Set PDU  |                |              |         |        |
   ---------+----------------+--------------+---------+--------+--------
   Session  |                | rollback     | undo    |        |
   Loss     |  ->done        |  ->done      |  ->done | ->done | ->done
   ---------+----------------+--------------+---------+--------+--------

   There are three possible sequences that a subagent may follow for a
   particular set transaction:

      1) TestSet CommitSet CleanupSet
      2) TestSet CommitSet UndoSet
      3) TestSet           CleanupSet

   Note that a single PDU sequence may result in multiple paths through
   the FSM.  For example, the sequence



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      TestSet CommitSet UndoSet

   may walk through either of these two state sequences:

      (initial) TestOK CommitOK   (done)
      (initial) TestOK CommitFail (done)















































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7.3.2  Transport Connection States

   The following table presents, from the master agent's perspective,
   the state transitions involved in transport connection setup
   and teardown:

                                STATE
                   +--------------+--------------
                   |      A       |      B
                   | No transport |  Transport
                   |              |  connected
                   |              |
   EVENT           |              |
   ----------------+--------------+--------------
   Transport       |              |
   connect         |     ->B      |      X
   indication      |              |
   ----------------+--------------+--------------
   Receive         |              | if duplicate
   Open-PDU        |              | session id,
                   |              | reject, else
                   |      X       | establish
                   |              | session
                   |              |
                   |              |     ->B
   ----------------+--------------+--------------
   Receive         |              | if matching
   Response-PDU    |              | session id,
                   |              | feed to that
                   |      X       | session's FSM
                   |              | else ignore
                   |              |
                   |              |     ->B
   ----------------+--------------+--------------
   Receive other   |              | if matching
   PDUs            |              | session id,
                   |              | feed to that
                   |      X       | session's FSM
                   |              | else reject
                   |              |
                   |              |     ->B
   ----------------+--------------+--------------
   Transport       |              |notify all
   disconnect      |              |sessions on
   indication      |      X       |this transport
                   |              |
                   |              |     ->A
   ----------------+--------------+--------------






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7.3.3  Session States

   The following table presents, from the master agent's perspective,
   the state transitions involved in session setup and teardown:

                              STATE
                  +-------------+----------------
                  |     A       |      B
                  |  No session |  Session
                  |             |  established
   EVENT          |             |
   ---------------+-------------+----------------
                  |  7.1.1      |
   Receive        |             |      X
   Open PDU       |    ->B      |
   ---------------+-------------+----------------
                  |             |  7.1.9
   Receive        |      X      |
   Close PDU      |             |    ->A
   ---------------+-------------+----------------
   Receive        |             |  7.1.5
   Register PDU   |      X      |
                  |             |    ->B
   ---------------+-------------+----------------
   Receive        |             |  7.1.6
   Unregister     |      X      |
   PDU            |             |    ->B
   ---------------+-------------+----------------
   Receive        |             |
   Get PDU        |             |
   GetNext PDU    |             |
   GetBulk PDU    |      X      |       X
   TestSet PDU    |             |
   CommitSet PDU  |             |
   UndoSet PDU    |             |
   CleanupSet PDU |             |
   ---------------+-------------+----------------
   Receive        |             |  7.1.11
   Notify PDU     |      X      |
                  |             |    ->B
   ---------------+-------------+----------------
   Receive Ping   |             |  7.1.12
   PDU            |      X      |
                  |             |    ->B
   ---------------+-------------+----------------
   Receive        |             |  7.1.2
   IndexAllocate  |      X      |
   PDU            |             |    ->B
   ---------------+-------------+----------------
   (continued next page)




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   ---------------+-------------+----------------
   Receive        |             |  7.1.4
   IndexDeallocate|      X      |
   PDU            |             |    ->B
   ---------------+-------------+----------------
   Receive        |             |  7.1.7
   AddAgentxCaps  |      X      |
   PDU            |             |    ->B
   ---------------+-------------+----------------
   Receive        |             |  7.1.8
   RemoveAgentxCap|      X      |
   PDU            |             |    ->B
   ---------------+-------------+----------------
   Receive        |             |  7.2.4
   Response PDU   |      X      |
                  |             |    ->B
   ---------------+-------------+----------------
   Receive        |             |
   Other PDU      |      X      |       X
   ---------------+-------------+----------------

8.  Transport Mappings

   The same AgentX PDU formats, encodings, and elements of procedure
   are used regardless of the underlying transport.

8.1.  AgentX over TCP

8.1.1.  Well-known Values

   The master agent accepts TCP connection requests for the well-known
   port 705.  Subagents connect to the master agent using this port
   number.

8.1.2.  Operation

   Once a TCP connection has been established, the AgentX peers use
   this connection to carry all AgentX PDUs. Multiple AgentX sessions
   may be established using the same TCP connection.  AgentX PDUs are
   sent within an AgentX session.  AgentX peers are responsible for
   mapping the h.sessionID to a particular TCP connection.

   All AgentX PDUs are presented individually to the TCP, to be sent as
   the data portion of a TCP PDU.

8.2.  AgentX over UNIX-domain Sockets

   Many (BSD-derived) implementations of the UNIX operating system
   support the UNIX pathname address family (AF_UNIX) for socket
   communications.  This provides a convenient method of sending and
   receiving data between processes on the same host.



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   Mapping AgentX to this transport is useful for environments that

       - wish to guarantee subagents are running on the same
         managed node as the master agent, and where

       - sockets provide better performance than TCP or UDP,
         especially in the presence of heavy network I/O

8.2.1.  Well-known Values

   The master agent creates a well-known UNIX-domain socket endpoint
   called "/var/agentx/master".  (It may create other, implementation-
   specific endpoints.)

   This endpoint name uses the character set encoding native to the
   managed node, and represents a UNIX-domain stream (SOCK_STREAM)
   socket.

8.2.2.  Operation

   Once a connection has been established, the AgentX peers use
   this connection to carry all AgentX PDUs.

   Multiple AgentX sessions may be established using the same
   connection.  AgentX PDUs are sent within an AgentX session.  AgentX
   peers are responsible for mapping the h.sessionID to a particular
   connection.

   All AgentX PDUs are presented individually to the socket layer, to
   be sent in the data stream.


9.  Security Considerations

   This memo defines a protocol between two processing entities,
   one of which (the master agent) is assumed to perform
   authentication of received SNMP requests and to control access
   to management information.  The master agent performs these
   security operations independently of the other processing
   entity (the subagent).

   Security considerations require three questions to be answered:

      1. Is a particular subagent allowed to initiate a session with a
         particular master agent?

      2. During an AgentX session, is any SNMP security-related
         information (for example, community names) passed from the
         master agent to the subagent?

      3. During an AgentX session, what part of the MIB tree is this



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         subagent allowed to register?

   The answer to the third question is: A subagent can register any
   subtree (subject to AgentX elements of procedure, section 7.1.5).
   Currently there is no access control mechanism
   defined in AgentX. A concern here is that a malicious subagent
   that registers an unauthorized "sensitive" subtree, could see
   modification requests to those objects, or by giving its own
   clever answer to NMS queries, could cause the NMS to do something
   that leads to information disclosure or other damage.

   The answer to the second question is: No.

   Now we can answer the first question.
   AgentX does not contain a mechanism for authorizing/refusing session
   initiations.  Thus, controlling subagent access to the master
   agent may only be done at a lower layer (e.g., transport).

   An AgentX subagent can connect to a master agent
   using either a network transport mechanism (e.g., TCP), or a "local"
   mechanism (e.g., shared memory, named pipes).

   In the case where a local transport mechanism is used and both
   subagent and master agent are running on the same host, connection
   authorization can be delegated to the operating system features.
   The answer to the first security question then becomes:
   "If and only if the subagent has sufficient privileges, then the
   operating system will allow the connection".

   If a network transport is used, currently there is no inherent
   security.  Transport Layer Security or SSL could be used
   to control subagent connections, but that is beyond the scope
   of this document.

   Thus it is recommended that subagents always run on the same
   host as the master agent and that operating system features be
   used to ensure that only properly authorized subagents
   can establish connections to the master agent.

10.  Acknowledgements

   The initial draft of this memo was heavily influenced by the DPI
   2.0 specification RFC 1592 [7].

   This document was produced by the IETF Agent Extensibility
   (AgentX) Working Group, and benefited especially from the
   contributions of the following working group members:

      David Battle, Uri Blumenthal, Jeff Case, Maria Greene,
      Dave Keeney, Harmen van der Linde, Bob Natale, Randy Presuhn,
      Aleksey Romanov, Don Ryan, and Juergen Schoenwaelder.



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   The AgentX Working Group is chaired by:

      Bob Natale
      ACE*COMM Corporation
      704 Quince Orchard Road
      Gaithersburg MD  20878

      Phone: +1-301-721-3000
      Fax:   +1-301-721-3001
      EMail: bnatale@acecomm.com


11.  Authors' and Editor's Addresses

      Mike Daniele
      Digital Equipment Corporation
      110 Spit Brook Rd
      Nashua, NH 03062

      Phone: +1-603-881-1423
      EMail: daniele@zk3.dec.com


      Bert Wijnen
      IBM Professional Services
      Watsonweg 2
      1423 ND Uithoorn
      The Netherlands

      Phone: +31-79-322-8316
      EMail: wijnen@vnet.ibm.com


      Dale Francisco (editor)
      Cisco Systems
      150 Castilian Dr
      Goleta CA 93117

      Phone: +1-805-961-3642
      Fax:   +1-805-961-3600
      EMail: dfrancis@cisco.com


12.  References

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

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



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     S. Waldbusser, "Structure of Management Information for Version 2
     of the Simple Network Management Protocol (SNMPv2)", RFC 1902,
     January 1996.

[3]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
     S. Waldbusser, "Textual Conventions for Version 2 of the Simple
     Network Management Protocol (SNMPv2)", RFC 1903, January 1996.

[4]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
     S. Waldbusser, "Protocol Operations for Version 2 of the Simple
     Network Management Protocol (SNMPv2)", RFC 1905, January 1996.

[5]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
     S. Waldbusser, "Management Information Base for Version 2 of the
     Simple Network Management Protocol (SNMPv2)", RFC 1907,
     January 1996.

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

[7]  Wijnen, B., Carpenter, G., Curran, K., Sehgal, A., and G. Waters,
     "Simple Network Management Protocol: Distributed Protocol
     Interface, Version 2.0", RFC 1592, T.J. Watson Research Center,
     IBM Corp., Bell Northern Research, Ltd., March 1994.

[8]  SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
     S. Waldbusser, "Coexistence between Version 1 and Version 2 of the
     Internet-standard Network Management Framework", RFC 1908,
     January 1996.

[9]  Wijnen, B., and Levi, D., "V2ToV1: Mapping SNMPv2 onto SNMPv1
     Within a Bilingual SNMP Agent", RFC 2089, T.J. Watson Research
     Center, IBM Corp., SNMP Research, Inc., January 1997.

[10] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
     S. Waldbusser, "Conformance Statements for Version 2 of the
     Simple Network Management Protocol (SNMPv2)", RFC 1904,
     January 1996.

[11] Interfaces MIB Working Group, McCloghrie, K., and F. Kastenholz,
     "Evolution of the Interfaces Group of MIB-II", RFC 1573,
     January 1994.

[12] FDDI MIB Working Group, J. Case, "FDDI Management Information
     Base", RFC 1285, January 1992.

[13] Application MIB Working Group, Krupczak, C., and J. Saperia,
     "Definitions of Managed Objects for Applications",
     draft-ietf-applmib-sysapplmib-05.txt, 11 Nov 1996.



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