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rfc:rfc2257

Network Working Group M. Daniele Request for Comments: 2257 Digital Equipment Corporation Category: Standards Track B. Wijnen

                                T.J. Watson Research Center, IBM Corp.
                                                     D. Francisco, Ed.
                                                   Cisco Systems, Inc.
                                                          January 1998
               Agent Extensibility (AgentX) Protocol
                             Version 1

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1998).  All Rights Reserved.

Table of Contents

 1 Introduction......................................................4
 2 The SNMP Framework................................................4
   2.1 A Note on Terminology.........................................4
 3 Extending the MIB.................................................5
   3.1 Motivation for AgentX.........................................5
 4 AgentX Framework..................................................6
   4.1 AgentX Roles..................................................7
   4.2 Applicability.................................................8
   4.3 Design Features of AgentX.....................................9
   4.4 Non-Goals....................................................10
 5 AgentX Encodings.................................................10
   5.1 Object Identifier............................................11
   5.2 SearchRange..................................................13
   5.3 Octet String.................................................14
   5.4 Value Representation.........................................14
 6 Protocol Definitions.............................................16
   6.1 AgentX PDU Header............................................16

Daniele, et. al. Standards Track [Page 1] RFC 2257 AgentX January 1998

     6.1.1 Context..................................................19
   6.2 AgentX PDUs..................................................20
     6.2.1 The agentx-Open-PDU......................................20
     6.2.2 The agentx-Close-PDU.....................................21
     6.2.3 The agentx-Register-PDU..................................22
     6.2.4 The agentx-Unregister-PDU................................25
     6.2.5 The agentx-Get-PDU.......................................27
     6.2.6 The agentx-GetNext-PDU...................................29
     6.2.7 The agentx-GetBulk-PDU...................................30
     6.2.8 The agentx-TestSet-PDU...................................31
     6.2.9 The agentx-CommitSet, -UndoSet, -CleanupSet
           PDUs.....................................................33
     6.2.10 The agentx-Notify-PDU...................................33
     6.2.11 The agentx-Ping-PDU.....................................34
     6.2.12 The agentx-IndexAllocate-PDU............................35
     6.2.13 The agentx-IndexDeallocate-PDU..........................36
     6.2.14 The agentx-AddAgentCaps-PDU.............................37
     6.2.15 The agentx-RemoveAgentCaps-PDU..........................38
     6.2.16 The agentx-Response-PDU.................................39
 7 Elements of Procedure............................................41
   7.1 Processing AgentX Administrative Messages....................42
     7.1.1 Processing the agentx-Open-PDU...........................42
     7.1.2 Processing the agentx-IndexAllocate-PDU..................43
     7.1.3 Using the agentx-IndexAllocate-PDU.......................45
     7.1.4 Processing the agentx-IndexDeallocate-PDU................47
     7.1.5 Processing the agentx-Register-PDU.......................48
       7.1.5.1 Handling Duplicate OID Ranges........................50
     7.1.6 Processing the agentx-Unregister-PDU.....................51
     7.1.7 Processing the agentx-AddAgentCaps-PDU...................51
     7.1.8 Processing the agentx-RemoveAgentCaps-PDU................52
     7.1.9 Processing the agentx-Close-PDU..........................52
     7.1.10 Detecting Connection Loss...............................53
     7.1.11 Processing the agentx-Notify-PDU........................53
     7.1.12 Processing the agentx-Ping-PDU..........................54
   7.2 Processing Received SNMP Protocol Messages...................54
     7.2.1 Dispatching AgentX PDUs..................................55
       7.2.1.1 agentx-Get-PDU.......................................57
       7.2.1.2 agentx-GetNext-PDU...................................58
       7.2.1.3 agentx-GetBulk-PDU...................................59
       7.2.1.4 agentx-TestSet-PDU...................................60
       7.2.1.5 Dispatch.............................................60
     7.2.2 Subagent Processing of agentx-Get, GetNext,
           GetBulk-PDUs.............................................61
       7.2.2.1 Subagent Processing of the agentx-Get-PDU............61
       7.2.2.2 Subagent Processing of the
               agentx-GetNext-PDU...................................62

Daniele, et. al. Standards Track [Page 2] RFC 2257 AgentX January 1998

       7.2.2.3 Subagent Processing of the
               agentx-GetBulk-PDU...................................62
     7.2.3 Subagent Processing of agentx-TestSet,
           -CommitSet, -UndoSet, -CleanupSet-PDUs...................63
       7.2.3.1 Subagent Processing of the
               agentx-TestSet-PDU...................................64
       7.2.3.2 Subagent Processing of the
               agentx-CommitSet-PDU.................................65
       7.2.3.3 Subagent Processing of the
               agentx-UndoSet-PDU...................................65
       7.2.3.4 Subagent Processing of the
               agentx-CleanupSet-PDU................................65
     7.2.4 Master Agent Processing of AgentX Responses..............66
       7.2.4.1 Common Processing of All AgentX Response
               PDUs.................................................66
       7.2.4.2 Processing of Responses to agentx-Get-PDUs...........66
       7.2.4.3 Processing of Responses to
               agentx-GetNext-PDU and agentx-GetBulk-PDU............67
       7.2.4.4 Processing of Responses to
               agentx-TestSet-PDUs..................................68
       7.2.4.5 Processing of Responses to
               agentx-CommitSet-PDUs................................68
       7.2.4.6 Processing of Responses to
               agentx-UndoSet-PDUs..................................69
     7.2.5 Sending the SNMP Response-PDU............................69
     7.2.6 MIB Views................................................69
   7.3 State Transitions............................................70
     7.3.1 Set Transaction States...................................70
     7.3.2 Transport Connection States..............................71
     7.3.3 Session States...........................................73
 8 Transport Mappings...............................................74
   8.1 AgentX over TCP..............................................74
     8.1.1 Well-known Values........................................74
     8.1.2 Operation................................................74
   8.2 AgentX over UNIX-domain Sockets..............................75
     8.2.1 Well-known Values........................................75
     8.2.2 Operation................................................75
 9 Security Considerations..........................................76
 10 Acknowledgements................................................77
 11 Authors' and Editor's Addresses.................................77
 12 References......................................................78
 13 Full Copyright Statement........................................80

Daniele, et. al. Standards Track [Page 3] RFC 2257 AgentX January 1998

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

Daniele, et. al. Standards Track [Page 4] RFC 2257 AgentX January 1998

 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
 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 nor version 2 framework describes how the
 set of managed objects supported by a particular agent may be changed
 dynamically.

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
  1. a "master" agent that is available on the standard transport

address and that accepts SNMP protocol messages

  1. a set of "subagents" that each contain management

instrumentation

  1. 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.
  1. 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.

Daniele, et. al. Standards Track [Page 5] RFC 2257 AgentX January 1998

 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.
 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
  1. 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.
  1. 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.

Daniele, et. al. Standards Track [Page 6] RFC 2257 AgentX January 1998

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

4.1. AgentX Roles

 An entity acting in a master agent role performs the following
 functions:
  1. Accepts AgentX session establishment requests from subagents.
  1. Accepts registration of MIB regions by subagents.
  1. Sends and accepts SNMP protocol messages on the agent's

specified transport addresses.

  1. 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.)
  1. Provides instrumentation for the MIB objects defined in RFC

1907 [5], and for any MIB objects relevant to any administrative

      framework it supports.
  1. Sends and receives AgentX protocol messages to access

management information, based on the current registry of MIB

      regions.
  1. Forwards notifications on behalf of subagents.
 An entity acting in a subagent role performs the following functions:
  1. Initiates an AgentX session with the master agent.
  1. Registers MIB regions with the master agent.
  1. Instantiates managed objects.
  1. Binds OIDs within its registered MIB regions to actual

variables.

  1. Performs management operations on variables.
  1. Initiates notifications.

Daniele, et. al. Standards Track [Page 7] RFC 2257 AgentX January 1998

4.2 Applicability

 It is intended that this memo 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.

Daniele, et. al. Standards Track [Page 8] RFC 2257 AgentX January 1998

 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).
 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
    (for the MIB variables it instantiates).  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.

Daniele, et. al. Standards Track [Page 9] RFC 2257 AgentX January 1998

 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 communication than a
    traditional communications protocol.
    Some of the design decisions made with this in mind include:
  1. 32-bit alignment of data within PDUs
  1. Native byte-order encoding by subagents
  1. 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 development 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.

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

Daniele, et. al. Standards Track [Page 10] RFC 2257 AgentX January 1998

 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                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 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.

Daniele, et. al. Standards Track [Page 11] RFC 2257 AgentX January 1998

    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.
 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                                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Daniele, et. al. Standards Track [Page 12] RFC 2257 AgentX January 1998

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.
 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.

Daniele, et. al. Standards Track [Page 13] RFC 2257 AgentX January 1998

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.

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

Daniele, et. al. Standards Track [Page 14] RFC 2257 AgentX January 1998

 (v.data)
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       data                                    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       data                                    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 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:
  1. 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.
  1. 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.

Daniele, et. al. Standards Track [Page 15] RFC 2257 AgentX January 1998

  1. Object Identifiers are encoded as described in section

5.1, Object Identifier.

  1. 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).
  1. 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 memo).

Daniele, et. al. Standards Track [Page 16] RFC 2257 AgentX January 1998

    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),
            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.

Daniele, et. al. Standards Track [Page 17] RFC 2257 AgentX January 1998

       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 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.

Daniele, et. al. Standards Track [Page 18] RFC 2257 AgentX January 1998

    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.
    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.

Daniele, et. al. Standards Track [Page 19] RFC 2257 AgentX January 1998

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)   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 An agentx-Open-PDU contains the following fields:

Daniele, et. al. Standards Track [Page 20] RFC 2257 AgentX January 1998

    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>                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 An agentx-Close-PDU contains the following field:

Daniele, et. al. Standards Track [Page 21] RFC 2257 AgentX January 1998

    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.

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

Daniele, et. al. Standards Track [Page 22] RFC 2257 AgentX January 1998

  (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               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 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).

Daniele, et. al. Standards Track [Page 23] RFC 2257 AgentX January 1998

    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.
    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):

Daniele, et. al. Standards Track [Page 24] RFC 2257 AgentX January 1998

 (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                                                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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.

Daniele, et. al. Standards Track [Page 25] RFC 2257 AgentX January 1998

 (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.priority   | 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               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 An agentx-Unregister-PDU contains the following fields:

Daniele, et. al. Standards Track [Page 26] RFC 2257 AgentX January 1998

    u.context
       An optional non-default context.
    u.priority
       The priority at which this region was originally registered.
    u.region
       Indicates a previously-registered region of the MIB that a
       subagent no longer wishes to support.

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

Daniele, et. al. Standards Track [Page 27] RFC 2257 AgentX January 1998

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

Daniele, et. al. Standards Track [Page 28] RFC 2257 AgentX January 1998

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

Daniele, et. al. Standards Track [Page 29] RFC 2257 AgentX January 1998

  ...
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |             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                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  ...

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

Daniele, et. al. Standards Track [Page 30] RFC 2257 AgentX January 1998

  (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) as in agentx-GetNext-PDU above
  ...

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)

Daniele, et. al. Standards Track [Page 31] RFC 2257 AgentX January 1998

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

Daniele, et. al. Standards Track [Page 32] RFC 2257 AgentX January 1998

    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.

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:

Daniele, et. al. Standards Track [Page 33] RFC 2257 AgentX January 1998

    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:
  1. If the subagent supplies sysUpTime.0, it must be

present as the first varbind.

  1. snmpTrapOID.0 must be present, as the second

varbind if sysUpTime.0 was supplied, as the first if it

             was not.

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:

Daniele, et. al. Standards Track [Page 34] RFC 2257 AgentX January 1998

    p.context
       An optional non-default context.
 Using p.context a subagent can retrieve the sysUpTime value for a
 specific context, if required.

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.

Daniele, et. al. Standards Track [Page 35] RFC 2257 AgentX January 1998

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

6.2.13. The agentx-IndexDeallocate-PDU

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

Daniele, et. al. Standards Track [Page 36] RFC 2257 AgentX January 1998

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

Daniele, et. al. Standards Track [Page 37] RFC 2257 AgentX January 1998

  ...
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |  Octet L - 1  |  Octet L      |       Optional Padding        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 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.

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

Daniele, et. al. Standards Track [Page 38] RFC 2257 AgentX January 1998

 (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                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 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                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Daniele, et. al. Standards Track [Page 39] RFC 2257 AgentX January 1998

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        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
       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)

Daniele, et. al. Standards Track [Page 40] RFC 2257 AgentX January 1998

       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
       section 5.4, Value Representation, the index values of variable
       bindings within a variable binding list are 1-based.)
 A VarBindList 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.

Daniele, et. al. Standards Track [Page 41] RFC 2257 AgentX January 1998

 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 (the coordinated actions of a
        master agent and one or more subagents in processing, for
        example, a received SNMP GetRequest-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.

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.

Daniele, et. al. Standards Track [Page 42] RFC 2257 AgentX January 1998

 4) The master agent retains session-specific information
    from the PDU for this subagent:
  1. 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 the h.flag NETWORK_BYTE_ORDER bit
       in the PDU, but does not need to toggle its retained value for
       the session if the subagent varies its byte ordering.
  1. The o.timeout value is used in calculating response

timeout conditions for this subagent.

  1. 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 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'.

Daniele, et. al. Standards Track [Page 43] RFC 2257 AgentX January 1998

 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:
  1. v.name is the name of the index for which a value is to be

allocated.

  1. v.type is the syntax of the index object.
  1. 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'.
    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'.

Daniele, et. al. Standards Track [Page 44] RFC 2257 AgentX January 1998

    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
  1. a specific index value - an index value that is not currently

allocated - an index value that has never been allocated

 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 System Application MIB [13]).  The need
 for subagents to share tables using such indexes is the main
 motivation for index allocation in AgentX.

Daniele, et. al. Standards Track [Page 45] RFC 2257 AgentX January 1998

 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.
    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.

Daniele, et. al. Standards Track [Page 46] RFC 2257 AgentX January 1998

    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 deallocation 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:
  1. v.name is the name of the index for which a value is to be

released

  1. v.type is the syntax of the index object
  1. 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 is
       set to `indexNotAllocated'.

Daniele, et. al. Standards Track [Page 47] RFC 2257 AgentX January 1998

 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 registration 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.

Daniele, et. al. Standards Track [Page 48] RFC 2257 AgentX January 1998

    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.
  1. 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)

Daniele, et. al. Standards Track [Page 49] RFC 2257 AgentX January 1998

  1. 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
       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) results in  a duplicate OID range, the
 master agent selects one to use, termed the 'authoritative region',
 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.

Daniele, et. al. Standards Track [Page 50] RFC 2257 AgentX January 1998

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 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 unregistration fails.  Otherwise:  The value of
    res.sysUpTime is set to the value of sysUpTime.0 for the indicated
    context.
 4) If u.region, u.priority, 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:
  1. 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.

Daniele, et. al. Standards Track [Page 51] RFC 2257 AgentX January 1998

 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 operation 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 operation 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.

Daniele, et. al. Standards Track [Page 52] RFC 2257 AgentX January 1998

 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.
  1. All MIB regions that have been registered during this session

are unregistered, as described in 7.1.6.

  1. All index values allocated during this session are freed, as

described in section 7.1.4.

  1. 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.

Daniele, et. al. Standards Track [Page 53] RFC 2257 AgentX January 1998

 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.

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.)

Daniele, et. al. Standards Track [Page 54] RFC 2257 AgentX January 1998

 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 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:
  1. The object identifier does not lexicographically precede

the range.

  1. 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).

Daniele, et. al. Standards Track [Page 55] RFC 2257 AgentX January 1998

 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 choose to "scope" the possible instances
    returned by a subagent by specifying an ending OID in the
    SearchRange.  If such scoping is used, typically the ending OID
    would be the first lexicographical successor to the target OID
    range that was registered by a subagent other than the target
    subagent.  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.

Daniele, et. al. Standards Track [Page 56] RFC 2257 AgentX January 1998

       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
          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 SNMP 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 authoritative region that
     contains the binding's name.

Daniele, et. al. Standards Track [Page 57] RFC 2257 AgentX January 1998

 (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:
  1. 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.
  1. The variable binding's name is encoded into the starting OID.
  1. The ending OID is encoded as null.

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

Daniele, et. al. Standards Track [Page 58] RFC 2257 AgentX January 1998

  1. 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.
  1. if (1a) applies, the variable binding's name is encoded

into the starting OID, and the OID's "include" field is set to

        0.
  1. 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 authoritative target OID range and target session,
     exactly as described for the agentx-GetNext-PDU (see 7.2.1.2).
 (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:
  1. 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.

Daniele, et. al. Standards Track [Page 59] RFC 2257 AgentX January 1998

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 SNMP 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 authoritative 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:
  1. 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).

Daniele, et. al. Standards Track [Page 60] RFC 2257 AgentX January 1998

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.
 (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.

Daniele, et. al. Standards Track [Page 61] RFC 2257 AgentX January 1998

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:
  1. if the "include" field of the starting OID is 0, the

variable's name is the closest lexicographical successor to the

       starting OID.
  1. 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.
  1. 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,
    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:

Daniele, et. al. Standards Track [Page 62] RFC 2257 AgentX January 1998

    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:
  1. 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.)
  1. 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
  1. For any iteration i, all s values of v.type are

`endOfMibView'.

  1. An AgentX transport constraint or other

implementation-specific constraint is reached.

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

  1. 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.

Daniele, et. al. Standards Track [Page 63] RFC 2257 AgentX January 1998

 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)
 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.

Daniele, et. al. Standards Track [Page 64] RFC 2257 AgentX January 1998

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.

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.

Daniele, et. al. Standards Track [Page 65] RFC 2257 AgentX January 1998

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
     `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).

Daniele, et. al. Standards Track [Page 66] RFC 2257 AgentX January 1998

 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.
     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.

Daniele, et. al. Standards Track [Page 67] RFC 2257 AgentX January 1998

 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.
 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.
 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.

Daniele, et. al. Standards Track [Page 68] RFC 2257 AgentX January 1998

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.

Daniele, et. al. Standards Track [Page 69] RFC 2257 AgentX January 1998

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

Daniele, et. al. Standards Track [Page 70] RFC 2257 AgentX January 1998

 Note that a single PDU sequence may result in multiple paths through
 the finite state machine (FSM).  For example, the sequence
    TestSet CommitSet UndoSet
 may walk through either of these two state sequences:
    (initial) TestOK CommitOK   (done)
    (initial) TestOK CommitFail (done)

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:

Daniele, et. al. Standards Track [Page 71] RFC 2257 AgentX January 1998

                              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
 ----------------+--------------+--------------

Daniele, et. al. Standards Track [Page 72] RFC 2257 AgentX January 1998

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
 ---------------+-------------+----------------
 (continued next page)

Daniele, et. al. Standards Track [Page 73] RFC 2257 AgentX January 1998

  1. ————–+————-+—————-

Receive | | 7.1.2

 IndexAllocate  |      X      |
 PDU            |             |    ->B
 ---------------+-------------+----------------
 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.

Daniele, et. al. Standards Track [Page 74] RFC 2257 AgentX January 1998

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.
 Mapping AgentX to this transport is useful for environments that
  1. wish to guarantee subagents are running on the same

managed node as the master agent, and where

  1. 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).

Daniele, et. al. Standards Track [Page 75] RFC 2257 AgentX January 1998

 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
       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.

Daniele, et. al. Standards Track [Page 76] RFC 2257 AgentX January 1998

10. Acknowledgements

 The initial development 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.
 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

Daniele, et. al. Standards Track [Page 77] RFC 2257 AgentX January 1998

 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] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,

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

[3] 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] 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] 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, March 1994.

[8] 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 D. Levi, "V2ToV1: Mapping SNMPv2 onto SNMPv1

   Within a Bilingual SNMP Agent", RFC 2089, January 1997.

Daniele, et. al. Standards Track [Page 78] RFC 2257 AgentX January 1998

[10] 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] McCloghrie, K. and F. Kastenholz, "Evolution of the

   Interfaces Group of MIB-II", RFC 1573, January 1994.

[12] Case, J., "FDDI Management Information Base", RFC 1285,

   January 1992.

[13] Application MIB Working Group, Krupczak, C., and J. Saperia,

   "Definitions of System-Level Managed Objects for Applications",
   draft-ietf-applmib-sysapplmib-08.txt, 15 Apr 1997.

Daniele, et. al. Standards Track [Page 79] RFC 2257 AgentX January 1998

13. Full Copyright Statement

 Copyright (C) The Internet Society (1998).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Daniele, et. al. Standards Track [Page 80]

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