RFC2257 - Agent Extensibility (AgentX) Protocol Version 1

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.

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

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

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

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 RFC1902 [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 (RFC1903

[3]). The term "variable binding" normally refers to the pairing of

the name of a variable and its associated value. However, if certain

kinds of exceptional conditions occur during processing of a

retrieval request, a variable binding will pair a name and an

indication of that exception.

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

The name of a variable is an OBJECT IDENTIFIER, which is the

concatenation of the OBJECT IDENTIFIER of the corresponding object

type together with an OBJECT IDENTIFIER fragment identifying the

instance. The OBJECT IDENTIFIER of the corresponding object-type is

called the OBJECT IDENTIFIER prefix of the variable. For the purpose

of eXPosition, the original Internet-standard

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

- a "master" agent that is available on the standard transport

address and that accepts SNMP protocol messages

- a set of "subagents" that each contain management

instrumentation

- a protocol that operates between the master agent and subagents,

permitting subagents to "connect" to the master agent, and the

master agent to multiplex received SNMP protocol messages

amongst the subagents.

- a set of tools to aid subagent development, and a runtime (API)

environment that hides much of the protocol operation between a

subagent and the master agent.

The wide deployment of extensible SNMP agents, coupled with the lack

of Internet standards in this area, makes it difficult to field

SNMP-manageable applications. A vendor may have to support several

different subagent environments (APIs) in order to support different

target platforms.

It can also become quite cumbersome to configure subagents and

(possibly multiple) master agents on a particular managed node.

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

- a single processing entity called the master agent, which sends

and receives SNMP protocol messages in an agent role (as

specified by the SNMP version 1 and version 2 framework

documents) but typically has little or no direct access to

management information.

- 0 or more processing entities called subagents, which are

"shielded" from the SNMP protocol messages processed by the

master agent, but which have access to management information.

The master and subagent entities communicate via AgentX protocol

messages, as specified in this memo. Other interfaces (if any) on

these entities, and their associated protocols, are outside the scope

of this document. While some of the AgentX protocol messages appear

similar in syntax and semantics to the SNMP, bear in mind that AgentX

is not SNMP.

The internal operations of AgentX are invisible to an SNMP entity

operating in a manager role. From a manager's point of view, an

extensible agent behaves exactly as would a non-extensible

(monolithic) agent that has access to the same management

instrumentation.

This transparency to managers is a fundamental requirement of AgentX,

and is what differentiates AgentX subagents from SNMP proxy agents.

4.1. AgentX Roles

An entity acting in a master agent role performs the following

functions:

- Accepts AgentX session establishment requests from subagents.

- Accepts registration of MIB regions by subagents.

- Sends and accepts SNMP protocol messages on the agent's

specified transport addresses.

- Implements the agent role Elements of Procedure specified

for the administrative framework applicable to the SNMP protocol

message, except where they specify performing management

operations. (The application of MIB views, and the access

control policy for the managed node, are implemented by the

master agent.)

- Provides instrumentation for the MIB objects defined in RFC

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

framework it supports.

- Sends and receives AgentX protocol messages to access

management information, based on the current registry of MIB

regions.

- Forwards notifications on behalf of subagents.

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

- Initiates an AgentX session with the master agent.

- Registers MIB regions with the master agent.

- Instantiates managed objects.

- Binds OIDs within its registered MIB regions to actual

variables.

- Performs management operations on variables.

- Initiates notifications.

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

the nature of the MIB's index structure. Examples include

registering ipNetToMediaEntry.n, where n represents the ifIndex

value for an interface implemented by the subagent, and

tcpConnEntry.a.b.c.d, where a.b.c.d represents an IP address on an

interface implemented by the subagent.

AgentX supports these three common configurations, and all

permutations of them, completely. The consensus is that they

comprise a very large majority of current and likely future uses of

multi-vendor extensible agent configurations.

4) Subagents implement rows in "complex tables". Complex tables

here are defined as tables permitting row creation, or whose MIB

also defines an object that counts entries in the table. Examples

include the MIB-2 ifTable (due to ifNumber), and the RMON

historyControlTable.

The subagent that implements such a counter object (like ifNumber)

must go beyond AgentX to correctly implement it. This is an

implementation issue (and most new MIB designs no longer include such

objects).

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.

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:

- 32-bit alignment of data within PDUs

- Native byte-order encoding by subagents

- Large AgentX PDU payload sizes.

4.4 Non-Goals

1) Subagent-to-subagent communication. This is out of scope,

due to the security ramifications and complexity involved.

2) Subagent access (via the master agent) to MIB variables.

This is not addressed, since various other mechanisms are

available and it was not a fundamental requirement.

3) The ability to accommodate every conceivable extensible

agent configuration option. This was the most contentious ASPect

in the 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

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.

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

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

1.2.3.4

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

4 0 0 0

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

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

(start)

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

3 2 1 0

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

(end)

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

4 2 0 0

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

A SearchRangeList is a contiguous list of SearchRanges.

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

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

(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:

- Integer, Counter32, Gauge32, and TimeTicks are encoded as

4 contiguous bytes. If the NETWORK_BYTE_ORDER bit is set

in h.flags, the bytes are ordered most significant to least

significant, otherwise they are ordered least significant

to most significant.

- Counter64 is encoded as 8 contiguous bytes. If the

NETWORK_BYTE_ORDER bit is set in h.flags, the bytes are

ordered most significant to least significant, otherwise

they are ordered least significant to most significant.

- Object Identifiers are encoded as described in section

5.1, Object Identifier.

- IpAddress, Opaque, and Octet String are all octet strings

and are encoded as described in section 5.3, Octet String.

Value data always follows v.name whenever v.type is one

of the above types. These data bytes are present even if

they will not be used (as, for example, in certain types

of index allocation).

- 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).

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.

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-

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 RFC1905 [4]), nor

can it be, since a master agent might receive SNMP requests

with the same request-ids from different managers.

The transaction ID has no significance and no defined value in

AgentX administrative PDUs, i.e., AgentX PDUs that are not

associated with an SNMP management request.

h.packetID

A packet ID generated by the sender for all AgentX PDUs except

the agentx-Response-PDU. In an agentx-Response-PDU, the packet

ID must be the same as that in the received AgentX PDU to which

it is a response. A master agent might use this field to

associate subagent response PDUs with their corresponding

request PDUs. A subagent might use this field to correlate

responses to multiple (batched) registrations.

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.

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:

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:

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

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

(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).

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):

(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>

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

(r.upper_bound)

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

6.2.4. The agentx-Unregister-PDU

The agentx-Unregister-PDU is sent by a subagent to remove a

previously registered MIB region from the master agent's OID space.

(AgentX header)

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

h.version (1) h.type (4) h.flags <reserved>

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

h.sessionID

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

h.transactionID

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

h.packetID

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

h.payload_length

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

(u.context) OPTIONAL

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

Octet String Length (L)

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

Octet 1 Octet 2 Octet 3 Octet 4

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

...

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

Octet L - 1 Octet L Padding (as required)

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

<reserved> u.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:

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

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

...

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

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.

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

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

...

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

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

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

(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)

(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.

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:

n.context

An optional non-default context.

n.vb

A VarBindList whose contents define the actual PDU to be sent.

This memo places the following restrictions on its contents:

- If the subagent supplies sysUpTime.0, it must be

present as the first varbind.

- snmpTrapOID.0 must be present, as the second

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

was not.

6.2.11 The agentx-Ping-PDU

The agentx-Ping-PDU is sent by a subagent to the master agent to

monitor the master agent's ability to receive and send AgentX PDUs

over their AgentX session.

(AgentX header)

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

h.version (1) h.type (13) h.flags <reserved>

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

h.sessionID

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

h.transactionID

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

h.packetID

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

h.payload_length

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

(p.context) OPTIONAL

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

Octet String Length (L)

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

Octet 1 Octet 2 Octet 3 Octet 4

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

...

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

Octet L - 1 Octet L Padding (as required)

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

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

p.context

An optional non-default context.

Using p.context a subagent can retrieve the sysUpTime value for a

specific context, if required.

6.2.12. The agentx-IndexAllocate-PDU

An agentx-IndexAllocate-PDU is sent by a subagent to request

allocation of a value for specific index objects. Refer to section

7.1.3 (Using the agentx-IndexAllocate-PDU) for suggested usage.

(AgentX header)

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

h.version (1) h.type (14) h.flags <reserved>

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

h.sessionID

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

h.transactionID

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

h.packetID

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

h.payload_length

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

(i.context) OPTIONAL

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

Octet String Length (L)

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

Octet 1 Octet 2 Octet 3 Octet 4

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

...

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

Octet L - 1 Octet L Padding (as required)

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

(i.vb)

...

An agentx-IndexAllocate-PDU contains the following fields:

i.context

An optional non-default context.

i.vb

A VarBindList containing the index names and values requested

for allocation.

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.

6.2.14. The agentx-AddAgentCaps-PDU

An agentx-AddAgentCaps-PDU is generated by a subagent to inform the

master agent of its agent capabilities.

(AgentX header)

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

h.version (1) h.type (16) h.flags <reserved>

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

h.sessionID

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

h.transactionID

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

h.packetID

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

h.payload_length

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

(a.context) (OPTIONAL)

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

Octet String Length (L)

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

Octet 1 Octet 2 Octet 3 Octet 4

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

...

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

Octet L - 1 Octet L Optional Padding

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

(a.id)

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

n_subid prefix 0 <reserved>

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

sub-identifier #1

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

...

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

sub-identifier #n_subid

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

(a.descr)

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

Octet String Length (L)

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

Octet 1 Octet 2 Octet 3 Octet 4

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

...

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

Octet L - 1 Octet L Optional Padding

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

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 RFC1904 [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

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

(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

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

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)

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 (RFC1905

[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.

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.

4) The master agent retains session-specific information

from the PDU for this subagent:

- The NETWORK_BYTE_ORDER value in h.flags is retained.

All subsequent AgentX protocol operations initiated by the

master agent for this session must use this byte ordering and

set this bit accordingly.

The subagent typically sets this bit to correspond to its

native byte ordering, and typically does not vary byte ordering

for an initiated session. The master agent must be able to

decode each PDU according to 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.

- The o.timeout value is used in calculating response

timeout conditions for this subagent.

- The o.id and o.descr fields are used for informational

purposes. (Such purposes are implementation-specific for now,

and may be used in a possible future standard AgentX MIB.)

5) The agentx-Response-PDU is sent with the res.error field

set to `noError'.

At this point, an AgentX session is considered established between

the master agent and the subagent. An AgentX session is a distinct

channel for the exchange of AgentX protocol messages between a master

agent and one subagent, qualified by the session-specific attributes

listed in 4) above. AgentX session establishment is initiated by the

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

agent or the subagent.

7.1.2. Processing the agentx-IndexAllocate-PDU

When the master agent receives an agentx-IndexAllocate-PDU, it

processes it as follows:

1) An agentx-Response-PDU is created and res.sysUpTime is set to

the value of sysUpTime.0 for the default context.

2) If h.sessionID does not correspond to a currently established

session with this subagent, the agentx-Response-PDU is sent in

reply with res.error set to `notOpen'.

3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent

supports only a default context, the agentx-Response-PDU is

returned with res.error set to `unsupportedContext', and the

requested allocation fails. Otherwise: The value of res.sysUpTime

is set to the value of sysUpTime.0 for the indicated context.

4) Each VarBind in the VarBindList is processed until either all

are successful, or one fails. If any VarBind fails, the agentx-

Response-PDU is sent in reply containing the original VarBindList,

with res.index set to indicate the failed VarBind, and with

res.error set as described subsequently. All other VarBinds are

ignored; no index values are allocated.

VarBinds are processed as follows:

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

allocated.

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

- v.data indicates the specific index value requested.

If the NEW_INDEX or the ANY_INDEX bit is set, the actual value

in v.data is ignored and an appropriate index value is

generated.

a) If there are no currently allocated index values for v.name

in the indicated context, and v.type does not correspond to a

valid index type value, the VarBind fails and res.error is set

to `indexWrongType'.

b) If there are currently allocated index values for v.name

in the indicated context, but the syntax of those values does

not match v.type, the VarBind fails and res.error is set to

`indexWrongType'.

c) Otherwise, if both the NEW_INDEX and ANY_INDEX bits are

clear, allocation of a specific index value is being requested.

If the requested index is already allocated for v.name in the

indicated context, the VarBind fails and res.error is set to

`indexAlreadyAllocated'.

d) Otherwise, if the NEW_INDEX bit is set, the master agent

should generate the next available index value for v.name in

the indicated context, with the constraint that this value must

not have been allocated (even if subsequently released) to any

subagent since the last re-initialization of the master agent.

If no such value can be generated, the VarBind fails and

res.error is set to `indexNoneAvailable'.

e) Otherwise, if the ANY_INDEX bit is set, the master agent

should generate an index value for v.name in the indicated

context, with the constraint that this value is not currently

allocated to any subagent. If no such value can be generated,

then the VarBind fails and res.error is set to

`indexNoneAvailable'.

5) If all VarBinds are processed successfully, the

agentx-Response-PDU is sent in reply with res.error set to

`noError'. A VarBindList is included that is identical to the one

sent in the agentx-IndexAllocate-PDU, except that VarBinds

requesting a NEW_INDEX or ANY_INDEX value are generated with an

appropriate value.

7.1.3. Using the agentx-IndexAllocate-PDU

Index allocation is a service provided by an AgentX master agent. It

provides generic support for sharing MIB conceptual tables among

subagents who are assumed to have no knowledge of each other.

Each subagent sharing a table should first request allocation of

index values, then use those index values to qualify MIB regions in

its subsequent registrations.

The master agent maintains a database of index objects (OIDs), and,

for each index, the values that have been allocated for it. It is

unaware of what MIB variables (if any) the index objects represent.

By convention, subagents use the MIB variable listed in the INDEX

clause as the index object for which values must be allocated. For

tables indexed by multiple variables, values may be allocated for

each index (although this is frequently unnecessary; see example 2

below). The subagent may request allocation of

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

allocated - an index value that has never been allocated

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 (RFC1573 [11]),

snmpFddiSMTIndex in the FDDI MIB (RFC1285 [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.

Example 1:

A subagent implements an interface, and wishes to register a

single row of the RFC1573 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.

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:

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

released

- v.type is the syntax of the index object

- v.data indicates the specific index value to be released.

The NEW_INDEX and ANY_INDEX bits are ignored.

a) If the index value for the named index is not currently

allocated to this subagent, the VarBind fails and res.error is

set to `indexNotAllocated'.

5) If all VarBinds are processed successfully, res.error is

set to `noError' and the agentx-Response-PDU is sent. A

VarBindList is included which is identical to the one sent in the

agentx-IndexDeallocate-PDU.

All released index values are now available, and may be used in

response to subsequent allocation requests for ANY_INDEX values

for the particular index.

7.1.5. Processing the agentx-Register-PDU

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

it as follows:

1) An agentx-Response-PDU is created and res.sysUpTime is set to

the value of sysUpTime.0 for the default context.

2) If h.sessionID does not correspond to a currently

established session with this subagent, the agentx-Response-PDU is

sent in reply with res.error set to `notOpen'.

3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent

supports only a default context, the agentx-Response-PDU is

returned with res.error set to `unsupportedContext', and the

requested 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.

Otherwise this region is to be logically registered within the

default context.

A registration that would result in a duplicate region with the

same priority and within the same context as that of a current

registration is termed a duplicate registration.

5) Otherwise, if this is a duplicate registration, the

agentx-Response-PDU is returned with res.error set to

`duplicateRegistration', and the requested registration fails.

6) Otherwise, the agentx-Response-PDU is returned with res.error

set to `noError'.

The master agent adds this region to its registered OID space for

the indicated context, to be considered during the dispatching

phase for subsequently received SNMP protocol messages.

Note: The following algorithm describes maintaining a set of OID

ranges derived from "splitting" registered regions. The algorithm

for operational dispatching is also stated in terms of these OID

ranges.

These OID ranges are a useful explanatory device, but are not

required for a correct implementation.

- If r.region (R1) is a subtree of a currently registered

region (R2), split R2 into 3 new regions (R2a, R2b, and R2c)

such that R2b is an exact duplicate of R1. Now remove R2 and

add R1, R2a, R2b, and R2c to the master agent's

lexicographically ordered set of ranges (the registered OID

space). Note: Though newly-added ranges R1 and R2b are

identical in terms of the MIB objects they contain, they are

registered by different subagents, possibly at different

priorities.

For instance, if subagent S2 registered "ip" (R2 is

1.3.6.1.2.1.4) and subagent S1 subsequently registered

"ipNetToMediaTable" (R1 is 1.3.6.1.2.1.4.22), the resulting set

of registered regions would be:

1.3.6.1.2.1.4 up to but not including 1.3.6.1.2.1.4.22 (by S2)

1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S2)

1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S1)

1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5 (by S2)

- If r.region (R1) overlaps one or more currently registered

regions, then for each overlapped region (R2) split R1 into 3

new ranges (R1a, R1b, R1c) such that R1b is an exact

duplicate of R2. Add R1b and R2 into the lexicographically

ordered set of regions. Apply (5) above iteratively to R1a and

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-

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.

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:

- The master agent removes u.region from its registered OID space

within the indicated context. If the original region had been

split, all such related regions are removed.

For instance, given the example registry above, if subagent S2

unregisters "ip", the resulting registry would be:

1.3.6.1.2.1 up to but not including 1.3.6.1.2.1.4 (by S3)

1.3.6.1.2.1.4 up to but not including 1.3.6.1.2.1.4.22 (by S3)

1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S1)

1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S3)

1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5 (by S3)

1.3.6.1.2.1.5 up to but not including 1.3.6.1.2.2 (by S3)

7.1.7. Processing the agentx-AddAgentCaps-PDU

When the master agent receives an agentx-AddAgentCaps-PDU, it

processes it as follows:

1) An agentx-Response-PDU is created and res.sysUpTime is set to

the value of sysUpTime.0 for the default context.

2) If h.sessionID does not correspond to a currently

established session with this subagent, the agentx-Response-PDU is

sent in reply with res.error set to `notOpen'.

3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent

supports only a default context, the agentx-Response-PDU is

returned with res.error set to `unsupportedContext', and the

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.

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.

- All MIB regions that have been registered during this session

are unregistered, as described in 7.1.6.

- All index values allocated during this session are freed, as

described in section 7.1.4.

- All sysORID values that were registered during this session

are removed, as described in section 7.1.8.

The master agent does not maintain state for closed sessions. If a

subagent wishes to re-establish a session after receiving an agentx-

Close-PDU, it needs to re-register MIB regions, agent capabilities,

etc.

7.1.10. Detecting Connection Loss

If a master agent is able to detect (from the underlying transport)

that a subagent cannot receive AgentX PDUs, it should close all

affected AgentX sessions as described in 7.1.9, step 3).

7.1.11. Processing the agentx-Notify-PDU

A subagent sending SNMPv1 trap information must map this into

(minimally) a value of snmpTrapOID.0, as described in 3.1.2 of RFC

1908 [8].

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

1) If h.sessionID does not correspond to a currently

established session with this subagent, an agentx-Response-PDU

is sent in reply with res.error set to `notOpen', and

res.sysUpTime set to the value of sysUpTime.0 for the indicated

context.

2) The VarBindList is parsed. If it does not contain a value for

sysUpTime.0, the master agent supplies the current value of

sysUpTime.0 for the indicated context. If the next VarBind

(either the first or second VarBind; see section 6.2.10.1) is

not snmpTrapOID.0, the master agent ceases further processing

of the notification.

3) Notifications are sent according to the implementation-specific

configuration of the master agent.

If SNMPv1 Trap PDUs are generated, the recommended mapping is

as described in RFC2089 [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 RFC1157 [6] that

apply to receiving entities. (For other versions of SNMP, the master

agent applies the access control policy defined in the Elements of

Procedure for those versions.)

In the SNMPv1 or v2c frameworks, the master agent uses the community

string as an index into a local repository of configuration

information that may include community profiles or more complex

context information.

If application of the access control policy results in a valid SNMP

request PDU, then an SNMP Response-PDU is constructed from

information gathered in the exchange of AgentX PDUs between the

master agent and one or more subagents. Upon receipt and initial

validation of an SNMP request PDU, a master agent uses the procedures

described below to dispatch AgentX PDUs to the proper subagents,

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

7.2.1. Dispatching AgentX PDUs

Upon receipt and initial validation of an SNMP request PDU, a master

agent uses the procedures described below to dispatch AgentX PDUs to

the proper subagents.

Note: In the following procedures, an object identifier is said to be

"contained" within an OID range when both of the following are true:

- The object identifier does not lexicographically precede

the range.

- The object identifier lexicographically precedes the end

of the range.

General Rules of Procedure

While processing a particular SNMP request, the master agent may send

one or more AgentX PDUs to one or more subagents. The following

rules of procedure apply in general to the AgentX master agent. PDU-

specific rules are listed in the applicable sections.

1) Honoring the registry

Because AgentX supports overlapping registrations, it is possible

for the master agent to obtain a value for a requested varbind

from within multiple registered MIB regions.

The master agent must ensure that the value (or exception)

actually returned in the SNMP response PDU is taken from the

authoritative region (as defined in section 7.1.5.1).

2) GetNext and GetBulk Processing

The master agent may choose to send agentx-Get-PDUs while

servicing an SNMP GetNextRequest-PDU. The master agent may choose

to send agentx-Get-PDUs or agentx-GetNext-PDUs while servicing an

SNMP GetBulkRequest-PDU. One possible reason for this would be if

the current iteration has targeted instance-level registrations.

The master agent may 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.

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.

(2) If no such OID range exists, the variable binding is not

processed further, and its value is set to `noSuchObject'.

(3) Identify the subagent session in which this region was

registered, termed the target session.

(4) If this is the first variable binding to be dispatched over

the target session in a request-response exchange entailed in the

processing of this management request:

- Create an agentx-Get-PDU for this session, with the header

fields initialized as described above (see 6.1 AgentX PDU

Header).

(5) Add a SearchRange to the end of the target session's PDU

for this variable binding.

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

- The ending OID is encoded as null.

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:

- Create an agentx-GetNext-PDU for the session, with

the header fields initialized as described above (see 6.1

AgentX PDU Header).

(5) Add a SearchRange to the end of the target session's

agentx-GetNext-PDU for this variable binding.

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

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

- 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 RFC1905 [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:

- Create an agentx-GetBulk-PDU for the session, with

the header fields initialized as described above (see 6.1

AgentX PDU Header).

(3) Add a SearchRange to the end of the target session's

agentx-GetBulk-PDU for this variable binding, as described for

the agentx-GetNext-PDU. If the variable binding was a non-

repeater in the original request PDU, it must be a non-repeater

in the agentx-GetBulk-PDU.

The value of g.max_repetitions in the agentx-GetBulk-PDU may be less

than (but not greater than) the value in the original request PDU.

The master agent may make such alterations due to simple sanity

checking, optimizations for the current iteration based on the

registry, the maximum possible size of a potential Response-PDU,

known constraints of the AgentX transport, or any other

implementation-specific constraint.

7.2.1.4. agentx-TestSet-PDU

AgentX employs test-commit-undo-cleanup phases to achieve "as if

simultaneous" semantics of the SNMP SetRequest-PDU within the

extensible agent. The initial phase involves the agentx-TestSet-PDU.

Each variable binding in the 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:

- create an agentx-TestSet-PDU for the session, with the

header fields initialized as described above (see 6.1 AgentX

PDU Header).

(5) Add a VarBind to the end of the target session's PDU

for this variable binding, as described in section 5.4.

Note that all VarBinds applicable to a given session must be sent in

a single agentx-TestSet-PDU.

7.2.1.5. Dispatch

A timeout value is calculated for each PDU to be sent, which is the

maximum value of the timeouts determined for each of the PDU's

SearchRanges (as described above in 7.2.1 Dispatching AgentX PDUs,

item 4). Each pending PDU is mapped (via its h.sessionID value) to a

particular transport domain/endpoint, as described in section 8

(Transport Mappings).

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

A conformant AgentX subagent must support the agentx-Get, -GetNext,

and -GetBulk PDUs, and must support multiple variables being supplied

in each PDU.

When a subagent receives an agentx-Get-, GetNext-, or GetBulk-PDU, it

performs the indicated management operations and returns an agentx-

Response-PDU.

The agentx-Response-PDU header fields are identical to the received

request PDU except that, at the start of processing, the subagent

initializes h.type to Response, res.error to `noError', res.index to

0, and the VarBindList to null.

Each SearchRange in the request PDU's SearchRangeList is processed as

described below, and a VarBind is added in the corresponding location

of the agentx-Response-PDU's VarbindList. If processing should fail

for any reason not described below, res.error is set to `genErr',

res.index to the index of the failed SearchRange, the VarBindList is

reset to null, and this agentx-Response-PDU is returned to the master

agent.

7.2.2.1. Subagent Processing of the agentx-Get-PDU

Upon the subagent's receipt of an agentx-Get-PDU, each SearchRange in

the request is processed as follows:

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

(2) If the starting OID exactly matches the name of a

variable instantiated by this subagent within the indicated

context and session, v.type and v.data are encoded to represent

the variable's syntax and value, as described in section 5.4,

Value Representation.

(3) Otherwise, if the starting OID does not match the object

identifier prefix of any variable instantiated within the

indicated context and session, the VarBind is set to

`noSuchObject', in the manner described in section 5.4, Value

Representation.

(4) Otherwise, the VarBind is set to `noSuchInstance'

in the manner described in section 5.4, Value Representation.

7.2.2.2. Subagent Processing of the agentx-GetNext-PDU

Upon the subagent's receipt of an agentx-GetNext-PDU, each

SearchRange in the request is processed as follows:

(1) The subagent searches for a variable within the

lexicographically ordered list of variable names for all

variables it instantiates (without regard to registration of

regions) within the indicated context and session, for which the

following are all true:

- if the "include" field of the starting OID is 0, the

variable's name is the closest lexicographical successor to the

starting OID.

- if the "include" field of the starting OID is 1, the

variable's name is either equal to, or the closest

lexicographical successor to, the starting OID.

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

lexicographically precedes the ending OID.

If all of these conditions are met, v.name is set to the located

variable's name. v.type and v.data are encoded to represent the

variable's syntax and value, as described in section 5.4, Value

Representation.

(2) If no such variable exists, v.name is set to the starting OID,

and the VarBind is set to `endOfMibView', in the manner described

in section 5.4, Value Representation.

7.2.2.3. Subagent Processing of the agentx-GetBulk-PDU

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

N equals g.non_repeaters,

M equals g.max_repetitions, and

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

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

GetNext-PDU.

If M and R are both non-zero, the remaining R SearchRanges are

processed iteratively to produce potentially many VarBinds. For each

iteration i, such that i is greater than zero and less than or equal

to M, and for each repeated SearchRange s, such that s is greater

than zero and less than or equal to R, the (N+((i-1)*R)+s)-th VarBind

is added to the agentx-Response-PDU as follows:

1) The subagent searches for a variable within the

lexicographically ordered list of variable names for all

variables it instantiates (without regard to registration of

regions) within the indicated context and session, for which

the following are all true:

- The variable's name is the (i)-th lexicographical successor

to the (N+s)-th requested OID.

(Note that if i is 0 and the "include" field is 1, the

variable's name may be equivalent to, or the first

lexicographical successor to, the (N+s)-th requested OID.)

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

lexicographically precedes the ending OID.

If all of these conditions are met, v.name is set to the

located variable's name. v.type and v.data are encoded to

represent the variable's syntax and value, as described in

section 5.4, Value Representation.

2) If no such variable exists, the VarBind is set to

`endOfMibView' as described in section 5.4, Value

Representation. v.name is set to v.name of the (N+((i-

2)*R)+s)-th VarBind unless i is currently 1, in which case it

is set to the value of the starting OID in the (N+s)-th

SearchRange.

Note that further iterative processing should stop if

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

`endOfMibView'.

- An AgentX transport constraint or other

implementation-specific constraint is reached.

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

-CleanupSet-PDUs

A conformant AgentX subagent must support the agentx-TestSet,

-CommitSet, -UndoSet, and -CleanupSet PDUs, and must support multiple

variables being supplied in each PDU.

These four PDUs are used to collectively perform the indicated

management operation. An agentx-Response-PDU is sent in reply to

each of the PDUs, to inform the master agent of the state of the

operation.

The agentx-Response-PDU header fields are identical to the received

request PDU except that, at the start of processing, the subagent

initializes h.type to Response, res.error to `noError', and res.index

to 0.

These Response-PDUs do not contain a VarBindList.

7.2.3.1. Subagent Processing of the agentx-TestSet-PDU

Upon the subagent's receipt of an agentx-TestSet-PDU, each VarBind in

the PDU is validated until they are all successful, or until one

fails, as described in section 4.2.5 of RFC1905 [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.

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 RFC1905 [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.

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).

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.

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.

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 RFC2089 [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.

7.3. State Transitions

State diagrams are presented from the master agent's perspective for

transport connection and session establishment, and from the

subagent's perspective for Set transaction processing.

7.3.1. Set Transaction States

The following table presents, from the subagent's perspective, the

state transitions involved in Set transaction processing:

STATE

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

A B C D E

(Initial TestOK Commit Test Commit

State) OK Fail Fail

EVENT

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

7.2.3.1

Receive All varbinds

TestSet OK? X X X X

PDU Yes ->B

No ->D

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

7.2.3.2

Receive NoError?

Commit- X Yes ->C X X X

Set PDU No ->E

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

Receive 7.2.3.3 7.2.4.5

UndoSet X X ->done X ->done

PDU

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

Receive 7.2.4.4 7.2.3.4 7.2.4.4

Cleanup- X ->done ->done ->done X

Set PDU

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

Session rollback undo

Loss ->done ->done ->done ->done ->done

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

There are three possible sequences that a subagent may follow for a

particular set transaction:

1) TestSet CommitSet CleanupSet

2) TestSet CommitSet UndoSet

3) TestSet CleanupSet

Note that a single PDU sequence may result in multiple paths through

the 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:

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

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

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

->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)

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

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.

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

- wish to guarantee subagents are running on the same

managed node as the master agent, and where

- sockets provide better performance than TCP or UDP,

especially in the presence of heavy network I/O

8.2.1. Well-known Values

The master agent creates a well-known UNIX-domain socket endpoint

called "/var/agentx/master". (It may create other, implementation-

specific endpoints.)

This endpoint name uses the character set encoding native to the

managed node, and represents a UNIX-domain stream (SOCK_STREAM)

socket.

8.2.2. Operation

Once a connection has been established, the AgentX peers use this

connection to carry all AgentX PDUs.

Multiple AgentX sessions may be established using the same

connection. AgentX PDUs are sent within an AgentX session. AgentX

peers are responsible for mapping the h.sessionID to a particular

connection.

All AgentX PDUs are presented individually to the socket layer, to be

sent in the data stream.

9. Security Considerations

This memo defines a protocol between two processing entities, one of

which (the master agent) is assumed to perform authentication of

received SNMP requests and to control access to management

information. The master agent performs these security operations

independently of the other processing entity (the subagent).

Security considerations require three questions to be answered:

1. Is a particular subagent allowed to initiate a session with a

particular master agent?

2. During an AgentX session, is any SNMP security-related

information (for example, community names) passed from the

master agent to the subagent?

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

subagent allowed to register?

The answer to the third question is: A subagent can register any

subtree (subject to AgentX elements of procedure, section 7.1.5).

Currently there is no access control mechanism defined in AgentX. A

concern here is that a malicious subagent that registers an

unauthorized "sensitive" subtree, could see modification requests to

those objects, or by giving its own clever answer to NMS queries,

could cause the NMS to do something that leads to information

disclosure or other damage.

The answer to the second question is: No.

Now we can answer the first question. AgentX does not contain a

mechanism for authorizing/refusing session initiations. Thus,

controlling subagent access to the master agent may only be done at a

lower layer (e.g., transport).

An AgentX subagent can connect to a master agent using either a

network transport mechanism (e.g., TCP), or a "local" mechanism

(e.g., shared memory, named pipes).

In the case where a local transport mechanism is used and both

subagent and master agent are running on the same host, connection

authorization can be delegated to the operating system features. The

answer to the first security question then becomes: "If and only if

the subagent has sufficient privileges, then the operating system

will allow the connection".

If a network transport is used, currently there is no inherent

security. Transport Layer Security or SSL could be used to control

subagent connections, but that is beyond the scope of this document.

Thus it is recommended that subagents always run on the same host as

the master agent and that operating system features be used to ensure

that only properly authorized subagents can establish connections to

the master agent.

10. Acknowledgements

The initial development of this memo was heavily influenced by the

DPI 2.0 specification RFC1592 [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

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)", RFC1902, January 1996.

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

"Textual Conventions for Version 2 of the Simple Network Management

Protocol (SNMPv2)", RFC1903, January 1996.

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

"Protocol Operations for Version 2 of the Simple Network Management

Protocol (SNMPv2)", RFC1905, 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)", RFC1907, January 1996.

[6] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network

Management Protocol", STD 15, RFC1157, 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", RFC1592, 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", RFC1908, January 1996.

[9] Wijnen, B. and D. Levi, "V2ToV1: Mapping SNMPv2 onto SNMPv1

Within a Bilingual SNMP Agent", RFC2089, January 1997.

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

"Conformance Statements for Version 2 of the Simple Network

Management Protocol (SNMPv2)", RFC1904, January 1996.

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

Interfaces Group of MIB-II", RFC1573, January 1994.

[12] Case, J., "FDDI Management Information Base", RFC1285,

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.

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