RFC 2257
Network Working Group M. Daniele
Request for Comments: 2257 Digital Equipment Corporation
Category: Standards Track B. Wijnen
T.J. Watson Research Center, IBM Corp.
D. Francisco, Ed.
Cisco Systems, Inc.
January 1998
Agent Extensibility (AgentX) Protocol
Version 1
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Table of Contents
1 Introduction......................................................4
2 The SNMP Framework................................................4
2.1 A Note on Terminology.........................................4
3 Extending the MIB.................................................5
3.1 Motivation for AgentX.........................................5
4 AgentX Framework..................................................6
4.1 AgentX Roles..................................................7
4.2 Applicability.................................................8
4.3 Design Features of AgentX.....................................9
4.4 Non-Goals....................................................10
5 AgentX Encodings.................................................10
5.1 Object Identifier............................................11
5.2 SearchRange..................................................13
5.3 Octet String.................................................14
5.4 Value Representation.........................................14
6 Protocol Definitions.............................................16
6.1 AgentX PDU Header............................................16
Daniele, et. al. Standards Track [Page 1]
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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
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7.2.2.3 Subagent Processing of the
agentx-GetBulk-PDU...................................62
7.2.3 Subagent Processing of agentx-TestSet,
-CommitSet, -UndoSet, -CleanupSet-PDUs...................63
7.2.3.1 Subagent Processing of the
agentx-TestSet-PDU...................................64
7.2.3.2 Subagent Processing of the
agentx-CommitSet-PDU.................................65
7.2.3.3 Subagent Processing of the
agentx-UndoSet-PDU...................................65
7.2.3.4 Subagent Processing of the
agentx-CleanupSet-PDU................................65
7.2.4 Master Agent Processing of AgentX Responses..............66
7.2.4.1 Common Processing of All AgentX Response
PDUs.................................................66
7.2.4.2 Processing of Responses to agentx-Get-PDUs...........66
7.2.4.3 Processing of Responses to
agentx-GetNext-PDU and agentx-GetBulk-PDU............67
7.2.4.4 Processing of Responses to
agentx-TestSet-PDUs..................................68
7.2.4.5 Processing of Responses to
agentx-CommitSet-PDUs................................68
7.2.4.6 Processing of Responses to
agentx-UndoSet-PDUs..................................69
7.2.5 Sending the SNMP Response-PDU............................69
7.2.6 MIB Views................................................69
7.3 State Transitions............................................70
7.3.1 Set Transaction States...................................70
7.3.2 Transport Connection States..............................71
7.3.3 Session States...........................................73
8 Transport Mappings...............................................74
8.1 AgentX over TCP..............................................74
8.1.1 Well-known Values........................................74
8.1.2 Operation................................................74
8.2 AgentX over UNIX-domain Sockets..............................75
8.2.1 Well-known Values........................................75
8.2.2 Operation................................................75
9 Security Considerations..........................................76
10 Acknowledgements................................................77
11 Authors' and Editor's Addresses.................................77
12 References......................................................78
13 Full Copyright Statement........................................80
Daniele, et. al. Standards Track [Page 3]
RFC 2257 AgentX January 1998
1. Introduction
This memo defines a standardized framework for extensible SNMP
agents. It defines processing entities called master agents and
subagents, a protocol (AgentX) used to communicate between them, and
the elements of procedure by which the extensible agent processes
SNMP protocol messages.
2. The SNMP Framework
A management system contains: several (potentially many) nodes, each
with a processing entity, termed an agent, which has access to
management instrumentation; at least one management station; and, a
management protocol, used to convey management information between
the agents and management stations. Operations of the protocol are
carried out under an administrative framework which defines
authentication, authorization, access control, and privacy policies.
Management stations execute management applications which monitor and
control managed elements. Managed elements are devices such as
hosts, routers, terminal servers, etc., which are monitored and
controlled via access to their management information.
Management information is viewed as a collection of managed objects,
residing in a virtual information store, termed the Management
Information Base (MIB). Collections of related objects are defined
in MIB modules. These modules are written using a subset of OSI's
Abstract Syntax Notation One (ASN.1) [1], termed the Structure of
Management Information (SMI) (see RFC 1902 [2]).
2.1. A Note on Terminology
The term "variable" refers to an instance of a non-aggregate object
type defined according to the conventions set forth in the SMI (RFC
1902, [2]) or the textual conventions based on the SMI (RFC 1903
[3]). The term "variable binding" normally refers to the pairing of
the name of a variable and its associated value. However, if certain
kinds of exceptional conditions occur during processing of a
retrieval request, a variable binding will pair a name and an
indication of that exception.
A variable-binding list is a simple list of variable bindings.
The name of a variable is an OBJECT IDENTIFIER, which is the
concatenation of the OBJECT IDENTIFIER of the corresponding object
type together with an OBJECT IDENTIFIER fragment identifying the
Daniele, et. al. Standards Track [Page 4]
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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.
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The wide deployment of extensible SNMP agents, coupled with the lack
of Internet standards in this area, makes it difficult to field
SNMP-manageable applications. A vendor may have to support several
different subagent environments (APIs) in order to support different
target platforms.
It can also become quite cumbersome to configure subagents and
(possibly multiple) master agents on a particular managed node.
Specifying a standard protocol for agent extensibility (AgentX)
provides the technical foundation required to solve both of these
problems. Independently developed AgentX-capable master agents and
subagents will be able to interoperate at the protocol level.
Vendors can continue to differentiate their products in all other
respects.
4. AgentX Framework
Within the SNMP framework, a managed node contains a processing
entity, called an agent, which has access to management information.
Within the AgentX framework, an agent is further defined to consist
of
- 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.
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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.
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4.2 Applicability
It is intended that this memo specify the smallest amount of required
behavior necessary to achieve the largest benefit, that is, to cover
a very large number of possible MIB implementations and
configurations with minimum complexity and low "cost of entry".
This section discusses several typical usage scenarios.
1) Subagents implement separate MIB modules--for example,
subagent A implements "mib-2", subagent b implements "host-
resources".
It is anticipated that this will be the most common subagent
configuration.
2) Subagents implement rows in a "simple table". A simple table
is one in which row creation is not specified, and for which the
MIB does not define an object that counts entries in the table.
Examples of simple tables are rdbmsDbTable, udpTable, and
hrSWRunTable.
This is the most commonly defined type of MIB table, and probably
represents the next most typical configuration that AgentX would
support.
3) Subagents share MIBs along non-row partitions. Subagents
register "chunks" of the MIB that represent multiple rows, due to
the nature of the MIB's index structure. Examples include
registering ipNetToMediaEntry.n, where n represents the ifIndex
value for an interface implemented by the subagent, and
tcpConnEntry.a.b.c.d, where a.b.c.d represents an IP address on an
interface implemented by the subagent.
AgentX supports these three common configurations, and all
permutations of them, completely. The consensus is that they
comprise a very large majority of current and likely future uses of
multi-vendor extensible agent configurations.
4) Subagents implement rows in "complex tables". Complex tables
here are defined as tables permitting row creation, or whose MIB
also defines an object that counts entries in the table. Examples
include the MIB-2 ifTable (due to ifNumber), and the RMON
historyControlTable.
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RFC 2257 AgentX January 1998
The subagent that implements such a counter object (like ifNumber)
must go beyond AgentX to correctly implement it. This is an
implementation issue (and most new MIB designs no longer include such
objects).
To implement row creation in such tables, at least one AgentX
subagent must register at a point "higher" in the OID tree than an
individual row (per AgentX's dispatching procedure). Again, this is
an implementation issue.
Scenarios in this category were thought to occur somewhat rarely in
configurations where subagents are independently implemented by
different vendors. The focus of a standard protocol, however, must
be in just those areas where multi- vendor interoperability must be
assured.
Note that it would be inefficient (due to AgentX registration
overhead) to share a table among AgentX subagents if the table
contains very dynamic instances, and each subagent registers fully
qualified instances. ipRouteTable could be an example of such a
table in some environments.
4.3. Design Features of AgentX
The primary features of the design described in this memo are:
1) A general architectural division of labor between master agent
and subagent: The master agent is MIB ignorant and SNMP
omniscient, while the subagent is SNMP ignorant and MIB omniscient
(for the MIB variables it instantiates). That is, master agents,
exclusively, are concerned with SNMP protocol operations and the
translations to and from AgentX protocol operations needed to
carry them out; subagents are exclusively concerned with
management instrumentation; and neither should intrude on the
other's territory.
2) A standard protocol and "rules of engagement" to enable
interoperability between management instrumentation and extensible
agents.
3) Mechanisms for independently developed subagents to
integrate into the extensible agent on a particular managed node
in such a way that they need not be aware of any other existing
subagents.
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RFC 2257 AgentX January 1998
4) A simple, deterministic registry and dispatching algorithm.
For a given extensible agent configuration, there is a single
subagent who is "authoritative" for any particular region of the
MIB (where "region" may extend from an entire MIB down to a single
object-instance).
5) Performance considerations. It is likely that the master
agent and all subagents will reside on the same host, and in such
cases AgentX is more a form of inter-process communication than a
traditional communications protocol.
Some of the design decisions made with this in mind include:
- 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
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RFC 2257 AgentX January 1998
a contiguous byte stream. The data within this stream is organized
to provide natural alignment with respect to the start of the PDU,
permitting direct (integer) access by the processing entities.
The first four fields in the header are single-byte values. A bit
(NETWORK_BYTE_ORDER) in the third field (h.flags) is used to indicate
the byte ordering of all multi-byte integer values in the PDU,
including those which follow in the header itself. This is described
in more detail in Section 6.1, "AgentX PDU Header", below.
PDUs are depicted in this memo using the following convention (where
byte 1 is the first transmitted byte):
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| byte 1 | byte 2 | byte 3 | byte 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| byte 5 | byte 6 | byte 7 | byte 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields marked "" 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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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.
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RFC 2257 AgentX January 1998
prefix
An unsigned value used to reduce the length of object
identifier encodings. A non-zero value "x" is interpreted as
the first sub-identifier after "internet" (1.3.6.1), and
indicates an implicit prefix "internet.x" to the actual sub-
identifiers encoded in the Object Identifier. For example, a
prefix field value 2 indicates an implicit prefix "1.3.6.1.2".
A value of 0 in the prefix field indicates there is no prefix
to the sub-identifiers.
include
Used only when the Object Identifier is the start of a
SearchRange, as described in section 5.2.
A null Object Identifier consists of the 4-byte header with all bytes
set to 0.
Examples:
sysDescr.0 (1.3.6.1.2.1.1.1.0)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | 2 | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1.2.3.4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | 0 | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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RFC 2257 AgentX January 1998
5.2. SearchRange
A SearchRange consists of two Object Identifiers. In its
communication with a subagent, the master agent uses a SearchRange to
identify a requested variable binding, and, in GetNext and GetBulk
operations, to set an upper bound on the names of managed object
instances the subagent may send in reply.
The first Object Identifier in a SearchRange (called the starting
OID) indicates the beginning of the range. It is frequently (but not
necessarily) the name of a requested variable binding.
The "include" field in this OID's header is a boolean value (0 or 1)
indicating whether or not the starting OID is included in the range.
The second object identifier indicates the non-inclusive end of the
range, and its "include" field is always 0.
Example: To indicate a search range from 1.3.6.1.2.1.25.2
(inclusive) to 1.3.6.1.2.1.25.2.1 (exclusive), the SearchRange would
be
(start)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | 2 | 1 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 25 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(end)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | 2 | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 25 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A SearchRangeList is a contiguous list of SearchRanges.
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5.3. Octet String
An octet string is represented by a contiguous series of bytes,
beginning with a 4-byte integer whose value is the number of octets
in the octet string, followed by the octets themselves. This
representation is termed an Octet String. If the last octet does not
end on a 4-byte offset from the start of the Octet String, padding
bytes are appended to achieve alignment of following data. This
padding must be added even if the Octet String is the last item in
the PDU. Padding bytes must be zero filled.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A null Octet String consists of a 4-byte length field set to 0.
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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(v.name)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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RFC 2257 AgentX January 1998
(v.data)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
VarBind fields:
v.type
Indicates the variable binding's syntax, and must be one of
the following values:
Integer (2),
Octet String (4),
Null (5),
Object Identifier (6),
IpAddress (64),
Counter32 (65),
Gauge32 (66),
TimeTicks (67),
Opaque (68),
Counter64 (70),
noSuchObject (128),
noSuchInstance (129),
endOfMibView (130)
v.name
The Object Identifier which names the variable.
v.data
The actual value, encoded as follows:
- 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.
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RFC 2257 AgentX January 1998
- 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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An AgentX PDU header contains the following fields:
h.version
The version of the AgentX protocol (1 for this memo).
Daniele, et. al. Standards Track [Page 16]
RFC 2257 AgentX January 1998
h.type
The PDU type; one of the following values:
agentx-Open-PDU (1),
agentx-Close-PDU (2),
agentx-Register-PDU (3),
agentx-Unregister-PDU (4),
agentx-Get-PDU (5),
agentx-GetNext-PDU (6),
agentx-GetBulk-PDU (7),
agentx-TestSet-PDU (8),
agentx-CommitSet-PDU (9),
agentx-UndoSet-PDU (10),
agentx-CleanupSet-PDU (11),
agentx-Notify-PDU (12),
agentx-Ping-PDU (13),
agentx-IndexAllocate-PDU (14),
agentx-IndexDeallocate-PDU (15),
agentx-AddAgentCaps-PDU (16),
agentx-RemoveAgentCaps-PDU (17),
agentx-Response-PDU (18)
h.flags
A bitmask, with bit 0 the least significant bit. The bit
definitions are as follows:
Bit Definition
--- ----------
0 INSTANCE_REGISTRATION
1 NEW_INDEX
2 ANY_INDEX
3 NON_DEFAULT_CONTEXT
4 NETWORK_BYTE_ORDER
5-7 (reserved)
The NETWORK_BYTE_ORDER bit applies to all multi-byte integer
values in the entire AgentX packet, including the remaining
header fields. If set, then network byte order (most
significant byte first; "big endian") is used. If not set,
then least significant byte first ("little endian") is used.
The NETWORK_BYTE_ORDER bit applies to all AgentX PDUs.
The NON_DEFAULT_CONTEXT bit is used only in the AgentX PDUs
described in section 6.1.1.
Daniele, et. al. Standards Track [Page 17]
RFC 2257 AgentX January 1998
The NEW_INDEX and ANY_INDEX bits are used only within the
agentx-IndexAllocate-, and -IndexDeallocate-PDUs.
The INSTANCE_REGISTRATION bit is used only within the agentx-
Register-PDU.
h.sessionID
The session ID uniquely identifies a session over which AgentX
PDUs are exchanged between a subagent and the master agent.
The session ID has no significance and no defined value in the
agentx-Open-PDU sent by a subagent to open a session with the
master agent; in this case, the master agent will assign a
unique sessionID that it will pass back in the corresponding
agentx-Response-PDU. From that point on, that same sessionID
will appear in every AgentX PDU exchanged over that session
between the master and the subagent. A subagent may establish
multiple AgentX sessions by sending multiple agentx-Open-PDUs
to the master agent.
In master agents that support multiple transport protocols, the
sessionID should be globally unique rather than unique just to
a particular transport.
h.transactionID
The transaction ID uniquely identifies, for a given session,
the single SNMP management request (and single SNMP PDU) with
which an AgentX PDU is associated. If a single SNMP management
request results in multiple AgentX PDUs being sent by the
master agent with the same sessionID, each of these AgentX PDUs
must contain the same transaction ID; conversely, AgentX PDUs
sent during a particular session, that result from distinct
SNMP management requests, must have distinct transaction IDs
within the limits of the 32-bit field).
Note that the transaction ID is not the same as the SNMP PDU's
request-id (as described in section 4.1 of RFC 1905 [4]), nor
can it be, since a master agent might receive SNMP requests
with the same request-ids from different managers.
The transaction ID has no significance and no defined value in
AgentX administrative PDUs, i.e., AgentX PDUs that are not
associated with an SNMP management request.
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RFC 2257 AgentX January 1998
h.packetID
A packet ID generated by the sender for all AgentX PDUs except
the agentx-Response-PDU. In an agentx-Response-PDU, the packet
ID must be the same as that in the received AgentX PDU to which
it is a response. A master agent might use this field to
associate subagent response PDUs with their corresponding
request PDUs. A subagent might use this field to correlate
responses to multiple (batched) registrations.
h.payload_length
The size in octets of the PDU contents, excluding the 20-byte
header. As a result of the encoding schemes and PDU layouts,
this value will always be either 0, or a multiple of 4.
6.1.1. Context
In the SNMPv1 or v2c frameworks, the community string may be used as
an index into a local repository of configuration information that
may include community profiles or more complex context information.
Future versions of the SNMP will likely formalize this notion of
"context".
AgentX provides a mechanism for transmitting a context specification
within relevant PDUs, but does not place any constraints on the
content of that specification.
An optional context field may be present in the agentx-Register-,
UnRegister-, AddAgentCaps-, RemoveAgentCaps-, Get-, GetNext-,
GetBulk-, IndexAllocate-, IndexDeallocate-, Notify-, TestSet-, and
Ping- PDUs.
If the NON_DEFAULT_CONTEXT bit in the AgentX header field h.flags is
clear, then there is no context field in the PDU, and the operation
refers to the default context.
If the NON_DEFAULT_CONTEXT bit is set, then a context field
immediately follows the AgentX header, and the operation refers to
that specific context. The context is represented as an Octet
String. There are no constraints on its length or contents.
Thus, all of these AgentX PDUs (that is, those listed immediately
above) refer to, or "indicate" a context, which is either the default
context, or a non-default context explicitly named in the PDU.
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RFC 2257 AgentX January 1998
6.2. AgentX PDUs
6.2.1. The agentx-Open-PDU
An agentx-Open-PDU is generated by a subagent to request
establishment of an AgentX session with the master agent.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (1) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| o.timeout | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(o.id)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subidentifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subidentifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(o.descr)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An agentx-Open-PDU contains the following fields:
Daniele, et. al. Standards Track [Page 20]
RFC 2257 AgentX January 1998
o.timeout
The length of time, in seconds, that a master agent should
allow to elapse after dispatching a message to a subagent
before it regards the subagent as not responding. This is a
subagent-wide default value that may be overridden by values
associated with specific registered MIB regions. The default
value of 0 indicates that no subagent-wide value is requested.
o.id
An Object Identifier that identifies the subagent. Subagents
that do not support such an notion may send a null Object
Identifier.
o.descr
An Octet String containing a DisplayString describing the
subagent.
6.2.2. The agentx-Close-PDU
An agentx-Close-PDU issued by either a subagent or the master agent
terminates an AgentX session.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (2) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| c.reason | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An agentx-Close-PDU contains the following field:
Daniele, et. al. Standards Track [Page 21]
RFC 2257 AgentX January 1998
c.reason
An enumerated value that gives the reason that the master agent
or subagent closed the AgentX session. This field may take one
of the following values:
reasonOther(1)
None of the following reasons
reasonParseError(2)
Too many AgentX parse errors from peer
reasonProtocolError(3)
Too many AgentX protocol errors from peer
reasonTimeouts(4)
Too many timeouts waiting for peer
reasonShutdown(5)
Sending entity is shutting down
reasonByManager(6)
Due to Set operation; this reason code can be used only
by the master agent, in response to an SNMP management
request.
6.2.3. The agentx-Register-PDU
An agentx-Register-PDU is generated by a subagent for each region of
the MIB variable naming tree (within one or more contexts) that it
wishes to support.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (3) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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RFC 2257 AgentX January 1998
(r.context) (OPTIONAL)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| r.timeout | r.priority | r.range_subid | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.region)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.upper_bound)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| optional upper-bound sub-identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An agentx-Register-PDU contains the following fields:
r.context
An optional non-default context.
r.timeout
The length of time, in seconds, that a master agent should
allow to elapse after dispatching a message to a subagent
before it regards the subagent as not responding. r.timeout
applies only to messages that concern MIB objects within
r.region. It overrides both the subagent-wide value (if any)
indicated when the AgentX session with the master agent was
established, and the master agent's default timeout. The
default value for r.timeout is 0 (no override).
Daniele, et. al. Standards Track [Page 23]
RFC 2257 AgentX January 1998
r.priority
A value between 1 and 255, used to achieve a desired
configuration when different subagents register identical or
overlapping regions. Subagents with no particular knowledge of
priority should register with the default value of 255 (lowest
priority).
In the master agent's dispatching algorithm, smaller values of
r.priority take precedence over larger values, as described in
section 7.1.5.1.
r.region
An Object Identifier that, in conjunction with r.range_subid,
indicates a region of the MIB that a subagent wishes to
support. It may be a fully-qualified instance name, a partial
instance name, a MIB table, an entire MIB, or ranges of any of
these.
The choice of what to register is implementation-specific; this
memo does not specify permissible values. Standard practice
however is for a subagent to register at the highest level of
the naming tree that makes sense. Registration of fully-
qualified instances is typically done only when a subagent can
perform management operations only on particular rows of a
conceptual table.
If r.region is in fact a fully qualified instance name, the
INSTANCE_REGISTRATION bit in h.flags must be set, otherwise it
must be cleared. The master agent may save this information to
optimize subsequent operational dispatching.
r.range_subid
Permits specifying a range in place of one of r.region's sub-
identifiers. If this value is 0, no range is specified.
Otherwise the "r.range_subid"-th sub-identifier in r.region is
a range lower bound, and the range upper bound sub-identifier
(r.upper_bound) immediately follows r.region.
This permits registering a conceptual row with a single PDU.
For example, the following PDU would register row 7 of the RFC
1573 ifTable (1.3.6.1.2.1.2.2.1.1-22.7):
Daniele, et. al. Standards Track [Page 24]
RFC 2257 AgentX January 1998
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (3) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| r.timeout | r.priority | 5 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.region)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 | 2 | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.upper_bound)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 22 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.2.4. The agentx-Unregister-PDU
The agentx-Unregister-PDU is sent by a subagent to remove a
previously registered MIB region from the master agent's OID space.
Daniele, et. al. Standards Track [Page 25]
RFC 2257 AgentX January 1998
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (4) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | u.priority | u.range_subid | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(u.region)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(u.upper_bound)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| optional upper-bound sub-identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An agentx-Unregister-PDU contains the following fields:
Daniele, et. al. Standards Track [Page 26]
RFC 2257 AgentX January 1998
u.context
An optional non-default context.
u.priority
The priority at which this region was originally registered.
u.region
Indicates a previously-registered region of the MIB that a
subagent no longer wishes to support.
6.2.5. The agentx-Get-PDU
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (5) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Daniele, et. al. Standards Track [Page 27]
RFC 2257 AgentX January 1998
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(end 1)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | 0 | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
(start n)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | include | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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.
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RFC 2257 AgentX January 1998
6.2.6. The agentx-GetNext-PDU
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (6) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(end 1)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Daniele, et. al. Standards Track [Page 29]
RFC 2257 AgentX January 1998
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
(start n)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | include | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(end n)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
6.2.7. The agentx-GetBulk-PDU
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (7) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Daniele, et. al. Standards Track [Page 30]
RFC 2257 AgentX January 1998
(g.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| g.non_repeaters | g.max_repetitions |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(g.sr) as in agentx-GetNext-PDU above
...
6.2.8. The agentx-TestSet-PDU
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (8) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(t.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(t.vb)
Daniele, et. al. Standards Track [Page 31]
RFC 2257 AgentX January 1998
(VarBind 1)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| v.type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
(VarBind n)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| v.type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An agentx-TestSet-PDU contains the following fields:
t.context
An optional non-default context.
Daniele, et. al. Standards Track [Page 32]
RFC 2257 AgentX January 1998
t.vb
A VarBindList containing the requested VarBinds for this
subagent.
6.2.9. The agentx-CommitSet, -UndoSet, -CleanupSet PDUs
These PDUs consist of the AgentX header only.
The agentx-CommitSet-, -UndoSet-, and -Cleanup-PDUs are used in
processing an SNMP SetRequest operation.
6.2.10. The agentx-Notify-PDU
An agentx-Notify-PDU is sent by a subagent to cause the master agent
to forward a notification.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (12) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(n.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(n.vb)
...
An agentx-Notify-PDU contains the following fields:
Daniele, et. al. Standards Track [Page 33]
RFC 2257 AgentX January 1998
n.context
An optional non-default context.
n.vb
A VarBindList whose contents define the actual PDU to be sent.
This memo places the following restrictions on its contents:
- 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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(p.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An agentx-Ping-PDU may contain the following field:
Daniele, et. al. Standards Track [Page 34]
RFC 2257 AgentX January 1998
p.context
An optional non-default context.
Using p.context a subagent can retrieve the sysUpTime value for a
specific context, if required.
6.2.12. The agentx-IndexAllocate-PDU
An agentx-IndexAllocate-PDU is sent by a subagent to request
allocation of a value for specific index objects. Refer to section
7.1.3 (Using the agentx-IndexAllocate-PDU) for suggested usage.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (14) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(i.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(i.vb)
...
An agentx-IndexAllocate-PDU contains the following fields:
i.context
An optional non-default context.
Daniele, et. al. Standards Track [Page 35]
RFC 2257 AgentX January 1998
i.vb
A VarBindList containing the index names and values requested
for allocation.
6.2.13. The agentx-IndexDeallocate-PDU
An agentx-IndexDeallocate-PDU is sent by a subagent to release
previously allocated index values.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (15) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(i.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(i.vb)
...
An agentx-IndexDeallocate-PDU contains the following fields:
i.context
An optional non-default context.
i.vb
A VarBindList containing the index names and values to be
released.
Daniele, et. al. Standards Track [Page 36]
RFC 2257 AgentX January 1998
6.2.14. The agentx-AddAgentCaps-PDU
An agentx-AddAgentCaps-PDU is generated by a subagent to inform the
master agent of its agent capabilities.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (16) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a.descr)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Daniele, et. al. Standards Track [Page 37]
RFC 2257 AgentX January 1998
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Optional Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An agentx-AddAgentCaps-PDU contains the following fields:
a.context
An optional non-default context.
a.id
An Object Identifier containing the value of an invocation of
the AGENT-CAPABILITIES macro, which the master agent exports as
a value of sysORID for the indicated context. (Recall that the
value of an invocation of an AGENT-CAPABILITIES macro is an
object identifier that describes a precise level of support
with respect to implemented MIB modules. A more complete
discussion of the AGENT-CAPABILITIES macro and related sysORID
values can be found in section 6 of RFC 1904 [10].)
a.descr
An Octet String containing a DisplayString to be used as the
value of sysORDescr corresponding to the sysORID value above.
6.2.15. The agentx-RemoveAgentCaps-PDU
An agentx-RemoveAgentCaps-PDU is generated by a subagent to request
that the master agent stop exporting a particular value of sysORID.
This value must have previously been advertised by the subagent in an
agentx-AddAgentCaps-PDU.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (17) | h.flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Daniele, et. al. Standards Track [Page 38]
RFC 2257 AgentX January 1998
(a.context) (OPTIONAL)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Optional Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a.id)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.sessionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.transactionID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.packetID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Daniele, et. al. Standards Track [Page 39]
RFC 2257 AgentX January 1998
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| res.sysUpTime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| res.error | res.index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
An agentx-Response-PDU contains the following fields:
h.sessionID
If this is a response to a agentx-Open-PDU, then it contains
the new and unique sessionID (as assigned by the master agent)
for this session.
Otherwise it must be identical to the h.sessionID value in the
PDU to which this PDU is a response.
h.transactionID
Must be identical to the h.transactionID value in the PDU to
which this PDU is a response.
In an agentx response PDU from the master agent to the
subagent, the value of h.transactionID has no significance and
can be ignored by the subagent.
h.packetID
Must be identical to the h.packetID value in the PDU to which
this PDU is a response.
res.sysUpTime
This field contains the current value of sysUpTime for the
indicated context. It is relevant only in agentx response PDUs
sent from the master agent to a subagent in response to the
following agentx PDUs:
agentx-Open-PDU (1),
agentx-Close-PDU (2),
agentx-Register-PDU (3),
agentx-Unregister-PDU (4),
agentx-Ping-PDU (13),
agentx-IndexAllocate-PDU (14),
agentx-IndexDeallocate-PDU (15),
agentx-AddAgentCaps-PDU (16),
agentx-RemoveAgentCaps-PDU (17)
Daniele, et. al. Standards Track [Page 40]
RFC 2257 AgentX January 1998
In an agentx response PDU from the subagent to the master
agent, the value of res.sysUpTime has no significance and is
ignored by the master agent.
res.error
Indicates error status (including `noError'). Values are
limited to those defined for errors in the SNMPv2 SMI (RFC 1905
[4]), and the following AgentX-specific values:
openFailed (256),
notOpen (257),
indexWrongType (258),
indexAlreadyAllocated (259),
indexNoneAvailable (260),
indexNotAllocated (261),
unsupportedContext (262),
duplicateRegistration (263),
unknownRegistration (264),
unknownAgentCaps (265)
res.index
In error cases, this is the index of the failed variable
binding within a received request PDU. (Note: As explained in
section 5.4, Value Representation, the index values of variable
bindings within a variable binding list are 1-based.)
A VarBindList may follow these latter two fields, depending on which
AgentX PDU is being responded to. These data are specified in the
subsequent elements of procedure.
7. Elements of Procedure
This section describes the actions of protocol entities (master
agents and subagents) implementing the AgentX protocol. Note,
however, that it is not intended to constrain the internal
architecture of any conformant implementation.
Specific error conditions and associated actions are described in
various places. Other error conditions not specifically mentioned
fall into one of two categories, "parse" errors and "protocol"
errors.
A parse error occurs when a receiving entity cannot decode the PDU.
For instance, a VarBind contains an unknown type, or a PDU contains a
malformed Object Identifier.
Daniele, et. al. Standards Track [Page 41]
RFC 2257 AgentX January 1998
A protocol error occurs when a receiving entity can parse a PDU, but
the resulting data is unspecified. For instance, an agentx-
Response-PDU is successfully parsed, but contains an unknown
res.error value.
An implementation may choose either to ignore such messages, or to
close the session on which they are received, using the appropriate
reason code as defined in the agentx-Close-PDU.
The actions of AgentX protocol entities can be broadly categorized
under two headings, each of which is described separately:
(1) processing AgentX administrative messages (e.g., connection
requests from a subagent to a master agent); and
(2) processing SNMP messages (the coordinated actions of a
master agent and one or more subagents in processing, for
example, a received SNMP GetRequest-PDU).
7.1. Processing AgentX Administrative Messages
This subsection describes the actions of AgentX protocol entities in
processing AgentX administrative messages. Such messages include
those involved in establishing and terminating an AgentX session
between a subagent and a master agent, those by which a subagent
requests allocation of instance index values, and those by which a
subagent communicates to a master agent which MIB regions it
supports.
7.1.1. Processing the agentx-Open-PDU
When the master agent receives an agentx-Open-PDU, it processes it as
follows:
1) An agentx-Response-PDU is created and res.sysUpTime is set to
the value of sysUpTime.0 for the indicated context.
2) If the master agent is unable to open an AgentX session for
any reason, it may refuse the session establishment request,
sending in reply the agentx-Response-PDU, with res.error field set
to `openFailed'.
3) Otherwise: The master agent assigns a sessionID to the new
session and puts the value in the h.sessionID field of the
agentx-Response-PDU. This value must be unique among all existing
open sessions.
Daniele, et. al. Standards Track [Page 42]
RFC 2257 AgentX January 1998
4) The master agent retains session-specific information
from the PDU for this subagent:
- 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'.
Daniele, et. al. Standards Track [Page 43]
RFC 2257 AgentX January 1998
3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
supports only a default context, the agentx-Response-PDU is
returned with res.error set to `unsupportedContext', and the
requested allocation fails. Otherwise: The value of res.sysUpTime
is set to the value of sysUpTime.0 for the indicated context.
4) Each VarBind in the VarBindList is processed until either all
are successful, or one fails. If any VarBind fails, the agentx-
Response-PDU is sent in reply containing the original VarBindList,
with res.index set to indicate the failed VarBind, and with
res.error set as described subsequently. All other VarBinds are
ignored; no index values are allocated.
VarBinds are processed as follows:
- 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'.
Daniele, et. al. Standards Track [Page 44]
RFC 2257 AgentX January 1998
e) Otherwise, if the ANY_INDEX bit is set, the master agent
should generate an index value for v.name in the indicated
context, with the constraint that this value is not currently
allocated to any subagent. If no such value can be generated,
then the VarBind fails and res.error is set to
`indexNoneAvailable'.
5) If all VarBinds are processed successfully, the
agentx-Response-PDU is sent in reply with res.error set to
`noError'. A VarBindList is included that is identical to the one
sent in the agentx-IndexAllocate-PDU, except that VarBinds
requesting a NEW_INDEX or ANY_INDEX value are generated with an
appropriate value.
7.1.3. Using the agentx-IndexAllocate-PDU
Index allocation is a service provided by an AgentX master agent. It
provides generic support for sharing MIB conceptual tables among
subagents who are assumed to have no knowledge of each other.
Each subagent sharing a table should first request allocation of
index values, then use those index values to qualify MIB regions in
its subsequent registrations.
The master agent maintains a database of index objects (OIDs), and,
for each index, the values that have been allocated for it. It is
unaware of what MIB variables (if any) the index objects represent.
By convention, subagents use the MIB variable listed in the INDEX
clause as the index object for which values must be allocated. For
tables indexed by multiple variables, values may be allocated for
each index (although this is frequently unnecessary; see example 2
below). The subagent may request allocation of
- a specific index value - an index value that is not currently
allocated - an index value that has never been allocated
The last two alternatives reflect the uniqueness and constancy
requirements present in many MIB specifications for arbitrary integer
indexes (e.g., ifIndex in the IF MIB (RFC 1573 [11]),
snmpFddiSMTIndex in the FDDI MIB (RFC 1285 [12]), or
sysApplInstallPkgIndex in the System Application MIB [13]). The need
for subagents to share tables using such indexes is the main
motivation for index allocation in AgentX.
Daniele, et. al. Standards Track [Page 45]
RFC 2257 AgentX January 1998
Example 1:
A subagent implements an interface, and wishes to register a
single row of the RFC 1573 ifTable. It requests an allocation for
the index object "ifIndex", for a value that has never been
allocated (since ifIndex values must be unique). The master agent
returns the value "7".
The subagent now attempts to register row 7 of ifTable, by
specifying a MIB region in the agentx-Register-PDU of
1.3.6.1.2.1.2.2.1.[1-22].7. If the registration succeeds, no
further processing is required. The master agent will dispatch to
this subagent correctly.
But the registration may fail. Index allocation and MIB region
registration are not coupled in the master agent. Some other
subagent may have already registered ifTable row 7 without first
having requested allocation of the index. The current state of
index allocations is not considered when processing registration
requests, and the current registry is not considered when
processing index allocation requests. If subagents follow the
model of "first request allocation of an index, then register the
corresponding region", then a successful index allocation request
gives a subagent a good hint (but no guarantee) of what it should
be able to register.
If the registration failed, the subagent should request allocation
of a new index i, and attempt to register ifTable.[1-22].i, until
successful.
Example 2:
This same subagent wishes to register ipNetToMediaTable rows
corresponding to its interface (ifIndex i). Due to structure of
this table, no further index allocation need be done. The
subagent can register the MIB region ipNetToMediaTable.[1-4].i, It
is claiming responsibility for all rows of the table whose value
of ipNetToMediaIfIndex is i.
Example 3:
A network device consists of a set of processors, each of which
accepts network connections for a unique set of IP addresses.
Further, each processor contains a subagent that implements
tcpConnTable. In order to represent tcpConnTable for the entire
managed device, the subagents need to share tcpConnTable.
Daniele, et. al. Standards Track [Page 46]
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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'.
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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.
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Otherwise this region is to be logically registered within the
default context.
A registration that would result in a duplicate region with the
same priority and within the same context as that of a current
registration is termed a duplicate registration.
5) Otherwise, if this is a duplicate registration, the
agentx-Response-PDU is returned with res.error set to
`duplicateRegistration', and the requested registration fails.
6) Otherwise, the agentx-Response-PDU is returned with res.error
set to `noError'.
The master agent adds this region to its registered OID space for
the indicated context, to be considered during the dispatching
phase for subsequently received SNMP protocol messages.
Note: The following algorithm describes maintaining a set of OID
ranges derived from "splitting" registered regions. The algorithm
for operational dispatching is also stated in terms of these OID
ranges.
These OID ranges are a useful explanatory device, but are not
required for a correct implementation.
- If r.region (R1) is a subtree of a currently registered
region (R2), split R2 into 3 new regions (R2a, R2b, and R2c)
such that R2b is an exact duplicate of R1. Now remove R2 and
add R1, R2a, R2b, and R2c to the master agent's
lexicographically ordered set of ranges (the registered OID
space). Note: Though newly-added ranges R1 and R2b are
identical in terms of the MIB objects they contain, they are
registered by different subagents, possibly at different
priorities.
For instance, if subagent S2 registered "ip" (R2 is
1.3.6.1.2.1.4) and subagent S1 subsequently registered
"ipNetToMediaTable" (R1 is 1.3.6.1.2.1.4.22), the resulting set
of registered regions would be:
1.3.6.1.2.1.4 up to but not including 1.3.6.1.2.1.4.22 (by S2)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S2)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S1)
1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5 (by S2)
Daniele, et. al. Standards Track [Page 49]
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- If r.region (R1) overlaps one or more currently registered
regions, then for each overlapped region (R2) split R1 into 3
new ranges (R1a, R1b, R1c) such that R1b is an exact
duplicate of R2. Add R1b and R2 into the lexicographically
ordered set of regions. Apply (5) above iteratively to R1a and
R1c (since they may overlap, or be subtrees of, other regions).
For instance, given the currently registered regions in the
example above, if subagent S3 now registers mib-2 (R1 is
1.3.6.1.2.1) the resulting set of regions would be:
1.3.6.1.2.1 up to but not including 1.3.6.1.2.1.4 (by S3)
1.3.6.1.2.1.4 up to but not including 1.3.6.1.2.1.4.22 (by S2)
1.3.6.1.2.1.4 up to but not including 1.3.6.1.2.1.4.22 (by S3)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S2)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S1)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S3)
1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5 (by S2)
1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5 (by S3)
1.3.6.1.2.1.5 up to but not including 1.3.6.1.2.2 (by S3)
Note that at registration time a region may be split into multiple
OID ranges due to pre-existing registrations, or as a result of any
subsequent registration. This region splitting is transparent to
subagents. Hence the master agent must always be able to associate
any OID range with the information contained in its original agentx-
Register-PDU.
7.1.5.1. Handling Duplicate OID Ranges
As a result of this registration algorithm there are likely to be
duplicate OID ranges (regions of identical MIB objects registered to
different subagents) in the master agent's registered OID space.
Whenever the master agent's dispatching algorithm (see 7.2.1,
Dispatching AgentX PDUs) results in a duplicate OID range, the
master agent selects one to use, termed the 'authoritative region',
as follows:
1) Choose the one whose original agentx-Register-PDU
r.region contained the most subids, i.e., the most specific
r.region. Note: The presence or absence of a range subid has
no bearing on how "specific" one object identifier is compared
to another.
2) If still ambiguous, there were duplicate regions. Choose the
one whose original agentx-Register-PDU specified the smaller
value of r.priority.
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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.
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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.
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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.
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3) Notifications are sent according to the implementation-specific
configuration of the master agent.
If SNMPv1 Trap PDUs are generated, the recommended mapping is
as described in RFC 2089 [9].
Except in the case of a `notOpen' error as described in (1)
above, no agentx-Response-PDU is sent to the subagent when the
master agent finishes processing the notification.
7.1.12. Processing the agentx-Ping-PDU
When the master agent receives an agentx-Ping-PDU, it processes it as
follows:
1) An agentx-Response-PDU is created and res.sysUpTime is set to
the value of sysUpTime.0 for the default context.
2) If h.sessionID does not correspond to a currently
established session with this subagent, the agentx-Response-PDU is
sent in reply with res.error set to `notOpen'.
3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
supports only a default context, the agentx-Response-PDU is
returned with res.error set to `unsupportedContext'. Otherwise:
The value of res.sysUpTime is set to the value of sysUpTime.0 for
the indicated context.
4) The agentx-Response-PDU is sent, with res.error set to
`noError'.
If a subagent does not receive a response to its pings, or if it is
able to detect (from the underlying transport) that the master agent
is not able to receive AgentX messages, then it eventually must
initiate a new AgentX session, re-register its regions, etc.
7.2. Processing Received SNMP Protocol Messages
When an SNMP GetRequest, GetNextRequest, GetBulkRequest, or
SetRequest protocol message is received by the master agent, the
master agent applies its access control policy.
In particular, for SNMPv1 or SNMPv2c PDUs, the master agent applies
the Elements of Procedure defined in section 4.1 of RFC 1157 [6] that
apply to receiving entities. (For other versions of SNMP, the master
agent applies the access control policy defined in the Elements of
Procedure for those versions.)
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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).
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RFC 2257 AgentX January 1998
2) GetNext and GetBulk Processing
The master agent may choose to send agentx-Get-PDUs while
servicing an SNMP GetNextRequest-PDU. The master agent may choose
to send agentx-Get-PDUs or agentx-GetNext-PDUs while servicing an
SNMP GetBulkRequest-PDU. One possible reason for this would be if
the current iteration has targeted instance-level registrations.
The master agent may choose to "scope" the possible instances
returned by a subagent by specifying an ending OID in the
SearchRange. If such scoping is used, typically the ending OID
would be the first lexicographical successor to the target OID
range that was registered by a subagent other than the target
subagent. Regardless of this choice, rule (1) must be obeyed.
The master agent may require multiple request-response iterations
on the same subagent session, to determine the final value of all
requested variables.
All AgentX PDUs sent on the session while processing a given SNMP
request must contain identical values of transactionID. Each
different SNMP request processed by the master agent must present
a unique value of transactionID (within the limits of the 32-bit
field) to the session.
3) Number and order of variables sent per AgentX PDU
For Get/GetNext/GetBulk operations, at any stage of the possibly
iterative process, the master agent may need to dispatch several
SearchRanges to a particular subagent session. The master agent
may send one, some, or all of the SearchRanges in a single AgentX
PDU.
The master agent must ensure that the correct contents and
ordering of the VarBindList in the SNMP Response-PDU are
maintained.
The following rules govern the number of VarBinds in a given
AgentX PDU:
a) The subagent must support processing of AgentX PDUs
with multiple VarBinds.
b) When processing an SNMP Set request, the master agent
must send all of the VarBinds applicable to a particular
subagent session in a single Test/Set transaction.
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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.
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RFC 2257 AgentX January 1998
(2) If no such OID range exists, the variable binding is not
processed further, and its value is set to `noSuchObject'.
(3) Identify the subagent session in which this region was
registered, termed the target session.
(4) If this is the first variable binding to be dispatched over
the target session in a request-response exchange entailed in the
processing of this management request:
- 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:
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- Create an agentx-GetNext-PDU for the session, with
the header fields initialized as described above (see 6.1
AgentX PDU Header).
(5) Add a SearchRange to the end of the target session's
agentx-GetNext-PDU for this variable binding.
- if (1a) applies, the variable binding's name is encoded
into the starting OID, and the OID's "include" field is set to
0.
- if (1b) applies, the target OID is encoded into the starting
OID, and its "include" field is set to 1.
7.2.1.3. agentx-GetBulk-PDU
(Note: The outline of the following procedure is based closely on
section 4.2.3, "The GetBulkRequest-PDU" of RFC 1905 [4]. Please
refer to it for details on the format of the SNMP GetBulkRequest-PDU
itself.)
Each variable binding in the request PDU is processed as follows:
(1) Identify the 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.
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RFC 2257 AgentX January 1998
7.2.1.4. agentx-TestSet-PDU
AgentX employs test-commit-undo-cleanup phases to achieve "as if
simultaneous" semantics of the SNMP SetRequest-PDU within the
extensible agent. The initial phase involves the agentx-TestSet-PDU.
Each variable binding in the SNMP request PDU is processed in order,
as follows:
(1) Identify the target OID range.
Within a lexicographically ordered set of OID ranges, valid for
the indicated context, locate the authoritative range that
contains the variable binding's name.
(2) If no such OID range exists, this variable binding fails with an
error of `notWritable'. Processing is complete for this request.
(3) Identify the single subagent responsible for this OID range,
termed the target subagent, and the applicable session, termed
the target session.
(4) If this is the first variable binding to be dispatched over
the target session in a request-response exchange entailed in the
processing of this management request:
- 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).
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7.2.2. Subagent Processing of agentx-Get, GetNext, GetBulk-PDUs
A conformant AgentX subagent must support the agentx-Get, -GetNext,
and -GetBulk PDUs, and must support multiple variables being supplied
in each PDU.
When a subagent receives an agentx-Get-, GetNext-, or GetBulk-PDU, it
performs the indicated management operations and returns an agentx-
Response-PDU.
The agentx-Response-PDU header fields are identical to the received
request PDU except that, at the start of processing, the subagent
initializes h.type to Response, res.error to `noError', res.index to
0, and the VarBindList to null.
Each SearchRange in the request PDU's SearchRangeList is processed as
described below, and a VarBind is added in the corresponding location
of the agentx-Response-PDU's VarbindList. If processing should fail
for any reason not described below, res.error is set to `genErr',
res.index to the index of the failed SearchRange, the VarBindList is
reset to null, and this agentx-Response-PDU is returned to the master
agent.
7.2.2.1. Subagent Processing of the agentx-Get-PDU
Upon the subagent's receipt of an agentx-Get-PDU, each SearchRange in
the request is processed as follows:
(1) The starting OID is copied to v.name.
(2) If the starting OID exactly matches the name of a
variable instantiated by this subagent within the indicated
context and session, v.type and v.data are encoded to represent
the variable's syntax and value, as described in section 5.4,
Value Representation.
(3) Otherwise, if the starting OID does not match the object
identifier prefix of any variable instantiated within the
indicated context and session, the VarBind is set to
`noSuchObject', in the manner described in section 5.4, Value
Representation.
(4) Otherwise, the VarBind is set to `noSuchInstance'
in the manner described in section 5.4, Value Representation.
Daniele, et. al. Standards Track [Page 61]
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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:
Daniele, et. al. Standards Track [Page 62]
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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.
Daniele, et. al. Standards Track [Page 63]
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The agentx-Response-PDU header fields are identical to the received
request PDU except that, at the start of processing, the subagent
initializes h.type to Response, res.error to `noError', and res.index
to 0.
These Response-PDUs do not contain a VarBindList.
7.2.3.1. Subagent Processing of the agentx-TestSet-PDU
Upon the subagent's receipt of an agentx-TestSet-PDU, each VarBind in
the PDU is validated until they are all successful, or until one
fails, as described in section 4.2.5 of RFC 1905 [4]. The subagent
validates variables with respect to the context and session indicated
in the testSet-PDU.
If each VarBind is successful, the subagent has a further
responsibility to ensure the availability of all resources (memory,
write access, etc.) required for successfully carrying out a
subsequent agentx-CommitSet operation. If this cannot be guaranteed,
the subagent should set res.error to `resourceUnavailable'.
As a result of this validation step, an agentx-Response-PDU is sent
in reply whose res.error field is set to one of the following (SNMPv2
SMI) values:
noError (0),
genErr (5),
noAccess (6),
wrongType (7),
wrongLength (8),
wrongEncoding (9),
wrongValue (10),
noCreation (11),
inconsistentValue (12),
resourceUnavailable (13),
notWritable (17),
inconsistentName (18)
If this value is not `noError', the res.index field must be set to
the index of the VarBind for which validation failed.
Implementation of rigorous validation code may be one of the most
demanding aspects of subagent development. Implementors are strongly
encouraged to do this right, so as to avoid if at all possible the
extensible agent's having to return `commitFailed' or `undoFailed'
during subsequent processing.
Daniele, et. al. Standards Track [Page 64]
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7.2.3.2. Subagent Processing of the agentx-CommitSet-PDU
The agentx-CommitSet-PDU indicates that the subagent should actually
perform (as described in the post-validation sections of 4.2.5 of RFC
1905 [4]) the management operation indicated by the previous
TestSet-PDU. After carrying out the management operation, the
subagent sends in reply an agentx-Response-PDU whose res.error field
is set to one of the following (SNMPv2 SMI) values:
noError (0),
commitFailed (14)
If this value is `commitFailed', the res.index field must be set to
the index of the VarBind for which the operation failed. Otherwise
res.index is set to 0.
7.2.3.3. Subagent Processing of the agentx-UndoSet-PDU
The agentx-UndoSet-PDU indicates that the subagent should undo the
management operation requested in a preceding CommitSet-PDU. The
undo process is as described in section 4.2.5 of RFC 1905 [4].
After carrying out the undo process, the subagent sends in reply an
agentx-Response-PDU whose res.index field is set to 0, and whose
res.error field is set to one of the following (SNMPv2 SMI) values:
noError (0),
undoFailed (15)
If this value is `undoFailed', the res.index field must be set to the
index of the VarBind for which the operation failed. Otherwise
res.index is set to 0.
This PDU also signals the end of processing of the management
operation initiated by the previous TestSet-PDU. The subagent should
release resources, etc. as described in section 7.2.3.4.
7.2.3.4. Subagent Processing of the agentx-CleanupSet-PDU
The agentx-CleanupSet-PDU signals the end of processing of the
management operation requested in the previous TestSet-PDU. This is
an indication to the subagent that it may now release any resources
it may have reserved in order to carry out the management request.
No response is sent by the subagent.
Daniele, et. al. Standards Track [Page 65]
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7.2.4. Master Agent Processing of AgentX Responses
The master agent now marshals all subagent AgentX response PDUs and
builds an SNMP response PDU. In the next several subsections, the
initial processing of all subagent AgentX response PDUs is described,
followed by descriptions of subsequent processing for each specific
subagent Response.
7.2.4.1. Common Processing of All AgentX Response PDUs
1) If a subagent does not respond within the timeout interval for
this dispatch, it is treated as if the subagent had returned
`genErr' and processed as described below.
A timeout may be due to a variety of reasons, and does not
necessarily denote a failed or malfunctioning subagent. As such,
the master agent's response to a subagent timeout is
implementation-specific, but with the following constraint:
A subagent that times out on three consecutive requests is
considered unable to respond, and the master agent must close
the AgentX session as described in 7.1.9, step (2).
2) Otherwise, the h.packetID, h.sessionID, and h.transactionID
fields of the AgentX response PDU are used to correlate subagent
responses. If the response does not pertain to this SNMP
operation, it is ignored.
3) Otherwise, the responses are processed jointly to form the SNMP
response PDU.
7.2.4.2. Processing of Responses to agentx-Get-PDUs
After common processing of the subagent's response to an agentx-Get-
PDU (see 7.2.4.1 above), processing continues with the following
steps:
1) For any received AgentX response PDU, if res.error is not
`noError', the SNMP response PDU's error code is set to this
value, and its error index to the index of the variable binding
corresponding to the failed VarBind in the subagent's AgentX
response PDU.
All other AgentX response PDUs received due to processing this
SNMP request are ignored. Processing is complete; the SNMP
Response PDU is ready to be sent (see section 7.2.5, Sending the
SNMP Response-PDU).
Daniele, et. al. Standards Track [Page 66]
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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.
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6) The AgentX PDUs are sent to the subagent(s), and the responses
are received and processed according to the steps described in
section 7.2.4.
7) This process continues iteratively until a complete SNMP
Response-PDU has been built, or until there remain no target OID
range lexicographical successors.
7.2.4.4. Processing of Responses to agentx-TestSet-PDUs
After common processing of the subagent's response to an agentx-
TestSet-PDU (see 7.2.4.1 above), processing continues with the
further exchange of AgentX PDUs. The value of h.transactionID in the
agentx-CommitSet, -UndoSet, and -CleanupSet-PDUs must be identical to
the value sent in the testSet-PDU.
The state transitions and PDU sequences are depicted in section 7.3.
1) If any target subagent's response is not `noError', all other
agentx-Response-PDUs received due to processing this SNMP request
are ignored.
An agentx-CleanupSet-PDU is sent to each target subagent that has
been sent a agentx-TestSet-PDU.
Processing is complete; the SNMP response PDU is constructed as
described below in 7.2.4.6.
2) Otherwise an agentx-CommitSet-PDU is sent to each target
subagent.
7.2.4.5. Processing of Responses to agentx-CommitSet-PDUs
After common processing of the subagent's response to an agentx-
CommitSet-PDU (see 7.2.4.1 above), processing continues with the
following steps:
1) If any response is not `noError', all other
agentx-Response-PDUs received due to processing this SNMP request
are ignored.
An agentx-UndoSet-PDU is sent to each target subagent that has
been sent a agentx-CommitSet-PDU. All other subagents are sent a
agentx-CleanupSet-PDU.
2) Otherwise an agentx-CleanupSet-PDU is sent to each target
subagent. Processing is complete; the SNMP response PDU is
constructed as described below in 7.2.4.6.
Daniele, et. al. Standards Track [Page 68]
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7.2.4.6. Processing of Responses to agentx-UndoSet-PDUs
After common processing of the subagent's response to an agentx-
UndoSet-PDU (see 7.2.4.1 above), processing continues with the
following steps:
1) If any response is not `noError' the SNMP response
PDU's error code is set to this value, and its error index to the
index of the VarBind corresponding to the failed VarBind in the
agentx-TestSet-PDU.
Otherwise the SNMP response PDU's error code is set to `noError'
and its error index to 0.
7.2.5. Sending the SNMP Response-PDU
Once the processing described in sections 7.2.1 - 7.2.4 is complete,
there is an SNMP response PDU available. The master agent now
implements the Elements of Procedure for the applicable version of
the SNMP protocol in order to encapsulate the PDU into a message, and
transmit it to the originator of the SNMP management request. Note
that this may involve altering the PDU contents (for instance, to
replace the original VarBinds if an error condition is to be
returned).
The response PDU may also be altered in order to support the SNMP
version 1 framework. In such cases the required mapping is that
defined in RFC 2089 [9]. (Note in particular that the rules for
handling Counter64 syntax may require re-sending AgentX GetBulk or
GetNext PDUs until a VarBind of suitable syntax is returned.)
7.2.6. MIB Views
AgentX subagents are not aware of MIB views, since view information
is not contained in AgentX PDUs.
As stated above, the descriptions of procedures in section 7 of this
memo are not intended to constrain the internal architecture of any
conformant implementation. In particular, the master agent
procedures described in sections 7.2.1 and 7.2.4 may be altered so as
to optimize AgentX exchanges when implementing MIB views.
Such optimizations are beyond the scope of this memo. But note that
section 7.2.3 defines subagent behavior in such a way that alteration
of SearchRanges may be used in such optimizations.
Daniele, et. al. Standards Track [Page 69]
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7.3. State Transitions
State diagrams are presented from the master agent's perspective for
transport connection and session establishment, and from the
subagent's perspective for Set transaction processing.
7.3.1. Set Transaction States
The following table presents, from the subagent's perspective, the
state transitions involved in Set transaction processing:
STATE
+----------------+--------------+---------+--------+--------
| A | B | C | D | E
| (Initial | TestOK | Commit | Test | Commit
| State) | | OK | Fail | Fail
| | | | |
EVENT | | | | |
---------+----------------+--------------+---------+--------+--------
| 7.2.3.1 | | | |
Receive | All varbinds | | | |
TestSet | OK? | X | X | X | X
PDU | Yes ->B | | | |
| No ->D | | | |
---------+----------------+--------------+---------+--------+--------
| | 7.2.3.2 | | |
Receive | | NoError? | | |
Commit- | X | Yes ->C | X | X | X
Set PDU | | No ->E | | |
---------+----------------+--------------+---------+--------+--------
Receive | | | 7.2.3.3 | |7.2.4.5
UndoSet | X | X | ->done | X | ->done
PDU | | | | |
---------+----------------+--------------+---------+--------+--------
Receive | | 7.2.4.4 | 7.2.3.4 |7.2.4.4 |
Cleanup- | X | ->done | ->done | ->done | X
Set PDU | | | | |
---------+----------------+--------------+---------+--------+--------
Session | | rollback | undo | |
Loss | ->done | ->done | ->done | ->done | ->done
---------+----------------+--------------+---------+--------+--------
There are three possible sequences that a subagent may follow for a
particular set transaction:
1) TestSet CommitSet CleanupSet
2) TestSet CommitSet UndoSet
3) TestSet CleanupSet
Daniele, et. al. Standards Track [Page 70]
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Note that a single PDU sequence may result in multiple paths through
the finite state machine (FSM). For example, the sequence
TestSet CommitSet UndoSet
may walk through either of these two state sequences:
(initial) TestOK CommitOK (done)
(initial) TestOK CommitFail (done)
7.3.2 Transport Connection States
The following table presents, from the master agent's perspective,
the state transitions involved in transport connection setup and
teardown:
Daniele, et. al. Standards Track [Page 71]
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STATE
+--------------+--------------
| A | B
| No transport | Transport
| | connected
| |
EVENT | |
----------------+--------------+--------------
Transport | |
connect | ->B | X
indication | |
----------------+--------------+--------------
Receive | | if duplicate
Open-PDU | | session id,
| | reject, else
| X | establish
| | session
| |
| | ->B
----------------+--------------+--------------
Receive | | if matching
Response-PDU | | session id,
| | feed to that
| X | session's FSM
| | else ignore
| |
| | ->B
----------------+--------------+--------------
Receive other | | if matching
PDUs | | session id,
| | feed to that
| X | session's FSM
| | else reject
| |
| | ->B
----------------+--------------+--------------
Transport | |notify all
disconnect | |sessions on
indication | X |this transport
| |
| | ->A
----------------+--------------+--------------
Daniele, et. al. Standards Track [Page 72]
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7.3.3 Session States
The following table presents, from the master agent's perspective,
the state transitions involved in session setup and teardown:
STATE
+-------------+----------------
| A | B
| No session | Session
| | established
EVENT | |
---------------+-------------+----------------
| 7.1.1 |
Receive | | X
Open PDU | ->B |
---------------+-------------+----------------
| | 7.1.9
Receive | X |
Close PDU | | ->A
---------------+-------------+----------------
Receive | | 7.1.5
Register PDU | X |
| | ->B
---------------+-------------+----------------
Receive | | 7.1.6
Unregister | X |
PDU | | ->B
---------------+-------------+----------------
Receive | |
Get PDU | |
GetNext PDU | |
GetBulk PDU | X | X
TestSet PDU | |
CommitSet PDU | |
UndoSet PDU | |
CleanupSet PDU | |
---------------+-------------+----------------
Receive | | 7.1.11
Notify PDU | X |
| | ->B
---------------+-------------+----------------
Receive Ping | | 7.1.12
PDU | X |
| | ->B
---------------+-------------+----------------
(continued next page)
Daniele, et. al. Standards Track [Page 73]
RFC 2257 AgentX January 1998
---------------+-------------+----------------
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.
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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).
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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.
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10. Acknowledgements
The initial development of this memo was heavily influenced by the
DPI 2.0 specification RFC 1592 [7].
This document was produced by the IETF Agent Extensibility (AgentX)
Working Group, and benefited especially from the contributions of the
following working group members:
David Battle, Uri Blumenthal, Jeff Case, Maria Greene, Dave
Keeney, Harmen van der Linde, Bob Natale, Randy Presuhn, Aleksey
Romanov, Don Ryan, and Juergen Schoenwaelder.
The AgentX Working Group is chaired by:
Bob Natale
ACE*COMM Corporation
704 Quince Orchard Road
Gaithersburg MD 20878
Phone: +1-301-721-3000
Fax: +1-301-721-3001
EMail: bnatale@acecomm.com
11. Authors' and Editor's Addresses
Mike Daniele
Digital Equipment Corporation
110 Spit Brook Rd
Nashua, NH 03062
Phone: +1-603-881-1423
EMail: daniele@zk3.dec.com
Bert Wijnen
IBM Professional Services
Watsonweg 2
1423 ND Uithoorn
The Netherlands
Phone: +31-79-322-8316
EMail: wijnen@vnet.ibm.com
Daniele, et. al. Standards Track [Page 77]
RFC 2257 AgentX January 1998
Dale Francisco (editor)
Cisco Systems
150 Castilian Dr
Goleta CA 93117
Phone: +1-805-961-3642
Fax: +1-805-961-3600
EMail: dfrancis@cisco.com
12. References
[1] Information processing systems - Open Systems Interconnection -
Specification of Abstract Syntax Notation One (ASN.1),
International Organization for Standardization. International
Standard 8824, (December, 1987).
[2] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Structure of Management Information for Version 2 of the Simple
Network Management Protocol (SNMPv2)", RFC 1902, January 1996.
[3] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Textual Conventions for Version 2 of the Simple Network Management
Protocol (SNMPv2)", RFC 1903, January 1996.
[4] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Protocol Operations for Version 2 of the Simple Network Management
Protocol (SNMPv2)", RFC 1905, January 1996.
[5] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Management Information Base for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1907, January 1996.
[6] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network
Management Protocol", STD 15, RFC 1157, SNMP Research, Performance
Systems International, MIT Laboratory for Computer Science, May
1990.
[7] Wijnen, B., Carpenter, G., Curran, K., Sehgal, A. and G. Waters,
"Simple Network Management Protocol: Distributed Protocol
Interface, Version 2.0", RFC 1592, March 1994.
[8] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Coexistence between Version 1 and Version 2 of the Internet-
standard Network Management Framework", RFC 1908, January 1996.
[9] Wijnen, B. and D. Levi, "V2ToV1: Mapping SNMPv2 onto SNMPv1
Within a Bilingual SNMP Agent", RFC 2089, January 1997.
Daniele, et. al. Standards Track [Page 78]
RFC 2257 AgentX January 1998
[10] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Conformance Statements for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1904, January 1996.
[11] McCloghrie, K. and F. Kastenholz, "Evolution of the
Interfaces Group of MIB-II", RFC 1573, January 1994.
[12] Case, J., "FDDI Management Information Base", RFC 1285,
January 1992.
[13] Application MIB Working Group, Krupczak, C., and J. Saperia,
"Definitions of System-Level Managed Objects for Applications",
draft-ietf-applmib-sysapplmib-08.txt, 15 Apr 1997.
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13. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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