INTERNET-DRAFT
<draft-ietf-agentx-ext-pro-01.txt>
Expire in six months
Agent Extensibility (AgentX) Protocol
Version 1
November 26, 1996
Mike Daniele
Digital Equipment Corporation
daniele@zk3.dec.com
Bert Wijnen
T.J. Watson Research Center, IBM Corp.
wijnen@vnet.ibm.com
Dale Francisco (editor)
Cisco Systems, Inc.
dfrancis@cisco.com
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as ``work in
progress.''
To learn the current status of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in the Internet-Drafts
Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net
(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
Rim).
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1 Introduction......................................................5
2 The SNMP Framework................................................5
2.1 A Note on Terminology.........................................5
3 Extending the MIB.................................................6
3.1 Motivation for AgentX.........................................6
4 AgentX Framework..................................................7
4.1 AgentX Roles..................................................7
4.2 Design Goals for AgentX.......................................8
5 AgentX Encodings..................................................9
5.1 Object Identifier............................................10
5.2 SearchRange..................................................12
5.3 Octet String.................................................13
5.4 Value Representation.........................................14
6 Protocol Definitions.............................................16
6.1 AgentX PDU Header............................................16
6.1.1 Context..................................................17
6.2 AgentX PDUs..................................................18
6.2.1 The agentx-Open-PDU......................................18
6.2.1.1 agentx-Open-PDU Fields...............................18
6.2.2 The agentx-Close-PDU.....................................19
6.2.2.1 agentx-Close-PDU Fields..............................20
6.2.3 The agentx-Register-PDU..................................21
6.2.3.1 agentx-Register-PDU Fields...........................22
6.2.4 The agentx-Unregister-PDU................................24
6.2.4.1 agentx-Unregister-PDU Fields.........................25
6.2.5 The agentx-Get-PDU.......................................26
6.2.5.1 agentx-Get-PDU Fields................................27
6.2.6 The agentx-GetNext-PDU...................................28
6.2.7 The agentx-GetBulk-PDU...................................29
6.2.8 The agentx-TestSet-PDU...................................30
6.2.8.1 agentx-TestSet-PDU Fields............................31
6.2.9 The agentx-CommitSet, -UndoSet, -CleanupSet,
and -Ping PDUs...........................................31
6.2.10 The agentx-Notify-PDU...................................32
6.2.10.1 agentx-Notify-PDU Fields............................32
6.2.11 The agentx-IndexAllocate-PDU............................33
6.2.11.1 agentx-IndexAllocate-PDU fields.....................33
6.2.12 The agentx-IndexDeallocate-PDU..........................34
6.2.12.1 agentx-IndexDeallocate-PDU fields...................34
6.2.13 The agentx-AddAgentCaps-PDU.............................35
6.2.13.1 agentx-AddAgentCaps-PDU Fields......................36
6.2.14 The agentx-RemoveAgentCaps-PDU..........................37
6.2.14.1 agentx-RemoveAgentCaps-PDU Fields...................37
6.2.15 The agentx-Response-PDU.................................38
6.2.15.1 agentx-Response-PDU Fields..........................38
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7 Elements of Procedure............................................39
7.1 Processing AgentX Administrative Messages....................39
7.1.1 Processing the agentx-Open-PDU...........................39
7.1.2 Processing the agentx-IndexAllocate-PDU..................40
7.1.3 Using the agentx-IndexAllocate-PDU.......................42
7.1.4 Processing the agentx-IndexDeallocate-PDU................43
7.1.5 Processing the agentx-Register-PDU.......................44
7.1.5.1 Handling Duplicate OID Ranges........................46
7.1.6 Processing the agentx-Unregister-PDU.....................47
7.1.7 Processing the agentx-AddAgentCaps-PDU...................47
7.1.8 Processing the agentx-RemoveAgentCaps-PDU................48
7.1.9 Processing the agentx-Close-PDU..........................48
7.1.10 Detecting Connection Loss...............................48
7.1.11 Processing the agentx-Notify-PDU........................48
7.1.12 Processing the agentx-Ping-PDU..........................49
7.2 Processing Received SNMP Protocol Messages...................49
7.2.1 Dispatching AgentX PDUs..................................50
7.2.1.1 agentx-Get-PDU.......................................50
7.2.1.2 agentx-GetNext-PDU...................................51
7.2.1.3 agentx-GetBulk-PDU...................................53
7.2.1.4 agentx-TestSet-PDU...................................54
7.2.1.5 Dispatch.............................................55
7.2.2 Subagent Processing of agentx-Get, GetNext,
GetBulk-PDUs.............................................55
7.2.2.1 Subagent Processing of the agentx-Get-PDU............56
7.2.2.2 Subagent Processing of the
agentx-GetNext-PDU...................................56
7.2.2.3 Subagent Processing of the
agentx-GetBulk-PDU...................................57
7.2.3 Subagent Processing of agentx-TestSet,
-CommitSet, -UndoSet, -CleanupSet-PDUs...................58
7.2.3.1 Subagent Processing of the
agentx-TestSet-PDU...................................59
7.2.3.2 Subagent Processing of the
agentx-CommitSet-PDU.................................60
7.2.3.3 Subagent Processing of the
agentx-UndoSet-PDU...................................60
7.2.3.4 Subagent Processing of the
agentx-CleanupSet-PDU................................60
7.2.4 Master Agent Processing of AgentX Responses..............60
7.2.4.1 Common Processing of All AgentX Response
PDUs.................................................61
7.2.4.2 Processing of Responses to agentx-Get-PDUs...........61
7.2.4.3 Processing of Responses to
agentx-GetNext- and agentx-GetBulk-PDUs..............62
7.2.4.4 Processing of Responses to
agentx-TestSet-PDUs..................................63
7.2.4.5 Processing of Responses to
agentx-CommitSet-PDUs................................64
7.2.4.6 Processing of Responses to
agentx-UndoSet-PDUs..................................64
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7.2.5 Sending the SNMP Response-PDU............................64
7.2.6 MIB Views................................................65
8 Transport Mappings...............................................65
8.1 AgentX over TCP..............................................65
8.1.1 Well-known Values........................................65
8.1.2 Operation................................................65
8.2 AgentX over UNIX-domain Sockets..............................65
8.2.1 Well-known Values........................................66
8.2.2 Operation................................................66
9 Security Considerations..........................................66
10 Acknowledgements................................................66
11 Questions and Issues............................................67
11.1 Design......................................................67
11.2 Miscellaneous Issues/Decisions..............................67
11.3 New in this version.........................................69
12 Authors' and Editor's Addresses.................................70
13 References......................................................70
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1. Introduction
This memo defines a framework for extensible SNMP agents. It defines
processing entities called master agents and subagents, a protocol
(AgentX) used to communicate between them, and the elements of
procedure by which the extensible agent processes SNMP protocol
messages.
2. The SNMP Framework
A management system contains: several (potentially many) nodes,
each with a processing entity, termed an agent, which has access to
management instrumentation; at least one management station; and, a
management protocol, used to convey management information between
the agents and management stations. Operations of the protocol are
carried out under an administrative framework which defines
authentication, authorization, access control, and privacy
policies.
Management stations execute management applications which monitor
and control managed elements. Managed elements are devices such as
hosts, routers, terminal servers, etc., which are monitored and
controlled via access to their management information.
Management information is viewed as a collection of managed objects,
residing in a virtual information store, termed the Management
Information Base (MIB). Collections of related objects are defined
in MIB modules. These modules are written using a subset of OSI's
Abstract Syntax Notation One (ASN.1) [1], termed the Structure of
Management Information (SMI) (see RFC 1902 [2]).
2.1. A Note on Terminology
The term "variable" refers to an instance of a non-aggregate
object type defined according to the conventions set forth in the
SMI (RFC 1902, [2]) or the textual conventions based on the SMI
(RFC 1903 [3]). The term "variable binding" normally refers to
the pairing of the name of a variable and its associated value.
However, if certain kinds of exceptional conditions occur during
processing of a retrieval request, a variable binding will pair a
name and an indication of that exception.
A variable-binding list is a simple list of variable bindings.
The name of a variable is an OBJECT IDENTIFIER, which is the
concatenation of the OBJECT IDENTIFIER of the corresponding object
type together with an OBJECT IDENTIFIER fragment identifying the
instance. The OBJECT IDENTIFIER of the corresponding object-type is
called the OBJECT IDENTIFIER prefix of the variable.
For the purpose of exposition, the original Internet-standard
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Network Management Framework, as described in RFCs 1155 (STD 16),
1157 (STD 15), and 1212 (STD 16), is termed the SNMP version 1
framework (SNMPv1). The current framework, as described in RFCs
1902-1908, is termed the SNMP version 2 framework (SNMPv2).
3. Extending the MIB
New MIB modules that extend the Internet-standard MIB are
continuously being defined by various IETF working groups. It is
also common for enterprises or individuals to create or extend
enterprise-specific or experimental MIBs.
As a result, managed devices are frequently complex collections of
manageable components that have been independently installed on a
managed node. Each component provides instrumentation for the
managed objects defined in the MIB module(s) it implements.
Neither the SNMP version 1 or version 2 framework addresses how
managed objects may be dynamically added to or removed from the
agent view within a particular managed node.
3.1. Motivation for AgentX
This very real need to dynamically extend the management objects
within a node has given rise to a variety of "extensible agents",
which typically comprise
- a "master" agent that is available on the standard transport
address and that accepts SNMP protocol messages
- a set of "subagents" that each contain management
instrumentation
- a protocol that operates between the master agent and subagents,
permitting subagents to "connect" to the master agent, and the
master agent to multiplex received SNMP protocol messages
amongst the subagents.
- a set of tools to aid subagent development, and a runtime (API)
environment that hides much of the protocol operation between a
subagent and the master agent.
The wide deployment of extensible SNMP agents, coupled with the
lack of Internet standards in this area, makes it difficult to field
SNMP-manageable applications. A vendor may have to support several
different subagent environments (APIs) in order to support different
target platforms.
It can also become quite cumbersome to configure subagents and
(possibly multiple) master agents on a particular managed node.
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Specifying a standard protocol for agent extensibility (AgentX)
provides the technical foundation required to solve both of
these problems. Independently developed AgentX-capable master
agents and subagents will be able to interoperate at the protocol
level. Vendors can continue to differentiate their products
in all other respects.
4. AgentX Framework
Within the SNMP framework, a managed node contains a processing
entity, called an agent, which has access to management
information.
Within the AgentX framework, an agent is further defined to
consist of
- a single processing entity called the master agent, which sends
and receives SNMP protocol messages in an agent role (as
specified by the SNMP version 1 and version 2 framework
documents) but typically has little or no direct access to
management information.
- 0 or more processing entities called subagents, which are
"shielded" from the SNMP protocol messages processed by the
master agent, but which have access to management information.
The master and subagent entities communicate via AgentX protocol
messages, as specified in this memo. Other interfaces (if any) on
these entities, and their associated protocols, are outside the
scope of this document. While some of the AgentX protocol messages
appear similar in syntax and semantics to the SNMP, bear in mind
that AgentX is not SNMP.
The internal operations of AgentX are invisible to an SNMP entity
operating in a manager role. From a manager's point of view, an
extensible agent behaves exactly as would a non-extensible
(monolithic) agent that has access to the same management
instrumentation.
This transparency to managers is a fundamental requirement of
AgentX, and is what differentiates AgentX subagents from SNMP proxy
agents.
4.1. AgentX Roles
An entity acting in a master agent role performs the following
functions:
- Accepts AgentX session establishment requests from subagents.
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- Accepts registration of MIB regions by subagents.
- Sends and accepts SNMP protocol messages on the agent's
specified transport addresses.
- Implements the agent role Elements of Procedure specified
for the administrative framework applicable to the SNMP
protocol message, except where they specify performing
management operations. (The application of MIB views, and
the access control policy for the managed node, are
implemented by the master agent.)
- Provides instrumentation for the MIB objects defined in RFC
1907 [5], and for any MIB objects relevant to any
administrative framework it supports.
- Sends and receives AgentX protocol messages to access
management information, based on the current registry of MIB
regions.
- Forwards notifications on behalf of subagents.
An entity acting in a subagent role performs the following functions:
- Initiates an AgentX session with the master agent.
- Registers MIB regions with the master agent.
- Instantiates managed objects.
- Binds OIDs within its registered MIB regions to actual
variables.
- Performs management operations on variables.
- Initiates notifications.
4.2. Design Goals for AgentX
The primary goals of the design described in this memo are to
1) Define a standard protocol and "rules of engagement" for
interoperability between management instrumentation and extensible
agents.
2) Provide a mechanism 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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As described below, support for index allocation, overlapping
registration, and the open registration method ("open" in the
sense that subagents are not required to know the state of
pre-existing registrations in order for registration to work)
provide such a mechanism.
3) Enhance performance where possible. Some of the design decisions
made with this in mind include:
- 32-bit alignment of data within PDUs
- Native byte-order encoding by subagents
- In any single request/response exchange between master agent
and subagent, all variable bindings targeted for a subagent
are included in a single AgentX PDU sent to that subagent.
Note: In some cases multiple request/response
exchanges may be required in order to process a
single management request; for example, in processing
some SNMP GetBulk or GetNext requests.
- Subagent returns a single response PDU, which contains as
much data as possible; its limits (for Next/Bulk) are its
own size constraints, or the upper bound on variable binding
names established by the master agent.
As a general architectural principle, this memo proposes that there
should be a division of labor between master agent and subagent: The
master agent is MIB ignorant and SNMP omniscient, while the subagent
is SNMP ignorant and MIB omniscient. That is, master agents are
exclusively concerned with SNMP 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.
For questions and open issues, see section 11 at the end of this
memo.
5. AgentX Encodings
AgentX PDUs consist of a common header, followed by PDU-specific
data of variable length. Unlike SNMP PDUs, AgentX PDUs are not
encoded using the BER (as specified in ISO 8824 [1]), but are
transmitted as a contiguous byte stream. The data within this
stream is organized to provide natural alignment with respect to the
start of the PDU, permitting direct (integer) access by the
processing entities.
The fields in the header are always encoded in network byte order
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(most significant byte first), regardless of the setting of the
NETWORK_BYTE_ORDER flag in the h.flags field (see section 6.1).
Fields within the PDUs are encoded either most significant byte
first, or least significant byte first. The subagent selects which
byte ordering to use when it establishes an AgentX session.
PDUs are depicted in this memo using the following convention
(where byte 1 is the first transmitted byte):
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| byte 1 | byte 2 | byte 3 | byte 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| byte 5 | byte 6 | byte 7 | byte 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Fields marked "<reserved>" are reserved for future use and must be
zero-filled.
5.1. Object Identifier
An object identifier is encoded as a 4-byte header, followed by a
variable number of contiguous 4-byte fields representing
sub-identifiers. This representation (termed Object Identifier) is
as follows:
Object Identifier
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | include | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Object Identifier header fields:
n_subid
The number (0-128) of sub-identifiers in the object
identifier. An ordered list of `n_subid' 4-byte
sub-identifiers follows the 4-byte header.
prefix
An unsigned value used to reduce the length of object
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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.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A null Object Identifier consists of the 4-byte header with all
bytes set to 0.
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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
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.
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5.4. Value Representation
Variable bindings may be encoded within the variable-length portion
of some PDUs. The representation of a variable binding (termed a
VarBind) consists of a 2-byte type field, a name (Object
Identifier), and the actual value data.
VarBind
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| v.type | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(v.name)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(v.data)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
VarBind fields:
v.type
Indicates the variable binding's syntax, and must be one of
the following (SNMPv2 SMI) values:
Integer (2),
Octet String (4),
Object Identifier (6),
IpAddress (64),
Counter32 (65),
Gauge32 (66),
TimeTicks (67),
Opaque (68),
Counter64 (70),
noSuchObject (128),
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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 subagent chose network byte
ordering (see 7.1.1., Processing the agentx-Open-PDU,
item 3), 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
subagent chose network byte ordering (see 7.1.1.,
Processing the agentx-Open-PDU, item 3), the bytes are
ordered most significant to least significant, otherwise
they are ordered least significant to most significant.
- Object Identifiers are encoded as described in section
5.1, Object Identifier.
- IpAddress, Opaque, and Octet String are all octet strings
and are encoded as described in section 5.3, Octet String.
Value data always follows v.name whenever v.type is one
of the above types. These data bytes are present even if
they will not be used (as, for example, in certain types
of index allocation).
- 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.
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6. Protocol Definitions
6.1. AgentX PDU Header
The AgentX PDU header is a fixed-format, 12-octet structure, whose
data are always transmitted in network byte order:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version | h.type | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An AgentX PDU header contains the following fields:
h.version
The version of the AgentX protocol (1 for this draft).
h.type
The PDU type; one of the following values:
agentx-Open-PDU (1),
agentx-Close-PDU (2),
agentx-Register-PDU (3),
agentx-Unregister-PDU (4),
agentx-Get-PDU (5),
agentx-GetNext-PDU (6),
agentx-GetBulk-PDU (7),
agentx-TestSet-PDU (8),
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.payload_length
The size in octets of the PDU contents, excluding the 12-byte
header. As a result of the encoding schemes and PDU layouts,
this value will always be either 0, or a multiple of 4.
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h.ID
A packet ID that should be kept unique by the sending entity.
The response to this PDU will contain the same value in its
h.ID field. Master agents typically increment this value for
each PDU sent, and wrap if the maximum value is reached.
h.flags
A bitmask, with bit 0 the leftmost 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
5-15 (reserved)
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-, and TestSet-PDUs.
If the NON_DEFAULT_CONTEXT bit in the AgentX header field h.flags is
clear, then there is no context field in the PDU, and the operation
refers to the default context.
If the NON_DEFAULT_CONTEXT bit is set, then a context field
immediately follows the AgentX header, and the operation refers
to that specific context. The context is represented as an Octet
String. There are no constraints on its length or contents.
Thus, all of these AgentX PDUs (that is, those listed immediately
above) refer to, or "indicate" a context, which is either the
default context, or a non-default context explicitly named in the
PDU.
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6.2. AgentX PDUs
6.2.1. The agentx-Open-PDU
An agentx-Open-PDU is generated by a subagent to request
establishment of an AgentX session with the master agent.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (1) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| o.timeout | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(o.id)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subidentifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subidentifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(o.descr)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.2.1.1. agentx-Open-PDU Fields
An agentx-Open-PDU contains the following fields:
o.timeout
The length of time, in seconds, that a master agent should
allow to elapse after dispatching a message to a subagent
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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.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| c.reason | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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6.2.2.1. agentx-Close-PDU Fields
An agentx-Close-PDU contains the following field:
c.reason
An enumerated value that gives the reason that the master
agent or subagent closed the AgentX session. This field may
take one of the following values:
reasonOther(1)
None of the following reasons
reasonProtocolError(2)
Too many AgentX protocol errors from peer
reasonTimeouts(3)
Too many timeouts waiting for peer
reasonShutdown(4)
Sending entity is shutting down
reasonByManager(5)
Due to Set operation
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6.2.3. The agentx-Register-PDU
An agentx-Register-PDU is generated by a subagent for each region of
the MIB variable naming tree (within one or more contexts) that it
wishes to support.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (3) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.context) (OPTIONAL)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| r.timeout | r.priority | r.range_subid | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.region)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.upper_bound)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| optional upper-bound sub-identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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6.2.3.1. agentx-Register-PDU Fields
An agentx-Register-PDU contains the following fields:
r.context
An optional non-default context.
r.timeout
The length of time, in seconds, that a master agent should
allow to elapse after dispatching a message to a subagent
before it regards the subagent as not responding. r.timeout
applies only to messages that concern MIB objects within
r.region. It overrides both the subagent-wide value (if any)
indicated when the AgentX session with the master agent was
established, and the master agent's default timeout. The
default value for r.timeout is `0' (no override).
r.priority
A value between 1 and 255, used to achieve a desired
configuration when different subagents register identical or
overlapping regions. Subagents with no particular knowledge
of priority should register with the default value of `255'
(lowest priority).
In the master agent's dispatching algorithm, smaller
values of r.priority take precedence over larger values,
as described in section 7.1.5.1.
r.region
An Object Identifier that, in conjunction with r.range_subid,
indicates a region of the MIB that a subagent wishes to
support. It may be a fully-qualified instance name, a partial
instance name, a MIB table, or ranges of any of these.
The choice of what to register is implementation-specific;
this memo does not specify permissible values. Standard
practice however is for a subagent to register at the
highest level of the naming tree that makes sense.
Registration of fully-qualified instances is typically done
only when a subagent can perform management operations only
on particular rows of a conceptual table.
If r.region is in fact a fully qualified instance name, the
INSTANCE_REGISTRATION bit in h.flags must be set, otherwise it
must be cleared. The master agent may save this information
to optimize subsequent operational dispatching.
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r.range_subid
Permits specifying a range in place of one of r.region's
sub-identifiers. If this value is 0, no range is specified.
Otherwise the `r.range_subid'-th sub-identifier in
r.region is a range lower bound, and the range upper
bound sub-identifier (r.upper_bound) immediately follows
r.region.
This permits registering a conceptual row with a single
PDU. For example, the following PDU would register row
7 of the RFC 1573 ifTable (1.3.6.1.2.1.2.2.1.1-22.7):
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (3) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| r.timeout | r.priority | 5 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.region)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 | 2 | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(r.upper_bound)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 22 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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6.2.4. The agentx-Unregister-PDU
The agentx-Unregister-PDU is sent by a subagent to remove a
previously registered MIB region from the master agent's OID space.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (4) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(u.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| <reserved> | u.range_subid | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(u.region)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(u.upper_bound)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| optional upper-bound sub-identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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6.2.4.1. agentx-Unregister-PDU Fields
An agentx-Unregister-PDU contains the following fields:
u.context
An optional non-default context.
u.region
Indicates a previously-registered region of the MIB that a
subagent no longer wishes to support. It may be a
fully-qualified instance name, a partial instance name, a MIB
table or group, or ranges of any of these.
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6.2.5. The agentx-Get-PDU
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (5) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(g.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(g.sr)
(start 1)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | include | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(end 1)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
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(start n)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | include | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(end n)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.2.5.1 agentx-Get-PDU Fields
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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6.2.6. The agentx-GetNext-PDU
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (6) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(g.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(g.sr)
...
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6.2.7. The agentx-GetBulk-PDU
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (7) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(g.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| g.non_repeaters | g.max_repetitions |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(g.sr)
...
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6.2.8. The agentx-TestSet-PDU
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (8) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(t.context) OPTIONAL
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Padding (as required) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(t.vb)
(VarBind 1)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| v.type | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
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(VarBind n)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| v.type | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.2.8.1. agentx-TestSet-PDU Fields
An agentx-TestSet-PDU contains the following fields:
t.context
An optional non-default context.
t.vb
A VarBindList containing the requested variable bindings for
this subagent.
6.2.9. The agentx-CommitSet, -UndoSet, -CleanupSet, and -Ping PDUs
These PDUs consist of the AgentX header only.
The agentx-CommitSet-, -UndoSet-, and -Cleanup-PDUs are used in
processing an SNMP SetRequest operation.
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.
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6.2.10. The agentx-Notify-PDU
An agentx-Notify-PDU is sent by a subagent to cause the master agent
to forward a notification.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (12) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(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)
...
6.2.10.1. agentx-Notify-PDU Fields
An agentx-Notify-PDU contains the following fields:
n.context
An optional non-default context.
n.vb
A VarBindList whose contents define the actual PDU to be
sent. This memo places the following restrictions on its
contents:
- If the subagent supplies sysUpTime.0, it must be
present as the first varbind.
- snmpTrapOID.0 must be present, as the second
varbind if sysUpTime.0 was supplied, as the
first if it was not.
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6.2.11. The agentx-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.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(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)
...
6.2.11.1 agentx-IndexAllocate-PDU fields
An agentx-IndexAllocate-PDU contains the following fields:
i.context
An optional non-default context.
i.vb
A VarBindList containing the index names and values requested
for allocation.
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6.2.12. The agentx-IndexDeallocate-PDU
An agentx-IndexDeallocate-PDU is sent by a subagent to release
previously allocated index values.
(AgentX header)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (15) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(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)
...
6.2.12.1 agentx-IndexDeallocate-PDU fields
An agentx-IndexDeallocate-PDU contains the following fields:
i.context
An optional non-default context.
i.vb
A VarBindList containing the index names and values to be
released.
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6.2.13. 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.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a.context) (OPTIONAL)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Optional Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a.id)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a.descr)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Optional Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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6.2.13.1. agentx-AddAgentCaps-PDU Fields
An agentx-AddAgentCaps-PDU contains the following fields:
a.context
An optional non-default context.
a.id
An Object Identifier containing the value of an invocation of
the AGENT-CAPABILITIES macro, which the master agent exports
as a value of sysORID for the indicated context. (Recall that
the value of an invocation of an AGENT-CAPABILITIES macro is
an object identifier that describes a precise level of support
with respect to implemented MIB modules. A more complete
discussion of the AGENT-CAPABILITIES macro and related sysORID
values can be found in section 6 of RFC 1904 [10].)
a.descr
An Octet String containing a DisplayString to be used as the
value of sysORDescr corresponding to the sysORID value above.
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6.2.14. 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.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a.context) (OPTIONAL)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet String Length (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet 1 | Octet 2 | Octet 3 | Octet 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octet L - 1 | Octet L | Optional Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a.id)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_subid | prefix | 0 | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier #n_subid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.2.14.1. agentx-RemoveAgentCaps-PDU Fields
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.
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6.2.15. The agentx-Response-PDU
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.version (1) | h.type (18) | h.payload_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| h.flags | <reserved> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| res.error | res.index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
(optional fields)
6.2.15.1. agentx-Response-PDU Fields
An agentx-Response-PDU contains the following fields:
h.ID
Must be identical to the h.ID value in the PDU to which this
PDU is a response.
h.flags
This field is ignored during response PDU processing.
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:
alreadyOpen (256),
openFailed (257),
notOpen (258),
indexUnsupportedType (259),
indexWrongType (260),
indexAlreadyAllocated (261),
indexNoneAvailable (262),
indexNotCurrentlyAllocated (263),
unsupportedContext (264),
duplicateRegistration (265),
unknownRegistration (266),
unknownAgentCaps (267)
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res.index
In error cases, this is the index of the failed variable
binding within a received request PDU.
Other data may follow these latter two fields, depending on
which AgentX PDU is being responded to. These data are
specified in the subsequent elements of procedure.
7. Elements of Procedure
This section describes the actions of protocol entities (master
agents and subagents) implementing the AgentX protocol. Note,
however, that it is not intended to constrain the internal
architecture of any conformant implementation.
The actions of AgentX protocol entities can be broadly categorized
under two headings:
(1) processing AgentX administrative messages (e.g, connection
requests from a subagent to a master agent); and
(2) processing SNMP messages (e.g., the coordinated actions of a
master agent and one or more subagents in processing a
received SNMP Get-PDU).
7.1. Processing AgentX Administrative Messages
This subsection describes the actions of AgentX protocol entities in
processing AgentX administrative messages. Such messages include
those involved in establishing and terminating an AgentX session
between a subagent and a master agent, those by which a subagent
requests allocation of instance index values, and those by which a
subagent communicates to a master agent which MIB regions it
supports.
7.1.1. Processing the agentx-Open-PDU
When the master agent receives an agentx-Open-PDU, it processes it
as follows:
1) If an AgentX session for this subagent has already been
established (via an agentx-Open-PDU from the same transport
endpoint), an agentx-Response-PDU is sent with res.error set
to 'alreadyOpen'.
2) If the master agent is unable to open an AgentX session for
some other reason, it may refuse the session establishment
request, sending in reply an agentx-Response-PDU whose
res.error field is set to `openFailed'.
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3) Otherwise, the master agent retains session-specific
information from the PDU for this subagent:
- The subagent sets the NETWORK_BYTE_ORDER bit to indicate its
native byte ordering. If set, all numeric data transmitted
during this AgentX session are in network byte order (most
significant byte first), else they are transmitted least
significant byte first. All PDUs exchanged over this AgentX
session will use this byte ordering (including this Open-PDU
and its Response-PDU). The Open-PDU is the only one for which
the NETWORK_BYTE_ORDER bit has meaning; byte ordering is an
attribute of the session, not of each subsequent PDU.
(Note: The 12-byte AgentX header is always transmitted in
network byte order regardless of how the rest of the PDU
is transmitted.)
- The o.timeout value is used in calculating timeout
conditions for this subagent.
- The o.id and o.descr fields are used to create an entry in
the agentxSubAgentTable defined in [TBD].
4) An agentx-Response-PDU is sent with the res.error field
set to `noError'. The 4 bytes immediately following the
header are encoded with the value of sysUpTime.0 for the
default context.
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 (3) 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) If an AgentX session for this subagent has not been
established, an agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
supports only a default context, an agentx-Response-PDU is
returned with res.error set to `unsupportedContext' and the
requested allocation fails.
3) Each VarBind in the VarBindList is processed until either all
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are successful, or one fails. If any VarBind fails, an
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 v.type is not supported by the master agent, the VarBind
fails and res.error is set to `indexUnsupportedType'.
Note: A master agent must support a v.type of INTEGER.
b) If there are currently allocated index values for v.name
in the indicated context, but the syntax of those values
does not match v.type, the VarBind fails and res.error is
set to `indexWrongType'.
c) Otherwise, if both the NEW_INDEX and ANY_INDEX bits are
clear, allocation of a specific index value is being
requested. If the requested index is already allocated
for v.name in the indicated context, the VarBind fails
and res.error is set to `indexAlreadyAllocated'.
d) Otherwise, if the NEW_INDEX bit is set, the master agent
should generate the next available index value for v.name
in the indicated context, with the constraint that this
value must not have been allocated (even if subsequently
released) to any subagent since the last re-initialization
of the master agent. If no such value can be generated,
the VarBind fails and res.error is set to `indexNoneAvailable'.
e) Otherwise, if the ANY_INDEX bit is set, the master agent
should generate an index value for v.name in the
indicated context, with the constraint that this value is
not currently allocated to any subagent. If no such value
can be generated, then the VarBind fails and res.error is
set to `indexNoneAvailable'.
4) If all VarBinds are processed successfully, an
agentx-Response-PDU is sent in reply with res.error set to
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`noError'. A VarBindList is included that is identical to the
one sent in the agentx-IndexAllocate-PDU, except that VarBinds
requesting the next available index value are updated 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 Application MIB [13]). The need for
subagents to share tables using such indexes is the main motivation
for index allocation in AgentX.
Example 1:
A subagent implements an interface, and wishes to register a
single row of the RFC 1573 ifTable. It requests an allocation
for the index object `ifIndex', for a value that has never been
allocated (since ifIndex values must be unique). The master agent
returns the value "7".
The subagent now attempts to register row 7 of ifTable, by
specifying a MIB region in the agentx-Register-PDU of
1.3.6.1.2.1.2.2.1.[1-22].7. If the registration succeeds, no
further processing is required. The master agent will dispatch
to this subagent correctly.
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But the registration may fail. Index allocation and MIB region
registration are not coupled in the master agent. Some other
subagent may have already registered ifTable row 7 without first
having requested allocation of the index. The current state of
index allocations is not considered when processing registration
requests, and the current registry is not considered when
processing index allocation requests. If subagents follow the
model of "first request allocation of an index, then register the
corresponding region", then a successful index allocation request
gives a subagent a good hint (but no guarantee) of what it should
be able to register.
If the registration failed, the subagent should request allocation
of a new index i, and attempt to register ifTable.[1-22].i, until
successful.
Example 2:
This same subagent wishes to register ipNetToMediaTable rows
corresponding to its interface (ifIndex i). Due to structure of
this table, no further index allocation need be done. The
subagent can register the MIB region ipNetToMediaTable.[1-4].i,
It is claiming responsibility for all rows of the table whose
value of ipNetToMediaIfIndex is i.
Example 3:
A network device consists of a set of processors, each of which
accepts network connections for a unique set of ip addresses.
Further, each processor contains a subagent that implements
tcpConnTable. In order to represent tcpConnTable for the entire
managed device, the subagents need to share tcpConnTable.
In this case, no index allocation need be done at all. Each
subagent can register a MIB region of tcpConnTable.[1-5].a.b.c.d,
where a.b.c.d represents an unique IP address of the individual
processor.
Each subagent is claiming responsibility for the region of
tcpConnTable where the value of tcpConnLocalAddress is a.b.c.d.
7.1.4 Processing the agentx-IndexDeallocate-PDU
When the master agent receives an agentx-IndexDeallocate-PDU, it
processes it as follows:
1) If an AgentX session for this subagent has not been
established, an agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) Each VarBind in the VarBindList is processed until either all
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are successful, or one fails. If any VarBind fails, an
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 and
should be cleared.
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'.
3) If all VarBinds are processed successfully, an agentx-Response-PDU
is sent in reply with res.error set to `noError'. 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) If an AgentX session for this subagent has not been
established, an agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) 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.
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If the NON_DEFAULT_CONTEXT bit is set, this region is to be
logically registered within the context indicated by r.context.
Otherwise this region is to be logically registered within the
default context.
A registration that would result in a duplicate region with the
same priority and within the same context as that of a current
registration is termed a duplicate registration.
3) If the NON_DEFAULT_CONTEXT bit is set, and the master agent
supports only a default context, an agentx-Response-PDU is
returned with res.error set to `unsupportedContext' and the
requested registration fails.
Note: A conformant AgentX master agent must support the notion
of a default context, and may support non-default contexts.
4) Otherwise, if this is a duplicate registration, an
agentx-Response-PDU is returned with res.error set to
`duplicateRegistration', and the requested registration fails.
5) Otherwise, an agentx-Response-PDU is returned with res.error
set to `noError', and a 4-byte TimeTicks value following the
header. The latter is the current value of sysUpTime.0 for
the context that was indicated in the registration message.
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
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set of registered regions would be:
1.3.6.1.2.1.4 up to but not including 1.3.6.1.2.1.4.22 (by S2)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S2)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S1)
1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5 (by S2)
- If r.region (R1) overlaps one or more currently registered
regions, then for each overlapped region (R2) split R1 into 3
new ranges (R1a, R1b, R1c) such that R1b is an exact
duplicate of R2. Add R1b and R2 into the lexicographically
ordered set of regions. Apply (5) above iteratively to R1a and
R1c (since they may overlap, or be subtrees of, other regions).
For instance, given the currently registered regions in the
example above, if subagent S3 now registers mib-2 (R1 is
1.3.6.1.2.1) the resulting set of regions would be:
1.3.6.1.2.1 up to but not including 1.3.6.1.2.1.4 (by S3)
1.3.6.1.2.1.4 up to but not including 1.3.6.1.2.1.4.22 (by S2)
1.3.6.1.2.1.4 up to but not including 1.3.6.1.2.1.4.22 (by S3)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S2)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S1)
1.3.6.1.2.1.4.22 up to but not including 1.3.6.1.2.1.4.23 (by S3)
1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5 (by S2)
1.3.6.1.2.1.4.23 up to but not including 1.3.6.1.2.1.5 (by S3)
1.3.6.1.2.1.5 up to but not including 1.3.6.1.2.2 (by S3)
Note that at registration time a region may be split into multiple
OID ranges due to pre-existing registrations, or as a result of any
subsequent registration. This region splitting is transparent to
subagents. Hence the master agent must always be able to associate
any OID range with the information contained in its original
agentx-Register-PDU.
7.1.5.1. Handling Duplicate OID Ranges
As a result of this registration algorithm there are likely to be
duplicate OID ranges (regions of identical MIB objects registered to
different subagents) in the master agent's registered OID space.
Whenever the master agent's dispatching algorithm (see 7.2.1,
Dispatching AgentX PDUs) selects a duplicate OID range, the
determination of which one to use proceeds as follows:
1) Choose the one whose original agentx-Register-PDU
r.region contained the most subids, i.e., the most specific
r.region. Note: The presence or absence of a range subid
has no bearing on how "specific" one object identifier is
compared to another.
2) If still ambiguous, there were duplicate regions. Choose the
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one whose original agentx-Register-PDU specified the smaller
value of r.priority.
7.1.6. Processing the agentx-Unregister-PDU
1) If an AgentX session for this subagent has not been
established, an agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) If u.region and the indicated context do not match an existing
registration of this subagent, an agentx-Response-PDU is returned
with res.error set to 'unknownRegistration'.
3) Otherwise, an 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) If an AgentX session for this subagent has not been
established, a agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) Otherwise, if the NON_DEFAULT_CONTEXT bit is set, and the master
agent supports only a default context, an agentx-Response-PDU
is returned with res.error set to `unsupportedContext'.
3) 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
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`noError'.
7.1.8. Processing the agentx-RemoveAgentCaps-PDU
1) If an AgentX session for this subagent has not been
established, an agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) If the combination of a.id and the optional a.context does not
represent a sysORTable entry that was added by this subagent,
an agentx-Response-PDU is returned with res.error set to
'unknownAgentCaps'.
3) Otherwise the master agent deletes the corresponding sysORTable
entry and sends in reply an 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) If an AgentX session for this subagent has not been
established, an agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) Otherwise, the master agent closes the AgentX session
as described below. No agentx-Response-PDU is sent.
- All MIB regions that have been registered by this subagent
are unregistered, as described in 7.1.6.
- All index values allocated to this subagent are freed, as
described in section 7.1.4.
- All sysORID values being exported on behalf of this subagent
are removed, as described in section 7.1.8.
When a subagent receives an agentx-Close-PDU, it must reestablish an
AgentX session and reregister its MIB regions.
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 the
AgentX session as described in 7.1.9, step (2).
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
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RFC 1908 [8].
When the master agent receives an agentx-Notify-PDU, it processes it
as follows:
1) If an AgentX session for this subagent has not been
established, an agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) The VarBindList is parsed. If it does not contain a value for
sysUpTime.0, the master agent supplies the current value of
sysUpTime.0 for the indicated context. If the next VarBind
(either the first or second VarBind; see section 6.2.10.1)
is not snmpTrapOID.0, the master agent ceases further processing
of the notification.
3) Notifications are sent according to the implementation-specific
configuration of the master agent.
If SNMPv1 Trap PDUs are generated, the recommended mapping is as
described in FYI V2ToV1 [9].
No agentx-Response-PDU is sent.
7.1.12. Processing the agentx-Ping-PDU
When the master agent receives an agentx-Ping-PDU, it processes it
as follows:
1) If an AgentX session for this subagent has not been
established, an agentx-Response-PDU is sent in reply with
res.error set to `notOpen'.
2) Otherwise, an agentx-Response-PDU is sent, whose res.error
field is noError(0), and containing no other data.
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.
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In particular, for SNMPv1 or SNMPv2c PDUs, the master agent
applies the Elements of Procedure defined in section 4.1 of RFC
1157 [6] that apply to receiving entities. (For other versions
of SNMP, the master agent applies the access control policy
defined in the Elements of Procedure for those versions.)
In the SNMPv1 or v2c frameworks, the master agent uses the community
string as an index into a local repository of configuration
information that may include community profiles or more complex
context information.
If application of the access control policy results in a valid SNMP
request PDU, then an SNMP Response-PDU is constructed from
information gathered in the exchange of AgentX PDUs between the
master agent and one or more subagents. Upon receipt and initial
validation of an SNMP request PDU, a master agent uses the
procedures described below to dispatch AgentX PDUs to the proper
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.
7.2.1.1. agentx-Get-PDU
An SNMP Response-PDU is constructed whose fields all contain the
same values as in the SNMP Request-PDU, except that the value of
each variable binding is set to 'noSuchObject'.
Each variable binding in the Request-PDU is processed in order, as
follows:
(1) Identify the target OID range.
Within a lexicographically ordered set of OID ranges, valid for
the indicated context, locate the region that contains the
binding's name.
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(2) If no such OID range exists the variable binding is not
processed further, and retains its initialized value
(`noSuchObject').
(3) Identify the single subagent responsible for this OID range,
termed the target subagent.
(4) Determine the timeout value for this OID range, which is
a) the value specified during registration of the region
containing the OID range, if it was non-zero
b) otherwise, the value specified during the target
subagent's AgentX session establishment, if it was non-zero
c) otherwise, the master agent's default value
(5) If this is the first variable binding to be dispatched to the
target subagent in a request/response exchange entailed in the
processing of this management request:
- Create an agentx-Get-PDU for the subagent, with
the header fields initialized as described above (see 6.1
AgentX PDU Header).
- If the master agent has determined that a specific
non-default context is associated with the Request-PDU,
that context is encoded into g.context 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.
(6) Add a SearchRange to the end of the target subagent'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
An SNMP Response-PDU is constructed whose fields all contain the same
values as in the SNMP Request-PDU, except that the value of each
variable binding is set to 'endOfMibView'.
Each variable binding in the Request-PDU is processed in order, as
follows:
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(1) Identify the target OID range.
Within a lexicographically ordered set of OID ranges, valid for
the indicated context, locate
a) the OID range that contains the variable binding's name and
is not a fully qualified instance, or
b) the OID range that is the first lexicographical successor to
the variable binding's name.
(2) If no such OID range exists the variable binding is not processed
further, and retains its initialized value (`endOfMibView').
(3) Identify the single subagent responsible for this OID range,
termed the target subagent.
(4) Determine the timeout value for this OID range, which is
a) the value specified during registration of the region
containing the OID range, if it was non-zero
b) otherwise, the value specified during the target
subagent's AgentX session establishment, if it was non-zero
c) otherwise, the master agent's default value
(5) If this is the first variable binding to be dispatched to the
target subagent in a request/response exchange entailed in the
processing of this management request:
- Create an agentx-GetNext-PDU for the subagent, with
the header fields initialized as described above (see 6.1
AgentX PDU Header).
- If the master agent has determined that a specific
non-default context is associated with the Request-PDU,
that context is encoded into g.context 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.
(6) Add a SearchRange to the end of the target subagent'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
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OID, and its `include' field is set to 1.
- the ending OID is encoded with the OID range that is the
first lexicographical successor to the target OID range, and
that was not registered by the target subagent. If no such
OID range exists, it is encoded as a null OID.
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.)
An SNMP Response-PDU is constructed whose fields all contain the same
values as in the SNMP Request-PDU. The SNMP Response-PDU contains
N + (M * R) variable bindings whose values are set to `EndOfMibView',
where
N ("non-repeaters") is the minimum of:
a) the value of the non-repeaters field in the request, and
b) the number of variable bindings in the request
M ("max-repetitions") is the value of the max-repetitions field
in the request
R ("repeaters") is the maximum of:
a) (number of variable bindings in the request) - N, and
b) zero
Each variable binding in the Request-PDU is processed in order, as
follows:
(1) Identify the target OID range and target subagent, exactly as
described for the agentx-GetNext-PDU (see 7.2.1.2).
(2) If this is the first variable binding to be dispatched to the
target subagent in a request/response exchange entailed in the
processing of this management request:
- Create an agentx-GetBulk-PDU for the subagent, with
the header fields initialized as described above (see 6.1
AgentX PDU Header).
- If the master agent has determined that a specific
non-default context is associated with the Request-PDU,
that context is encoded into g.context 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.
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- Set g.non_repeaters to 0.
- g.max_repetitions is generally set to the max_repetitions
value in the Request-PDU. However, the master agent may
elect a smaller value based on the maximum possible size of a
potential Response-PDU, known constraints of the AgentX
transport, or any other implementation-specific constraint.
(3) Add a SearchRange to the end of the target subagent's
agentx-GetBulk-PDU for this variable binding, as described
for the agentx-GetNext-PDU. If the variable binding was
within the non_repeaters range in the original Request-PDU,
increment the value of g.non_repeaters.
7.2.1.4. agentx-TestSet-PDU
AgentX employs the well-known 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.
An SNMP Response-PDU is constructed whose fields all contain the
same values as in the SNMP Request-PDU.
Each variable binding in the Request-PDU is processed in order, as
follows:
(1) Identify the target OID range.
Within a lexicographically ordered set of OID ranges, valid for
the indicated context, locate the range that contains the
variable binding's name.
(2) If no such OID range exists, the SNMP Response-PDU is modified to
indicate this variable binding failed with `noAccess', and
processing is complete for this request.
(3) Identify the single subagent responsible for this OID range,
termed the target subagent.
(4) Determine the timeout value for this OID range, which is
a) the value specified during registration of the region
containing the OID range, if it was non-zero
b) otherwise, the value specified during the target
subagent's AgentX session establishment, if it was non-zero
c) otherwise, the master agent's default value
(5) If this is the first variable binding to be dispatched to the
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target subagent in a request/response exchange entailed in the
processing of this management request:
- create an agentx-TestSet-PDU for the subagent, with
the header fields initialized as described above (see 6.1
AgentX PDU Header).
- If the master agent has determined that a specific
non-default context is associated with the Request-PDU,
that context is encoded into t.context 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.
(6) Add a VarBind to the end of the target subagent's PDU
for this variable binding, as described in section 5.4.
7.2.1.5. Dispatch
A timeout value is calculated for each PDU to be sent,
which is the maximum value of the timeouts associated for each of the
PDU's SearchRanges (as described above).
7.2.2. Subagent Processing of agentx-Get, GetNext, GetBulk-PDUs
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.error_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.error_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.
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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, 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, the VarBind is set to `noSuchObject',
in the manner described in section 5.4, Value Representation.
(4) Otherwise, the VarBind is set to `noSuchInstance'
in the manner described in section 5.4, Value Representation.
7.2.2.2. Subagent Processing of the agentx-GetNext-PDU
Upon the subagent's receipt of an agentx-GetNext-PDU, each
SearchRange in the request is processed as follows:
(1) The subagent searches for a variable within the
lexicographically ordered list of variable names for all
variables it instantiates (without regard to registration of
regions) within the indicated context, 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.
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7.2.2.3. Subagent Processing of the agentx-GetBulk-PDU
A maximum of N + (M * R) VarBinds are returned, where
N equals g.non_repeaters,
M equals g.max_repetitions, and
R is (number of SearchRanges in the GetBulk request) - N.
The first N SearchRanges are processed exactly as for the
agentx-GetNext-PDU.
If M and R are both non-zero, the remaining R SearchRanges are
processed iteratively to produce potentially many VarBinds. For
each iteration i, such that i is greater than zero and less than or
equal to M, and for each repeated SearchRange s, such that s is
greater than zero and less than or equal to R, the
(N+((i-1)*R)+s)-th VarBind is added to the agentx-Response-PDU
as follows:
1) The subagent searches for a variable within the
lexicographically ordered list of variable names for all
variables it instantiates (without regard to registration of
regions) within the indicated context, 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.
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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
These four PDUs are used to collectively perform the indicated
management operation. An agentx-Response-PDU is sent in reply to
each of the PDUs, to inform the master agent of the state of the
operation.
The agentx-Response-PDU header fields are identical to the received
request PDU except that, at the start of processing, the subagent
initializes h.type to Response, res.error to `noError', and
res.error_index to 0.
These Response-PDUs do not contain a VarBindList.
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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].
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(13).
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(0), 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.
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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(14), 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)
This ends subagent processing of the management request.
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 CommitSet-PDU. This
is an indication to the subagent that it may now release any
resources it may have reserved in order to carry out the management
request.
No response is sent by the subagent.
7.2.4. Master Agent Processing of AgentX Responses
The master agent now marshals all subagent agentx-Response-PDUs and
builds an SNMP Response-PDU. In the next several sub-sections, the
initial processing of all subagent agentx-Response-PDUs is
described, followed by descriptions of subsequent processing
for each specific subagent Response.
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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, if the h.ID field of an agentx-Response-PDU does not
match that of the request PDU sent to this subagent, the PDU is
ignored.
3) Otherwise, the responses are processed jointly to form the SNMP
Response-PDU.
7.2.4.2. Processing of Responses to agentx-Get-PDUs
After common processing of the subagent's response to an
agentx-Get-PDU (see 7.2.4.1 above), processing continues with
the following steps:
1) For any received agentx-Response-PDU, if res.error is not
`noError', the SNMP response PDU's error code is set to this
value, and its error index to the index of the variable binding
corresponding to the failed VarBind in the subagent's
agentx-Response-PDU.
All other agentx-Response-PDUs received due to processing this
SNMP Request are ignored. Processing is complete; the SNMP
Response PDU is ready to be sent (see section 7.2.5, Sending
the SNMP Response-PDU).
2) Otherwise, the content of each VarBind in the agentx-Response-PDU
is used to update the corresponding variable binding in the SNMP
Response-PDU.
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7.2.4.3. Processing of Responses to agentx-GetNext- and
agentx-GetBulk-PDUs
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 variable binding
corresponding to the failed VarBind in the subagent's
agentx-Response-PDU.
All other agentx-Response-PDUs received due to processing this
SNMP Request are ignored. Processing is complete; the SNMP
Response PDU is ready to be sent (see section 7.2.5, Sending
the SNMP Response-PDU).
2) Otherwise, the content of each VarBind in the agentx-Response-PDU
is used to update the corresponding variable binding in the SNMP
Response-PDU.
After all expected agentx-Response-PDUs have been processed, if any
variable bindings still contain the value `endOfMibView', processing
must continue:
3) For each such variable binding, a target OID range is
identified which is the lexicographical successor to the
target OID range for this variable binding on the last
iteration. The target subagent is the one that registered
the target OID range.
4) If this is the first variable binding to be dispatched to the
target subagent in this request/response exchange, create an
agentx-GetNext or GetBulk-PDU for the subagent, with the
header and context fields initialized as described previously
for these PDUs.
5a) For responses to agentx-GetNext-PDUs:
i) Add a SearchRange to the end of the target subagent's
PDU for this variable binding. The starting OID is set
to the target OID range, and its `include' field is set to 1.
The ending OID is set to the OID range that is the first
lexicographical successor to the target OID range, and that
was not registered by the target subagent. If no such
OID range exists, the ending OID is set to null.
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5b) For responses to agentx-GetBulk-PDUs:
i) Set the value of g.non_repeaters and g.max_repetitions
to 0.
ii) Add a SearchRange to the end of the target subagent's
PDU for this variable binding. The starting OID is set
to the target OID range, and its `include' field is set to 1.
The ending OID is set to the OID range that is the first
lexicographical successor to the target OID range, and that
was not registered by the target subagent. If no such
OID range exists, the ending OID is set to null.
iii) If the variable binding was within the non_repeaters range
in the original Request-PDU, increment the value of
g.non_repeaters.
Otherwise, set the value of g.max_repetitions to the
maximum of its current value, or the number of response
variable bindings still required for this requested
variable binding.
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.
<<
<< TBD: Include example
<<
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
following steps:
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.
Processing is complete; the SNMP Response-PDU is constructed as
described below in 7.2.4.6, step (2).
2) Otherwise an agentx-CommitSet-PDU is sent to each target
subagent.
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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.
2) Otherwise an agentx-CleanupSet-PDU is sent to each target
subagent. Processing is complete; the SNMP Response-PDU is
constructed as described below in 7.2.4.6, step (2).
7.2.4.6. Processing of Responses to agentx-UndoSet-PDUs
After common processing of the subagent's response to an
agentx-UndoSet-PDU (see 7.2.4.1 above), processing continues with the
following steps:
1) An agentx-CleanupSet-PDU is sent to each target subagent.
2) 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 variable binding 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 variable bindings 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 FYI V2ToV1 [9]. (Note in particular that the rules for
handling Counter64 syntax may require resending AgentX GetBulk or
GetNext PDUs until a VarBind of suitable syntax is returned.)
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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.
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 [TBD]. 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. Only a single logical
connection may be established per transport connection.
All AgentX PDUs are presented individually to the TCP, to be sent as
the data portion of a TCP PDU.
8.2. AgentX over UNIX-domain Sockets
Many (BSD-derived) implementations of the UNIX operating system
support the UNIX pathname address family (AF_UNIX) for socket
communications. This provides a convenient method of sending and
receiving data between processes on the same host.
Mapping AgentX to this transport is useful for environments that
- wish to guarantee subagents are running on the same
managed node as the master agent, and where
- sockets provide better performance than TCP or UDP,
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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. Only a single logical
connection may be established per transport 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 also 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).
Thus, security issues are outside the scope of this protocol
definition.
10. Acknowledgements
The initial draft of this memo was heavily influenced by the DPI
2.0 specification RFC 1592 [7].
This document was produced by the IETF Agent Extensibility
(AgentX) Working Group, and benefited especially from the
contributions of the following working group members:
David Battle, Uri Blumenthal, Jeff Case, Maria Greene,
Dave Keeney, Harmen van der Linde, Bob Natale, Randy Presuhn,
Aleksey Romanov, Don Ryan, and Juergen Schoenwaelder.
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11. Questions and Issues
11.1 Design
The consensus is to proceed with multiple variables per PDU. If we
need to go back and revisit this, the thinking is to provide a
choice at connection time, allowing the subagent to choose either one
varbind per PDU or all varbinds per PDU.
11.2 Miscellaneous Issues/Decisions
1) How to transfer binary OIDs?
The current encoding is unchanged in this version
of this memo.
2) Unionized registrations
Removed by consensus in this version.
3) Contexts
Consensus was to remove "all". It's either the default,
or non-default. Non-default is an Octet String of any length
(including 0).
4) sysUpTime
Returned with the response to an Open or Register PDU.
For Register, it's the value within the specified context.
5) sysORTable
This information moved to specific PDUs.
6) SNMP version in the AgentX header
Removed by consensus in this version.
7) Options
The following optional features are allowed by this memo.
The decision of whether or not to support these features
is implementation specific.
Master agent:
- Supporting non-default contexts
- Supporting next-available-index allocation for
non-integer indexes
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Subagent:
none
8) Index allocation
- There is currently no *guaranteed* mechanism for a
subagent that closes its AgentX session to re-connect
and acquire the previously allocated indexes. Is this a
problem?
9) States
Haven't specified any yet; may need Test/Commit/Undo/cleanup to
finish before other requests are forwarded to a subagent?
10) SNMP request identifier
In the normal case, AgentX processing results in a single agentx
PDU being sent to any particular subagent while processing an
SNMP request. It is possible however for a subagent to receive
multiple PDUs during the processing of a single SNMP request.
(Subs A and B each are dispatched to while processing a request.
A returns endOfMibView for a variable and when the variable is
redispatched, it get sent to B.)
There is currently no information carried in AgentX that would
inform the subagent that this PDU is part of processing the same
SNMP request that a previous PDU was.
We're not sure that this is an issue. Possible solutions
discussed were:
1) Add a request-id field to the request PDUs.
2) Structure h.ID so that the first 3 bytes are unique packet
ids, and the last byte counts the number of PDUs sent to a
particular subagent per SNMP request. Thus h.ID is still
always unique per packet, but carries an implicit notion of
SNMP request id.
3) Use a bit in h.flags to indicate NEW_SNMP_REQUEST or
SAME_SNMP_REQUEST. (Won't work for master agents that
service multiple SNMP requests concurrently.)
11) Session ID
We don't carry a session/connection identifier in the protocol.
It's not an issue currently, because transports we've provided
mappings for are connection oriented, and we've specified a
single session per transport connection. So AgentX peers can map
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transport information -> session.
Mapping transport info -> AgentX sessions can be done for other
transports as well (UDP, shared memory, etc.). So it seems like
the use of a session identifier would ultimately be to support
multiple AgentX sessions on a single transport connection (as in
HTTP).
From Don Ryan:
The reason I added the Connection Identifier was to separate
the subagent logical connection and transport connection.
This allows connectionless protocol support but also helps
limit the number of connections a subagent shim needs to
open. Each connection to the shim can be represented as a
logical connection to the AgentX master agent piggybacking on
the same transport connection. I found it very useful myself.
12) Traps
What traps (if any) should be generated when subagents open/close
or modify sysORTable?
11.3 New in this version
1) Octet String
A specific encoding rule for octet strings.
2) NETWORK_BYTE_ORDER bit
Subagent declares its preferred (native) ordering in
the Open-PDU.
3) IndexDeallocate-PDU and "new vs. any" semantics for allocation
requests.
4) AddAgentCaps and RemoveAgentCaps PDUs for transmitting
sysORTable information.
5) Added (DPI) reason codes for Close-PDU.
6) Removed reason code from Unregister-PDU.
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12. Authors' and Editor's Addresses
Mike Daniele
Digital Equipment Corporation
110 Spit Brook Rd
Nashua, NH 03062
EMail: daniele@zk3.dec.com
Bert Wijnen
IBM Professional Services
Watsonweg 2
1423 ND Uithoorn
The Netherlands
Phone: +31-79-322-8316
EMail: wijnen@vnet.ibm.com
Dale Francisco (editor)
Cisco Systems
150 Castilian Dr
Goleta CA 93117
Phone: +1-805-961-3642
Fax: +1-805-961-3600
EMail: dfrancis@cisco.com
13. References
[1] Information processing systems - Open Systems Interconnection -
Specification of Abstract Syntax Notation One (ASN.1),
International Organization for Standardization. International
Standard 8824, (December, 1987).
[2] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
S. Waldbusser, "Structure of Management Information for Version 2
of the Simple Network Management Protocol (SNMPv2)", RFC 1902,
January 1996.
[3] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
S. Waldbusser, "Textual Conventions for Version 2 of the Simple
Network Management Protocol (SNMPv2)", RFC 1903, January 1996.
[4] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
S. Waldbusser, "Protocol Operations for Version 2 of the Simple
Network Management Protocol (SNMPv2)", RFC 1905, January 1996.
[5] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
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S. Waldbusser, "Management Information Base for Version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC 1907,
January 1996.
[6] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network
Management Protocol", STD 15, RFC 1157, SNMP Research, Performance
Systems International, MIT Laboratory for Computer Science, May
1990.
[7] Wijnen, B., Carpenter, G., Curran, K., Sehgal, A., and G. Waters,
"Simple Network Management Protocol: Distributed Protocol
Interface, Version 2.0", RFC 1592, T.J. Watson Research Center,
IBM Corp., Bell Northern Research, Ltd., March 1994.
[8] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
S. Waldbusser, "Coexistence between Version 1 and Version 2 of the
Internet-standard Network Management Framework", RFC 1908,
January 1996.
[9] Wijnen, B., and Levi, D., "V2ToV1: Mapping SNMPv2 onto SNMPv1
Within a Bilingual SNMP Agent", FYI ???, T.J. Watson Research
Center, IBM Corp., SNMP Research, Inc., August 1996.
[10] SNMPv2 Working Group, Case, J., McCloghrie, K., Rose, M., and
S. Waldbusser, "Conformance Statements for Version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC 1904,
January 1996.
[11] Interfaces MIB Working Group, McCloghrie, K., and F. Kastenholz,
"Evolution of the Interfaces Group of MIB-II", RFC 1573,
January 1994.
[12] FDDI MIB Working Group, J. Case, "FDDI Management Information
Base", RFC 1285, January 1992.
[13] Application MIB Working Group, Krupczak, C., and J. Saperia,
"Definitions of Managed Objects for Applications",
draft-ietf-applmib-sysapplmib-05.txt, 11 Nov 1996.
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