SNMP--RFC2272

RFC2272 - Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)

Network Working Group J. Case
Request for Comments: 2272 SNMP Research, Inc.
Obsoletes: 2262 D. Harrington
Category: Standards Track Cabletron Systems, Inc.
R. Presuhn
BMC Software, Inc.
B. Wijnen
IBM T. J. Watson Research
January 1998

Message Processing and Dispatching for the
Simple Network Management Protocol (SNMP)

Status of this Memo

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

Copyright Notice

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

IANA Note

Due to a clerical error in the assignment of the snmpModules in this
memo, this RFCprovides the corrected number assignment for this
protocol. This memo obsoletes RFC2262.

Abstract

This document describes the Message Processing and Dispatching for
SNMP messages within the SNMP architecture [RFC2271]. It defines the
procedures for dispatching potentially multiple versions of SNMP
messages to the proper SNMP Message Processing Models, and for
dispatching PDUs to SNMP applications. This document also describes
one Message Processing Model - the SNMPv3 Message Processing Model.

Table of Contents

1. IntrodUCtion ............................................... 2
2. Overview ................................................... 3
2.1. The Dispatcher. .......................................... 5
2.2. Message Processing Subsystem ............................. 5
3. Elements of Message Processing and Dispatching ............. 6

3.1. messageProcessingModel ................................... 6
3.2. pduVersion ............................................... 6
3.3. pduType .................................................. 7
3.4. sendPduHandle ............................................ 7
4. Dispatcher Elements of Procedure ........................... 7
4.1. Sending an SNMP Message to the Network ................... 7
4.1.1. Sending a Request or Notification ...................... 7
4.1.2. Sending a Response to the Network ...................... 9
4.2. Receiving an SNMP Message from the Network ............... 10
4.2.1. Message Dispatching of received SNMP Messages .......... 10
4.2.2. PDU Dispatching for Incoming Messages .................. 11
4.2.2.1. Incoming Requests and Notifications .................. 12
4.2.2.2. Incoming Responses ................................... 13
4.3. Application Registration for Handling PDU types .......... 14
4.4. Application Unregistration for Handling PDU Types ........ 14
5. Definitions ................................................ 15
5.1. Definitions for SNMP Message Processing and Dispatching .. 15
6. The SNMPv3 Message Format .................................. 18
6.1. msgVersion ............................................... 19
6.2. msgID .................................................... 19
6.3. msgMaxSize ............................................... 19
6.4. msgFlags ................................................. 20
6.5. msgSecurityModel ......................................... 22
6.6. msgSecurityParameters .................................... 22
6.7. scopedPduData ............................................ 22
6.8. scopedPDU ................................................ 22
6.8.1. contextEngineID ........................................ 22
6.8.2. contextName ............................................ 23
6.8.3. data ................................................... 23
7. Elements of Procedure for v3MP ............................. 23
7.1. Prepare an Outgoing SNMP Message ......................... 24
7.2. Prepare Data Elements from an Incoming SNMP Message ...... 29
8. Intellectual Property ...................................... 34
9. Acknowledgements ........................................... 35
10. Security Considerations ................................... 36
11. References ................................................ 36
12. Editors' Addresses ........................................ 38
13. Full Copyright Statement .................................. 39

1. Introduction

The Architecture for describing Internet Management Frameworks
[RFC2271] describes that an SNMP engine is composed of:

1) a Dispatcher
2) a Message Processing Subsystem,
3) a Security Subsystem, and
4) an Access Control Subsystem.

Applications make use of the services of these subsystems.

It is important to understand the SNMP architecture and its
terminology to understand where the Message Processing Subsystem and
Dispatcher described in this document fit into the architecture and
interact with other subsystems within the architecture. The reader
is eXPected to have read and understood the description of the SNMP
architecture, defined in [RFC2271].

The Dispatcher in the SNMP engine sends and receives SNMP messages.
It also dispatches SNMP PDUs to SNMP applications. When an SNMP
message needs to be prepared or when data needs to be extracted from
an SNMP message, the Dispatcher delegates these tasks to a message
version-specific Message Processing Model within the Message
Processing Subsystem.

A Message Processing Model is responsibile for processing a SNMP
version-specific message and for coordinating the interaction with
the Security Subsystem to ensure proper security is applied to the
SNMP message being handled.

Interactions between the Dispatcher, the Message Processing
Subsystem, and applications are modelled using abstract data elements
and abstract service interface primitives defined by the SNMP
architecture.

Similarly, interactions between the Message Processing Subsystem and
the Security Subsystem are modelled using abstract data elements and
abstract service interface primitives as defined by the SNMP
architecture.

The key Words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119.

2. Overview

The following illustration depicts the Message Processing in relation
to SNMP applications, the Security Subsystem and Transport Mappings.

+-------------------------------------------------------------------+
SNMP Entity

+---------------------------------------------------------------+
Applications
+-----------+ +--------------+
Command Notification
Generator Originator +-----------+ +--------------+
+-----------+ +--------------+ Proxy Other
+-----------+ +--------------+ Forwarder Application(s)
Command Notification +-----------+ +--------------+
Responder Receiver
+-----------+ +--------------+
+---------------------------------------------------------------+
^ ^ ^ ^

v v v v
+--------+-------+---------------+-----------+
^
+---------------------+ +-----------------+
Message Processing Security
Dispatcher v Subsystem Subsystem
+------------------+ +------------+
PDU Dispatcher +-> v1MP * <---> +-------------+
+------------+ Other
+------------+ Security
+-> v2cMP * <---> Model
Message +------------+ +-------------+
Dispatcher <-------->+
+------------+ +-------------+
+-> v3MP * <---> User-based
Transport +------------+ Security
Mapping +------------+ Model
(e.g RFC1906) +-> otherMP * <---> +-------------+
+------------------+ +------------+
^ +---------------------+ +-----------------+

+------------------------------------------------------------------+
v
+------------------+
Network
+------------------+

2.1. The Dispatcher.

The Dispatcher is a key piece of an SNMP engine. There is only one in
an SNMP engine, and its job is to dispatch tasks to the multiple
version-specific Message Processing Models, and to dispatch PDUs to
various applications.

For outgoing messages, an application provides a PDU to be sent, plus
the data needed to prepare and send the message, and the application
specifies which version-specific Message Processing Model will be
used to prepare the message with the desired security processing.
Once the message is prepared, the Dispatcher sends the message.

For incoming messages, the Dispatcher determines the SNMP version of
the incoming message and passes the message to the version-specific
Message Processing Model to extract the components of the message and
to coordinate the processing of security services for the message.
After version-specific processing, the PDU Dispatcher determines
which application, if any, should receive the PDU for processing and
forwards it accordingly.

The Dispatcher, while sending and receiving SNMP messages, collects
statistics about SNMP messages and the behavior of the SNMP engine in
managed objects to make them accessible to remote SNMP entities.
This document defines these managed objects, the MIB module which
contains them, and how these managed objects might be used to provide
useful management.

2.2. Message Processing Subsystem

The SNMP Message Processing Subsystem is the part of an SNMP engine
which interacts with the Dispatcher to handle the version-specific
SNMP messages. It contains one or more Message Processing Models.

This document describes one Message Processing Model, the SNMPv3
Message Processing Model, in Section 6. The SNMPv3 Message Processing
Model is defined in a separate section to show that multiple
(independent) Message Processing Models can exist at the same time
and that such Models can be described in different documents. The
SNMPv3 Message Processing Model can be replaced or supplemented with
other Message Processing Models in the future. Two Message Processing
Models which are expected to be developed in the future are the
SNMPv1 message format [RFC1157] and the SNMPv2c message format
[RFC1901]. Others may be developed as needed.

3. Elements of Message Processing and Dispatching

See [RFC2271] for the definitions of
contextEngineID
contextName
scopedPDU
maxSizeResponseScopedPDU
securityModel
securityName
securityLevel
messageProcessingModel

For incoming messages, a version-specific message processing module
provides these values to the Dispatcher. For outgoing messages, an
application provides these values to the Dispatcher.

For some version-specific processing, the values may be extracted
from received messages; for other versions, the values may be
determined by algorithm, or by an implementation-defined mechanism.
The mechanism by which the value is determined is irrelevant to the
Dispatcher.

The following additional or expanded definitions are for use within
the Dispatcher.

3.1. messageProcessingModel

The value of messageProcessingModel identifies a Message Processing
Model. A Message Processing Model describes the version-specific
procedures for extracting data from messages, generating messages,
calling upon a securityModel to apply its security services to
messages, for converting data from a version-specific message format
into a generic format usable by the Dispatcher, and for converting
data from Dispatcher format into a version-specific message format.

3.2. pduVersion

The value of pduVersion represents a specific version of protocol
operation and its associated PDU formats, such as SNMPv1 or SNMPv2
[RFC1905]. The values of pduVersion are specific to the version of
the PDU contained in a message, and the PDUs processed by
applications. The Dispatcher does not use the value of pduVersion
directly.

An application specifies the pduVersion when it requests the PDU
Dispatcher to send a PDU to another SNMP engine. The Dispatcher
passes the pduVersion to a Message Processing Model, so it knows how
to handle the PDU properly.

For incoming messages, pduVersion is provided to the Dispatcher by a
version-specific Message Processing module. The PDU Dispatcher passes
the pduVersion to the application so it knows how to handle the PDU
properly. For example, a command responder application needs to know
whether to use [RFC1905] elements of procedure and syntax instead of
those specified for SNMPv1.

3.3. pduType

A value of pduType represents a specific type of protocol operation.
The values of pduType are specific to the version of the PDU
contained in a message.

Applications register to support particular pduTypes for particular
contextEngineIDs.

For incoming messages, pduType is provided to the Dispatcher by a
version-specific Message Processing module. It is subsequently used
to dispatch the PDU to the application which registered for the
pduType for the contextEngineID of the associated scopedPDU.

3.4. sendPduHandle

This handle is generated for coordinating the processing of requests
and responses between the SNMP engine and an application. The handle
must be unique across all version-specific Message Processing Models,
and is of local significance only.

4. Dispatcher Elements of Procedure

This section describes the procedures followed by the Dispatcher when
generating and processing SNMP messages.

4.1. Sending an SNMP Message to the Network

This section describes the procedure followed by an SNMP engine
whenever it sends an SNMP message.

4.1.1. Sending a Request or Notification

The following procedures are followed by the Dispatcher when an
application wants to send an SNMP PDU to another (remote)
application, i.e., to initiate a communication by originating a
message, such as one containing a request or a trap.

1) The application requests this using the abstract service
primitive:

statusInformation = -- sendPduHandle if success
-- errorIndication if failure
sendPdu(
IN transportDomain -- transport domain to be used
IN transportAddress -- destination network address
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE
)

2) If the messageProcessingModel value does not represent a Message
Processing Model known to the Dispatcher, then an errorIndication
(implementation-dependent) is returned to the calling application.
No further processing is performed.

3) The Dispatcher generates a sendPduHandle to coordinate
subsequent processing.

4) The Message Dispatcher sends the request to the version-specific
Message Processing module identified by messageProcessingModel
using the abstract service primitive:

statusInformation = - success or error indication
prepareOutgoingMessage(
IN transportDomain -- as specified by application
IN transportAddress -- as specified by application
IN messageProcessingModel -- as specified by application
IN securityModel -- as specified by application
IN securityName -- as specified by application
IN securityLevel -- as specified by application
IN contextEngineID -- as specified by application
IN contextName -- as specified by application
IN pduVersion -- the version of the PDU
IN PDU -- as specified by application
IN expectResponse -- as specified by application
IN sendPduHandle -- as determined in step 3.
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- the message length
)

5) If the statusInformation indicates an error, the errorIndication
is returned to the calling application. No further processing is
performed.

6) If the statusInformation indicates success, the sendPduHandle is
returned to the application, and the outgoingMessage is sent via
the transport specified by the transportDomain to the address
specified by the transportAddress.

Outgoing Message Processing is complete.

4.1.2. Sending a Response to the Network

The following procedure is followed when an application wants to
return a response back to the originator of an SNMP Request.

1) An application can request this using the abstract service
primitive:

returnResponsePDU(
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model in use
IN securityName -- on behalf of this principal
IN securityLevel -- same as on incoming request
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- the version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size of Response PDU
IN stateReference -- reference to state information
-- as presented with the request
IN statusInformation -- success or errorIndication
) -- (error counter OID and value
-- when errorIndication)

2) The Message Dispatcher sends the request to the appropriate
Message Processing Model indicated by the received value of
messageProcessingModel using the abstract service primitive:

result = -- SUCCESS or errorIndication
prepareResponseMessage(
IN messageProcessingModel -- specified by application
IN securityModel -- specified by application
IN securityName -- specified by application
IN securityLevel -- specified by application
IN contextEngineID -- specified by application
IN contextName -- specified by application
IN pduVersion -- specified by application

IN PDU -- specified by application
IN maxSizeResponseScopedPDU -- specified by application
IN stateReference -- specified by application
IN statusInformation -- specified by application
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- the message length
)

3) If the result is an errorIndication, the errorIndication is
returned to the calling application. No further processing is
performed.

4) If the result is success, the outgoingMessage is sent over the
transport specified by the transportDomain to the address
specified by the transportAddress.

Message Processing is complete.

4.2. Receiving an SNMP Message from the Network

This section describes the procedure followed by an SNMP engine
whenever it receives an SNMP message.

Please note, that for the sake of clarity and to prevent the text
from being even longer and more complicated, some details were
omitted from the steps below. In particular, The elements of
procedure do not always explicitly indicate when state information
needs to be released. The general rule is that if state information
is available when a message is to be "discarded without further
processing", then the state information must also be released at that
same time.

4.2.1. Message Dispatching of received SNMP Messages

1) The snmpInPkts counter [RFC1907] is incremented.

2) The version of the SNMP message is determined in an
implementation-dependent manner. If the packet cannot be
sufficiently parsed to determine the version of the SNMP message,
then the snmpInASNParseErrs [RFC1907] counter is incremented, and
the message is discarded without further processing. If the
version is not supported, then the snmpInBadVersions [RFC1907]
counter is incremented, and the message is discarded without
further processing.

3) The origin transportDomain and origin transportAddress are
determined.

4) The message is passed to the version-specific Message Processing
Model which returns the abstract data elements required by the
Dispatcher. This is performed using the abstract service
primitive:

result = -- SUCCESS or errorIndication
prepareDataElements(
IN transportDomain -- origin as determined in step 3.
IN transportAddress -- origin as determined in step 3.
IN wholeMsg -- as received from the network
IN wholeMsgLength -- as received from the network
OUT messageProcessingModel -- typically, SNMP version
OUT securityModel -- Security Model to use
OUT securityName -- on behalf of this principal
OUT securityLevel -- Level of Security requested
OUT contextEngineID -- data from/at this entity
OUT contextName -- data from/in this context
OUT pduVersion -- the version of the PDU
OUT PDU -- SNMP Protocol Data Unit
OUT pduType -- SNMP PDU type
OUT sendPduHandle -- handle for a matched request
OUT maxSizeResponseScopedPDU -- maximum size of Response PDU
OUT statusInformation -- success or errorIndication
-- (error counter OID and value
-- when errorIndication)
OUT stateReference -- reference to state information
-- to be used for a possible
) -- Response

5) If the result is a FAILURE errorIndication, the message is
discarded without further processing.

6) At this point, the abstract data elements have been prepared and
processing continues as described in Section 4.2.2, PDU
Dispatching for Incoming Messages.

4.2.2. PDU Dispatching for Incoming Messages

The elements of procedure for the dispatching of PDUs depends on the
value of sendPduHandle. If the value of sendPduHandle is <none>,
then this is a request or notification and the procedures specified
in Section 4.2.2.1 apply. If the value of snmpPduHandle is not
<none>, then this is a response and the procedures specified in
Section 4.2.2.2 apply.

4.2.2.1. Incoming Requests and Notifications

The following procedures are followed for the dispatching of PDUs
when the value of sendPduHandle is <none>, indicating this is a
request or notification.

1) The combination of contextEngineID and pduType is used to
determine which application has registered for this request or
notification.

2) If no application has registered for the combination, then

a) The snmpUnknownPDUHandlers counter is incremented.

b) A Response message is generated using the abstract service
primitive:

result = -- SUCCESS or FAILURE
prepareResponseMessage(
IN messageProcessingModel -- as provided by MP module
IN securityModel -- as provided by MP module
IN securityName -- as provided by MP module
IN securityLevel -- as provided by MP module
IN contextEngineID -- as provided by MP module
IN contextName -- as provided by MP module
IN pduVersion -- as provided by MP module
IN PDU -- as provided by MP module
IN maxSizeResponseScopedPDU -- as provided by MP module
IN stateReference -- as provided by MP module
IN statusInformation -- errorIndication plus
-- snmpUnknownPDUHandlers OID
-- value pair.
OUT transportDomain -- destination transportDomain
OUT transportAddress -- destination transportAddress
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- its length
)

c) If the result is SUCCESS, then the prepared message is sent to
the originator of the request as identified by the
transportDomain and transportAddress.

d) The incoming message is discarded without further processing.
Message Processing for this message is complete.

3) The PDU is dispatched to the application, using the abstract
service primitive:

processPdu( -- process Request/Notification
IN messageProcessingModel -- as provided by MP module
IN securityModel -- as provided by MP module
IN securityName -- as provided by MP module
IN securityLevel -- as provided by MP module
IN contextEngineID -- as provided by MP module
IN contextName -- as provided by MP module
IN pduVersion -- as provided by MP module
IN PDU -- as provided by MP module
IN maxSizeResponseScopedPDU -- as provided by MP module
IN stateReference -- as provided by MP module
-- needed when sending response
)

Message processing for this message is complete.

4.2.2.2. Incoming Responses

The following procedures are followed for the dispatching of PDUs
when the value of sendPduHandle is not <none>, indicating this is a
response.

1) The value of sendPduHandle is used to determine, in an
implementation-defined manner, which application is waiting for
a response PDU associated with this sendPduHandle.

2) If no waiting application is found, the message is discarded
without further processing, and the stateReference is released.
The snmpUnknownPDUHandlers counter is incremented. Message
Processing is complete for this message.

3) Any cached information, including stateReference, about the
message is discarded.

4) The response is dispatched to the application using the
abstract service primitive:

processResponsePdu( -- process Response PDU
IN messageProcessingModel -- provided by the MP module
IN securityModel -- provided by the MP module
IN securityName -- provided by the MP module
IN securityLevel -- provided by the MP module
IN contextEngineID -- provided by the MP module
IN contextName -- provided by the MP module
IN pduVersion -- provided by the MP module
IN PDU -- provided by the MP module

IN statusInformation -- provided by the MP module
IN sendPduHandle -- provided by the MP module
)

Message Processing is complete for this message.

4.3. Application Registration for Handling PDU types

Applications that want to process certain PDUs must register with the
PDU Dispatcher. Applications specify the combination of
contextEngineID and pduType(s) for which they want to take
responsibility

1) An application registers according to the abstract interface
primitive:

statusInformation = -- success or errorIndication
registerContextEngineID(
IN contextEngineID -- take responsibility for this one
IN pduType -- the pduType(s) to be registered
)

Note: implementations may provide a means of requesting
registration for simultaneous multiple contextEngineID values,
e.g., all contextEngineID values, and may also provide means for
requesting simultaneous registration for multiple values of
pduType.

2) The parameters may be checked for validity; if they are not, then
an errorIndication (invalidParameter) is returned to the
application.

3) Each combination of contextEngineID and pduType can be registered
only once. If another application has already registered for the
specified combination, then an errorIndication (alreadyRegistered)
is returned to the application.

4) Otherwise, the registration is saved so that SNMP PDUs can be
dispatched to this application.

4.4. Application Unregistration for Handling PDU Types

Applications that no longer want to process certain PDUs must
unregister with the PDU Dispatcher.

1) An application unregisters using the abstract service primitive:

unregisterContextEngineID(
IN contextEngineID -- give up responsibility for this
IN pduType -- the pduType(s) to be unregistered
)
Note: implementations may provide means for requesting
unregistration for simultaneous multiple contextEngineID values,
e.g., all contextEngineID values, and may also provide means for
requesting simultaneous unregistration for multiple values of
pduType.

2) If the contextEngineID and pduType combination has been
registered, then the registration is deleted.

If no such registration exists, then the request is ignored.

5. Definitions

5.1. Definitions for SNMP Message Processing and Dispatching

SNMP-MPD-MIB DEFINITIONS ::= BEGIN

IMPORTS
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF
MODULE-IDENTITY, OBJECT-TYPE,
snmpModules, Counter32 FROM SNMPv2-SMI;

snmpMPDMIB MODULE-IDENTITY
LAST-UPDATED "9711200000Z" -- 20 November 1997
ORGANIZATION "SNMPv3 Working Group"
CONTACT-INFO "WG-email: [e-mail]
Subscribe: [e-mail]
In message body: subscribe snmpv3

Chair: Russ Mundy
Trusted Information Systems
postal: 3060 Washington Road
Glenwood, MD 21738
USA
email: [e-mail]
phone: [phone]

Co-editor: Jeffrey Case
SNMP Research, Inc.
postal: 3001 Kimberlin Heights Road
Knoxville, TN 37920-9716
USA
email: [e-mail]
phone: [phone]

Co-editor Dave Harrington
Cabletron Systems, Inc.
postal: Post Office Box 5005
MailStop: Durham
35 Industrial Way
Rochester, NH 03867-5005
USA
email: [e-mail]
phone: [phone]

Co-editor: Randy Presuhn
BMC Software, Inc.
postal: 1190 Saratoga Ave, Suite 190
San Jose, CA 95120
USA
email: [e-mail]
phone: [phone]

Co-editor: Bert Wijnen
IBM T. J. Watson Research
postal: Schagen 33
3461 GL Linschoten
Netherlands
email: [e-mail]
phone: [phone]

"
DESCRIPTION "The MIB for Message Processing and Dispatching"
::= { snmpModules 11 }

-- Administrative assignments ***************************************

snmpMPDAdmin OBJECT IDENTIFIER ::= { snmpMPDMIB 1 }
snmpMPDMIBObjects OBJECT IDENTIFIER ::= { snmpMPDMIB 2 }
snmpMPDMIBConformance OBJECT IDENTIFIER ::= { snmpMPDMIB 3 }

-- Statistics for SNMP Messages *************************************

snmpMPDStats OBJECT IDENTIFIER ::= { snmpMPDMIBObjects 1 }

snmpUnknownSecurityModels OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The total number of packets received by the SNMP
engine which were dropped because they referenced a
securityModel that was not known to or supported by
the SNMP engine.

"
::= { snmpMPDStats 1 }

snmpInvalidMsgs OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The total number of packets received by the SNMP
engine which were dropped because there were invalid
or inconsistent components in the SNMP message.
"
::= { snmpMPDStats 2 }

snmpUnknownPDUHandlers OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The total number of packets received by the SNMP
engine which were dropped because the PDU contained
in the packet could not be passed to an application
responsible for handling the pduType, e.g. no SNMP
application had registered for the proper
combination of the contextEngineID and the pduType.
"
::= { snmpMPDStats 3 }

-- Conformance information ******************************************

snmpMPDMIBCompliances OBJECT IDENTIFIER ::= {snmpMPDMIBConformance 1}
snmpMPDMIBGroups OBJECT IDENTIFIER ::= {snmpMPDMIBConformance 2}

-- Compliance statements

snmpMPDCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION "The compliance statement for SNMP entities which
implement the SNMP-MPD-MIB.
"

MODULE -- this module

MANDATORY-GROUPS { snmpMPDGroup }

::= { snmpMPDMIBCompliances 1 }

snmpMPDGroup OBJECT-GROUP
OBJECTS {
snmpUnknownSecurityModels,

snmpInvalidMsgs,
snmpUnknownPDUHandlers
}
STATUS current
DESCRIPTION "A collection of objects providing for remote
monitoring of the SNMP Message Processing and
Dispatching process.
"
::= { snmpMPDMIBGroups 1 }

END

6. The SNMPv3 Message Format

This section defines the SNMPv3 message format and the corresponding
SNMP version 3 Message Processing Model (v3MP).

SNMPv3MessageSyntax DEFINITIONS IMPLICIT TAGS ::= BEGIN

SNMPv3Message ::= SEQUENCE {
-- identify the layout of the SNMPv3Message
-- this element is in same position as in SNMPv1
-- and SNMPv2c, allowing recognition
msgVersion INTEGER { snmpv3 (3) },
-- administrative parameters
msgGlobalData HeaderData,
-- security model-specific parameters
-- format defined by Security Model
msgSecurityParameters OCTET STRING,
msgData ScopedPduData
}

HeaderData ::= SEQUENCE {
msgID INTEGER (0..2147483647),
msgMaxSize INTEGER (484..2147483647),

msgFlags OCTET STRING (SIZE(1)),
-- .... ...1 authFlag
-- .... ..1. privFlag
-- .... .1.. reportableFlag
-- Please observe:
-- .... ..00 is OK, means noAuthNoPriv
-- .... ..01 is OK, means authNoPriv
-- .... ..10 reserved, must NOT be used.
-- .... ..11 is OK, means authPriv

msgSecurityModel INTEGER (0..2147483647)
}

ScopedPduData ::= CHOICE {
plaintext ScopedPDU,
encryptedPDU OCTET STRING -- encrypted scopedPDU value
}

ScopedPDU ::= SEQUENCE {
contextEngineID OCTET STRING,
contextName OCTET STRING,
data ANY -- e.g., PDUs as defined in RFC1905
}
END

6.1. msgVersion

The msgVersion field is set to snmpv3(3) and identifies the message
as an SNMP version 3 Message.

6.2. msgID

The msgID is used between two SNMP entities to coordinate request
messages and responses, and by the v3MP to coordinate the processing
of the message by different subsystem models within the architecture.

Values for msgID should be generated in a manner that avoids re-use
of any outstanding values. Doing so provides protection against some
replay attacks. One possible implementation strategy would be to use
the low-order bits of snmpEngineBoots [RFC2271] as the high-order
portion of the msgID value and a monotonically increasing integer for
the low-order portion of msgID.

Note that the request-id in a PDU is used by SNMP applications to
identify the PDU; the msgID is used by the engine to identify the
message which carries a PDU. The engine may need to identify the
message even if decrypting of the PDU (and request-id) fails. No
assumption should be made that the value of the msgID and the value
of the request-id are equivalent.

6.3. msgMaxSize

The msgMaxSize field of the message conveys the maximum message size
supported by the sender of the message, i.e., the maximum message
size that the sender can accept when another SNMP engine sends an
SNMP message (be it a response or any other message) to the sender of
this message.

When an SNMP message is being generated, the msgMaxSize is provided
by the SNMP engine which generates the message. At the receiving
SNMP engine, the msgMaxSize is used to determine how big the Response
to a Request message can be.

6.4. msgFlags

The msgFlags field of the message contains several bit fields which
control processing of the message.

When the reportableFlag is one, a Report PDU must be returned to the
sender under those conditions which can cause the generation of
Report PDUs. When the reportableFlag is zero, then a Report PDU must
not be sent. The reportableFlag must always be zero when the message
contains a Report PDU, a response-type PDU (such as a Response PDU),
or an unacknowledged notification-type PDU (such as an SNMPv2-trap
PDU). The reportableFlag must always be one for a request-type PDU
(such as a Get PDU) and an acknowledged notification-type PDU (such
as an Inform PDU).

If the reportableFlag is set to one for a message containing a Report
PDU, a response-type PDU (such as a Response PDU), or an
unacknowledged notification-type PDU (such as an SNMPv2-trap PDU),
then the receiver of that message must process it as though the
reportableFlag had been set to zero.

If the reportableFlag is set to zero for a message containing a
request-type PDU (such as a Get PDU) or an acknowledged notification-
type PDU (such as an Inform PDU), then the receiver of that message
must process it as though the reportableFlag had been set to one.

Report PDUs are engine-to-engine communications and are processed
directly by the SNMPv3 Message Processing Model, and are generally
not passed to applications for processing, unlike all other PDU
types.

Note that the reportableFlag is a secondary aid in determining
whether a Report PDU must be sent. It is only used in cases where
the PDU portion of a message cannot be decoded, due to, for example,
an incorrect ecryption key. If the PDU can be decoded, the PDU type
forms the basis for decisions on sending Report PDUs.

The authFlag and privFlag portions of the msgFlags field are set by
the sender to indicate the securityLevel that was applied to the
message before it was sent on the wire. The receiver of the message
must apply the same securityLevel when the message is received and
the contents are being processed.

There are three securityLevels, namely noAuthNoPriv, which is less
than authNoPriv, which is in turn less than authPriv. See the SNMP
architecture document [RFC2271] for details about the securityLevel.

a) authFlag

If the authFlag is set to one, then the securityModel used by the
SNMP engine which sent the message must identify the securityName
on whose behalf the SNMP message was generated and must provide,
in a securityModel-specific manner, sufficient data for the
receiver of the message to be able to authenticate that
identification. In general, this authentication will allow the
receiver to determine with reasonable certainty that the message
was:

- sent on behalf of the principal associated with the
securityName,

- was not redirected,

- was not modified in transit, and

- was not replayed.

If the authFlag is zero, then the securityModel used by the SNMP
engine which sent the message must identify the securityName on
whose behalf the SNMP message was generated but it does not need
to provide sufficient data for the receiver of the message to
authenticate the identification, as there is no need to
authenticate the message in this case.

b) privFlag

If the privFlag is set, then the securityModel used by the SNMP
engine which sent the message must also protect the scopedPDU in
an SNMP message from disclosure, i.e., must encrypt/decrypt the
scopedPDU. If the privFlag is zero, then the securityModel in use
does not need to protect the data from disclosure.

It is an explicit requirement of the SNMP architecture that if
privacy is selected, then authentication is also required. That
means that if the privFlag is set, then the authFlag must also be
set to one.

The combination of the authFlag and the privFlag comprises a Level
of Security as follows:

authFlag zero, privFlag zero -> securityLevel is noAuthNoPriv

authFlag zero, privFlag one -> invalid combination
authFlag one, privFlag zero -> securityLevel is authNoPriv
authFlag one, privFlag one -> securityLevel is authPriv

6.5. msgSecurityModel

The v3MP supports the concurrent existence of multiple Security
Models to provide security services for SNMPv3 messages. The
msgSecurityModel field in an SNMPv3 Message identifies which Security
Model was used by the sender to generate the message and therefore
which securityModel must be used by the receiver to perform security
processing for the message. The mapping to the appropriate
securityModel implementation within an SNMP engine is accomplished in
an implementation-dependent manner.

6.6. msgSecurityParameters

The msgSecurityParameters field of the SNMPv3 Message is used for
communication between the Security Model modules in the sending and
receiving SNMP engines. The data in the msgSecurityParameters field
is used exclusively by the Security Model, and the contents and
format of the data is defined by the Security Model. This OCTET
STRING is not interpreted by the v3MP, but is passed to the local
implementation of the Security Model indicated by the
msgSecurityModel field in the message.

6.7. scopedPduData

The scopedPduData field represents either the plain text scopedPDU if
the privFlag in the msgFlags is zero, or it represents an
encryptedPDU (encoded as an OCTET STRING) which must be decrypted by
the securityModel in use to produce a plaintext scopedPDU.

6.8. scopedPDU

The scopedPDU contains information to identify an administratively
unique context and a PDU. The object identifiers in the PDU refer to
managed objects which are (expected to be) accessible within the
specified context.

6.8.1. contextEngineID

The contextEngineID in the SNMPv3 message, uniquely identifies,
within an administrative domain, an SNMP entity that may realize an
instance of a context with a particular contextName.

For incoming messages, the contextEngineID is used to determine to
which application the scopedPDU will be sent for processing.

For outgoing messages, the v3MP sets the contextEngineID to the value
provided by the application in the request for a message to be sent.

6.8.2. contextName

The contextName field in an SNMPv3 message, in conjunction with the
contextEngineID field, identifies the particular context associated
with the management information contained in the PDU portion of the
message. The contextName is unique within the SNMP entity specified
by the contextEngineID, which may realize the managed objects
referenced within the PDU. An application which originates a message
provides the value for the contextName field and this value may be
used during processing by an application at the receiving SNMP
Engine.

6.8.3. data

The data field of the SNMPv3 Message contains the PDU. Among other
things, the PDU contains the PDU type that is used by the v3MP to
determine the type of the incoming SNMP message. The v3MP specifies
that the PDU must be one of those specified in [RFC1905].

7. Elements of Procedure for v3MP

This section describes the procedures followed by an SNMP engine when
generating and processing SNMP messages according to the SNMPv3
Message Processing Model.

Please note, that for the sake of clarity and to prevent the text
from being even longer and more complicated, some details were
omitted from the steps below.

a) Some steps specify that when some error conditions are
encountered when processing a received message, a message
containing a Report PDU is generated and the received message
is discarded without further processing. However, a Report-PDU
must not be generated unless the reportableFlag is set in the
received message.

b) The elements of procedure do not always explicitly indicate
when state information needs to be released. The general rule
is that if state information is available when a message is to
be "discarded without further processing", then the state
information must also be released at that same time.

7.1. Prepare an Outgoing SNMP Message

This section describes the procedure followed to prepare an SNMPv3
message from the data elements passed by the Message Dispatcher.

1) The Message Dispatcher may request that an SNMPv3 message
containing a GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-
PDU, SetRequest-PDU, InformRequest-PDU, or SNMPv2-Trap-PDU be
prepared for sending.

a) It makes such a request according to the abstract service
primitive:

statusInformation = -- success or errorIndication
prepareOutgoingMessage(
IN transportDomain -- requested transport domain
IN transportAddress -- requested destination address
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- Security Model to use
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN contextEngineID -- data from/at this entity
IN contextName -- data from/in this context
IN pduVersion -- version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN expectResponse -- TRUE or FALSE
IN sendPduHandle -- the handle for matching
-- incoming responses
OUT destTransportDomain -- destination transport domain
OUT destTransportAddress -- destination transport address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- the length of the message
)

b) A unique msgID is generated. The number used for msgID should
not have been used recently, and must not be the same as was
used for any outstanding request.

* SNMPv3 does not use the values of expectResponse or
pduVersion.

2) The Message Dispatcher may request that an SNMPv3 message
containing a Response-PDU or Report-PDU be prepared for sending.

a) It makes such a request according to the abstract service
primitive:

result = -- SUCCESS or FAILURE
prepareResponseMessage(
IN messageProcessingModel -- typically, SNMP version
IN securityModel -- same as on incoming request
IN securityName -- same as on incoming request
IN securityLevel -- same as on incoming request
IN contextEngineID -- data from/at this SNMP entity
IN contextName -- data from/in this context
IN pduVersion -- version of the PDU
IN PDU -- SNMP Protocol Data Unit
IN maxSizeResponseScopedPDU -- maximum size of Response PDU
IN stateReference -- reference to state
-- information presented with
-- the request
IN statusInformation -- success or errorIndication
-- error counter OID and value
-- when errorIndication
OUT transportDomain -- destination transport domain
OUT transportAddress -- destination transport address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- the length of the message
)

b) The cached information for the original request is retrieved
via the stateReference, including

- msgID,
- contextEngineID,
- contextName,
- securityModel,
- securityName,
- securityLevel,
- securityStateReference,
- reportableFlag,
- transportDomain, and
- transportAddress.

The SNMPv3 Message Processing Model does not allow cached data
to be overridden, except by error indications as detailed in
(3) below.

3) If statusInformation contains values for an OID/value combination
(potentially also containing a securityLevel value,
contextEngineID value, or contextName value), then

a) If reportableFlag is zero, then the original message is
discarded, and no further processing is done. A result of
FAILURE is returned. SNMPv3 Message Processing is complete.

b) If a PDU is provided, it is the PDU from the original request.
If possible, extract the request-id.

c) A Report PDU is prepared:

1) the varBindList is set to contain the OID and value from the
statusInformation

2) error-status is set to 0

3) error-index is set to 0.

4) request-id is set to the value extracted in step b)
Otherwise, request-id is set to 0

d) The errorIndication in statusInformation may be accompanied by
a securityLevel value, a contextEngineID value, or a
contextName value.

1) If statusInformation contains a value for securityLevel,
then securityLevel is set to that value, otherwise it is set
to noAuthNoPriv.

2) If statusInformation contains a value for contextEngineID,
then contextEngineID is set to that value, otherwise it is
set to the value of this entity's snmpEngineID.

3) If statusInformation contains a value for contextName, then
contextName is set to that value, otherwise it is set to the
default context of "" (zero-length string).

e) PDU is set to refer to the new Report-PDU. The old PDU is
discarded.

f) Processing continues with step 6) below.

4) If contextEngineID is not yet determined, then the contextEngineID
is determined, in an implementation-dependent manner, possibly
using the transportDomain and transportAddress.

5) If the contextName is not yet determined, the contextName is set
to the default context.

6) A scopedPDU is prepared from the contextEngineID, contextName, and
PDU.

7) msgGlobalData is constructed as follows

a) The msgVersion field is set to snmpv3(3).

b) msgID is set as determined in step 1 or 2 above.

c) msgMaxSize is set to an implementation-dependent value.

d) msgFlags are set as follows:

- If securityLevel specifies noAuthNoPriv, then authFlag and
privFlag are both set to zero.

- If securityLevel specifies authNoPriv, then authFlag is set
to one and privFlag is set to zero.

- If securityLevel specifies authPriv, then authFlag is set to
one and privFlag is set to one.

- If the PDU is a Response-PDU, Report-PDU or SNMPv2-Trap-PDU,
then the reportableFlag is set to zero.

- If the PDU is a GetRequest-PDU, GetNextRequest-PDU,
GetBulkRequest-PDU, SetRequest-PDU, or InformRequest-PDU
then the reportableFlag is set to one.

- All other msgFlags bits are set to zero.

e) msgSecurityModel is set to the value of securityModel

8) If the PDU is a Response-PDU or Report-PDU, then

a) The specified Security Model is called to generate the message
according to the primitive:

statusInformation =
generateResponseMsg(
IN messageProcessingModel -- SNMPv3 Message Processing
-- Model
IN globalData -- msgGlobalData from step 7
IN maxMessageSize -- from msgMaxSize (step 7c)
IN securityModel -- as determined in step 7e
IN securityEngineID -- the value of snmpEngineID
IN securityName -- on behalf of this principal
IN securityLevel -- for the outgoing message
IN scopedPDU -- as prepared in step 6)
IN securityStateReference -- as determined in step 2
OUT securityParameters -- filled in by Security Module

OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of generated message
)

If, upon return from the Security Model, the statusInformation
includes an errorIndication, then any cached information about
the outstanding request message is discarded, and an
errorIndication is returned, so it can be returned to the
calling application. SNMPv3 Message Processing is complete.

b) A SUCCESS result is returned. SNMPv3 Message Processing is
complete.

9) If the PDU is a GetRequest-PDU, GetNextRequest-PDU,
GetBulkRequest-PDU, SetRequest-PDU, InformRequest-PDU, or or
SNMPv2-Trap-PDU, then

a) If the PDU is an SNMPv2-Trap-PDU, then securityEngineID is set
to the value of this entity's snmpEngineID.

Otherwise, the snmpEngineID of the target entity is determined,
in an implementation-dependent manner, possibly using
transportDomain and transportAddress. The value of
securityEngineID is set to the value of the target entity's
snmpEngineID.

b) The specified Security Model is called to generate the message
according to the primitive:

statusInformation =
generateRequestMsg(
IN messageProcessingModel -- SNMPv3 Message Processing Model
IN globalData -- msgGlobalData, from step 7
IN maxMessageSize -- from msgMaxSize in step 7 c)
IN securityModel -- as provided by caller
IN securityEngineID -- authoritative SNMP entity
IN securityName -- as provided by caller
IN securityLevel -- as provided by caller
IN snmpEngineID -- as determined in step 9 a)
IN scopedPDU -- as prepared in step 6
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of the generated message
)

If, upon return from the Security Model, the statusInformation
includes an errorIndication, then the message is discarded, and
the errorIndication is returned, so it can be returned to the
calling application, and no further processing is done.
SNMPv3 Message Processing is complete.

c) Information about the outgoing message is cached, and a
stateReference is created (implementation-specific).
Information to be cached includes the values of:

- sendPduHandle
- msgID
- snmpEngineID
- securityModel
- securityName
- securityLevel
- contextEngineID
- contextName

d) A SUCCESS result is returned. SNMPv3 Message Processing is
complete.

7.2. Prepare Data Elements from an Incoming SNMP Message

This section describes the procedure followed to extract data from an
SNMPv3 message, and to prepare the data elements required for further
processing of the message by the Message Dispatcher.

1) The message is passed in from the Message Dispatcher according to
the abstract service primitive:

result = -- SUCCESS or errorIndication
prepareDataElements(
IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address
IN wholeMsg -- as received from the network
IN wholeMsgLength -- as received from the network
OUT messageProcessingModel -- typically, SNMP version
OUT securityModel -- Security Model to use
OUT securityName -- on behalf of this principal
OUT securityLevel -- Level of Security requested
OUT contextEngineID -- data from/at this entity
OUT contextName -- data from/in this context
OUT pduVersion -- version of the PDU
OUT PDU -- SNMP Protocol Data Unit
OUT pduType -- SNMP PDU type
OUT sendPduHandle -- handle for matched request
OUT maxSizeResponseScopedPDU -- maximum size of Response PDU

OUT statusInformation -- success or errorIndication
-- error counter OID and value
-- when errorIndication
OUT stateReference -- reference to state information
-- to be used for a possible
) -- Response

2) If the received message is not the serialization (according to
the conventions of [RFC1906]) of an SNMPv3Message value, then the
snmpInASNParseErrs counter [RFC1907] is incremented, the message
is discarded without further processing, and a FAILURE result is
returned. SNMPv3 Message Processing is complete.

3) The values for msgVersion, msgID, msgMaxSize, msgFlags,
msgSecurityModel, msgSecurityParameters, and msgData are extracted
from the message.

4) If the value of the msgSecurityModel component does not match a
supported securityModel, then the snmpUnknownSecurityModels
counter is incremented, a Report PDU is generated, the message is
discarded without further processing, and a FAILURE result is
returned. SNMPv3 Message Processing is complete.

5) The securityLevel is determined from the authFlag and the
privFlag bits of the msgFlags component as follows:

a) If the authFlag is not set and the privFlag is not set, then
securityLevel is set to noAuthNoPriv.

b) If the authFlag is set and the privFlag is not set, then
securityLevel is set to authNoPriv.

c) If the authFlag is set and the privFlag is set, then
securityLevel is set to authPriv.

d) If the authFlag is not set and privFlag is set, then the
snmpInvalidMsgs counter is incremented, a Report PDU is
generated, the message is discarded without further processing,
and a FAILURE result is returned. SNMPv3 Message Processing is
complete.

6) The security module implementing the Security Model as specified
by the securityModel component is called for authentication and
privacy services. This is done according to the abstract service
primitive:

statusInformation = -- errorIndication or success
-- error counter OID and

-- value if error
processIncomingMsg(
IN messageProcessingModel -- SNMPv3 Message Processing Model
IN expectResponse -- TRUE or FALSE
IN maxMessageSize -- of the sending SNMP entity
IN securityParameters -- for the received message
IN securityModel -- for the received message
IN securityLevel -- Level of Security
IN wholeMsg -- as received on the wire
IN wholeMsgLength -- length as received on the wire
OUT securityEngineID -- authoritative SNMP entity
OUT securityName -- identification of the principal
OUT scopedPDU, -- message (plaintext) payload
OUT maxSizeResponseScopedPDU -- maximum size of Response PDU
OUT securityStateReference -- reference to security state
) -- information, needed for
-- response

If an errorIndication is returned by the security module, then

a) If statusInformation contains values for an OID/value pair,
then a Report PDU is generated.

1) If the scopedPDU has been returned from ProcessIncomingMsg
then determine contextEngineID, contextName, and PDU.

2) Information about the message is cached and a
stateReference is created (implementation-specific).
Information to be cached includes the values of:

msgVersion,
msgID,
securityLevel,
msgFlags,
msgMaxSize,
securityModel,
maxSizeResponseScopedPDU,
securityStateReference

3) Request that a Report-PDU be prepared and sent, according
to the abstract service primitive:

result = -- SUCCESS or FAILURE
returnResponsePDU(
IN messageProcessingModel -- SNMPv3(3)
IN securityModel -- same as on incoming request
IN securityName -- from ProcessIncomingMsg
IN securityLevel -- same as on incoming request

IN contextEngineID -- from step 6 a) 1)
IN contextName -- from step 6 a) 1)
IN pduVersion -- SNMPv2-PDU
IN PDU -- from step 6 a) 1)
IN maxSizeResponseScopedPDU -- from ProcessIncomingMsg
IN stateReference -- from step 6 a) 2)
IN statusInformation -- from ProcessIncomingMsg
OUT transportDomain -- destination's transport
-- domain
OUT transportAddress -- destination's transport
-- address
OUT outgoingMessage -- the message to send
OUT outgoingMessageLength -- the length of the message
)

b) The incoming message is discarded without further processing,
and a FAILURE result is returned. SNMPv3 Message Processing is
complete.

7) The scopedPDU is parsed to extract the contextEngineID, the
contextName and the PDU. If any parse error occurs, then the
snmpInASNParseErrs counter [RFC1907] is incremented, the security
state information is discarded, the message is discarded without
further processing, and a FAILURE result is returned. SNMPv3
Message Processing is complete.

8) The pduVersion is set to an SNMPv2-PDU.

9) The pduType is determined, in an implementation-dependent manner,
to be:

- a GetRequest-PDU,
- a GetNextRequest-PDU,
- a GetBulkRequest-PDU,
- a SetRequest-PDU,
- an InformRequest-PDU,
- an SNMPv2-Trap-PDU,
- a Response-PDU, or
- a Report-PDU.

10) If the pduType is a Response-PDU or Report-PDU, then

a) The value of the msgID component is used to find the cached
information for a corresponding outstanding Request message.
If no such outstanding Request message is found, then the
security state information is discarded, the message is
discarded without further processing, and a FAILURE result is
returned. SNMPv3 Message Processing is complete.

b) sendPduHandle is retrieved from the cached information.

Otherwise, sendPduHandle is set to <none>, an implementation
defined value.

11) If the pduType is a Report-PDU, then

a) statusInformation is created using the contents of the
Report-PDU, in an implementation-dependent manner. This
statusInformation will be forwarded to the application
associated with the sendPduHandle.

b) Any cached information about the outstanding Request message
message is discarded.

c) The security state information for this incoming message is
discarded.

d) stateReference is set to <none>

e) A SUCCESS result is returned. SNMPv3 Message Processing is
complete.

12) If the pduType is a Response-PDU, then

a) The cached data for the outstanding request, referred to by
stateReference, is retrieved, including

- snmpEngineID
- securityModel
- securityName
- securityLevel
- contextEngineID
- contextName

b) If the values extracted from the incoming message differ from
the cached data, then the security state information is
discarded, any cached information about the outstanding
Request message is discarded, the incoming message is
discarded without further processing, and a FAILURE result is
returned. SNMPv3 Message Processing is complete.

c) Otherwise, any cached information about the outstanding
Request message is discarded, and stateReference is set to
<none>.

d) A SUCCESS result is returned. SNMPv3 Message Processing is
complete.

13) If the pduType is a GetRequest-PDU, GetNextRequest-PDU,
GetBulkRequest-PDU, SetRequest-PDU, or InformRequest-PDU, then

a) If the value of securityEngineID is not equal to the value of
snmpEngineID, then the security state information is
discarded, any cached information about the outstanding
Request message is discarded, the incoming message is
discarded without further processing, and a FAILURE result is
returned. SNMPv3 Message Processing is complete.

b) Information about the message is cached and a stateReference
is created (implementation-specific). Information to be
cached includes the values of:

msgVersion,
msgID,
securityLevel,
msgFlags,
msgMaxSize,
securityModel,
maxSizeResponseScopedPDU,
securityStateReference

c) A SUCCESS result is returned. SNMPv3 Message Processing is
complete.

14) If the pduType is an SNMPv2-Trap-PDU, then A SUCCESS result is
returned. SNMPv3 Message Processing is complete.

8. Intellectual Property

The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
oBTain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.

9. Acknowledgements

This document is the result of the efforts of the SNMPv3 Working
Group. Some special thanks are in order to the following SNMPv3 WG
members:

Dave Battle (SNMP Research, Inc.)
Uri Blumenthal (IBM T.J. Watson Research Center)
Jeff Case (SNMP Research, Inc.)
John Curran (BBN)
T. Max Devlin (Hi-TECH Connections)
John Flick (Hewlett Packard)
David Harrington (Cabletron Systems Inc.)
N.C. Hien (IBM T.J. Watson Research Center)
Dave Levi (SNMP Research, Inc.)
Louis A Mamakos (UUNET Technologies Inc.)
Paul Meyer (Secure Computing Corporation)
Keith McCloghrie (Cisco Systems)
Russ Mundy (Trusted Information Systems, Inc.)
Bob Natale (ACE*COMM Corporation)
Mike O'Dell (UUNET Technologies Inc.)
Dave Perkins (DeskTalk)
Peter Polkinghorne (Brunel University)
Randy Presuhn (BMC Software, Inc.)
David Reid (SNMP Research, Inc.)
Shawn Routhier (Epilogue)
Juergen Schoenwaelder (TU Braunschweig)
Bob Stewart (Cisco Systems)
Bert Wijnen (IBM T.J. Watson Research Center)

The document is based on recommendations of the IETF Security and
Administrative Framework Evolution for SNMP Advisory Team. Members
of that Advisory Team were:

David Harrington (Cabletron Systems Inc.)
Jeff Johnson (Cisco Systems)
David Levi (SNMP Research Inc.)
John Linn (Openvision)
Russ Mundy (Trusted Information Systems) chair
Shawn Routhier (Epilogue)
Glenn Waters (Nortel)
Bert Wijnen (IBM T. J. Watson Research Center)

As recommended by the Advisory Team and the SNMPv3 Working Group
Charter, the design incorporates as much as practical from previous
RFCs and drafts. As a result, special thanks are due to the authors
of previous designs known as SNMPv2u and SNMPv2*:

Jeff Case (SNMP Research, Inc.)
David Harrington (Cabletron Systems Inc.)
David Levi (SNMP Research, Inc.)
Keith McCloghrie (Cisco Systems)
Brian O'Keefe (Hewlett Packard)
Marshall T. Rose (Dover Beach Consulting)
Jon Saperia (BGS Systems Inc.)
Steve Waldbusser (International Network Services)
Glenn W. Waters (Bell-Northern Research Ltd.)

10. Security Considerations

The Dispatcher coordinates the processing of messages to provide a
level of security for management messages and to direct the SNMP PDUs
to the proper SNMP application(s).

A Message Processing Model, and in particular the V3MP defined in
this document, interacts as part of the Message Processing with
Security Models in the Security Subsystem via the abstract service
interface primitives defined in [RFC2271] and elaborated above.

The level of security actually provided is primarily determined by
the specific Security Model implementation(s) and the specific SNMP
application implementation(s) incorporated into this framework.
Applications have access to data which is not secured. Applications
should take reasonable steps to protect the data from disclosure, and
when they send data across the network, they should obey the
securityLevel and call upon the services of an Access Control Model
as they apply access control.

The values for the msgID element used in communication between SNMP
entities must be chosen to avoid replay attacks. The values do not
need to be unpredictable; it is sufficient that they not repeat.

11. References

[RFC1901] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Introduction to Community-based SNMPv2",
RFC1901, January 1996.

[RFC1902] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Structure of Management Information for
Version 2 of the Simple Network Management Protocol (SNMPv2)",
RFC1902, January 1996.

[RFC1905] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Protocol Operations for Version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC1905, January
1996.

[RFC1906] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Transport Mappings for Version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC1906, January
1996.

[RFC1907] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Management Information Base for Version 2
of the Simple Network Management Protocol (SNMPv2)", RFC1907
January 1996.

[RFC1908] 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.

[RFC2028] Hovey, R., and S. Bradner, "The Organizations Involved in
the IETF Standards Process", BCP 11, RFC2028, October 1996.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC2119, BCP 14, March 1997.

[RFC2271] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for describing SNMP Management Frameworks",
RFC2271, January 1998.

[RFC2274] Blumenthal, U., and B. Wijnen, "The User-Based
Security Model for Version 3 of the Simple Network
Management Protocol (SNMPv3)", RFC2274, January 1998.

[RFC2275] Wijnen, B., Presuhn, R., and K. McCloghrie,
"View-based Access Control Model for the Simple
Network Management Protocol (SNMP)", RFC2275, January 1998.

[RFC2273] Levi, D., Meyer, P., and B. Stewart, "SNMPv3
Applications", RFC2273, January 1998.

12. Editors' Addresses

Jeffrey Case
SNMP Research, Inc.
3001 Kimberlin Heights Road
Knoxville, TN 37920-9716
USA

Phone: [phone]
EMail: [e-mail]

Dave Harrington
Cabletron Systems, Inc
Post Office Box 5005
Mail Stop: Durham
35 Industrial Way
Rochester, NH 03867-5005
USA

Phone: [phone]
EMail: [e-mail]

Randy Presuhn
BMC Software, Inc.
1190 Saratoga Avenue
Suite 130
San Jose, CA 95129
USA

Phone: [phone]
EMail: [e-mail]

Bert Wijnen
IBM T. J. Watson Research
Schagen 33
3461 GL Linschoten
Netherlands

Phone: [phone]
EMail: [e-mail]

13. Full Copyright Statement

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