Network Working Group D. Harrington
Internet-Draft Huawei Technologies (USA)
Intended status: Standards Track January 25, 2007
Expires: July 29, 2007
Transport Security Model for SNMP
draft-ietf-isms-transport-security-model-02
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This memo describes a Transport Security Model for the Simple Network
Management Protocol.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. The Internet-Standard Management Framework . . . . . . . . 3
1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Modularity . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4
1.5. Constraints . . . . . . . . . . . . . . . . . . . . . . . 5
2. How Transport Security Model Fits in the Architecture . . . . 5
2.1. Security Capabilities of this Model . . . . . . . . . . . 5
2.1.1. Threats . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2. Security Levels . . . . . . . . . . . . . . . . . . . 6
2.2. No Sessions . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Coexistence . . . . . . . . . . . . . . . . . . . . . . . 7
2.4. Security Parameter Passing . . . . . . . . . . . . . . . . 7
2.5. Notifications and Proxy . . . . . . . . . . . . . . . . . 8
3. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. SNMPv3 Message Fields . . . . . . . . . . . . . . . . . . 9
3.1.1. msgGlobalData . . . . . . . . . . . . . . . . . . . . 10
3.1.2. securityLevel and msgFlags . . . . . . . . . . . . . . 10
3.1.3. msgSecurityParameters . . . . . . . . . . . . . . . . 11
3.2. Cached Information and References . . . . . . . . . . . . 11
3.2.1. securityStateReference . . . . . . . . . . . . . . . . 12
3.2.2. tmStateReference . . . . . . . . . . . . . . . . . . . 12
4. Processing an Outgoing Message . . . . . . . . . . . . . . . . 13
4.1. Security Processing for an Outgoing Message . . . . . . . 13
4.2. Elements of Procedure for Outgoing Messages . . . . . . . 14
5. Processing an Incoming SNMP Message . . . . . . . . . . . . . 15
5.1. Security Processing for an Incoming Message . . . . . . . 15
5.2. Elements of Procedure for Incoming Messages . . . . . . . 16
6. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.1. Structure of the MIB Module . . . . . . . . . . . . . . . 17
6.2. Textual Conventions . . . . . . . . . . . . . . . . . . . 17
6.3. The transportStats Subtree . . . . . . . . . . . . . . . . 17
6.4. Relationship to Other MIB Modules . . . . . . . . . . . . 17
6.4.1. Relationship to the SNMPv2-MIB . . . . . . . . . . . . 17
6.4.2. MIB Modules Required for IMPORTS . . . . . . . . . . . 18
7. MIB module definition . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
8.1. MIB module security . . . . . . . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1. Normative References . . . . . . . . . . . . . . . . . . . 22
10.2. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Notification Tables Configuration . . . . . . . . . . 24
A.1. Transport Security Model Processing . . . . . . . . . . . 25
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
This memo describes a Transport Security Model for the Simple Network
Management Protocol, for use with secure transport models in the
Transport Subsystem [I-D.ietf-isms-tmsm].
This memo also defines a portion of the Management Information Base
(MIB) for use with network management protocols in TCP/IP based
internets. In particular it defines objects for monitoring and
managing the Transport Security Model for SNMP.
It is important to understand the SNMP architecture and the
terminology of the architecture to understand where the Transport
Security Model described in this memo fits into the architecture and
interacts with other subsystems and models within the architecture.
1.1. The Internet-Standard Management Framework
For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
RFC 3410 [RFC3410].
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP).
Objects in the MIB are defined using the mechanisms defined in the
Structure of Management Information (SMI). This memo specifies a MIB
module that is compliant to the SMIv2, which is described in STD 58,
RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
[RFC2580].
1.2. Conventions
The terms "manager" and "agent" are not used in this document,
because in the RFC 3411 architecture, all SNMP entities have the
capability of acting as either manager or agent or both depending on
the SNMP applications included in the engine. Where distinction is
required, the application names of Command Generator, Command
Responder, Notification Originator, Notification Receiver, and Proxy
Forwarder are used. See "SNMP Applications" [RFC3413] for further
information.
While security protocols frequently refer to a user, the terminology
used in RFC3411 [RFC3411] and in this memo is "principal". A
principal is the "who" on whose behalf services are provided or
processing takes place. A principal can be, among other things, an
individual acting in a particular role; a set of individuals, with
each acting in a particular role; an application or a set of
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applications, or a combination of these within an administrative
domain.
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].
1.3. Modularity
The reader is expected to have read and understood the description of
the SNMP architecture, as defined in [RFC3411],and the architecture
extension specified in "Transport Subsystem for the Simple Network
Management Protocol" [I-D.ietf-isms-tmsm], which enables the use of
external "lower layer transport" protocols to provide message
security, tied into the SNMP architecture through the transport
subsystem. The Transport Security Model is designed to work with
such lower-layer secure transport models.
In keeping with the RFC 3411 design decisions to use self-contained
documents, this memo includes the elements of procedure plus
associated MIB objects which are needed for processing the Transport
Security Model for SNMP. These MIB objects SHOULD not be referenced
in other documents. This allows the Transport Security Model to be
designed and documented as independent and self-contained, having no
direct impact on other modules, and allowing this module to be
upgraded and supplemented as the need arises, and to move along the
standards track on different time-lines from other modules.
This modularity of specification is not meant to be interpreted as
imposing any specific requirements on implementation.
1.4. Motivation
Version 3 of the Simple Network Management Protocol (SNMPv3) added
security to the previous versions of the protocol. The User-based
Security Model (USM) [RFC3414] was designed to be independent of
other existing security infrastructures, to ensure it could function
when third party authentication services were not available, such as
in a broken network. As a result, USM typically utilizes a separate
user and key management infrastructure. Operators have reported that
deploying another user and key management infrastructure in order to
use SNMPv3 is a reason for not deploying SNMPv3 at this point in
time.
This memo describes a security model that will make use of transport
models that rely on lower layer secure transports and existing and
commonly deployed security infrastructures. This security model is
designed to meet the security and operational needs of network
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administrators, maximize usability in operational environments to
achieve high deployment success and at the same time minimize
implementation and deployment costs to minimize the time until
deployment is possible.
1.5. Constraints
The design of this SNMP Security Model is also influenced by the
following constraints:
1. When the requirements of effective management in times of network
stress are inconsistent with those of security, the design of
this model gives preference to effective management.
2. In times of network stress, the security protocol and its
underlying security mechanisms SHOULD NOT depend upon the ready
availability of other network services (e.g., Network Time
Protocol (NTP) or AAA protocols).
3. When the network is not under stress, the security model and its
underlying security mechanisms MAY depend upon the ready
availability of other network services.
4. It may not be possible for the security model to determine when
the network is under stress.
5. A security model should require no changes to the SNMP
architecture.
6. A security model should require no changes to the underlying
security protocol.
2. How Transport Security Model Fits in the Architecture
The Transport Security Model is designed to fit into the RFC3411
architecture as a security model in the security subsystem, and to
utilize the services of a secure transport model.
The transport model of an SNMP engine will perform the translation
between transport-specific security parameters and the SNMP-specific,
model-independent parameters securityName and securityLevel. To
maintain the RFC3411 modularity, the transport model does not know
which securityModel will be used for an incoming message; the message
processing model will determine the securityModel to be used, in a
message processing model dependent manner. In an SNMPv3 message, the
Transport Security Model should be specified in the message header.
2.1. Security Capabilities of this Model
2.1.1. Threats
The Transport Security Model, when used with suitable secure
transport models, provides protection against the threats identified
by the RFC 3411 architecture [RFC3411].
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Which threats are addressed depends on the transport model. The
Transport Security Model does not address any threats itself, but
delegates that responsibility to a secure transport model.
The Transport Security Model is called a security model to be
compatible with the RFC3411 architecure. However, this security
model does not provide security mechanisms such as authenticatio and
encryption itself, so it SHOULD always be used with a transport model
that provides appropriate security.
2.1.2. Security Levels
The RFC 3411 architecture recognizes three levels of security:
- without authentication and without privacy (noAuthNoPriv)
- with authentication but without privacy (authNoPriv)
- with authentication and with privacy (authPriv)
The model-independent securityLevel parameter is used to request
specific levels of security for outgoing messages, and to assert that
specific levels of security were applied during the transport and
processing of incoming messages.
The transport layer algorithms used to provide security SHOULD NOT be
exposed to the Transport Security Model, as the Transport Security
Model has no mechanisms by which it can test whether an assertion
made by a transport model is accurate.
The Transport Security Model trusts that the underlying secure
transport connection has been properly configured to support security
characteristics at least as strong as requested in securityLevel.
2.2. No Sessions
The Transport Security Model will associate state regarding each
message and each known remote engine with a single combination of
transportType, transportAddress, securityName, securityModel, and
securityLevel.
Some transport models will utilize sessions to maintain long-lived
state; others will use stateless transport. For reasons of module
independence, the Transport Security Model will make no assumptions
about there being a session of any kind. Each message may be totally
independent of other messages. Any binding of multiples messages
into a session is specific to the transport model. There may be
circumstances where having an snmp-specific session provided by a
security model is useful; such functionality is left to future
security models.
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2.3. Coexistence
There are two primary factors which determine whether security modles
can coexist. First, there must be a mechanism to select different
security models at run-time. Second, the processing of one security
should not impact the processing of another security model.
In the RFC3411 architecture, a message processing model determines
which security model should be called. As of this writing, there are
three message processing models and three other security models:
SNMPv1, SNMPv2c, and the User-based Security Model.
The SNMPv1 and SNMPv2c message processing described in RFC3584 (BCP
74) [RFC3584] always selects the SNMPv1(1) security model for an
SNMPv1 message, or the SNMPv2c(2) security model for an SNMPv2c
message. Since there is no field in the message format that permits
specifying a security model, RFC3584 message processing does not
permit the selection of security models other than SNMPv1 or SNMPv2.
Therefore, the Transport Security Model can coexist with SNMPv1 and
SNMPv2c community-based security models, but the Transport Security
Model cannot be used with SNMPv1 or SNMPv2c messages.
The SNMPv3 message processing defined in RFC3412 [RFC3412], extracts
the securityModel from the msgSecurityModel field of an incoming
SNMPv3Message. When the extracted value of msgSecurityModel is
transportSecurityModel(YY), security processing is directed to the
Transport Security Model. So for an outgoing message secured using
the Transport Security Model, msgSecurityModel should be set to
transportSecurityModel(YY).
The Transport Security Model uses its own MIB module for processing
to maintain independence from other security models. This allows the
Transport Security Model to coexist with other security models, such
as the User-based Security Model.
Note that the Transport Security Model may work with multiple
transport models, but the isAccessAllowed() primitive only accepts a
value for the security model, not for transport models. As a result,
it is not possible to have different access control rules for
different transport models that use the Transport Security Model.
2.4. Security Parameter Passing
For outgoing messages, Transport Security Model takes input provided
by the SNMP application, converts that information into suitable
transport and security parameters in a cache referenced by
tmStateReference. The wholeMsg and the tmStateReference are passed
to the appropriate transport model through a series of APIs, as
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described in "Transport Subsystem for the Simple Network Management
Protocol" [I-D.ietf-isms-tmsm].
For incoming messages, the transport model accepts messages from the
lower layer transport, and records the transport-related information
and security-related information, including a securityName that
represents the authenticated identity, and a securityLevel that
represents the security features provided during transport, in a
cache referenced by tmStateReference. The wholeMsg and the
tmStateReference are passed to the appropriate security model through
a series of APIs, as described in "Transport Subsystem for the Simple
Network Management Protocol" [I-D.ietf-isms-tmsm].
For an incoming SNMPv3 message, the messaging model extracts the
requested securityLevel from the msgFlags field, and passes this to
the security model. The Transport Security Model verifies that the
securityLevel passed in the cache is at least as strong as the
securityLevel passed in the ASI securityLevel parameter.
2.5. Notifications and Proxy
The SNMP-TARGET-MIB module [RFC3413] contains objects for defining
management targets, including transportType, transportAddress,
securityName, securityModel, and securityLevel parameters, for
applications such as notifications and proxy. For the Transport
Security Model, transport type and address are configured in the
snmpTargetAddrTable, and the securityModel, securityName, and
securityLevel parameters are configured in the snmpTargetParamsTable.
The default approach is for an administrator to statically
preconfigure this information to identify the targets authorized to
receive notifications or perform proxy.
3. Message Formats
The syntax of an SNMP message using this Security Model adheres to
the message format defined in the version-specific Message Processing
Model document (for example [RFC3412]). At the time of this writing,
there are three defined message formats - SNMPv1, SNMPv2c, and
SNMPv3. The Transport Security Model deos not work with SNMPv1 and
SNMPv2c for reasons described above, so this memo only deals with
SNMPv3 messages.
The processing is compatible with the RFC 3412 primitives,
generateRequestMsg() and processIncomingMsg(), that show the data
flow between the Message Processor and the security model.
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3.1. SNMPv3 Message Fields
The SNMPv3Message SEQUENCE is defined in [RFC3412] and [RFC3416].
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
-- the value 3 is used for snmpv3
msgVersion INTEGER ( 0 .. 2147483647 ),
-- 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 (1..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 RFC3416
}
END
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The following describes how the Transport Security Model treats
certain fields in the message:
3.1.1. msgGlobalData
The msgGlobalData values are set by the Message Processing model
(e.g., SNMPv3 Message Processing), and are not modified by the
Transport Security Model.
msgMaxSize is determined by the implementation.
For outgoing messages, msgSecurityModel is set by the Message
Processing model (e.g., SNMPv3) to the IANA-assigned value for the
Transport Security Model. See
http://www.iana.org/assignments/snmp-number-spaces.
For outgoing messages, the value of msgFlags is set by the Message
Processing model (e.g., SNMPv3 Message Processing), which is not
necessarily the actual securityLevel applied to the message by the
transport model.
For incoming messages, the value of msgFlags is determined by the
Message Processing model (e.g., SNMPv3 Message Processing), and the
value is passed in the securityLevel parameter in the ASI between the
messaging model and the security model.
3.1.2. securityLevel and msgFlags
For an outgoing message, securityLevel is the requested security for
the message, passed in the ASIs. If a Transport Model cannot provide
the requested securityLevel, the model MUST describe a standard
behavior that is followed for that situation. If the Transport Model
is able to provide stronger than requested security, that may be
acceptable. If the Transport Model cannot provide at least the
requested level of security, the Transport Model MUST discard the
request and SHOULD notify the message processing model that the
request failed.
The msgFlags field in the SNMPv3 message is closely related to
securityLevel. msgFlags is Messaging Model dependent, while
securityLevel is Messaging Model independent. To maintain the
separation between subsystems, the Transport Model SHOULD NOT modify
Message Model dependent fields. As a result, msgFlags in the SNMPv3
message MAY reflect the requested securityLevel, not the actual
securityLevel applied to the message by the Transport Model.
Part of the responsibility of a Security Model is to ensure that the
actual security provided by the underlying transport layer security
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mechanisms is configured to meet or exceed the securityLevel
requested. When the Security Model processes the incoming message,
it should compare the securityLevel provided by the messaging model
to the securityLevel provided by the transport model in
tmStateReference. If they differ, the Security Model should
determine whether the securityLevel provided by the transport model
is acceptable (e.g. the transport securityLevel is greater than or
equal to the requested securityLevel. If not, it should discard the
message. Depending on the model, the Security Model may issue a
reportPDU with a model-specific counter.
3.1.3. msgSecurityParameters
Since message security is provided by a "lower layer", and the
securityName parameter is always determined by the transport model
from the lower layer authentication method, the SNMP message does not
need to carry message security parameters within the
msgSecurityParameters field.
The field msgSecurityParameters in SNMPv3 messages has a data type of
OCTET STRING. To prevent its being used in a manner that could be
damaging, such as for carrying a virus or worm, when used with
Transport Security Model its value MUST be the BER serialization of a
zero-length OCTET STRING.
TransportSecurityParametersSyntax DEFINITIONS IMPLICIT TAGS
::= BEGIN
TransportSecurityParameters ::=
OCTET STRING
END
3.2. Cached Information and References
The RFC3411 architecture uses caches to store dynamic model-specific
information, and uses references in the ASIs to indicate in a model-
independent manner which cached information must flow between
subsystems.
There are two levels of state that may need to be maintained: the
security state in a request-response pair, and potentially long-term
state relating to transport and security.
This state is maintained in caches and a Local Configuration
Datastore (LCD). To simplify the elements of procedure, the release
of state information is not always explicitly specified. As a
general rule, if state information is available when a message being
processed gets discarded, the state related to that message should
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also be discarded, and if state information is available when a
relationship between engines is severed, such as the closing of a
transport session, the state information for that relationship might
also be discarded.
This document differentiates the tmStateReference from the
securityStateReference. This document does not specify an
implementation strategy, only an abstract discussion of the data that
must flow between subsystems. An implementation MAY use one cache
and one reference to serve both functions, but an implementer must be
aware of the cache-release issues to prevent the cache from being
released before a security or transport model has had an opportunity
to extract the information it needs.
3.2.1. securityStateReference
From RFC3411: "For each message received, the Security Model caches
the state information such that a Response message can be generated
using the same security information, even if the Local Configuration
Datastore is altered between the time of the incoming request and the
outgoing response.
A Message Processing Model has the responsibility for explicitly
releasing the cached data if such data is no longer needed. To
enable this, an abstract securityStateReference data element is
passed from the Security Model to the Message Processing Model. The
cached security data may be implicitly released via the generation of
a response, or explicitly released by using the stateRelease
primitive, as described in RFC3411 section 4.5.1."
The information saved should include the model-independent parameters
(transportType, transportAddress, securityName, securityModel, and
securityLevel), related security parameters, and other information
needed to match the response with the request. The Message
Processing Model has the responsibility for explicitly releasing the
securityStateReference when such data is no longer needed. The
securityStateReference cached data may be implicitly released via the
generation of a response, or explicitly released by using the
stateRelease primitive, as described in RFC 3411 section 4.5.1."
If the transport model connection is closed between the time a
Request is received and a Response message is being prepared, then
the Response message MAY be discarded.
3.2.2. tmStateReference
For each message or transport session, information about the message
security is stored in the cache to pass model- and mechanism-specific
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parameters. The state referenced by tmStateReference may be saved
across multiple messages, in a Local Configuration Datastore (LCD),
as compared to securityStateReference which is only saved for the
life of a request-response pair of messages.
The format of the cache and the LCD are implementation-specific.
4. Processing an Outgoing Message
An error indication may return an OID and value for an incremented
counter and a value for securityLevel, and values for contextEngineID
and contextName for the counter, and the securityStateReference if
the information is available at the point where the error is
detected.
4.1. Security Processing for an Outgoing Message
This section describes the procedure followed by the Transport
Security Model.
The parameters needed for generating a message are supplied to the
security model by the message processing model via the
generateRequestMsg() or the generateResponseMsg() ASI. The Transport
Subsystem architectural extension has added the transportDomain,
transportAddress, and tmStateReference parameters to the original
RFC3411 ASIs.
statusInformation = -- success or errorIndication
generateRequestMsg(
IN messageProcessingModel -- typically, SNMP version
IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN transportDomain -- as specified by application
IN transportAddress -- as specified by application
IN securityModel -- for the outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN scopedPDU -- message (plaintext) payload
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of generated message
OUT tmStateReference -- reference to transport info
)
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statusInformation = -- success or errorIndication
generateResponseMsg(
IN messageProcessingModel -- typically, SNMP version
IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN transportDomain -- as specified by application
IN transportAddress -- as specified by application
IN securityModel -- for the outgoing message
IN securityEngineID -- authoritative SNMP entity
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
IN scopedPDU -- message (plaintext) payload
IN securityStateReference -- reference to security state
-- information from original
-- request
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of generated message
OUT tmStateReference -- reference to transport info
)
Note that the Transport Subystem architectural extension adds
transportDomain, transportAddress, and tmStateReference to these
ASIs.
4.2. Elements of Procedure for Outgoing Messages
1) verify that securityModel is transportSecurityModel(YY). If not,
then an error indication is returned to the calling message model,
and security model processing stops for this message.
2) If there is a securityStateReference, then this is a response to a
request, so extract the cached security data. This should include
transportDomain, transportAddress, securityName, securityLevel, and
securityModel, and a tmStateReference. The cachedSecurityData for
this message can now be discarded.
3) If there is no securityStateReference, then find or create an
entry in a Local Configuration Datastore containing the provided
transportDomain, transportAddress, securityName, securityLevel, and
securityModel, and create a tmStateReference to reference the entry.
4) fill in the msgSecurityModel with the value for
transportSecurityModel(YY).
5) fill in the msgFlags corresponding to the securityLevel specified
in the generateRequest() or generateResponse() parameter.
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6) fill in the securityParameters with the serialization of a zero-
length OCTET STRING.
7) The plaintext scopedPDU serves as the msgData of the message.
8) Combine the message parts into a wholeMsg and calculate
wholeMsgLength.
9) The completed message (wholeMsg) with its length (wholeMsgLength)
and securityParameters (a zero-length octet string) and
tmStateReference is returned to the calling messaging model with the
statusInformation set to success.
5. Processing an Incoming SNMP Message
An error indication may return an OID and value for an incremented
counter and a value for securityLevel, and values for contextEngineID
and contextName for the counter, and the securityStateReference if
the information is available at the point where the error is
detected.
5.1. Security Processing for an Incoming Message
This section describes the procedure followed by the Transport
Security Model whenever it receives an incoming message from a
Message Processing Model. The abstract service primitive from a
Message Processing Model to the Security Subsystem for a received
message is:
statusInformation = -- errorIndication or success
-- error counter OID/value if error
processIncomingMsg(
IN messageProcessingModel -- typically, SNMP version
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
IN tmStateReference -- from the transport model
OUT securityEngineID -- authoritative SNMP entity
OUT securityName -- identification of the principal
OUT scopedPDU, -- message (plaintext) payload
OUT maxSizeResponseScopedPDU -- maximum size sender can handle
OUT securityStateReference -- reference to security state
) -- information, needed for response
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5.2. Elements of Procedure for Incoming Messages
1) verify that securityModel is transportSecurityModel(YY). If not,
then an error indication is returned to the calling message model,
and security model processing stops for this message.
2) If the messageProcessingModel is SNMPv3, then the securityEngineID
is set to the local snmpEngineID, to satisfy the SNMPv3 message
processing defined in RFC 3412 section 7.2 13a).
3) If the received securityParameters is not the serialization of an
OCTET STRING formatted according to the transportSecurityParameters,
or the contained OCTET STRING is not empty, then the
snmpInASNParseErrs counter [RFC3418] is incremented, and an error
indication (parseError) is returned to the calling module, and
security model processing stops for this message.
4) if tmStateReference does not refer to a cache containing values
for securityName and securityLevel, then the tsmInvalidCache counter
is incremented, an error indication is returned to the calling
module, and security model processing stops for this message.
5) Extract the value of securityName from the cache referenced by
tmStateReference.
6) The scopedPDU component is extracted from the wholeMsg.
7) The maxSizeResponseScopedPDU is calculated. This is the maximum
size allowed for a scopedPDU for a possible Response message.
8) Compare the value of securityLevel in the cache referenced by
tmStateReference to the value of the securityLevel parameter passed
in the processIncomingMessage service primitive. If the parameter
specifies privacy (Priv), and the cache specifies no privacy (noPriv)
was provided by the transport model, or the parameter specifies
authentication (auth) and the cache specifies no authentication
(noAuth) was provided by the transport model, then the
tsmInadequateSecurity counter is incremented, and an error indication
(unsupportedSecurityLevel) together with the OID and value of the
incremented counter is returned to the calling module.
9) The information in the tmStateReference may be saved, in an
implementation-dependent manner, in a Local Configuration Datastore
(LCD) for subsequent usage.
10)The security data is cached as cachedSecurityData, so that a
possible response to this message can use the same security
parameters. Then securityStateReference is set for subsequent
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reference to this cached data. For Transport Security Model, the
securityStateReference should include a reference to the
tmStateReference cache.
11) The statusInformation is set to success and a return is made to
the calling module passing back the OUT parameters as specified in
the processIncomingMsg primitive.
6. Overview
This MIB module provides management of the Transport Security Model.
It defines some needed textual conventions, and some statistics.
6.1. Structure of the MIB Module
Objects in this MIB module are arranged into subtrees. Each subtree
is organized as a set of related objects. The overall structure and
assignment of objects to their subtrees, and the intended purpose of
each subtree, is shown below.
6.2. Textual Conventions
Generic and Common Textual Conventions used in this document can be
found summarized at http://www.ops.ietf.org/mib-common-tcs.html
6.3. The transportStats Subtree
This subtree contains counters specific to the Transport Security
Model, that provide information for identifying fault conditions.
6.4. Relationship to Other MIB Modules
Some management objects defined in other MIB modules are applicable
to an entity implementing Transport Security Model. In particular,
it is assumed that an entity implementing Transport Security Model
will implement the SNMPv2-MIB [RFC3418], the SNMP-FRAMEWORK-MIB
[RFC3411] and the SNMP-TRANSPORT-MIB [I-D.ietf-isms-tmsm].
6.4.1. Relationship to the SNMPv2-MIB
The 'system' group in the SNMPv2-MIB [RFC3418] is defined as being
mandatory for all systems, and the objects apply to the entity as a
whole. The 'system' group provides identification of the management
entity and certain other system-wide data. The snmpInASNParseErrs
counter is incremented during the elements of procedure. The SNMP-
TRANSPORT-SM-MIB does not duplicate those objects.
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6.4.2. MIB Modules Required for IMPORTS
The following MIB module imports items from [RFC2578] and [RFC2580]..
7. MIB module definition
SNMP-TRANSPORT-SM-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
snmpModules, Counter32
FROM SNMPv2-SMI
MODULE-COMPLIANCE, OBJECT-GROUP
FROM SNMPv2-CONF
;
tsmMIB MODULE-IDENTITY
LAST-UPDATED "200701250000Z"
ORGANIZATION "ISMS Working Group"
CONTACT-INFO "WG-EMail: isms@lists.ietf.org
Subscribe: isms-request@lists.ietf.org
Chairs:
Juergen Quittek
NEC Europe Ltd.
Network Laboratories
Kurfuersten-Anlage 36
69115 Heidelberg
Germany
+49 6221 90511-15
quittek@netlab.nec.de
Juergen Schoenwaelder
International University Bremen
Campus Ring 1
28725 Bremen
Germany
+49 421 200-3587
j.schoenwaelder@iu-bremen.de
Editor:
David Harrington
Huawei Technologies USA
1700 Alma Dr.
Plano TX 75075
USA
+1 603-436-8634
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ietfdbh@comcast.net
"
DESCRIPTION "The Transport Security Model MIB
Copyright (C) The IETF Trust (2007). This
version of this MIB module is part of RFC XXXX;
see the RFC itself for full legal notices.
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note
"
REVISION "200701250000Z"
DESCRIPTION "The initial version, published in RFC XXXX.
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note
"
::= { snmpModules xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and
-- remove this note
-- ---------------------------------------------------------- --
-- subtrees in the SNMP-TRANSPORT-SM-MIB
-- ---------------------------------------------------------- --
tsmNotifications OBJECT IDENTIFIER ::= { tsmMIB 0 }
tsmMIBObjects OBJECT IDENTIFIER ::= { tsmMIB 1 }
tsmConformance OBJECT IDENTIFIER ::= { tsmMIB 2 }
-- -------------------------------------------------------------
-- Objects
-- -------------------------------------------------------------
-- Statistics for the Transport Security Model
tsmStats OBJECT IDENTIFIER ::= { tsmMIBObjects 1 }
tsmInvalidCache OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of messages dropped because the
tmStateReference referred to an invalid cache.
"
::= { tsmStats 1 }
tsmInadequateSecurity OBJECT-TYPE
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SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of incoming messages dropped because
the actual securtityLevel provided was less than
the requested securityLevel.
"
::= { tsmStats 2 }
-- -------------------------------------------------------------
-- tsmMIB - Conformance Information
-- -------------------------------------------------------------
tsmGroups OBJECT IDENTIFIER ::= { tsmConformance 1 }
tsmCompliances OBJECT IDENTIFIER ::= { tsmConformance 2 }
-- -------------------------------------------------------------
-- Units of conformance
-- -------------------------------------------------------------
tsmGroup OBJECT-GROUP
OBJECTS {
tsmInvalidCache,
tsmInadequateSecurity
}
STATUS current
DESCRIPTION "A collection of objects for maintaining
information of an SNMP engine which implements
the SNMP Transport Security Model.
"
::= { tsmGroups 2 }
-- -------------------------------------------------------------
-- Compliance statements
-- -------------------------------------------------------------
tsmCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines that support
the SNMP-TRANSPORT-SM-MIB"
MODULE
MANDATORY-GROUPS { tsmGroup }
::= { tsmCompliances 1 }
END
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8. Security Considerations
This document describes a security model that permits SNMP to utilize
security services provided through an SNMP transport model. The
Transport Security Model relies on transport models for mutual
authentication, binding of keys, confidentiality and integrity. The
security threats and how those threats are mitigated should be
covered in detail in the specification of the transport model and the
underlying secure transport.
Transport Security Model relies on a transport model to provide an
authenticated principal for mapping to securityName, and an assertion
for mapping to securityLevel, for access control purposes.
The Transport Security Model is called a security model to be
compatible with the RFC3411 architecure. However, this security
model provides no security itself. It SHOULD always be used with a
transport model that provides security, but this is a run-time
decision of the operator or management application, or a
configuration decision of an operator.
8.1. MIB module security
There are no management objects defined in this MIB module that have
a MAX-ACCESS clause of read-write and/or read-create. So, if this
MIB module is implemented correctly, then there is no risk that an
intruder can alter or create any management objects of this MIB
module via direct SNMP SET operations.
Some of the readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or
vulnerable in some network environments. It is thus important to
control even GET and/or NOTIFY access to these objects and possibly
to even encrypt the values of these objects when sending them over
the network via SNMP. These are the tables and objects and their
sensitivity/vulnerability:
o tmsInvalidCache and tmsInadeqauteSecuirty may make it easier for
an attacker to detect vulnerabilities.
SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example by using IPSec or
SSH), even then, there is no control as to who on the secure network
is allowed to access and GET/SET (read/change/create/delete) the
objects in this MIB module.
It is RECOMMENDED that implementers consider the security features as
provided by the SNMPv3 framework (see [RFC3410] section 8), including
full support for the USM and Transport Security Model cryptographic
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mechanisms (for authentication and privacy).
Further, deployment of SNMP versions prior to SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to
enable cryptographic security. It is then a customer/operator
responsibility to ensure that the SNMP entity giving access to an
instance of this MIB module is properly configured to give access to
the objects only to those principals (users) that have legitimate
rights to indeed GET or SET (change/create/delete) them.
9. IANA Considerations
IANA is requested to assign:
1. an SMI number under snmpModules, for the MIB module in this
document,
2. a value, preferably 4, to identify the Transport Security Model,
in the Security Models registry at
http://www.iana.org/assignments/snmp-number-spaces. This should
result in the following table of values:
Value Description References
----- ----------- ----------
0 reserved for 'any' [RFC2571, RFC3411]
1 reserved for SNMPv1 [RFC2571, RFC3411]
2 reserved for SNMPv2c [RFC2571, RFC3411]
3 User-Based Security Model (USM) [RFC2571, RFC3411]
YY Transport Security Model (TSM) [RFCXXXX]
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note
-- NOTE to RFC editor: replace YY with actual IANA-assigned number,
throughout this document and remove this note.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management
Information Version 2 (SMIv2)", STD 58,
RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for
SMIv2", STD 58, RFC 2579, April 1999.
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[RFC2580] McCloghrie, K., Perkins, D., and J.
Schoenwaelder, "Conformance Statements for
SMIv2", STD 58, RFC 2580, April 1999.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network
Management Protocol (SNMP) Management
Frameworks", STD 62, RFC 3411, December 2002.
[RFC3412] Case, J., Harrington, D., Presuhn, R., and B.
Wijnen, "Message Processing and Dispatching for
the Simple Network Management Protocol (SNMP)",
STD 62, RFC 3412, December 2002.
[RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple
Network Management Protocol (SNMP)
Applications", STD 62, RFC 3413, December 2002.
[RFC3414] Blumenthal, U. and B. Wijnen, "User-based
Security Model (USM) for version 3 of the
Simple Network Management Protocol (SNMPv3)",
STD 62, RFC 3414, December 2002.
[RFC3416] Presuhn, R., "Version 2 of the Protocol
Operations for the Simple Network Management
Protocol (SNMP)", STD 62, RFC 3416,
December 2002.
[RFC3418] Presuhn, R., "Management Information Base (MIB)
for the Simple Network Management Protocol
(SNMP)", STD 62, RFC 3418, December 2002.
[RFC3584] Frye, R., Levi, D., Routhier, S., and B.
Wijnen, "Coexistence between Version 1, Version
2, and Version 3 of the Internet-standard
Network Management Framework", BCP 74,
RFC 3584, August 2003.
[I-D.ietf-isms-tmsm] Harrington, D. and J. Schoenwaelder, "Transport
Subsystem for the Simple Network Management
Protocol (SNMP)", draft-ietf-isms-tmsm-05 (work
in progress), December 2006.
10.2. Informative References
[RFC3410] Case, J., Mundy, R., Partain, D., and B.
Stewart, "Introduction and Applicability
Statements for Internet-Standard Management
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Framework", RFC 3410, December 2002.
Appendix A. Notification Tables Configuration
The SNMP-TARGET-MIB and SNMP-NOTIFICATION-MIB [RFC3413] are used to
configure notification originators with the destinations to which
notifications should be sent.
Most of the configuration is security-model-independent and
transport-model-independent.
The values we will use in the examples for the five model-independent
security and transport parameters are:
transportType = snmpSSHDomain
transportAddress = 192.0.2.1:162
securityModel = Transport Security Model
securityName = sampleUser
securityLevel = authPriv
The following example will configure the Notification Originator to
send informs to a Notification Receiver at host 192.0.2.1 port 162
using the securityName "sampleUser". The columns marked with a "*"
are the items that are Security Model or Transport Model specific.
The configuration for the "sampleUser" settings in the SNMP-VIEW-
BASED-ACM-MIB objects are not shown here for brevity. First we
configure which type of notification should be sent for this taglist
(toCRTag). In this example, we choose to send an Inform.
snmpNotifyTable row:
snmpNotifyName CRNotif
snmpNotifyTag toCRTag
snmpNotifyType inform
snmpNotifyStorageType nonVolatile
snmpNotifyColumnStatus createAndGo
Then we configure a transport address to which notifications
associated with this taglist should be sent, and we specify which
snmpTargetParamsEntry should be used (toCR) when sending to this
transport address.
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snmpTargetAddrTable row:
snmpTargetAddrName toCRAddr
* snmpTargetAddrTDomain snmpSSHDomain
snmpTargetAddrTAddress 192.0.2.1:162
snmpTargetAddrTimeout 1500
snmpTargetAddrRetryCount 3
snmpTargetAddrTagList toCRTag
snmpTargetAddrParams toCR (must match below)
snmpTargetAddrStorageType nonVolatile
snmpTargetAddrColumnStatus createAndGo
Then we configure which prinicipal at the host should receive the
notifications associated with this taglist. Here we choose
"sampleUser", who uses the Transport Security Model.
snmpTargetParamsTable row:
snmpTargetParamsName toCR
snmpTargetParamsMPModel SNMPv3
* snmpTargetParamsSecurityModel TransportSecurityModel
* snmpTargetParamsSecurityName "sampleUser"
snmpTargetParamsSecurityLevel authPriv
snmpTargetParamsStorageType nonVolatile
snmpTargetParamsRowStatus createAndGo
A.1. Transport Security Model Processing
The Transport Security Model is called using the
generateRequestMessage() ASI, with the following parameters (* are
from the above tables):
statusInformation = -- success or errorIndication
generateRequestMsg(
IN messageProcessingModel -- *snmpTargetParamsMPModel
IN globalData -- message header, admin data
IN maxMessageSize -- of the sending SNMP entity
IN transportDomain -- *snmpTargetAddrTDomain
IN transportAddress -- *snmpTargetAddrTAddress
IN securityModel -- *snmpTargetParamsSecurityModel
IN securityEngineID -- immaterial; TSM will ignore.
IN securityName -- *snmpTargetParamsSecurityName
IN securityLevel -- *snmpTargetParamsSecurityLevel
IN scopedPDU -- message (plaintext) payload
OUT securityParameters -- filled in by Security Module
OUT wholeMsg -- complete generated message
OUT wholeMsgLength -- length of generated message
OUT tmStateReference -- reference to transport info
)
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The Transport Security Model will determine the transport model based
on the snmpTargetAddrTDomain. The selected transport model will
select the appropriate transport "session" using the
snmpTargetAddrTAddress, snmpTargetParamsSecurityName, and
snmpTargetParamsSecurityLevel.
Appendix B. Change Log
From -01- to -02-
Changed transportSecurityModel(4) to transportSecurityModel(YY),
waiting for assignment
cleaned up elements of procedure [todo]s
use the same errorIndication as USM for UnsupportedSecurityLevel
fixed syntax of tsmInadequateSecurity counter
changed the "can and will use" the same security parameters to
"can use", to allow responses that have different security
parameters than the request.
removed "Relationship to the SNMP-FRAMEWORK-MIB"
cleaned up "MIB Modules Required for IMPORTS"
From -00- to -01-
made the transport model not know anything about the security
model.
modified the elements of prcedure sections, given the implications
of this change.
simplified elelemnts of procedure, removing most info specified in
architecture/subsystem definitons.
rethought the coexistence section
noted the implications of the Transport Security Model on
isAccessAllowed()
modified all text related to the LCD.
removed most of the MIB (now the TSM has no configuration
parameters).
added counters needed to support elements of procedure
renamed MIB module, and registered under snmpModules
updated IANA and Security Considerations
updated references.
modified the notification configurations.
From SSHSM-04- to Transport-security-model-00
added tsmUserTable
updated Appendix - Notification Tables Configuration
remove open/closed issue appendices
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changed tmSessionReference to tmStateReference
Author's Address
David Harrington
Huawei Technologies (USA)
1700 Alma Dr. Suite 100
Plano, TX 75075
USA
Phone: +1 603 436 8634
EMail: dharrington@huawei.com
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Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
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Acknowledgement
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Harrington Expires July 29, 2007 [Page 28]
