Network Working Group D. Harrington
Internet-Draft Huawei Technologies (USA)
Intended status: Standards Track November 18, 2007
Expires: May 21, 2008
Transport Security Model for SNMP
draft-ietf-isms-transport-security-model-07
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Abstract
This memo describes a Transport Security Model for the Simple Network
Management Protocol.
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.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 5
1.5. Constraints . . . . . . . . . . . . . . . . . . . . . . . 5
2. How the Transport Security Model Fits in the Architecture . . 5
2.1. Security Capabilities of this Model . . . . . . . . . . . 6
2.1.1. Threats . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.2. Security Levels . . . . . . . . . . . . . . . . . . . 7
2.2. No Sessions . . . . . . . . . . . . . . . . . . . . . . . 7
2.3. Coexistence . . . . . . . . . . . . . . . . . . . . . . . 7
2.4. Security Parameter Passing . . . . . . . . . . . . . . . . 8
2.5. Notifications and Proxy . . . . . . . . . . . . . . . . . 9
3. Cached Information and References . . . . . . . . . . . . . . 9
3.1. tmStateReference . . . . . . . . . . . . . . . . . . . . . 10
3.2. securityStateReference . . . . . . . . . . . . . . . . . . 10
4. Processing an Outgoing Message . . . . . . . . . . . . . . . . 10
4.1. Security Processing for an Outgoing Message . . . . . . . 10
4.2. Elements of Procedure for Outgoing Messages . . . . . . . 12
5. Processing an Incoming SNMP Message . . . . . . . . . . . . . 12
5.1. Security Processing for an Incoming Message . . . . . . . 12
5.2. Elements of Procedure for Incoming Messages . . . . . . . 13
6. MIB Module Overview . . . . . . . . . . . . . . . . . . . . . 14
6.1. Structure of the MIB Module . . . . . . . . . . . . . . . 14
6.2. The tsmStats Subtree . . . . . . . . . . . . . . . . . . . 14
6.3. Relationship to Other MIB Modules . . . . . . . . . . . . 14
6.3.1. Relationship to the SNMPv2-MIB . . . . . . . . . . . . 14
6.3.2. Relationship to the SNMP-FRAMEWORK-MIB . . . . . . . . 15
6.3.3. MIB Modules Required for IMPORTS . . . . . . . . . . . 15
7. MIB module definition . . . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8.1. MIB module security . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . . 21
Appendix A. Notification Tables Configuration . . . . . . . . . . 21
A.1. Transport Security Model Processing for Notifications . . 22
Appendix B. Processing Differences between USM and Secure
Transport . . . . . . . . . . . . . . . . . . . . . . 23
B.1. USM and the RFC3411 Architecture . . . . . . . . . . . . . 24
B.2. Transport Subsystem and the RFC3411 Architecture . . . . . 24
Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . . 24
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 24
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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.
It is expected that reader will have also read and understood RFC3411
[RFC3411], RFC3412 [RFC3412], RFC3413 [RFC3413], and RFC3418
[RFC3418].
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
For consistency with SNMP-related specifications, this document
favors terminology as defined in STD62 rather than favoring
terminology that is consistent with non-SNMP specifications that use
different variations of the same terminology. This is consistent
with the IESG decision to not require the SNMPv3 terminology be
modified to match the usage of other non-SNMP specifications when
SNMPv3 was advanced to Full Standard.
Authentication in this document typically refers to the English
meaning of "serving to prove the authenticity of" the message, not
data source authentication or peer identity authentication.
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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
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.
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1.4. Motivation
This memo describes a Security Model to make use of Transport Models
that use 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 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. In times of network stress, the security protocol and its
underlying security mechanisms SHOULD NOT depend solely upon the
ready availability of other network services (e.g., Network Time
Protocol (NTP) or Authentication, Authorization, and Accounting
(AAA) protocols).
2. 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.
3. It may not be possible for the Security Model to determine when
the network is under stress.
4. A Security Model should require no changes to the SNMP
architecture.
5. A Security Model should require no changes to the underlying
security protocol.
2. How the 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.
A cache, referenced by tmStateReference, is used to pass information
between the Transport Security Model and a Transport Model, and vice
versa. If the Transport Security Model is used with an insecure
Transport Model, then the cache will not exist or be populated with
security parameters, which will cause the Transport Security Model to
return an error (see section 5.2) If another Security Model (eg
Community-based Security Model) is used with a secure Transport
Model, then the cache may be populated but the other Security Model
may be unaware of the cache and ignore its contents (eg deriving the
securityName from the Community name in the message instead of
deriving it from the tmSecurityName in the tmStateReference cache).
When a secure Transport Model creates a tmStateReference cache for an
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incoming message, it will include a tmTransport, tmAddress,
tmSecurityName and a tmTransportSecurityLevel, and it MAY include
transport-specific information. When the Transport Security Model
sends a message, it will create a cache containing the specified
transportDomain, transportAddress, securityName, and securityLevel
parameters. The Transport Security Model will pass the
tmStateReference to enable the transport model to extract
corresponding transport-specific information from the
tmStateReference cache, in an implementation-dependent manner.
When the Transport Security Model determines that a cache does not
yet exist corresponding to the specified transportDomain,
transportAddress, secuirtyName, and securityLevel parameters, it
creates one that contains a tmSecurityName and
tmRequestedSecurityLevel and passes the tmStateReference cache to the
specified Transport Model.
The Transport Security Model will determine the security-model-
independent securityName and securityLevel, and will verify for
incoming messages that tmTransportSecurityLevel is at least as strong
as the requested 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.
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].
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 architecture. However, this Security
Model does not provide security mechanisms such as authentication and
encryption itself, so it SHOULD always be used with a Transport Model
that provides appropriate security.
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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 reported in
tmTransportSecurityLevel.
2.2. No Sessions
The Transport Security Model will associate state regarding each
message and each known remote engine with a combination of
transportDomain, transportAddress, securityName, securityModel, and
securityLevel.
The Transport Security Model does not recognize sessions of any kind,
although they may be supported by a transport model.
2.3. Coexistence
There are two primary factors which determine whether Security Models
can coexist. First, there must be a mechanism to select different
Security Models at run-time. Second, the processing of one Security
Model 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, IANA has
registered four Message Processing Models (SNMPv1, SNMPv2c, SNMPv2u/
SNMPv2*, and SNMPv3) 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
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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, SNMPv1 or SNMPv2c messages that go through the SNMPv1 or
SNMPv2 Message Processing Models **as defined in RFC3584** cannot use
the Transport Security Model. (This does not mean an SNMPv1 or
SNMPv2 message cannot use a secure transport model, only that the
RFC3584 Message Processing Model will not invoke this security
model.)
The SNMPv2u/SNMPv2* Message Processing Model is a historic artifact
for which there is no existing IETF specification.
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. For an outgoing message to be secured
using the Transport Security Model, msgSecurityModel should be set to
transportSecurityModel(YY).
[-- NOTE to RFC editor: replace YY with actual IANA-assigned number,
and remove this note. ]
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() application service
interfaces (ASI) 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 uses parameters
provided by the SNMP application to determine if a corresponding
tmStateReference cache exists, or to create a suitable
tmStateReference cache. The wholeMsg and the tmStateReference are
passed to the appropriate Transport Model through a series of ASIs,
as 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
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and security-related information, including a tmSecurityName that
represents the transport-authenticated identity, and a
tmTransportSecurityLevel 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 ASIs, as described in "Transport
Subsystem for the Simple Network Management Protocol"
[I-D.ietf-isms-tmsm].
2.5. Notifications and Proxy
The SNMP-TARGET-MIB module [RFC3413] contains objects for defining
management targets, including transportDomain, transportAddress,
securityName, securityModel, and securityLevel parameters, for
applications such as notifications and proxy. Transport type and
address are configured in the snmpTargetAddrTable, and the
securityModel, securityName, and securityLevel parameters are
configured in the snmpTargetParamsTable.
For the Transport Security Model, these will be translated as needed
into tmSecurityName and tmRequestedSecurityLevel.
The default approach is for an administrator to statically configure
this information to identify the targets authorized to receive
notifications or perform proxy.
3. 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 document describes
caches, and differentiates the tmStateReference from the
securityStateReference, but how this is represented internally is an
implementation decision.
As a general rule, if state information is available when a message
being processed gets discarded, the state related to that message
should also be discarded, and if state information is available when
a relationship between engines is severed, such as the closing of a
transport connection, the state information for that relationship
might also be discarded.
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3.1. tmStateReference
For each transport model, information about the transport security
may be stored in a cache to pass model- and mechanism-specific
parameters.
For security reasons, the Transport Security Model REQUIRES that the
security parameters used for a response are the same as those used
for the corresponding request, and passes a tmSameSecurity parameter
in the tmStateReference cache for outgoing messages to indicate that
the same security MUST be used for the outgoing response as was used
for the corresponding incoming request. It is transport-model-
dependent and implementation-dependent how this is ensured at the
transport layer.
Since the contents of a cache are meaningful only within an
implementation, and not on-the-wire, the format of the cache is
implementation-specific.
3.2. securityStateReference
The securityStateReference parameter is defined in RFC3411. Its
primary purpose is to provide a mapping between a request and the
corresponding response. A sample model-specific cache can be found
in RFC3414 [RFC3414].
Transport models do not have access to the securityStateReference.
For the Transport Security Model, it is important to ensure that the
security parameters used for a request match those used for the
corresponding response. The Transport Security Model will
conceptually add the tmStateReference to the securityStateReference
cache, so the transport model can map transport-specific security
parameters for a request to its corresponding response. How the
tmStateReference is added to the securityStateReference is
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.
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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 -- (NEW) specified by application
IN transportAddress -- (NEW) 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 -- (NEW) transport info
)
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 -- (NEW) specified by application
IN transportAddress -- (NEW) 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 -- (NEW) transport info
)
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4.2. Elements of Procedure for Outgoing Messages
1) If there is a securityStateReference, then this is a response
message. Extract transportDomain, transportAddress, securityName,
securityLevel, securityModel, and tmStateReference from the
securityStateReference cache. Set the tmRequestedSecurityLevel to
the value of the extracted securityLevel. The cachedSecurityData for
this message can now be discarded. Set the tmSameSecurity parameter
in the tmStateReference cache to true.
2) If there is no securityStateReference, create a tmStateReference
cache with tmSecurityName set to the value of securityName,
tmRequestedSecurityLevel set to the value of securityLevel, and
tmSameSecurity set to false.
3) Fill in the securityParameters with a zero-length OCTET STRING
('0400').
4) Combine the message parts into a wholeMsg and calculate
wholeMsgLength.
5) The wholeMsg, wholeMsgLength, securityParameters and
tmStateReference are returned to the calling Message Processing 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 ASI from a Message Processing Model to
the Security Subsystem for a received message is:
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statusInformation = -- errorIndication or success
-- error counter OID/value if error
processIncomingMsg(
IN messageProcessingModel -- typically, SNMP version
IN maxMessageSize -- from the received message
IN securityParameters -- from the received message
IN securityModel -- from the received message
IN securityLevel -- from the received message
IN wholeMsg -- as received on the wire
IN wholeMsgLength -- length as received on the wire
IN tmStateReference -- (NEW) 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
5.2. Elements of Procedure for Incoming Messages
1) Set the securityEngineID to the local snmpEngineID.
2) If tmStateReference does not refer to a cache containing values
for tmSecurityName and tmTransportSecurityLevel, then the
snmpTsmInvalidCaches counter is incremented, an error indication is
returned to the calling module, and Security Model processing stops
for this message.
3) Set securityName to the value of tmSecurityName from the cache
referenced by tmStateReference.
4) Compare the value of tmTransportSecurityLevel in the
tmStateReference cache to the value of the securityLevel parameter
passed in the processIncomingMsg ASI. If securityLevel specifies
privacy (Priv), and tmTransportSecurityLevel specifies no privacy
(noPriv), or securityLevel specifies authentication (auth) and
tmTransportSecurityLevel specifies no authentication (noAuth) was
provided by the Transport Model, then the
snmpTsmInadequateSecurityLevels counter is incremented, and an error
indication (unsupportedSecurityLevel) together with the OID and value
of the incremented counter is returned to the calling module.
Transport Security Model processing stops for this message.
5)The security data is cached as cachedSecurityData, so that a
possible response to this message will use the same security
parameters. Then securityStateReference is set for subsequent
reference to this cached data. For Transport Security Model, the
securityStateReference includes a reference to the tmStateReference
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cache.
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) 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 ASI.
6. MIB Module 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. The tsmStats Subtree
This subtree contains counters specific to the Transport Security
Model, that provide information for identifying fault conditions.
6.3. Relationship to Other MIB Modules
Some management objects defined in other MIB modules are applicable
to an entity implementing the Transport Security Model In particular,
it is assumed that an entity implementing the Transport Security
Model will implement the SNMPv2-MIB [RFC3418] and the SNMP-FRAMEWORK-
MIB [RFC3411].
6.3.1. 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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6.3.2. Relationship to the SNMP-FRAMEWORK-MIB
The SNMP-FRAMEWORK-MIB provides definitions for the concepts of
SnmpEngineID, enumeration of Message Processing Models, Security
Models and Security Levels, and object definitions for snmpEngineID
These are important for implementing the Transport Security Model,
but are not needed to implement the SNMP-TRANSPORT-SM-MIB.
6.3.3. MIB Modules Required for IMPORTS
The following MIB module imports items from [RFC2578] and [RFC2580].
7. MIB module definition
SNMP-TSM-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
mib-2, Counter32
FROM SNMPv2-SMI
MODULE-COMPLIANCE, OBJECT-GROUP
FROM SNMPv2-CONF
;
snmpTsmMIB MODULE-IDENTITY
LAST-UPDATED "200710140000Z"
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
Jacobs University Bremen
Campus Ring 1
28725 Bremen
Germany
+49 421 200-3587
j.schoenwaelder@iu-bremen.de
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Editor:
David Harrington
Huawei Technologies USA
1700 Alma Dr.
Plano TX 75075
USA
+1 603-436-8634
ietfdbh@comcast.net
"
DESCRIPTION "The Transport Security Model MIB
In keeping with the RFC 3411 design decisions
to use self-contained documents, the RFC which
contains the definition of this MIB module also
includes the elements of procedure which are
needed for processing the Transport Security
Model for SNMP. These MIB objects
SHOULD NOT be modified via other documents.
This allows the Transport Security Model
for SNMP to be designed and documented as
independent and self- contained, having no
direct impact on other modules, and this
allows 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.
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 "200710140000Z"
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
"
::= { mib-2 xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and
-- remove this note
-- ---------------------------------------------------------- --
-- subtrees in the SNMP-TRANSPORT-SM-MIB
-- ---------------------------------------------------------- --
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snmpTsmNotifications OBJECT IDENTIFIER ::= { snmpTsmMIB 0 }
snmpTsmMIBObjects OBJECT IDENTIFIER ::= { snmpTsmMIB 1 }
snmpTsmConformance OBJECT IDENTIFIER ::= { snmpTsmMIB 2 }
-- -------------------------------------------------------------
-- Objects
-- -------------------------------------------------------------
-- Statistics for the Transport Security Model
snmpTsmStats OBJECT IDENTIFIER ::= { snmpTsmMIBObjects 1 }
snmpTsmInvalidCaches OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of messages dropped because the
tmStateReference referred to an invalid cache.
"
::= { snmpTsmStats 1 }
snmpTsmInadequateSecurityLevels OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The number of incoming messages dropped because
the actual securityLevel provided was less than
the requested securityLevel.
"
::= { snmpTsmStats 2 }
-- -------------------------------------------------------------
-- snmpTsmMIB - Conformance Information
-- -------------------------------------------------------------
snmpTsmCompliances OBJECT IDENTIFIER ::= { snmpTsmConformance 1 }
snmpTsmGroups OBJECT IDENTIFIER ::= { snmpTsmConformance 2 }
-- -------------------------------------------------------------
-- Compliance statements
-- -------------------------------------------------------------
snmpTsmCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines that support
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the SNMP-TRANSPORT-SM-MIB"
MODULE
MANDATORY-GROUPS { snmpTsmGroup }
::= { snmpTsmCompliances 1 }
-- -------------------------------------------------------------
-- Units of conformance
-- -------------------------------------------------------------
snmpTsmGroup OBJECT-GROUP
OBJECTS {
snmpTsmInvalidCaches,
snmpTsmInadequateSecurityLevels
}
STATUS current
DESCRIPTION "A collection of objects for maintaining
information of an SNMP engine which implements
the SNMP Transport Security Model.
"
::= { snmpTsmGroups 2 }
END
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
of tmTransportSecurityLevel.
The Transport Security Model is called a Security Model to be
compatible with the RFC3411 architecture. 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.
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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 snmpTsmInvalidCaches and snmpTsmInadequateSecurityLevels 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),
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
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 mib-2, 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:
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Value Description References
----- ----------- ----------
0 reserved for 'any' [RFC3411]
1 reserved for SNMPv1 [RFC3411]
2 reserved for SNMPv2c [RFC3411]
3 User-Based Security Model (USM) [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.
[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.
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[RFC3418] Presuhn, R., "Management Information Base (MIB)
for the Simple Network Management Protocol
(SNMP)", STD 62, RFC 3418, December 2002.
[I-D.ietf-isms-tmsm] Harrington, D. and J. Schoenwaelder, "Transport
Subsystem for the Simple Network Management
Protocol (SNMP)", draft-ietf-isms-tmsm-10 (work
in progress), September 2007.
10.2. Informative References
[RFC3410] Case, J., Mundy, R., Partain, D., and B.
Stewart, "Introduction and Applicability
Statements for Internet-Standard Management
Framework", RFC 3410, 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.
[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.
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:
transportDomain = 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.
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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.
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 principal 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 for Notifications
The Transport Security Model is called using the generateRequestMsg()
ASI, with the following parameters (* are from the above tables):
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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
)
The Transport Security Model will determine the Transport Model based
on the snmpTargetAddrTDomain. The selected Transport Model will
select the appropriate transport connection using the
snmpTargetAddrTAddress, snmpTargetParamsSecurityName, and
snmpTargetParamsSecurityLevel.
Appendix B. Processing Differences between USM and Secure Transport
USM and secure transports differ in the processing order and
responsibilities within the RFC3411 architecture. While the steps
are the same, they occur in a different order, and may be done by
different subsystems. The following lists illustrate the difference
in the flow and the responsibility for different processing steps for
incoming messages when using USM and when using a secure transport.
(Note that these lists are simplified for illustrative purposes, and
do not represent all details of processing. Transport Models must
provide the detailed elements of procedure.)
With USM and other Security Models, security processing starts when
the Message Processing Model decodes portions of the ASN.1 message to
extract an opaque block of security parameters and header parameters
that identify which Security Model should process the message to
perform authentication, decryption, timeliness checking, integrity
checking, and translation of parameters to model-independent
parameters. A secure transport performs those security functions on
the message, before the ASN.1 is decoded.
Step 6 cannot occur until after decryption occurs. Step 6 and beyond
are the same for USM and a secure transport.
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B.1. USM and the RFC3411 Architecture
1) decode the ASN.1 header (Message Processing Model)
2) determine the SNMP Security Model and parameters (Message
Processing Model)
3) verify securityLevel. [Security Model]
4) translate parameters to model-independent parameters (Security
Model)
5) authenticate the principal, check message integrity and
timeliness, and decrypt the message. [Security Model]
6) determine the pduType in the decrypted portions (Message
Processing Model), and
7) pass on the decrypted portions with model-independent parameters.
B.2. Transport Subsystem and the RFC3411 Architecture
1) authenticate the principal, check integrity and timeliness of the
message, and decrypt the message. [Transport Model]
2) translate parameters to model-independent parameters (Transport
Model)
3) decode the ASN.1 header (Message Processing Model)
4) determine the SNMP Security Model and parameters (Message
Processing Model)
5) verify securityLevel [Security Model]
6) determine the pduType in the decrypted portions (Message
Processing Model), and
7) pass on the decrypted portions with model-independent security
parameters
If a message is secured using a secure transport layer, then the
Transport Model should provide the translation from the authenticated
identity (e.g., an SSH user name) to a model-independent securityName
in step 2.
Appendix C. Open Issues
none.
Appendix D. Change Log
From -05- to -06-
Fixed a bunch of editorial nits
Fixed the note about terminology consistent with SNMPv3.
Updated MIB assignment to by rfc4181 compatible
Replaced tmSameSession with tmSameSecurity to eliminate session-
matching from the security model.
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Eliminated all reference to the LCD from the Transport Security
Model; the LCD is now TM-specific.
Added tmTransportSecurityLevel and tmRequestedSecurityLevel to
clarify incoming versus outgoing
From -04- to -05-
Removed check for empty securityParameters for incoming messages
Added a note about terminology, for consistency with SNMPv3 rather
than with RFC2828.
From -03- to -04-
Editorial changes requested by Tom Petch, to clarify behavior with
SNMPv1/v2c
Added early discussion of how TSM fits into the architecture to
clarify behavior when RFC3584 security models are co-resident.
Editorial changes requested by Bert Wijnen, to eliminate version-
specific discussions.
Removed sections on version-specific message formats.
Removed discussion of SNMPv3 in Motivation section.
Added discussion of request/response session matching.
From -02- to -03-
Editorial changes suggested by Juergen Schoenwaelder
Capitalized Transport Models, Security Models, and Message
Processing Models, to be consistent with RFC341x conventions.
Eliminated some text that duplicated RFC3412, especially in
Elements of Procedure.
Changed the encoding of msgSecurityParameters
Marked the (NEW) fields added to existing ASIs
Modified text intro discussing relationships to other MIB modules.
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"
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From -00- to -01-
made the Transport Model not know anything about the Security
Model.
modified the elements of procedure sections, given the
implications of this change.
simplified elements of procedure, removing most info specified in
architecture/subsystem definitions.
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
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
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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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THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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Harrington Expires May 21, 2008 [Page 27]
