ftp.cc.uoc.gr
[Note that this file is a concatenation of more than one RFC.]





Network Working Group                                   J. Schoenwaelder
Request for Comments: 5343                      Jacobs University Bremen
Updates: 3411                                             September 2008
Category: Standards Track


  Simple Network Management Protocol (SNMP) Context EngineID Discovery

Status of This Memo

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

Abstract

   The Simple Network Management Protocol (SNMP) version three (SNMPv3)
   requires that an application know the identifier (snmpEngineID) of
   the remote SNMP protocol engine in order to retrieve or manipulate
   objects maintained on the remote SNMP entity.

   This document introduces a well-known localEngineID and a discovery
   mechanism that can be used to learn the snmpEngineID of a remote SNMP
   protocol engine.  The proposed mechanism is independent of the
   features provided by SNMP security models and may also be used by
   other protocol interfaces providing access to managed objects.

   This document updates RFC 3411.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   3.  Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  Local EngineID  . . . . . . . . . . . . . . . . . . . . . . 4
     3.2.  EngineID Discovery  . . . . . . . . . . . . . . . . . . . . 4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7







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RFC 5343            SNMP Context EngineID Discovery       September 2008


1.  Introduction

   To retrieve or manipulate management information using the third
   version of the Simple Network Management Protocol (SNMPv3) [RFC3410],
   it is necessary to know the identifier of the remote SNMP protocol
   engine, the so-called snmpEngineID [RFC3411].  While an appropriate
   snmpEngineID can in principle be configured on each management
   application for each SNMP agent, it is often desirable to discover
   the snmpEngineID automatically.

   This document introduces a discovery mechanism that can be used to
   learn the snmpEngineID of a remote SNMP protocol engine.  The
   proposed mechanism is independent of the features provided by SNMP
   security models.  The mechanism has been designed to coexist with
   discovery mechanisms that may exist in SNMP security models, such as
   the authoritative engine identifier discovery of the User-based
   Security Model (USM) of SNMP [RFC3414].

   This document updates RFC 3411 [RFC3411] by clarifying the IANA rules
   for the maintenance of the SnmpEngineID format registry.

   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 RFC 2119 [RFC2119].

2.  Background

   Within an administrative domain, an SNMP engine is uniquely
   identified by an snmpEngineID value [RFC3411].  An SNMP entity, which
   consists of an SNMP engine and several SNMP applications, may provide
   access to multiple contexts.

   An SNMP context is a collection of management information accessible
   by an SNMP entity.  An item of management information may exist in
   more than one context and an SNMP entity potentially has access to
   many contexts [RFC3411].  A context is identified by the snmpEngineID
   value of the entity hosting the management information (also called a
   contextEngineID) and a context name that identifies the specific
   context (also called a contextName).

   To identify an individual item of management information within an
   administrative domain, a four tuple is used consisting of

   1.  a contextEngineID,

   2.  a contextName,





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RFC 5343            SNMP Context EngineID Discovery       September 2008


   3.  an object type, and

   4.  its instance identification.

   The last two elements are encoded in an object identifier (OID)
   value.  The contextName is a character string (following the
   SnmpAdminString textual convention of the SNMP-FRAMEWORK-MIB
   [RFC3411]) while the contextEngineID is an octet string constructed
   according to the rules defined as part of the SnmpEngineID textual
   convention of the SNMP-FRAMEWORK-MIB [RFC3411].

   The SNMP protocol operations and the protocol data units (PDUs)
   operate on OIDs and thus deal with object types and instances
   [RFC3416].  The SNMP architecture [RFC3411] introduces the concept of
   a scopedPDU as a data structure containing a contextEngineID, a
   contextName, and a PDU.  The SNMP version 3 (SNMPv3) message format
   uses ScopedPDUs to exchange management information [RFC3412].

   Within the SNMP framework, contextEngineIDs serve as end-to-end
   identifiers.  This becomes important in situations where SNMP proxies
   are deployed to translate between protocol versions or to cross
   middleboxes such as network address translators.  In addition,
   snmpEngineIDs separate the identification of an SNMP engine from the
   transport addresses used to communicate with an SNMP engine.  This
   property can be used to correlate management information easily, even
   in situations where multiple different transports were used to
   retrieve the information or where transport addresses can change
   dynamically.

   To retrieve data from an SNMPv3 agent, it is necessary to know the
   appropriate contextEngineID.  The User-based Security Model (USM) of
   SNMPv3 provides a mechanism to discover the snmpEngineID of the
   remote SNMP engine, since this is needed for security processing
   reasons.  The discovered snmpEngineID can subsequently be used as a
   contextEngineID in a ScopedPDU to access management information local
   to the remote SNMP engine.  Other security models, such as the
   Transport Security Model (TSM) [TSM], lack such a procedure and may
   use the discovery mechanism defined in this memo.

3.  Procedure

   The proposed discovery mechanism consists of two parts, namely (i)
   the definition of a special well-known snmpEngineID value, called the
   localEngineID, which always refers to a local default context, and
   (ii) the definition of a procedure to acquire the snmpEngineID scalar
   of the SNMP-FRAMEWORK-MIB [RFC3411] using the special well-known
   local localEngineID value.




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3.1.  Local EngineID

   An SNMP command responder implementing this specification MUST
   register their pduTypes using the localEngineID snmpEngineID value
   (defined below) by invoking the registerContextEngineID() Abstract
   Service Interface (ASI) defined in RFC 3412 [RFC3412].  This
   registration is done in addition to the normal registration under the
   SNMP engine's snmpEngineID.  This is consistent with the SNMPv3
   specifications since they explicitly allow registration of multiple
   engineIDs and multiple pduTypes [RFC3412].

   The SnmpEngineID textual convention [RFC3411] defines that an
   snmpEngineID value MUST be between 5 and 32 octets long.  This
   specification proposes to use the variable length format 3) of the
   SnmpEngineID textual convention and to allocate the reserved, unused
   format value 6, using the enterprise ID 0 for the localEngineID.  An
   ASN.1 definition for localEngineID would look like this:

               localEngineID OCTET STRING ::= '8000000006'H

   The localEngineID value always provides access to the default context
   of an SNMP engine.  Note that the localEngineID value is intended to
   be used as a special value for the contextEngineID field in the
   ScopedPDU.  It MUST NOT be used as a value to identify an SNMP
   engine; that is, this value MUST NOT be used in the snmpEngineID.0
   scalar [RFC3418] or in the msgAuthoritativeEngineID field in the
   securityParameters of the User-based Security Model (USM) [RFC3414].

3.2.  EngineID Discovery

   Discovery of the snmpEngineID is done by sending a Read Class
   protocol operation (see Section 2.8 of [RFC3411]) to retrieve the
   snmpEngineID scalar using the localEngineID defined above as a
   contextEngineID value.  Implementations SHOULD only perform this
   discovery step when it is needed.  In particular, if security models
   are used that already discover the remote snmpEngineID (such as USM),
   then no further discovery is necessary.  The same is true in
   situations where the application already knows a suitable
   snmpEngineID value.

   The procedure to discover the snmpEngineID of a remote SNMP engine
   can be described as follows:

   1.  Check whether a suitable contextEngineID value is already known.
       If yes, use the provided contextEngineID value and stop the
       discovery procedure.





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   2.  Check whether the selected security model supports discovery of
       the remote snmpEngineID (e.g., USM with its discovery mechanism).
       If yes, let the security model perform the discovery.  If the
       remote snmpEngineID value has been successfully determined,
       assign it to the contextEngineID and stop the discovery
       procedure.

   3.  Send a Read Class operation to the remote SNMP engine using the
       localEngineID value as the contextEngineID in order to retrieve
       the scalar snmpEngineID.0 of the SNMP-FRAMEWORK-MIB [RFC3411].
       If successful, set the contextEngineID to the retrieved value and
       stop the discovery procedure.

   4.  Return an error indication that a suitable contextEngineID could
       not be discovered.

   The procedure outlined above is an example and can be modified to
   retrieve more variables in step 3, such as the sysObjectID.0 scalar
   or the snmpSetSerialNo.0 scalar of the SNMPv2-MIB [RFC3418].

4.  IANA Considerations

   RFC 3411 requested that IANA create a registry for SnmpEngineID
   formats.  However, RFC 3411 did not ask IANA to record the initial
   assignments made by RFC 3411 nor did RFC 3411 spell out the precise
   allocation rules.  To address this issue, the following rules are
   hereby established.

   IANA maintains a registry for SnmpEngineID formats.  The first four
   octets of an SnmpEngineID carry an enterprise number, while the fifth
   octet in a variable length SnmpEngineID value, called the format
   octet, indicates how the following octets are formed.  The following
   format values were allocated in [RFC3411]:

     Format    Description                     References
     -------   -----------                     ----------
          0    reserved, unused                 [RFC3411]
          1    IPv4 address                     [RFC3411]
          2    IPv6 address                     [RFC3411]
          3    MAC address                      [RFC3411]
          4    administratively assigned text   [RFC3411]
          5    administratively assigned octets [RFC3411]
       6-127   reserved, unused                 [RFC3411]
     128-255   enterprise specific              [RFC3411]

   IANA can assign new format values out of the originally assigned and
   reserved number space 1-127.  For new assignments in this number




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RFC 5343            SNMP Context EngineID Discovery       September 2008


   space, a specification is required as per [RFC5226].  The number
   space 128-255 is enterprise specific and is not controlled by IANA.

   Per this document, IANA has made the following assignment:

     Format    Description                     References
     -------   -----------                     ----------
          6    local engine                     [RFC5343]

5.  Security Considerations

   SNMP version 3 (SNMPv3) provides cryptographic security to protect
   devices from unauthorized access.  This specification recommends use
   of the security services provided by SNMPv3.  In particular, it is
   RECOMMENDED to protect the discovery exchange.

   An snmpEngineID can contain information such as a device's MAC
   address, IPv4 address, IPv6 address, or administratively assigned
   text.  An attacker located behind a router / firewall / network
   address translator may not be able to obtain this information
   directly, and he therefore might discover snmpEngineID values in
   order to obtain this kind of device information.

   In many environments, making snmpEngineID values accessible via a
   security level of noAuthNoPriv will benefit legitimate tools that try
   to algorithmically determine some basic information about a device.
   For this reason, the default View-based Access Control Model (VACM)
   configuration in Appendix A of RFC 3415 [RFC3415] gives noAuthNoPriv
   read access to the snmpEngineID.  Furthermore, the USM discovery
   mechanism defined in RFC 3414 [RFC3414] uses unprotected messages and
   reveals snmpEngineID values.

   In highly secure environments, snmpEngineID values can be protected
   by using the discovery mechanism described in this document together
   with a security model that does not exchange cleartext SNMP messages,
   such as the Transport Security Model (TSM) [TSM].

   The isAccessAllowed() abstract service primitive of the SNMP access
   control subsystem does not take the contextEngineID into account when
   checking access rights [RFC3411].  As a consequence, it is not
   possible to define a special view for context engineID discovery.  A
   request with a localEngineID is thus treated like a request with the
   correct snmpEngineID by the access control subsystem.  This is inline
   with the SNMPv3 design where the authenticated identity is the
   securityName (together with the securityModel and securityLevel
   information), and transport addresses or knowledge of contextEngineID
   values do not impact the access-control decision.




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RFC 5343            SNMP Context EngineID Discovery       September 2008


6.  Acknowledgments

   Dave Perkins suggested the introduction of a "local" contextEngineID
   during the interim meeting of the ISMS (Integrated Security Model for
   SNMP) working group in Boston, 2006.  Joe Fernandez, David
   Harrington, Dan Romascanu, and Bert Wijnen provided helpful review
   and feedback, which helped to improve this document.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [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.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

7.2.  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.





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RFC 5343            SNMP Context EngineID Discovery       September 2008


   [RFC3415]  Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
              Access Control Model (VACM) for the Simple Network
              Management Protocol (SNMP)", STD 62, RFC 3415,
              December 2002.

   [TSM]      Harrington, D., "Transport Security Model for SNMP", Work
              in Progress, July 2008.

Author's Address

   Juergen Schoenwaelder
   Jacobs University Bremen
   Campus Ring 1
   28725 Bremen
   Germany

   Phone: +49 421 200-3587
   EMail: j.schoenwaelder@jacobs-university.de

































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RFC 5343            SNMP Context EngineID Discovery       September 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   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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   ietf-ipr@ietf.org.












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=========================================================================





Network Working Group                                      D. Harrington
Request for Comments: 5590                     Huawei Technologies (USA)
Updates: 3411, 3412, 3414, 3417                         J. Schoenwaelder
Category: Standards Track                       Jacobs University Bremen
                                                               June 2009


 Transport Subsystem for the Simple Network Management Protocol (SNMP)

Status of This Memo

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

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Abstract

   This document defines a Transport Subsystem, extending the Simple
   Network Management Protocol (SNMP) architecture defined in RFC 3411.
   This document defines a subsystem to contain Transport Models that is
   comparable to other subsystems in the RFC 3411 architecture.  As work
   is being done to expand the transports to include secure transports,
   such as the Secure Shell (SSH) Protocol and Transport Layer Security



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RFC 5590                SNMP Transport Subsystem               June 2009


   (TLS), using a subsystem will enable consistent design and modularity
   of such Transport Models.  This document identifies and describes
   some key aspects that need to be considered for any Transport Model
   for SNMP.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  The Internet-Standard Management Framework . . . . . . . .  3
     1.2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  3
     1.3.  Where This Extension Fits  . . . . . . . . . . . . . . . .  4
   2.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Requirements of a Transport Model  . . . . . . . . . . . . . .  7
     3.1.  Message Security Requirements  . . . . . . . . . . . . . .  7
       3.1.1.  Security Protocol Requirements . . . . . . . . . . . .  7
     3.2.  SNMP Requirements  . . . . . . . . . . . . . . . . . . . .  8
       3.2.1.  Architectural Modularity Requirements  . . . . . . . .  8
       3.2.2.  Access Control Requirements  . . . . . . . . . . . . . 11
       3.2.3.  Security Parameter Passing Requirements  . . . . . . . 12
       3.2.4.  Separation of Authentication and Authorization . . . . 12
     3.3.  Session Requirements . . . . . . . . . . . . . . . . . . . 13
       3.3.1.  No SNMP Sessions . . . . . . . . . . . . . . . . . . . 13
       3.3.2.  Session Establishment Requirements . . . . . . . . . . 14
       3.3.3.  Session Maintenance Requirements . . . . . . . . . . . 15
       3.3.4.  Message Security versus Session Security . . . . . . . 15
   4.  Scenario Diagrams and the Transport Subsystem  . . . . . . . . 16
   5.  Cached Information and References  . . . . . . . . . . . . . . 17
     5.1.  securityStateReference . . . . . . . . . . . . . . . . . . 17
     5.2.  tmStateReference . . . . . . . . . . . . . . . . . . . . . 17
       5.2.1.  Transport Information  . . . . . . . . . . . . . . . . 18
       5.2.2.  securityName . . . . . . . . . . . . . . . . . . . . . 19
       5.2.3.  securityLevel  . . . . . . . . . . . . . . . . . . . . 20
       5.2.4.  Session Information  . . . . . . . . . . . . . . . . . 20
   6.  Abstract Service Interfaces  . . . . . . . . . . . . . . . . . 21
     6.1.  sendMessage ASI  . . . . . . . . . . . . . . . . . . . . . 21
     6.2.  Changes to RFC 3411 Outgoing ASIs  . . . . . . . . . . . . 22
       6.2.1.  Message Processing Subsystem Primitives  . . . . . . . 22
       6.2.2.  Security Subsystem Primitives  . . . . . . . . . . . . 23
     6.3.  The receiveMessage ASI . . . . . . . . . . . . . . . . . . 24
     6.4.  Changes to RFC 3411 Incoming ASIs  . . . . . . . . . . . . 25
       6.4.1.  Message Processing Subsystem Primitive . . . . . . . . 25
       6.4.2.  Security Subsystem Primitive . . . . . . . . . . . . . 26
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 27
     7.1.  Coexistence, Security Parameters, and Access Control . . . 27
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 29
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 29
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 30



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RFC 5590                SNMP Transport Subsystem               June 2009


     10.2. Informative References . . . . . . . . . . . . . . . . . . 30
   Appendix A.  Why tmStateReference? . . . . . . . . . . . . . . . . 32
     A.1.  Define an Abstract Service Interface . . . . . . . . . . . 32
     A.2.  Using an Encapsulating Header  . . . . . . . . . . . . . . 32
     A.3.  Modifying Existing Fields in an SNMP Message . . . . . . . 32
     A.4.  Using a Cache  . . . . . . . . . . . . . . . . . . . . . . 33

1.  Introduction

   This document defines a Transport Subsystem, extending the Simple
   Network Management Protocol (SNMP) architecture defined in [RFC3411].
   This document identifies and describes some key aspects that need to
   be considered for any Transport Model for SNMP.

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].

1.2.  Conventions

   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 RFC 2119 [RFC2119].

   Lowercase versions of the keywords should be read as in normal
   English.  They will usually, but not always, be used in a context
   that relates to compatibility with the RFC 3411 architecture or the
   subsystem defined here but that might have no impact on on-the-wire
   compatibility.  These terms are used as guidance for designers of
   proposed IETF models to make the designs compatible with RFC 3411
   subsystems and Abstract Service Interfaces (ASIs).  Implementers are
   free to implement differently.  Some usages of these lowercase terms
   are simply normal English usage.

   For consistency with SNMP-related specifications, this document
   favors terminology as defined in STD 62, 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.

   This document discusses an extension to the modular RFC 3411
   architecture; this is not a protocol document.  An architectural
   "MUST" is a really sharp constraint; to allow for the evolution of
   technology and to not unnecessarily constrain future models, often a



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RFC 5590                SNMP Transport Subsystem               June 2009


   "SHOULD" or a "should" is more appropriate than a "MUST" in an
   architecture.  Future models MAY express tighter requirements for
   their own model-specific processing.

1.3.  Where This Extension Fits

   It is expected that readers of this document will have read RFCs 3410
   and 3411, and have a general understanding of the functionality
   defined in RFCs 3412-3418.

   The "Transport Subsystem" is an additional component for the SNMP
   Engine depicted in RFC 3411, Section 3.1.

   The following diagram depicts its place in the RFC 3411 architecture.

   +-------------------------------------------------------------------+
   |  SNMP entity                                                      |
   |                                                                   |
   |  +-------------------------------------------------------------+  |
   |  |  SNMP engine (identified by snmpEngineID)                   |  |
   |  |                                                             |  |
   |  |  +------------+                                             |  |
   |  |  | Transport  |                                             |  |
   |  |  | Subsystem  |                                             |  |
   |  |  +------------+                                             |  |
   |  |                                                             |  |
   |  |  +------------+ +------------+ +-----------+ +-----------+  |  |
   |  |  | Dispatcher | | Message    | | Security  | | Access    |  |  |
   |  |  |            | | Processing | | Subsystem | | Control   |  |  |
   |  |  |            | | Subsystem  | |           | | Subsystem |  |  |
   |  |  +------------+ +------------+ +-----------+ +-----------+  |  |
   |  +-------------------------------------------------------------+  |
   |                                                                   |
   |  +-------------------------------------------------------------+  |
   |  |  Application(s)                                             |  |
   |  |                                                             |  |
   |  |  +-------------+  +--------------+  +--------------+        |  |
   |  |  | Command     |  | Notification |  | Proxy        |        |  |
   |  |  | Generator   |  | Receiver     |  | Forwarder    |        |  |
   |  |  +-------------+  +--------------+  +--------------+        |  |
   |  |                                                             |  |
   |  |  +-------------+  +--------------+  +--------------+        |  |
   |  |  | Command     |  | Notification |  | Other        |        |  |
   |  |  | Responder   |  | Originator   |  |              |        |  |
   |  |  +-------------+  +--------------+  +--------------+        |  |
   |  +-------------------------------------------------------------+  |
   |                                                                   |
   +-------------------------------------------------------------------+



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RFC 5590                SNMP Transport Subsystem               June 2009


   The transport mappings defined in RFC 3417 do not provide lower-layer
   security functionality, and thus do not provide transport-specific
   security parameters.  This document updates RFC 3411 and RFC 3417 by
   defining an architectural extension and modifying the ASIs that
   transport mappings (hereafter called "Transport Models") can use to
   pass transport-specific security parameters to other subsystems,
   including transport-specific security parameters that are translated
   into the transport-independent securityName and securityLevel
   parameters.

   The Transport Security Model [RFC5591] and the Secure Shell Transport
   Model [RFC5592] utilize the Transport Subsystem.  The Transport
   Security Model is an alternative to the existing SNMPv1 Security
   Model [RFC3584], the SNMPv2c Security Model [RFC3584], and the User-
   based Security Model [RFC3414].  The Secure Shell Transport Model is
   an alternative to existing transport mappings as described in
   [RFC3417].

2.  Motivation

   Just as there are multiple ways to secure one's home or business, in
   a continuum of alternatives, there are multiple ways to secure a
   network management protocol.  Let's consider three general
   approaches.

   In the first approach, an individual could sit on his front porch
   waiting for intruders.  In the second approach, he could hire an
   employee, schedule the employee, position the employee to guard what
   he wants protected, hire a second guard to cover if the first gets
   sick, and so on.  In the third approach, he could hire a security
   company, tell them what he wants protected, and leave the details to
   them.  Considerations of hiring and training employees, positioning
   and scheduling the guards, arranging for cover, etc., are the
   responsibility of the security company.  The individual therefore
   achieves the desired security, with significantly less effort on his
   part except for identifying requirements and verifying the quality of
   service being provided.

   The User-based Security Model (USM) as defined in [RFC3414] largely
   uses the first approach -- it provides its own security.  It utilizes
   existing mechanisms (e.g., SHA), but provides all the coordination.
   USM provides for the authentication of a principal, message
   encryption, data integrity checking, timeliness checking, etc.

   USM was designed to be independent of other existing security
   infrastructures.  USM therefore uses a separate principal and key
   management infrastructure.  Operators have reported that deploying
   another principal and key management infrastructure in order to use



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   SNMPv3 is a deterrent to deploying SNMPv3.  It is possible to use
   external mechanisms to handle the distribution of keys for use by
   USM.  The more important issue is that operators wanted to leverage
   existing user management infrastructures that were not specific to
   SNMP.

   A USM-compliant architecture might combine the authentication
   mechanism with an external mechanism, such as RADIUS [RFC2865], to
   provide the authentication service.  Similarly, it might be possible
   to utilize an external protocol to encrypt a message, to check
   timeliness, to check data integrity, etc.  However, this corresponds
   to the second approach -- requiring the coordination of a number of
   differently subcontracted services.  Building solid security between
   the various services is difficult, and there is a significant
   potential for gaps in security.

   An alternative approach might be to utilize one or more lower-layer
   security mechanisms to provide the message-oriented security services
   required.  These would include authentication of the sender,
   encryption, timeliness checking, and data integrity checking.  This
   corresponds to the third approach described above.  There are a
   number of IETF standards available or in development to address these
   problems through security layers at the transport layer or
   application layer, among them are TLS [RFC5246], Simple
   Authentication and Security Layer (SASL) [RFC4422], and SSH [RFC4251]

   From an operational perspective, it is highly desirable to use
   security mechanisms that can unify the administrative security
   management for SNMPv3, command line interfaces (CLIs), and other
   management interfaces.  The use of security services provided by
   lower layers is the approach commonly used for the CLI, and is also
   the approach being proposed for other network management protocols,
   such as syslog [RFC5424] and NETCONF [RFC4741].

   This document defines a Transport Subsystem extension to the RFC 3411
   architecture that is based on the third approach.  This extension
   specifies how other lower-layer protocols with common security
   infrastructures can be used underneath the SNMP protocol and the
   desired goal of unified administrative security can be met.

   This extension allows security to be provided by an external protocol
   connected to the SNMP engine through an SNMP Transport Model
   [RFC3417].  Such a Transport Model would then enable the use of
   existing security mechanisms, such as TLS [RFC5246] or SSH [RFC4251],
   within the RFC 3411 architecture.






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RFC 5590                SNMP Transport Subsystem               June 2009


   There are a number of Internet security protocols and mechanisms that
   are in widespread use.  Many of them try to provide a generic
   infrastructure to be used by many different application-layer
   protocols.  The motivation behind the Transport Subsystem is to
   leverage these protocols where it seems useful.

   There are a number of challenges to be addressed to map the security
   provided by a secure transport into the SNMP architecture so that
   SNMP continues to provide interoperability with existing
   implementations.  These challenges are described in detail in this
   document.  For some key issues, design choices are described that
   might be made to provide a workable solution that meets operational
   requirements and fits into the SNMP architecture defined in
   [RFC3411].

3.  Requirements of a Transport Model

3.1.  Message Security Requirements

   Transport security protocols SHOULD provide protection against the
   following message-oriented threats:

   1.  modification of information

   2.  masquerade

   3.  message stream modification

   4.  disclosure

   These threats are described in Section 1.4 of [RFC3411].  The
   security requirements outlined there do not require protection
   against denial of service or traffic analysis; however, transport
   security protocols should not make those threats significantly worse.

3.1.1.  Security Protocol Requirements

   There are a number of standard protocols that could be proposed as
   possible solutions within the Transport Subsystem.  Some factors
   should be considered when selecting a protocol.

   Using a protocol in a manner for which it was not designed has
   numerous problems.  The advertised security characteristics of a
   protocol might depend on it being used as designed; when used in
   other ways, it might not deliver the expected security
   characteristics.  It is recommended that any proposed model include a
   description of the applicability of the Transport Model.




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   A Transport Model SHOULD NOT require modifications to the underlying
   protocol.  Modifying the protocol might change its security
   characteristics in ways that could impact other existing usages.  If
   a change is necessary, the change SHOULD be an extension that has no
   impact on the existing usages.  Any Transport Model specification
   should include a description of potential impact on other usages of
   the protocol.

   Since multiple Transport Models can exist simultaneously within the
   Transport Subsystem, Transport Models MUST be able to coexist with
   each other.

3.2.  SNMP Requirements

3.2.1.  Architectural Modularity Requirements

   SNMP version 3 (SNMPv3) is based on a modular architecture (defined
   in Section 3 of [RFC3411]) to allow the evolution of the SNMP
   protocol standards over time and to minimize the side effects between
   subsystems when changes are made.

   The RFC 3411 architecture includes a Message Processing Subsystem for
   permitting different message versions to be handled by a single
   engine, a Security Subsystem for enabling different methods of
   providing security services, Applications to support different types
   of Application processors, and an Access Control Subsystem for
   allowing multiple approaches to access control.  The RFC 3411
   architecture does not include a subsystem for Transport Models,
   despite the fact there are multiple transport mappings already
   defined for SNMP [RFC3417].  This document describes a Transport
   Subsystem that is compatible with the RFC 3411 architecture.  As work
   is being done to use secure transports such as SSH and TLS, using a
   subsystem will enable consistent design and modularity of such
   Transport Models.

   The design of this Transport Subsystem accepts the goals of the RFC
   3411 architecture that are defined in Section 1.5 of [RFC3411].  This
   Transport Subsystem uses a modular design that permits Transport
   Models (which might or might not be security-aware) to be "plugged
   into" the RFC 3411 architecture.  Such Transport Models would be
   independent of other modular SNMP components as much as possible.
   This design also permits Transport Models to be advanced through the
   standards process independently of other Transport Models.

   The following diagram depicts the SNMPv3 architecture, including the
   new Transport Subsystem defined in this document and a new Transport
   Security Model defined in [RFC5591].




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   +------------------------------+
   |    Network                   |
   +------------------------------+
      ^       ^              ^
      |       |              |
      v       v              v
   +-------------------------------------------------------------------+
   | +--------------------------------------------------+              |
   | |  Transport Subsystem                             |              |
   | | +-----+ +-----+ +-----+ +-----+       +-------+  |              |
   | | | UDP | | TCP | | SSH | | TLS | . . . | other |  |              |
   | | +-----+ +-----+ +-----+ +-----+       +-------+  |              |
   | +--------------------------------------------------+              |
   |              ^                                                    |
   |              |                                                    |
   | Dispatcher   v                                                    |
   | +-------------------+ +---------------------+  +----------------+ |
   | | Transport         | | Message Processing  |  | Security       | |
   | | Dispatch          | | Subsystem           |  | Subsystem      | |
   | |                   | |     +------------+  |  | +------------+ | |
   | |                   | |  +->| v1MP       |<--->| | USM        | | |
   | |                   | |  |  +------------+  |  | +------------+ | |
   | |                   | |  |  +------------+  |  | +------------+ | |
   | |                   | |  +->| v2cMP      |<--->| | Transport  | | |
   | | Message           | |  |  +------------+  |  | | Security   | | |
   | | Dispatch    <--------->|  +------------+  |  | | Model      | | |
   | |                   | |  +->| v3MP       |<--->| +------------+ | |
   | |                   | |  |  +------------+  |  | +------------+ | |
   | | PDU Dispatch      | |  |  +------------+  |  | | Other      | | |
   | +-------------------+ |  +->| otherMP    |<--->| | Model(s)   | | |
   |              ^        |     +------------+  |  | +------------+ | |
   |              |        +---------------------+  +----------------+ |
   |              v                                                    |
   |      +-------+-------------------------+---------------+          |
   |      ^                                 ^               ^          |
   |      |                                 |               |          |
   |      v                                 v               v          |
   | +-------------+   +---------+   +--------------+  +-------------+ |
   | |   COMMAND   |   | ACCESS  |   | NOTIFICATION |  |    PROXY    | |
   | |  RESPONDER  |<->| CONTROL |<->|  ORIGINATOR  |  |  FORWARDER  | |
   | | Application |   |         |   | Applications |  | Application | |
   | +-------------+   +---------+   +--------------+  +-------------+ |
   |      ^                                 ^                          |
   |      |                                 |                          |
   |      v                                 v                          |
   | +----------------------------------------------+                  |
   | |             MIB instrumentation              |      SNMP entity |
   +-------------------------------------------------------------------+



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RFC 5590                SNMP Transport Subsystem               June 2009


3.2.1.1.  Changes to the RFC 3411 Architecture

   The RFC 3411 architecture and the Security Subsystem assume that a
   Security Model is called by a Message Processing Model and will
   perform multiple security functions within the Security Subsystem.  A
   Transport Model that supports a secure transport protocol might
   perform similar security functions within the Transport Subsystem,
   including the translation of transport-security parameters to/from
   Security-Model-independent parameters.

   To accommodate this, an implementation-specific cache of transport-
   specific information will be described (not shown), and the data
   flows on this path will be extended to pass Security-Model-
   independent values.  This document amends some of the ASIs defined in
   RFC 3411; these changes are covered in Section 6 of this document.

   New Security Models might be defined that understand how to work with
   these modified ASIs and the transport-information cache.  One such
   Security Model, the Transport Security Model, is defined in
   [RFC5591].

3.2.1.2.  Changes to RFC 3411 Processing

   The introduction of secure transports affects the responsibilities
   and order of processing within the RFC 3411 architecture.  While the
   steps are the same, they might occur in a different order, and might
   be done by different subsystems.  With the existing RFC 3411
   architecture, security processing starts when the Message Processing
   Model decodes portions of the encoded message to extract parameters
   that identify which Security Model MUST handle the security-related
   tasks.

   A secure transport performs those security functions on the message,
   before the message is decoded.  Some of these functions might then be
   repeated by the selected Security Model.

3.2.1.3.  Passing Information between SNMP Engines

   A secure Transport Model will establish an authenticated and possibly
   encrypted tunnel between the Transport Models of two SNMP engines.
   After a transport-layer tunnel is established, then SNMP messages can
   be sent through the tunnel from one SNMP engine to the other.  While
   the Community Security Models [RFC3584] and the User-based Security
   Model establish a security association for each SNMP message, newer
   Transport Models MAY support sending multiple SNMP messages through
   the same tunnel to amortize the costs of establishing a security
   association.




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3.2.2.  Access Control Requirements

   RFC 3411 made some design decisions related to the support of an
   Access Control Subsystem.  These include establishing and passing in
   a model-independent manner the securityModel, securityName, and
   securityLevel parameters, and separating message authentication from
   data-access authorization.

3.2.2.1.  securityName and securityLevel Mapping

   SNMP data-access controls are expected to work on the basis of who
   can perform what operations on which subsets of data, and based on
   the security services that will be provided to secure the data in
   transit.  The securityModel and securityLevel parameters establish
   the protections for transit -- whether authentication and privacy
   services will be or have been applied to the message.  The
   securityName is a model-independent identifier of the security
   "principal".

   A Security Model plays a role in security that goes beyond protecting
   the message -- it provides a mapping between the Security-Model-
   specific principal for an incoming message to a Security-Model
   independent securityName that can be used for subsequent processing,
   such as for access control.  The securityName is mapped from a
   mechanism-specific identity, and this mapping must be done for
   incoming messages by the Security Model before it passes securityName
   to the Message Processing Model via the processIncoming ASI.

   A Security Model is also responsible to specify, via the
   securityLevel parameter, whether incoming messages have been
   authenticated and encrypted, and to ensure that outgoing messages are
   authenticated and encrypted based on the value of securityLevel.

   A Transport Model MAY provide suggested values for securityName and
   securityLevel.  A Security Model might have multiple sources for
   determining the principal and desired security services, and a
   particular Security Model might or might not utilize the values
   proposed by a Transport Model when deciding the value of securityName
   and securityLevel.

   Documents defining a new transport domain MUST define a prefix that
   MAY be prepended to all securityNames passed by the Security Model.
   The prefix MUST include one to four US-ASCII alpha-numeric
   characters, not including a ":" (US-ASCII 0x3a) character.  If a
   prefix is used, a securityName is constructed by concatenating the
   prefix and a ":" (US-ASCII 0x3a) character, followed by a non-empty
   identity in an snmpAdminString-compatible format.  The prefix can be
   used by SNMP Applications to distinguish "alice" authenticated by SSH



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RFC 5590                SNMP Transport Subsystem               June 2009


   from "alice" authenticated by TLS.  Transport domains and their
   corresponding prefixes are coordinated via the IANA registry "SNMP
   Transport Domains".

3.2.3.  Security Parameter Passing Requirements

   A Message Processing Model might unpack SNMP-specific security
   parameters from an incoming message before calling a specific
   Security Model to handle the security-related processing of the
   message.  When using a secure Transport Model, some security
   parameters might be extracted from the transport layer by the
   Transport Model before the message is passed to the Message
   Processing Subsystem.

   This document describes a cache mechanism (see Section 5) into which
   the Transport Model puts information about the transport and security
   parameters applied to a transport connection or an incoming message;
   a Security Model might extract that information from the cache.  A
   tmStateReference is passed as an extra parameter in the ASIs between
   the Transport Subsystem and the Message Processing and Security
   Subsystems in order to identify the relevant cache.  This approach of
   passing a model-independent reference is consistent with the
   securityStateReference cache already being passed around in the RFC
   3411 ASIs.

3.2.4.  Separation of Authentication and Authorization

   The RFC 3411 architecture defines a separation of authentication and
   the authorization to access and/or modify MIB data.  A set of model-
   independent parameters (securityModel, securityName, and
   securityLevel) are passed between the Security Subsystem, the
   Applications, and the Access Control Subsystem.

   This separation was a deliberate decision of the SNMPv3 WG, in order
   to allow support for authentication protocols that do not provide
   data-access authorization capabilities, and in order to support data-
   access authorization schemes, such as the View-based access Control
   Model (VACM), that do not perform their own authentication.

   A Message Processing Model determines which Security Model is used,
   either based on the message version (e.g., SNMPv1 and SNMPv2c) or
   possibly by a value specified in the message (e.g., msgSecurityModel
   field in SNMPv3).

   The Security Model makes the decision which securityName and
   securityLevel values are passed as model-independent parameters to an
   Application, which then passes them via the isAccessAllowed ASI to
   the Access Control Subsystem.



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   An Access Control Model performs the mapping from the model-
   independent security parameters to a policy within the Access Control
   Model that is Access-Control-Model-dependent.

   A Transport Model does not know which Security Model will be used for
   an incoming message, and so cannot know how the securityName and
   securityLevel parameters will be determined.  It can propose an
   authenticated identity (via the tmSecurityName field), but there is
   no guarantee that this value will be used by the Security Model.  For
   example, non-transport-aware Security Models will typically determine
   the securityName (and securityLevel) based on the contents of the
   SNMP message itself.  Such Security Models will simply not know that
   the tmStateReference cache exists.

   Further, even if the Transport Model can influence the choice of
   securityName, it cannot directly determine the authorization allowed
   to this identity.  If two different Transport Models each
   authenticate a transport principal that are then both mapped to the
   same securityName, then these two identities will typically be
   afforded exactly the same authorization by the Access Control Model.

   The only way for the Access Control Model to differentiate between
   identities based on the underlying Transport Model would be for such
   transport-authenticated identities to be mapped to distinct
   securityNames.  How and if this is done is Security-Model-dependent.

3.3.  Session Requirements

   Some secure transports have a notion of sessions, while other secure
   transports provide channels or other session-like mechanisms.
   Throughout this document, the term "session" is used in a broad sense
   to cover transport sessions, transport channels, and other transport-
   layer, session-like mechanisms.  Transport-layer sessions that can
   secure multiple SNMP messages within the lifetime of the session are
   considered desirable because the cost of authentication can be
   amortized over potentially many transactions.  How a transport
   session is actually established, opened, closed, or maintained is
   specific to a particular Transport Model.

   To reduce redundancy, this document describes aspects that are
   expected to be common to all Transport Model sessions.

3.3.1.  No SNMP Sessions

   The architecture defined in [RFC3411] and the Transport Subsystem
   defined in this document do not support SNMP sessions or include a
   session selector in the Abstract Service Interfaces.




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   The Transport Subsystem might support transport sessions.  However,
   the Transport Subsystem does not have access to the pduType (i.e.,
   the SNMP operation type), and so cannot select a given transport
   session for particular types of traffic.

   Certain parameters of the Abstract Service Interfaces might be used
   to guide the selection of an appropriate transport session to use for
   a given request by an Application.

   The transportDomain and transportAddress identify the transport
   connection to a remote network node.  Elements of the transport
   address (such as the port number) might be used by an Application to
   send a particular PDU type to a particular transport address.  For
   example, the SNMP-TARGET-MIB and SNMP-NOTIFICATION-MIB [RFC3413] are
   used to configure notification originators with the destination port
   to which SNMPv2-Trap PDUs or Inform PDUs are to be sent, but the
   Transport Subsystem never looks inside the PDU.

   The securityName identifies which security principal to communicate
   with at that address (e.g., different Network Management System (NMS)
   applications), and the securityLevel might permit selection of
   different sets of security properties for different purposes (e.g.,
   encrypted SET vs. non-encrypted GET operations).

   However, because the handling of transport sessions is specific to
   each Transport Model, some Transport Models MAY restrict selecting a
   particular transport session.  A user application might use a unique
   combination of transportDomain, transportAddress, securityModel,
   securityName, and securityLevel to try to force the selection of a
   given transport session.  This usage is NOT RECOMMENDED because it is
   not guaranteed to be interoperable across implementations and across
   models.

   Implementations SHOULD be able to maintain some reasonable number of
   concurrent transport sessions, and MAY provide non-standard internal
   mechanisms to select transport sessions.

3.3.2.  Session Establishment Requirements

   SNMP Applications provide the transportDomain, transportAddress,
   securityName, and securityLevel to be used to create a new session.

   If the Transport Model cannot provide at least the requested level of
   security, the Transport Model should discard the message and should
   notify the Dispatcher that establishing a session and sending the
   message failed.  Similarly, if the session cannot be established,
   then the message should be discarded and the Dispatcher notified.




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   Transport session establishment might require provisioning
   authentication credentials at an engine, either statically or
   dynamically.  How this is done is dependent on the Transport Model
   and the implementation.

3.3.3.  Session Maintenance Requirements

   A Transport Model can tear down sessions as needed.  It might be
   necessary for some implementations to tear down sessions as the
   result of resource constraints, for example.

   The decision to tear down a session is implementation-dependent.  How
   an implementation determines that an operation has completed is
   implementation-dependent.  While it is possible to tear down each
   transport session after processing for each message has completed,
   this is not recommended for performance reasons.

   The elements of procedure describe when cached information can be
   discarded, and the timing of cache cleanup might have security
   implications, but cache memory management is an implementation issue.

   If a Transport Model defines MIB module objects to maintain session
   state information, then the Transport Model MUST define what happens
   to the objects when a related session is torn down, since this will
   impact the interoperability of the MIB module.

3.3.4.  Message Security versus Session Security

   A Transport Model session is associated with state information that
   is maintained for its lifetime.  This state information allows for
   the application of various security services to multiple messages.
   Cryptographic keys associated with the transport session SHOULD be
   used to provide authentication, integrity checking, and encryption
   services, as needed, for data that is communicated during the
   session.  The cryptographic protocols used to establish keys for a
   Transport Model session SHOULD ensure that fresh new session keys are
   generated for each session.  This would ensure that a cross-session
   replay attack would be unsuccessful; that is, an attacker could not
   take a message observed on one session and successfully replay it on
   another session.

   A good security protocol would also protect against replay attacks
   within a session; that is, an attacker could not take a message
   observed on a session and successfully replay it later in the same
   session.  One approach would be to use sequence information within
   the protocol, allowing the participants to detect if messages were
   replayed or reordered within a session.




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   If a secure transport session is closed between the time a request
   message is received and the corresponding response message is sent,
   then the response message SHOULD be discarded, even if a new session
   has been established.  The SNMPv3 WG decided that this should be a
   "SHOULD" architecturally, and it is a Security-Model-specific
   decision whether to REQUIRE this.  The architecture does not mandate
   this requirement in order to allow for future Security Models where
   this might make sense; however, not requiring this could lead to
   added complexity and security vulnerabilities, so most Security
   Models SHOULD require this.

   SNMPv3 was designed to support multiple levels of security,
   selectable on a per-message basis by an SNMP Application, because,
   for example, there is not much value in using encryption for a
   command generator to poll for potentially non-sensitive performance
   data on thousands of interfaces every ten minutes; such encryption
   might add significant overhead to processing of the messages.

   Some Transport Models might support only specific authentication and
   encryption services, such as requiring all messages to be carried
   using both authentication and encryption, regardless of the security
   level requested by an SNMP Application.  A Transport Model MAY
   upgrade the security level requested by a transport-aware Security
   Model, i.e., noAuthNoPriv and authNoPriv might be sent over an
   authenticated and encrypted session.  A Transport Model MUST NOT
   downgrade the security level requested by a transport-aware Security
   Model, and SHOULD discard any message where this would occur.  This
   is a SHOULD rather than a MUST only to permit the potential
   development of models that can perform error-handling in a manner
   that is less severe than discarding the message.  However, any model
   that does not discard the message in this circumstance should have a
   clear justification for why not discarding will not create a security
   vulnerability.

4.  Scenario Diagrams and the Transport Subsystem

   Sections 4.6.1 and 4.6.2 of RFC 3411 provide scenario diagrams to
   illustrate how an outgoing message is created and how an incoming
   message is processed.  RFC 3411 does not define ASIs for the "Send
   SNMP Request Message to Network", "Receive SNMP Response Message from
   Network", "Receive SNMP Message from Network" and "Send SNMP message
   to Network" arrows in these diagrams.

   This document defines two ASIs corresponding to these arrows: a
   sendMessage ASI to send SNMP messages to the network and a
   receiveMessage ASI to receive SNMP messages from the network.  These
   ASIs are used for all SNMP messages, regardless of pduType.




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5.  Cached Information and References

   When performing SNMP processing, there are two levels of state
   information that might need to be retained: the immediate state
   linking a request-response pair and a potentially longer-term state
   relating to transport and security.

   The RFC 3411 architecture uses caches to maintain the short-term
   message state, and uses references in the ASIs to pass this
   information between subsystems.

   This document defines the requirements for a cache to handle
   additional short-term message state and longer-term transport state
   information, using a tmStateReference parameter to pass this
   information between subsystems.

   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 also be
   discarded.  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 should also be
   discarded.

   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.

5.1.  securityStateReference

   The securityStateReference parameter is defined in RFC 3411.  Its
   primary purpose is to provide a mapping between a request and the
   corresponding response.  This cache is not accessible to Transport
   Models, and an entry is typically only retained for the lifetime of a
   request-response pair of messages.

5.2.  tmStateReference

   For each transport session, information about the transport security
   is stored in a tmState cache or datastore that is referenced by a
   tmStateReference.  The tmStateReference parameter is used to pass
   model-specific and mechanism-specific parameters between the
   Transport Subsystem and transport-aware Security Models.

   In general, when necessary, the tmState is populated by the Security
   Model for outgoing messages and by the Transport Model for incoming
   messages.  However, in both cases, the model populating the tmState



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   might have incomplete information, and the missing information might
   be populated by the other model when the information becomes
   available.

   The tmState might contain both long-term and short-term information.
   The session information typically remains valid for the duration of
   the transport session, might be used for several messages, and might
   be stored in a local configuration datastore.  Some information has a
   shorter lifespan, such as tmSameSecurity and
   tmRequestedSecurityLevel, which are associated with a specific
   message.

   Since this cache is only used within an implementation, and not on-
   the-wire, the precise contents and format of the cache are
   implementation-dependent.  For architectural modularity between
   Transport Models and transport-aware Security Models, a fully-defined
   tmState MUST conceptually include at least the following fields:

      tmTransportDomain

      tmTransportAddress

      tmSecurityName

      tmRequestedSecurityLevel

      tmTransportSecurityLevel

      tmSameSecurity

      tmSessionID

   The details of these fields are described in the following
   subsections.

5.2.1.  Transport Information

   Information about the source of an incoming SNMP message is passed up
   from the Transport Subsystem as far as the Message Processing
   Subsystem.  However, these parameters are not included in the
   processIncomingMsg ASI defined in RFC 3411; hence, this information
   is not directly available to the Security Model.

   A transport-aware Security Model might wish to take account of the
   transport protocol and originating address when authenticating the
   request and setting up the authorization parameters.  It is therefore





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   necessary for the Transport Model to include this information in the
   tmStateReference cache so that it is accessible to the Security
   Model.

   o  tmTransportDomain: the transport protocol (and hence the Transport
      Model) used to receive the incoming message.

   o  tmTransportAddress: the source of the incoming message.

   The ASIs used for processing an outgoing message all include explicit
   transportDomain and transportAddress parameters.  The values within
   the securityStateReference cache might override these parameters for
   outgoing messages.

5.2.2.  securityName

   There are actually three distinct "identities" that can be identified
   during the processing of an SNMP request over a secure transport:

   o  transport principal: the transport-authenticated identity on whose
      behalf the secure transport connection was (or should be)
      established.  This value is transport-, mechanism-, and
      implementation-specific, and is only used within a given Transport
      Model.

   o  tmSecurityName: a human-readable name (in snmpAdminString format)
      representing this transport identity.  This value is transport-
      and implementation-specific, and is only used (directly) by the
      Transport and Security Models.

   o  securityName: a human-readable name (in snmpAdminString format)
      representing the SNMP principal in a model-independent manner.
      This value is used directly by SNMP Applications, the Access
      Control Subsystem, the Message Processing Subsystem, and the
      Security Subsystem.

   The transport principal might or might not be the same as the
   tmSecurityName.  Similarly, the tmSecurityName might or might not be
   the same as the securityName as seen by the Application and Access
   Control Subsystems.  In particular, a non-transport-aware Security
   Model will ignore tmSecurityName completely when determining the SNMP
   securityName.

   However, it is important that the mapping between the transport
   principal and the SNMP securityName (for transport-aware Security
   Models) is consistent and predictable in order to allow configuration
   of suitable access control and the establishment of transport
   connections.



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5.2.3.  securityLevel

   There are two distinct issues relating to security level as applied
   to secure transports.  For clarity, these are handled by separate
   fields in the tmStateReference cache:

   o  tmTransportSecurityLevel: an indication from the Transport Model
      of the level of security offered by this session.  The Security
      Model can use this to ensure that incoming messages were suitably
      protected before acting on them.

   o  tmRequestedSecurityLevel: an indication from the Security Model of
      the level of security required to be provided by the transport
      protocol.  The Transport Model can use this to ensure that
      outgoing messages will not be sent over an insufficiently secure
      session.

5.2.4.  Session Information

   For security reasons, if a secure transport session is closed between
   the time a request message is received and the corresponding response
   message is sent, then the response message SHOULD be discarded, even
   if a new session has been established.  The SNMPv3 WG decided that
   this should be a "SHOULD" architecturally, and it is a Security-
   Model-specific decision whether to REQUIRE this.

   o  tmSameSecurity: this flag is used by a transport-aware Security
      Model to indicate whether the Transport Model MUST enforce this
      restriction.

   o  tmSessionID: in order to verify whether the session has changed,
      the Transport Model must be able to compare the session used to
      receive the original request with the one to be used to send the
      response.  This typically needs some form of session identifier.
      This value is only ever used by the Transport Model, so the format
      and interpretation of this field are model-specific and
      implementation-dependent.

   When processing an outgoing message, if tmSameSecurity is true, then
   the tmSessionID MUST match the current transport session; otherwise,
   the message MUST be discarded and the Dispatcher notified that
   sending the message failed.









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6.  Abstract Service Interfaces

   Abstract service interfaces have been defined by RFC 3411 to describe
   the conceptual data flows between the various subsystems within an
   SNMP entity and to help keep the subsystems independent of each other
   except for the common parameters.

   This document introduces a couple of new ASIs to define the interface
   between the Transport and Dispatcher Subsystems; it also extends some
   of the ASIs defined in RFC 3411 to include transport-related
   information.

   This document follows the example of RFC 3411 regarding the release
   of state information and regarding error indications.

   1) The release of state information is not always explicitly
   specified in a Transport Model.  As a general rule, if state
   information is available when a message gets discarded, the message-
   state information should also be released, and if state information
   is available when a session is closed, the session-state information
   should also be released.  Keeping sensitive security information
   longer than necessary might introduce potential vulnerabilities to an
   implementation.

   2)An error indication in statusInformation will typically include the
   Object Identifier (OID) and value for an incremented error counter.
   This might be accompanied by values for contextEngineID and
   contextName for this counter, a value for securityLevel, and the
   appropriate state reference if the information is available at the
   point where the error is detected.

6.1.  sendMessage ASI

   The sendMessage ASI is used to pass a message from the Dispatcher to
   the appropriate Transport Model for sending.  The sendMessageASI
   defined in this document replaces the text "Send SNMP Request Message
   to Network" that appears in the diagram in Section 4.6.1 of RFC 3411
   and the text "Send SNMP Message to Network" that appears in Section
   4.6.2 of RFC 3411.

   If present and valid, the tmStateReference refers to a cache
   containing Transport-Model-specific parameters for the transport and
   transport security.  How a tmStateReference is determined to be
   present and valid is implementation-dependent.  How the information
   in the cache is used is Transport-Model-dependent and implementation-
   dependent.





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   This might sound underspecified, but a Transport Model might be
   something like SNMP over UDP over IPv6, where no security is
   provided, so it might have no mechanisms for utilizing a
   tmStateReference cache.

   statusInformation =
   sendMessage(
   IN   destTransportDomain           -- transport domain to be used
   IN   destTransportAddress          -- transport address to be used
   IN   outgoingMessage               -- the message to send
   IN   outgoingMessageLength         -- its length
   IN   tmStateReference              -- reference to transport state
    )

6.2.  Changes to RFC 3411 Outgoing ASIs

   Additional parameters have been added to the ASIs defined in RFC 3411
   that are concerned with communication between the Dispatcher and
   Message Processing Subsystems, and between the Message Processing and
   Security Subsystems.

6.2.1.  Message Processing Subsystem Primitives

   A tmStateReference parameter has been added as an OUT parameter to
   the prepareOutgoingMessage and prepareResponseMessage ASIs.  This is
   passed from the Message Processing Subsystem to the Dispatcher, and
   from there to the Transport Subsystem.

   How or if the Message Processing Subsystem modifies or utilizes the
   contents of the cache is Message-Processing-Model specific.

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





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   OUT  destTransportDomain     -- destination transport domain
   OUT  destTransportAddress    -- destination transport address
   OUT  outgoingMessage         -- the message to send
   OUT  outgoingMessageLength   -- its length
   OUT  tmStateReference        -- (NEW) reference to transport state
               )

   statusInformation =          -- success or errorIndication
   prepareResponseMessage(
   IN  messageProcessingModel   -- typically, SNMP version
   IN  securityModel            -- Security Model to use
   IN  securityName             -- on behalf of this principal
   IN  securityLevel            -- Level of Security requested
   IN  contextEngineID          -- data from/at this entity
   IN  contextName              -- data from/in this context
   IN  pduVersion               -- the version of the PDU
   IN  PDU                      -- SNMP Protocol Data Unit
   IN  maxSizeResponseScopedPDU -- maximum size able to accept
   IN  stateReference           -- reference to state information
                                -- as presented with the request
   IN  statusInformation        -- success or errorIndication
                                -- error counter OID/value if error
   OUT destTransportDomain      -- destination transport domain
   OUT destTransportAddress     -- destination transport address
   OUT outgoingMessage          -- the message to send
   OUT outgoingMessageLength    -- its length
   OUT tmStateReference         -- (NEW) reference to transport state
               )

6.2.2.  Security Subsystem Primitives

   transportDomain and transportAddress parameters have been added as IN
   parameters to the generateRequestMsg and generateResponseMsg ASIs,
   and a tmStateReference parameter has been added as an OUT parameter.
   The transportDomain and transportAddress parameters will have been
   passed into the Message Processing Subsystem from the Dispatcher and
   are passed on to the Security Subsystem.  The tmStateReference
   parameter will be passed from the Security Subsystem back to the
   Message Processing Subsystem, and on to the Dispatcher and Transport
   Subsystems.

   If a cache exists for a session identifiable from the
   tmTransportDomain, tmTransportAddress, tmSecurityName, and requested
   securityLevel, then a transport-aware Security Model might create a
   tmStateReference parameter to this cache and pass that as an OUT
   parameter.





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   statusInformation =
   generateRequestMsg(
     IN   transportDomain         -- (NEW) destination transport domain
     IN   transportAddress        -- (NEW) destination transport address
     IN   messageProcessingModel  -- typically, SNMP version
     IN   globalData              -- message header, admin data
     IN   maxMessageSize          -- of the sending SNMP entity
     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) reference to transport state
              )

   statusInformation =
   generateResponseMsg(
     IN   transportDomain         -- (NEW) destination transport domain
     IN   transportAddress        -- (NEW) destination transport address
     IN   messageProcessingModel -- Message Processing Model
     IN   globalData             -- msgGlobalData
     IN   maxMessageSize         -- from msgMaxSize
     IN   securityModel          -- as determined by MPM
     IN   securityEngineID       -- the value of snmpEngineID
     IN   securityName           -- on behalf of this principal
     IN   securityLevel          -- for the outgoing message
     IN   scopedPDU              -- as provided by MPM
     IN   securityStateReference -- as provided by MPM
     OUT  securityParameters     -- filled in by Security Module
     OUT  wholeMsg               -- complete generated message
     OUT  wholeMsgLength         -- length of generated message
     OUT  tmStateReference       -- (NEW) reference to transport state
              )

6.3.  The receiveMessage ASI

   The receiveMessage ASI is used to pass a message from the Transport
   Subsystem to the Dispatcher.  The receiveMessage ASI replaces the
   text "Receive SNMP Response Message from Network" that appears in the
   diagram in Section 4.6.1 of RFC 3411 and the text "Receive SNMP
   Message from Network" from Section 4.6.2 of RFC3411.

   When a message is received on a given transport session, if a cache
   does not already exist for that session, the Transport Model might
   create one, referenced by tmStateReference.  The contents of this



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   cache are discussed in Section 5.  How this information is determined
   is implementation- and Transport-Model-specific.

   "Might create one" might sound underspecified, but a Transport Model
   might be something like SNMP over UDP over IPv6, where transport
   security is not provided, so it might not create a cache.

   The Transport Model does not know the securityModel for an incoming
   message; this will be determined by the Message Processing Model in a
   Message-Processing-Model-dependent manner.

   statusInformation =
   receiveMessage(
   IN   transportDomain               -- origin transport domain
   IN   transportAddress              -- origin transport address
   IN   incomingMessage               -- the message received
   IN   incomingMessageLength         -- its length
   IN   tmStateReference              -- reference to transport state
    )

6.4.  Changes to RFC 3411 Incoming ASIs

   The tmStateReference parameter has also been added to some of the
   incoming ASIs defined in RFC 3411.  How or if a Message Processing
   Model or Security Model uses tmStateReference is message-processing-
   and Security-Model-specific.

   This might sound underspecified, but a Message Processing Model might
   have access to all the information from the cache and from the
   message.  The Message Processing Model might determine that the USM
   Security Model is specified in an SNMPv3 message header; the USM
   Security Model has no need of values in the tmStateReference cache to
   authenticate and secure the SNMP message, but an Application might
   have specified to use a secure transport such as that provided by the
   SSH Transport Model to send the message to its destination.

6.4.1.  Message Processing Subsystem Primitive

   The tmStateReference parameter of prepareDataElements is passed from
   the Dispatcher to the Message Processing Subsystem.  How or if the
   Message Processing Subsystem modifies or utilizes the contents of the
   cache is Message-Processing-Model-specific.

   result =                       -- SUCCESS or errorIndication
   prepareDataElements(
   IN   transportDomain           -- origin transport domain
   IN   transportAddress          -- origin transport address
   IN   wholeMsg                  -- as received from the network



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   IN   wholeMsgLength            -- as received from the network
   IN   tmStateReference          -- (NEW) from the Transport Model
   OUT  messageProcessingModel    -- typically, SNMP version
   OUT  securityModel             -- Security Model to use
   OUT  securityName              -- on behalf of this principal
   OUT  securityLevel             -- Level of Security requested
   OUT  contextEngineID           -- data from/at this entity
   OUT  contextName               -- data from/in this context
   OUT  pduVersion                -- the version of the PDU
   OUT  PDU                       -- SNMP Protocol Data Unit
   OUT  pduType                   -- SNMP PDU type
   OUT  sendPduHandle             -- handle for matched request
   OUT  maxSizeResponseScopedPDU  -- maximum size sender can accept
   OUT  statusInformation         -- success or errorIndication
                                  -- error counter OID/value if error
   OUT  stateReference            -- reference to state information
                                  -- to be used for possible Response
   )

6.4.2.  Security Subsystem Primitive

   The processIncomingMessage ASI passes tmStateReference from the
   Message Processing Subsystem to the Security Subsystem.

   If tmStateReference is present and valid, an appropriate Security
   Model might utilize the information in the cache.  How or if the
   Security Subsystem utilizes the information in the cache is Security-
   Model-specific.

   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          -- (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
   )




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7.  Security Considerations

   This document defines an architectural approach that permits SNMP to
   utilize transport-layer security services.  Each proposed Transport
   Model should discuss the security considerations of that Transport
   Model.

   It is considered desirable by some industry segments that SNMP
   Transport Models utilize transport-layer security that addresses
   perfect forward secrecy at least for encryption keys.  Perfect
   forward secrecy guarantees that compromise of long-term secret keys
   does not result in disclosure of past session keys.  Each proposed
   Transport Model should include a discussion in its security
   considerations of whether perfect forward secrecy is appropriate for
   that Transport Model.

   The denial-of-service characteristics of various Transport Models and
   security protocols will vary and should be evaluated when determining
   the applicability of a Transport Model to a particular deployment
   situation.

   Since the cache will contain security-related parameters,
   implementers SHOULD store this information (in memory or in
   persistent storage) in a manner to protect it from unauthorized
   disclosure and/or modification.

   Care must be taken to ensure that an SNMP engine is sending packets
   out over a transport using credentials that are legal for that engine
   to use on behalf of that user.  Otherwise, an engine that has
   multiple transports open might be "tricked" into sending a message
   through the wrong transport.

   A Security Model might have multiple sources from which to define the
   securityName and securityLevel.  The use of a secure Transport Model
   does not imply that the securityName and securityLevel chosen by the
   Security Model represent the transport-authenticated identity or the
   transport-provided security services.  The securityModel,
   securityName, and securityLevel parameters are a related set, and an
   administrator should understand how the specified securityModel
   selects the corresponding securityName and securityLevel.

7.1.  Coexistence, Security Parameters, and Access Control

   In the RFC 3411 architecture, the Message Processing Model makes the
   decision about which Security Model to use.  The architectural change
   described by this document does not alter that.





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   The architecture change described by this document does, however,
   allow SNMP to support two different approaches to security --
   message-driven security and transport-driven security.  With message-
   driven security, SNMP provides its own security and passes security
   parameters within the SNMP message; with transport-driven security,
   SNMP depends on an external entity to provide security during
   transport by "wrapping" the SNMP message.

   Using a non-transport-aware Security Model with a secure Transport
   Model is NOT RECOMMENDED for the following reasons.

   Security Models defined before the Transport Security Model (i.e.,
   SNMPv1, SNMPv2c, and USM) do not support transport-based security and
   only have access to the security parameters contained within the SNMP
   message.  They do not know about the security parameters associated
   with a secure transport.  As a result, the Access Control Subsystem
   bases its decisions on the security parameters extracted from the
   SNMP message, not on transport-based security parameters.

   Implications of combining older Security Models with Secure Transport
   Models are known.  The securityName used for access control decisions
   is based on the message-driven identity, which might be
   unauthenticated, and not on the transport-driven, authenticated
   identity:

   o  An SNMPv1 message will always be paired with an SNMPv1 Security
      Model (per RFC 3584), regardless of the transport mapping or
      Transport Model used, and access controls will be based on the
      unauthenticated community name.

   o  An SNMPv2c message will always be paired with an SNMPv2c Security
      Model (per RFC 3584), regardless of the transport mapping or
      Transport Model used, and access controls will be based on the
      unauthenticated community name.

   o  An SNMPv3 message will always be paired with the securityModel
      specified in the msgSecurityParameters field of the message (per
      RFC 3412), regardless of the transport mapping or Transport Model
      used.  If the SNMPv3 message specifies the User-based Security
      Model (USM) with noAuthNoPriv, then the access controls will be
      based on the unauthenticated USM user.

   o  For outgoing messages, if a Secure Transport Model is selected in
      combination with a Security Model that does not populate a
      tmStateReference, the Secure Transport Model SHOULD detect the
      lack of a valid tmStateReference and fail.





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   In times of network stress, a Secure Transport Model might not work
   properly if its underlying security mechanisms (e.g., Network Time
   Protocol (NTP) or Authentication, Authorization, and Accounting (AAA)
   protocols or certificate authorities) are not reachable.  The User-
   based Security Model was explicitly designed to not depend upon
   external network services, and provides its own security services.
   It is RECOMMENDED that operators provision authPriv USM as a fallback
   mechanism to supplement any Security Model or Transport Model that
   has external dependencies, so that secure SNMP communications can
   continue when the external network service is not available.

8.  IANA Considerations

   IANA has created a new registry in the Simple Network Management
   Protocol (SNMP) Number Spaces.  The new registry is called "SNMP
   Transport Domains".  This registry contains US-ASCII alpha-numeric
   strings of one to four characters to identify prefixes for
   corresponding SNMP transport domains.  Each transport domain MUST
   have an OID assignment under snmpDomains [RFC2578].  Values are to be
   assigned via [RFC5226] "Specification Required".

   The registry has been populated with the following initial entries:

   Registry Name: SNMP Transport Domains
   Reference: [RFC2578] [RFC3417] [RFC5590]
   Registration Procedures: Specification Required
   Each domain is assigned a MIB-defined OID under snmpDomains

   Prefix        snmpDomains                    Reference
   -------       -----------------------------  ---------
   udp           snmpUDPDomain                  [RFC3417] [RFC5590]
   clns          snmpCLNSDomain                 [RFC3417] [RFC5590]
   cons          snmpCONSDomain                 [RFC3417] [RFC5590]
   ddp           snmpDDPDomain                  [RFC3417] [RFC5590]
   ipx           snmpIPXDomain                  [RFC3417] [RFC5590]
   prxy          rfc1157Domain                  [RFC3417] [RFC5590]

9.  Acknowledgments

   The Integrated Security for SNMP WG would like to thank the following
   people for their contributions to the process.

   The authors of submitted Security Model proposals: Chris Elliot, Wes
   Hardaker, David Harrington, Keith McCloghrie, Kaushik Narayan, David
   Perkins, Joseph Salowey, and Juergen Schoenwaelder.

   The members of the Protocol Evaluation Team: Uri Blumenthal,
   Lakshminath Dondeti, Randy Presuhn, and Eric Rescorla.



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RFC 5590                SNMP Transport Subsystem               June 2009


   WG members who performed detailed reviews: Wes Hardaker, Jeffrey
   Hutzelman, Tom Petch, Dave Shield, and Bert Wijnen.

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.

   [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.

   [RFC3417]  Presuhn, R., "Transport Mappings for the Simple Network
              Management Protocol (SNMP)", STD 62, RFC 3417,
              December 2002.

10.2.  Informative References

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.





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RFC 5590                SNMP Transport Subsystem               June 2009


   [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.

   [RFC4251]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, January 2006.

   [RFC4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and
              Security Layer (SASL)", RFC 4422, June 2006.

   [RFC4741]  Enns, R., "NETCONF Configuration Protocol", RFC 4741,
              December 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.

   [RFC5591]  Harrington, D. and W. Hardaker, "Transport Security Model
              for the Simple Network Management Protocol (SNMP)",
              RFC 5591, June 2009.

   [RFC5592]  Harrington, D., Salowey, J., and W. Hardaker, "Secure
              Shell Transport Model for the Simple Network Management
              Protocol (SNMP)", RFC 5592, June 2009.





















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Appendix A.  Why tmStateReference?

   This appendix considers why a cache-based approach was selected for
   passing parameters.

   There are four approaches that could be used for passing information
   between the Transport Model and a Security Model.

   1.  One could define an ASI to supplement the existing ASIs.

   2.  One could add a header to encapsulate the SNMP message.

   3.  One could utilize fields already defined in the existing SNMPv3
       message.

   4.  One could pass the information in an implementation-specific
       cache or via a MIB module.

A.1.  Define an Abstract Service Interface

   Abstract Service Interfaces (ASIs) are defined by a set of primitives
   that specify the services provided and the abstract data elements
   that are to be passed when the services are invoked.  Defining
   additional ASIs to pass the security and transport information from
   the Transport Subsystem to the Security Subsystem has the advantage
   of being consistent with existing RFC 3411/3412 practice; it also
   helps to ensure that any Transport Model proposals pass the necessary
   data and do not cause side effects by creating model-specific
   dependencies between itself and models or subsystems other than those
   that are clearly defined by an ASI.

A.2.  Using an Encapsulating Header

   A header could encapsulate the SNMP message to pass necessary
   information from the Transport Model to the Dispatcher and then to a
   Message Processing Model.  The message header would be included in
   the wholeMessage ASI parameter and would be removed by a
   corresponding Message Processing Model.  This would imply the (one
   and only) Message Dispatcher would need to be modified to determine
   which SNMP message version was involved, and a new Message Processing
   Model would need to be developed that knew how to extract the header
   from the message and pass it to the Security Model.

A.3.  Modifying Existing Fields in an SNMP Message

   [RFC3412] defines the SNMPv3 message, which contains fields to pass
   security-related parameters.  The Transport Subsystem could use these
   fields in an SNMPv3 message (or comparable fields in other message



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   formats) to pass information between Transport Models in different
   SNMP engines and to pass information between a Transport Model and a
   corresponding Message Processing Model.

   If the fields in an incoming SNMPv3 message are changed by the
   Transport Model before passing it to the Security Model, then the
   Transport Model will need to decode the ASN.1 message, modify the
   fields, and re-encode the message in ASN.1 before passing the message
   on to the Message Dispatcher or to the transport layer.  This would
   require an intimate knowledge of the message format and message
   versions in order for the Transport Model to know which fields could
   be modified.  This would seriously violate the modularity of the
   architecture.

A.4.  Using a Cache

   This document describes a cache into which the Transport Model (TM)
   puts information about the security applied to an incoming message; a
   Security Model can extract that information from the cache.  Given
   that there might be multiple TM security caches, a tmStateReference
   is passed as an extra parameter in the ASIs between the Transport
   Subsystem and the Security Subsystem so that the Security Model knows
   which cache of information to consult.

   This approach does create dependencies between a specific Transport
   Model and a corresponding specific Security Model.  However, the
   approach of passing a model-independent reference to a model-
   dependent cache is consistent with the securityStateReference already
   being passed around in the RFC 3411 ASIs.






















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Authors' Addresses

   David Harrington
   Huawei Technologies (USA)
   1700 Alma Dr. Suite 100
   Plano, TX 75075
   USA

   Phone: +1 603 436 8634
   EMail: ietfdbh@comcast.net


   Juergen Schoenwaelder
   Jacobs University Bremen
   Campus Ring 1
   28725 Bremen
   Germany

   Phone: +49 421 200-3587
   EMail: j.schoenwaelder@jacobs-university.de































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=========================================================================





Network Working Group                                      D. Harrington
Request for Comments: 5591                     Huawei Technologies (USA)
Category: Standards Track                                    W. Hardaker
                                               Cobham Analytic Solutions
                                                               June 2009


                    Transport Security Model for the
               Simple Network Management Protocol (SNMP)

Status of This Memo

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

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.











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RFC 5591           Transport Security Model for SNMP           June 2009


Abstract

   This memo describes a Transport Security Model for the Simple Network
   Management Protocol (SNMP).

   This memo also defines a portion of the Management Information Base
   (MIB) for monitoring and managing the Transport Security Model for
   SNMP.

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 .......6
      2.1. Security Capabilities of this Model ........................6
           2.1.1. Threats .............................................6
           2.1.2. Security Levels .....................................7
      2.2. Transport Sessions .........................................7
      2.3. Coexistence ................................................7
           2.3.1. Coexistence with Message Processing Models ..........7
           2.3.2. Coexistence with Other Security Models ..............8
           2.3.3. Coexistence with Transport Models ...................8
   3. Cached Information and References ...............................8
      3.1. Transport Security Model Cached Information ................9
           3.1.1. securityStateReference ..............................9
           3.1.2. tmStateReference ....................................9
           3.1.3. Prefixes and securityNames ..........................9
   4. Processing an Outgoing Message .................................10
      4.1. Security Processing for an Outgoing Message ...............10
      4.2. Elements of Procedure for Outgoing Messages ...............11
   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
           6.1.1. The snmpTsmStats Subtree ...........................14
           6.1.2. The snmpTsmConfiguration Subtree ...................14
      6.2. Relationship to Other MIB Modules .........................14
           6.2.1. MIB Modules Required for IMPORTS ...................15
   7. MIB Module Definition ..........................................15
   8. Security Considerations ........................................20
      8.1. MIB Module Security .......................................20
   9. IANA Considerations ............................................21
   10. Acknowledgments ...............................................22



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   11. References ....................................................22
      11.1. Normative References .....................................22
      11.2. Informative References ...................................23
   Appendix A.  Notification Tables Configuration ....................24
     A.1.  Transport Security Model Processing for Notifications .....25
   Appendix B.  Processing Differences between USM and Secure
                Transport ............................................26
     B.1.  USM and the RFC 3411 Architecture .........................26
     B.2.  Transport Subsystem and the RFC 3411 Architecture .........27

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 [RFC5590].

   This memo also defines a portion of the Management Information Base
   (MIB) 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 readers will have also read and understood
   [RFC3411], [RFC3412], [RFC3413], and [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

   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].




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   Lowercase versions of the keywords should be read as in normal
   English.  They will usually, but not always, be used in a context
   that relates to compatibility with the RFC 3411 architecture or the
   subsystem defined here but that might have no impact on on-the-wire
   compatibility.  These terms are used as guidance for designers of
   proposed IETF models to make the designs compatible with RFC 3411
   subsystems and Abstract Service Interfaces (ASIs).  Implementers are
   free to implement differently.  Some usages of these lowercase terms
   are simply normal English usage.

   For consistency with SNMP-related specifications, this document
   favors terminology as defined in STD 62, 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.

   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 manager, agent, or both depending on the SNMP
   applications included in the engine.  Where distinction is needed,
   the application names of command generator, command responder,
   notification originator, notification receiver, and proxy forwarder
   are used.  See "Simple Network Management Protocol (SNMP)
   Applications" [RFC3413] for further information.

   While security protocols frequently refer to a user, the terminology
   used in [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 each acting in a
   particular role, an application or a set of applications, or a
   combination of these within an administrative domain.

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 (SNMP)" [RFC5590], which enables the use of
   external "lower-layer transport" protocols to provide message





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   security.  Transport Models are 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 that 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.  It also 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.

   This modularity of specification is not meant to be interpreted as
   imposing any specific requirements on implementation.

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 might not be possible for the Security Model to determine when
       the network is under stress.

   4.  A Security Model SHOULD NOT require changes to the SNMP
       architecture.




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   5.  A Security Model SHOULD NOT require 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 RFC 3411
   architecture as a Security Model in the Security Subsystem and to
   utilize the services of a secure Transport Model.

   For incoming messages, a secure Transport Model will pass a
   tmStateReference cache, described in [RFC5590].  To maintain RFC 3411
   modularity, the Transport Model will not know which securityModel
   will process the incoming message; the Message Processing Model will
   determine this.  If the Transport Security Model is used with a non-
   secure Transport Model, then the cache will not exist or will not be
   populated with security parameters, which will cause the Transport
   Security Model to return an error (see Section 5.2).

   The Transport Security Model will create the securityName and
   securityLevel to be passed to applications, and will verify that the
   tmTransportSecurityLevel reported by the Transport Model is at least
   as strong as the securityLevel requested by the Message Processing
   Model.

   For outgoing messages, the Transport Security Model will create a
   tmStateReference cache (or use an existing one), and will pass the
   tmStateReference to the specified Transport Model.

2.1.  Security Capabilities of this Model

2.1.1.  Threats

   The Transport Security Model is compatible with the RFC 3411
   architecture and provides protection against the threats identified
   by the RFC 3411 architecture.  However, the Transport Security Model
   does not provide security mechanisms such as authentication and
   encryption itself.  Which threats are addressed and how they are
   mitigated depends on the Transport Model used.  To avoid creating
   potential security vulnerabilities, operators should configure their
   system so this Security Model is always used with a Transport Model
   that provides appropriate security, where "appropriate" for a
   particular deployment is an administrative decision.









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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.  Transport Sessions

   The Transport Security Model does not work with transport sessions
   directly.  Instead the transport-related state is associated with a
   unique combination of transportDomain, transportAddress,
   securityName, and securityLevel, and is referenced via the
   tmStateReference parameter.  How and if this is mapped to a
   particular transport or channel is the responsibility of the
   Transport Subsystem.

2.3.  Coexistence

   In the RFC 3411 architecture, a Message Processing Model determines
   which Security Model SHALL 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).

2.3.1.  Coexistence with Message Processing Models

   The SNMPv1 and SNMPv2c message processing described in BCP 74
   [RFC3584] always selects the SNMPv1(1) and SNMPv2c(2) Security
   Models.  Since there is no mechanism defined in RFC 3584 to select an



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   alternative Security Model, SNMPv1 and SNMPv2c messages cannot use
   the Transport Security Model.  Messages might still be able to be
   conveyed over a secure transport protocol, but the Transport Security
   Model will not be invoked.

   The SNMPv2u/SNMPv2* Message Processing Model is an historic artifact
   for which there is no existing IETF specification.

   The SNMPv3 message processing defined in [RFC3412] extracts the
   securityModel from the msgSecurityModel field of an incoming
   SNMPv3Message.  When this value is transportSecurityModel(4),
   security processing is directed to the Transport Security Model.  For
   an outgoing message to be secured using the Transport Security Model,
   the application MUST specify a securityModel parameter value of
   transportSecurityModel(4) in the sendPdu Abstract Service Interface
   (ASI).

2.3.2.  Coexistence with Other Security Models

   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 (USM) [RFC3414].

2.3.3.  Coexistence with Transport Models

   The Transport Security Model (TSM) MAY work with multiple Transport
   Models, but the RFC 3411 Abstract Service Interfaces (ASIs) do not
   carry a value for the Transport Model.  The MIB module defined in
   this memo allows an administrator to configure whether or not TSM
   prepends a Transport Model prefix to the securityName.  This will
   allow SNMP applications to consider Transport Model as a factor when
   making decisions, such as access control, notification generation,
   and proxy forwarding.

   To have SNMP properly utilize the security services coordinated by
   the Transport Security Model, this Security Model MUST only be used
   with Transport Models that know how to process a tmStateReference,
   such as the Secure Shell Transport Model [RFC5592].

3.  Cached Information and References

   When performing SNMP processing, there are two levels of state
   information that might need to be retained: the immediate state
   linking a request-response pair and a potentially longer-term state
   relating to transport and security.  "Transport Subsystem for the
   Simple Network Management Protocol (SNMP)" [RFC5590] defines general
   requirements for caches and references.



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   This document defines additional cache requirements related to the
   Transport Security Model.

3.1.  Transport Security Model Cached Information

   The Transport Security Model has specific responsibilities regarding
   the cached information.

3.1.1.  securityStateReference

   The Transport Security Model adds the tmStateReference received from
   the processIncomingMsg ASI to the securityStateReference.  This
   tmStateReference can then be retrieved during the generateResponseMsg
   ASI so that it can be passed back to the Transport Model.

3.1.2.  tmStateReference

   For outgoing messages, the Transport Security Model uses parameters
   provided by the SNMP application to look up or create a
   tmStateReference.

   For the Transport Security Model, the security parameters used for a
   response MUST be the same as those used for the corresponding
   request.  This Security Model uses the tmStateReference stored as
   part of the securityStateReference when appropriate.  For responses
   and reports, this Security Model sets the tmSameSecurity flag to true
   in the tmStateReference before passing it to a Transport Model.

   For incoming messages, the Transport Security Model uses parameters
   provided in the tmStateReference cache to establish a securityName,
   and to verify adequate security levels.

3.1.3.  Prefixes and securityNames

   The SNMP-VIEW-BASED-ACM-MIB module [RFC3415], the SNMP-TARGET-MIB
   module [RFC3413], and other MIB modules contain objects to configure
   security parameters for use by applications such as access control,
   notification generation, and proxy forwarding.

   Transport domains and their corresponding prefixes are coordinated
   via the IANA registry "SNMP Transport Domains".

   If snmpTsmConfigurationUsePrefix is set to true, then all
   securityNames provided by, or provided to, the Transport Security
   Model MUST include a valid transport domain prefix.






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   If snmpTsmConfigurationUsePrefix is set to false, then all
   securityNames provided by, or provided to, the Transport Security
   Model MUST NOT include a transport domain prefix.

   The tmSecurityName in the tmStateReference stored as part of the
   securityStateReference does not contain a prefix.

4.  Processing an Outgoing Message

   An error indication might return an Object Identifier (OID) and value
   for an incremented counter, a value for securityLevel, values for
   contextEngineID and contextName for the counter, and the
   securityStateReference, if this 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 RFC
   3411 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



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          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
               )

4.2.  Elements of Procedure for Outgoing Messages

   1.  If there is a securityStateReference (Response or Report
       message), then this Security Model uses the cached information
       rather than the information provided by the ASI.  Extract the
       tmStateReference from the securityStateReference cache.  Set the
       tmRequestedSecurityLevel to the value of the extracted
       tmTransportSecurityLevel.  Set the tmSameSecurity parameter in
       the tmStateReference cache to true.  The cachedSecurityData for
       this message can now be discarded.

   2.  If there is no securityStateReference (e.g., a Request-type or
       Notification message), then create a tmStateReference cache.  Set
       tmTransportDomain to the value of transportDomain,
       tmTransportAddress to the value of transportAddress, and
       tmRequestedSecurityLevel to the value of securityLevel.
       (Implementers might optimize by pointing to saved copies of these
       session-specific values.)  Set the transaction-specific
       tmSameSecurity parameter to false.

       If the snmpTsmConfigurationUsePrefix object is set to false, then
       set tmSecurityName to the value of securityName.

       If the snmpTsmConfigurationUsePrefix object is set to true, then
       use the transportDomain to look up the corresponding prefix.
       (Since the securityStateReference stores the tmStateReference
       with the tmSecurityName for the incoming message, and since
       tmSecurityName never has a prefix, the prefix-stripping step only
       occurs when we are not using the securityStateReference).




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          If the prefix lookup fails for any reason, then the
          snmpTsmUnknownPrefixes counter is incremented, an error
          indication is returned to the calling module, and message
          processing stops.

          If the lookup succeeds, but there is no prefix in the
          securityName, or the prefix returned does not match the prefix
          in the securityName, or the length of the prefix is less than
          1 or greater than 4 US-ASCII alpha-numeric characters, then
          the snmpTsmInvalidPrefixes counter is incremented, an error
          indication is returned to the calling module, and message
          processing stops.

          Strip the transport-specific prefix and trailing ':' character
          (US-ASCII 0x3a) from the securityName.  Set tmSecurityName to
          the value of securityName.

   3.  Set securityParameters to 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 might return an OID and value for an incremented
   counter, a value for securityLevel, values for contextEngineID and
   contextName for the counter, and the securityStateReference, if this
   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:

   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



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   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 tmTransportDomain, tmTransportAddress, 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.  Copy the tmSecurityName to securityName.

       If the snmpTsmConfigurationUsePrefix object is set to true, then
       use the tmTransportDomain to look up the corresponding prefix.

          If the prefix lookup fails for any reason, then the
          snmpTsmUnknownPrefixes counter is incremented, an error
          indication is returned to the calling module, and message
          processing stops.

          If the lookup succeeds but the prefix length is less than 1 or
          greater than 4 octets, then the snmpTsmInvalidPrefixes counter
          is incremented, an error indication is returned to the calling
          module, and message processing stops.

          Set the securityName to be the concatenation of the prefix, a
          ':' character (US-ASCII 0x3a), and the tmSecurityName.

   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 if securityLevel specifies authentication
       (auth) and tmTransportSecurityLevel specifies no authentication
       (noAuth) was provided by the Transport Model, then the
       snmpTsmInadequateSecurityLevels counter is incremented, an error
       indication (unsupportedSecurityLevel) together with the OID and




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       value of the incremented counter is returned to the calling
       module, and Transport Security Model processing stops for this
       message.

   5.  The tmStateReference is cached as cachedSecurityData so that a
       possible response to this message will use the same security
       parameters.  Then securityStateReference is set for subsequent
       references to this cached data.

   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 objects for use only by the Transport
   Security Model.  It defines a configuration scalar and related error
   counters.

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.

6.1.1.  The snmpTsmStats Subtree

   This subtree contains error counters specific to the Transport
   Security Model.

6.1.2.  The snmpTsmConfiguration Subtree

   This subtree contains a configuration object that enables
   administrators to specify if they want a transport domain prefix
   prepended to securityNames for use by applications.

6.2.  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 SNMP-FRAMEWORK-MIB [RFC3411], the



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   SNMP-TARGET-MIB [RFC3413], the SNMP-VIEW-BASED-ACM-MIB [RFC3415], and
   the SNMPv2-MIB [RFC3418].  These are not needed to implement the
   SNMP-TSM-MIB.

6.2.1.  MIB Modules Required for IMPORTS

   The following MIB module imports items from [RFC2578], [RFC2579], and
   [RFC2580].

7.  MIB Module Definition

SNMP-TSM-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE,
    mib-2, Counter32
      FROM SNMPv2-SMI -- RFC2578
    MODULE-COMPLIANCE, OBJECT-GROUP
      FROM SNMPv2-CONF -- RFC2580
    TruthValue
       FROM SNMPv2-TC -- RFC2579
    ;

snmpTsmMIB MODULE-IDENTITY
    LAST-UPDATED "200906090000Z"
    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@jacobs-university.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

                    Wes Hardaker
                    Cobham Analytic Solutions
                    P.O. Box 382
                    Davis, CA  95617
                    USA
                    +1 530 792 1913
                    ietf@hardakers.net
                 "
    DESCRIPTION
       "The Transport Security Model MIB.

        In keeping with the RFC 3411 design decisions to use
        self-contained documents, the RFC that contains the definition
        of this MIB module also includes the elements of procedure
        that are needed for processing the Transport Security Model
        for SNMP.  These MIB objects SHOULD NOT be modified via other
        subsystems or models defined in 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) 2009 IETF Trust and the persons
        identified as authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, are permitted provided that the
        following conditions are met:

        - Redistributions of source code must retain the above copyright
          notice, this list of conditions and the following disclaimer.

        - Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.




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        - Neither the name of Internet Society, IETF or IETF Trust,
          nor the names of specific contributors, may be used to endorse
          or promote products derived from this software without
          specific prior written permission.

        THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
        CONTRIBUTORS 'AS IS' AND ANY EXPRESS OR IMPLIED WARRANTIES,
        INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
        MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
        DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
        CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
        SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
        NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
        LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
        CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
        OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
        EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

        This version of this MIB module is part of RFC 5591;
        see the RFC itself for full legal notices."

    REVISION    "200906090000Z"
    DESCRIPTION "The initial version, published in RFC 5591."

    ::= { mib-2 190 }

-- ---------------------------------------------------------- --
-- subtrees in the SNMP-TSM-MIB
-- ---------------------------------------------------------- --

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 incoming messages dropped because the



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                 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 securityLevel asserted by the Transport Model was
                 less than the securityLevel requested by the
                 application.
                "
    ::= { snmpTsmStats 2 }

snmpTsmUnknownPrefixes OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "The number of messages dropped because
                 snmpTsmConfigurationUsePrefix was set to true and
                 there is no known prefix for the specified transport
                 domain.
                "
    ::= { snmpTsmStats 3 }

snmpTsmInvalidPrefixes OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "The number of messages dropped because
                 the securityName associated with an outgoing message
                 did not contain a valid transport domain prefix.
                "
    ::= { snmpTsmStats 4 }

-- -------------------------------------------------------------
-- Configuration
-- -------------------------------------------------------------

-- Configuration for the Transport Security Model

snmpTsmConfiguration   OBJECT IDENTIFIER ::= { snmpTsmMIBObjects 2 }

snmpTsmConfigurationUsePrefix OBJECT-TYPE
    SYNTAX      TruthValue
    MAX-ACCESS  read-write
    STATUS      current



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    DESCRIPTION "If this object is set to true, then securityNames
                 passing to and from the application are expected to
                 contain a transport-domain-specific prefix.  If this
                 object is set to true, then a domain-specific prefix
                 will be added by the TSM to the securityName for
                 incoming messages and removed from the securityName
                 when processing outgoing messages.  Transport domains
                 and prefixes are maintained in a registry by IANA.
                 This object SHOULD persist across system reboots.
                "
    DEFVAL { false }
    ::= { snmpTsmConfiguration 1 }

-- -------------------------------------------------------------
-- 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
                 the SNMP-TSM-MIB.
                "
    MODULE
        MANDATORY-GROUPS { snmpTsmGroup }
    ::= { snmpTsmCompliances 1 }

-- -------------------------------------------------------------
-- Units of conformance
-- -------------------------------------------------------------
snmpTsmGroup OBJECT-GROUP
    OBJECTS {
        snmpTsmInvalidCaches,
        snmpTsmInadequateSecurityLevels,
        snmpTsmUnknownPrefixes,
        snmpTsmInvalidPrefixes,
        snmpTsmConfigurationUsePrefix
    }
    STATUS      current
    DESCRIPTION "A collection of objects for maintaining
                 information of an SNMP engine that implements



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                 the SNMP Transport Security Model.
                "

    ::= { snmpTsmGroups 2 }

END

8.  Security Considerations

   This document describes a Security Model, compatible with the RFC
   3411 architecture, 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 Transport Security Model relies on secure Transport Models to
   provide an authenticated principal identifier and an assertion of
   whether authentication and privacy are used during transport.  This
   Security Model SHOULD always be used with Transport Models that
   provide adequate security, but "adequate security" is a configuration
   and/or run-time decision of the operator or management application.
   The security threats and how these threats are mitigated should be
   covered in detail in the specifications of the Transport Models and
   the underlying secure transports.

   An authenticated principal identifier (securityName) is used in SNMP
   applications for purposes such as access control, notification
   generation, and proxy forwarding.  This Security Model supports
   multiple Transport Models.  Operators might judge some transports to
   be more secure than others, so this Security Model can be configured
   to prepend a prefix to the securityName to indicate the Transport
   Model used to authenticate the principal.  Operators can use the
   prefixed securityName when making application decisions about levels
   of access.

8.1.  MIB Module Security

   There are a number of management objects defined in this MIB module
   with a MAX-ACCESS clause of read-write and/or read-create.  Such
   objects may be considered sensitive or vulnerable in some network
   environments.  The support for SET operations in a non-secure
   environment without proper protection can have a negative effect on
   network operations.  These are the tables and objects and their
   sensitivity/vulnerability:







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   o  The snmpTsmConfigurationUsePrefix object could be modified,
      creating a denial of service or authorizing SNMP messages that
      would not have previously been authorized by an Access Control
      Model (e.g., the View-based Access Control Model (VACM)).

   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  All the counters in this module refer to configuration errors and
      do not expose sensitive information.

   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 has assigned:

   1.  An SMI number (190) with a prefix of mib-2 in the MIB module
       registry for the MIB module in this document.

   2.  A value (4) to identify the Transport Security Model, in the
       Security Models registry of the SNMP Number Spaces registry.
       This results 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]
     4     Transport Security Model (TSM)      [RFC5591]

10.  Acknowledgments

   The editors would like to thank Jeffrey Hutzelman for sharing his SSH
   insights and Dave Shield for an outstanding job wordsmithing the
   existing document to improve organization and clarity.

   Additionally, helpful document reviews were received from Juergen
   Schoenwaelder.

11.  References

11.1.  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.






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   [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.

   [RFC5590]  Harrington, D. and J. Schoenwaelder, "Transport Subsystem
              for the Simple Network Management Protocol (SNMP)",
              RFC 5590, June 2009.

11.2.  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.

   [RFC3415]  Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
              Access Control Model (VACM) for the Simple Network
              Management Protocol (SNMP)", STD 62, RFC 3415,
              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.

   [RFC5592]  Harrington, D., Salowey, J., and W. Hardaker, "Secure
              Shell Transport Model for the Simple Network Management
              Protocol (SNMP)", RFC 5592, June 2009.
















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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 = 192.0.2.1:5162

      securityModel = Transport Security Model

      securityName = alice

      securityLevel = authPriv

   The following example will configure the notification originator to
   send informs to a notification receiver at 192.0.2.1:5162 using the
   securityName "alice". "alice" is the name for the recipient from the
   standpoint of the notification originator and is used for processing
   access controls before sending a notification.

   The columns marked with an "*" are the items that are Security-Model-
   specific or Transport-Model-specific.

   The configuration for the "alice" settings in the SNMP-VIEW-BASED-
   ACM-MIB objects are not shown here for brevity.  First, we configure
   which type of notification will 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 will be sent, and we specify which
   snmpTargetParamsEntry will be used (toCR) when sending to this
   transport address.





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          snmpTargetAddrTable row:
             snmpTargetAddrName              toCRAddr
         *   snmpTargetAddrTDomain           snmpSSHDomain
         *   snmpTargetAddrTAddress          192.0.2.1:5162
             snmpTargetAddrTimeout           1500
             snmpTargetAddrRetryCount        3
             snmpTargetAddrTagList           toCRTag
             snmpTargetAddrParams            toCR   (MUST match below)
             snmpTargetAddrStorageType       nonVolatile
             snmpTargetAddrColumnStatus      createAndGo

   Then we configure which principal at the host will receive the
   notifications associated with this taglist.  Here, we choose "alice",
   who uses the Transport Security Model.
         snmpTargetParamsTable row:
             snmpTargetParamsName            toCR
             snmpTargetParamsMPModel         SNMPv3
         *   snmpTargetParamsSecurityModel   TransportSecurityModel
             snmpTargetParamsSecurityName    "alice"
             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 (those with an * 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 connection using the
   tmStateReference cache created from the values of
   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 RFC 3411 architecture.  While the steps
   are the same, they occur in a different order and might 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.
   (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, SNMPv1, and SNMPv2c Security Models, security processing
   starts when the Message Processing Model decodes portions of the
   ASN.1 message to extract header fields that are used to determine
   which Security Model will process the message to perform
   authentication, decryption, timeliness checking, integrity checking,
   and translation of parameters to model-independent parameters.  By
   comparison, a secure transport performs those security functions on
   the message, before the ASN.1 is decoded.

   Step 6 cannot occur until after decryption occurs.  Steps 6 and
   beyond are the same for USM and a secure transport.

B.1.  USM and the RFC 3411 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).






Harrington & Hardaker       Standards Track                    [Page 26]


RFC 5591           Transport Security Model for SNMP           June 2009


   6) Determine the pduType in the decrypted portions (Message
      Processing Model).

   7) Pass on the decrypted portions with model-independent parameters.

B.2.  Transport Subsystem and the RFC 3411 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).

   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 will provide the translation from the authenticated
   identity (e.g., an SSH user name) to a human-friendly identifier
   (tmSecurityName) in step 2.  The Security Model will provide a
   mapping from that identifier to a model-independent securityName.




















Harrington & Hardaker       Standards Track                    [Page 27]


RFC 5591           Transport Security Model for SNMP           June 2009


Authors' Addresses

   David Harrington
   Huawei Technologies (USA)
   1700 Alma Dr. Suite 100
   Plano, TX 75075
   USA

   Phone: +1 603 436 8634
   EMail: ietfdbh@comcast.net


   Wes Hardaker
   Cobham Analytic Solutions
   P.O. Box 382
   Davis, CA  95617
   US

   Phone: +1 530 792 1913
   EMail: ietf@hardakers.net































Harrington & Hardaker       Standards Track                    [Page 28]

=========================================================================





Internet Engineering Task Force (IETF)                       W. Hardaker
Request for Comments: 6353                                  SPARTA, Inc.
Obsoletes: 5953                                                July 2011
Category: Standards Track
ISSN: 2070-1721


           Transport Layer Security (TLS) Transport Model for
             the Simple Network Management Protocol (SNMP)

Abstract

   This document describes a Transport Model for the Simple Network
   Management Protocol (SNMP), that uses either the Transport Layer
   Security protocol or the Datagram Transport Layer Security (DTLS)
   protocol.  The TLS and DTLS protocols provide authentication and
   privacy services for SNMP applications.  This document describes how
   the TLS Transport Model (TLSTM) implements the needed features of an
   SNMP Transport Subsystem to make this protection possible in an
   interoperable way.

   This Transport Model is designed to meet the security and operational
   needs of network administrators.  It supports the sending of SNMP
   messages over TLS/TCP and DTLS/UDP.  The TLS mode can make use of
   TCP's improved support for larger packet sizes and the DTLS mode
   provides potentially superior operation in environments where a
   connectionless (e.g., UDP) transport is preferred.  Both TLS and DTLS
   integrate well into existing public keying infrastructures.

   This document also defines a portion of the Management Information
   Base (MIB) for use with network management protocols.  In particular,
   it defines objects for managing the TLS Transport Model for SNMP.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6353.





Hardaker                     Standards Track                    [Page 1]


RFC 6353              TLS Transport Model for SNMP             July 2011


Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  7
     1.2.  Changes Since RFC 5953 . . . . . . . . . . . . . . . . . .  8
   2.  The Transport Layer Security Protocol  . . . . . . . . . . . .  8
   3.  How the TLSTM Fits into the Transport Subsystem  . . . . . . .  8
     3.1.  Security Capabilities of This Model  . . . . . . . . . . . 11
       3.1.1.  Threats  . . . . . . . . . . . . . . . . . . . . . . . 11
       3.1.2.  Message Protection . . . . . . . . . . . . . . . . . . 12
       3.1.3.  (D)TLS Connections . . . . . . . . . . . . . . . . . . 13
     3.2.  Security Parameter Passing . . . . . . . . . . . . . . . . 14
     3.3.  Notifications and Proxy  . . . . . . . . . . . . . . . . . 14
   4.  Elements of the Model  . . . . . . . . . . . . . . . . . . . . 15
     4.1.  X.509 Certificates . . . . . . . . . . . . . . . . . . . . 15
       4.1.1.  Provisioning for the Certificate . . . . . . . . . . . 15
     4.2.  (D)TLS Usage . . . . . . . . . . . . . . . . . . . . . . . 17
     4.3.  SNMP Services  . . . . . . . . . . . . . . . . . . . . . . 18
       4.3.1.  SNMP Services for an Outgoing Message  . . . . . . . . 18
       4.3.2.  SNMP Services for an Incoming Message  . . . . . . . . 19




Hardaker                     Standards Track                    [Page 2]


RFC 6353              TLS Transport Model for SNMP             July 2011


     4.4.  Cached Information and References  . . . . . . . . . . . . 20
       4.4.1.  TLS Transport Model Cached Information . . . . . . . . 20
         4.4.1.1.  tmSecurityName . . . . . . . . . . . . . . . . . . 20
         4.4.1.2.  tmSessionID  . . . . . . . . . . . . . . . . . . . 21
         4.4.1.3.  Session State  . . . . . . . . . . . . . . . . . . 21
   5.  Elements of Procedure  . . . . . . . . . . . . . . . . . . . . 21
     5.1.  Procedures for an Incoming Message . . . . . . . . . . . . 21
       5.1.1.  DTLS over UDP Processing for Incoming Messages . . . . 22
       5.1.2.  Transport Processing for Incoming SNMP Messages  . . . 23
     5.2.  Procedures for an Outgoing SNMP Message  . . . . . . . . . 25
     5.3.  Establishing or Accepting a Session  . . . . . . . . . . . 26
       5.3.1.  Establishing a Session as a Client . . . . . . . . . . 26
       5.3.2.  Accepting a Session as a Server  . . . . . . . . . . . 28
     5.4.  Closing a Session  . . . . . . . . . . . . . . . . . . . . 29
   6.  MIB Module Overview  . . . . . . . . . . . . . . . . . . . . . 30
     6.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 30
     6.2.  Textual Conventions  . . . . . . . . . . . . . . . . . . . 30
     6.3.  Statistical Counters . . . . . . . . . . . . . . . . . . . 30
     6.4.  Configuration Tables . . . . . . . . . . . . . . . . . . . 30
       6.4.1.  Notifications  . . . . . . . . . . . . . . . . . . . . 31
     6.5.  Relationship to Other MIB Modules  . . . . . . . . . . . . 31
       6.5.1.  MIB Modules Required for IMPORTS . . . . . . . . . . . 31
   7.  MIB Module Definition  . . . . . . . . . . . . . . . . . . . . 31
   8.  Operational Considerations . . . . . . . . . . . . . . . . . . 54
     8.1.  Sessions . . . . . . . . . . . . . . . . . . . . . . . . . 54
     8.2.  Notification Receiver Credential Selection . . . . . . . . 54
     8.3.  contextEngineID Discovery  . . . . . . . . . . . . . . . . 55
     8.4.  Transport Considerations . . . . . . . . . . . . . . . . . 55
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 55
     9.1.  Certificates, Authentication, and Authorization  . . . . . 55
     9.2.  (D)TLS Security Considerations . . . . . . . . . . . . . . 56
       9.2.1.  TLS Version Requirements . . . . . . . . . . . . . . . 56
       9.2.2.  Perfect Forward Secrecy  . . . . . . . . . . . . . . . 57
     9.3.  Use with SNMPv1/SNMPv2c Messages . . . . . . . . . . . . . 57
     9.4.  MIB Module Security  . . . . . . . . . . . . . . . . . . . 57
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 59
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 59
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 60
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 60
     12.2. Informative References . . . . . . . . . . . . . . . . . . 61
   Appendix A.  Target and Notification Configuration Example . . . . 63
     A.1.  Configuring a Notification Originator  . . . . . . . . . . 63
     A.2.  Configuring TLSTM to Utilize a Simple Derivation of
           tmSecurityName . . . . . . . . . . . . . . . . . . . . . . 64
     A.3.  Configuring TLSTM to Utilize Table-Driven Certificate
           Mapping  . . . . . . . . . . . . . . . . . . . . . . . . . 64





Hardaker                     Standards Track                    [Page 3]


RFC 6353              TLS Transport Model for SNMP             July 2011


1.  Introduction

   It is important to understand the modular SNMPv3 architecture as
   defined by [RFC3411] and enhanced by the Transport Subsystem
   [RFC5590].  It is also important to understand the terminology of the
   SNMPv3 architecture in order to understand where the Transport Model
   described in this document fits into the architecture and how it
   interacts with the other architecture subsystems.  For a detailed
   overview of the documents that describe the current Internet-Standard
   Management Framework, please refer to Section 7 of [RFC3410].

   This document describes a Transport Model that makes use of the
   Transport Layer Security (TLS) [RFC5246] and the Datagram Transport
   Layer Security (DTLS) Protocol [RFC4347], within a Transport
   Subsystem [RFC5590].  DTLS is the datagram variant of the Transport
   Layer Security (TLS) protocol [RFC5246].  The Transport Model in this
   document is referred to as the Transport Layer Security Transport
   Model (TLSTM).  TLS and DTLS take advantage of the X.509 public
   keying infrastructure [RFC5280].  While (D)TLS supports multiple
   authentication mechanisms, this document only discusses X.509
   certificate-based authentication.  Although other forms of
   authentication are possible, they are outside the scope of this
   specification.  This transport model is designed to meet the security
   and operational needs of network administrators, operating in both
   environments where a connectionless (e.g., UDP) transport is
   preferred and in environments where large quantities of data need to
   be sent (e.g., over a TCP-based stream).  Both TLS and DTLS integrate
   well into existing public keying infrastructures.  This document
   supports sending of SNMP messages over TLS/TCP and DTLS/UDP.

   This document also defines a portion of the Management Information
   Base (MIB) for use with network management protocols.  In particular,
   it defines objects for managing the TLS Transport Model for SNMP.

   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:
   [RFC2578], [RFC2579], and [RFC2580].










Hardaker                     Standards Track                    [Page 4]


RFC 6353              TLS Transport Model for SNMP             July 2011


   The diagram shown below gives a conceptual overview of two SNMP
   entities communicating using the TLS Transport Model (shown as
   "TLSTM").  One entity contains a command responder and notification
   originator application, and the other a command generator and
   notification receiver application.  It should be understood that this
   particular mix of application types is an example only and other
   combinations are equally valid.

   Note: this diagram shows the Transport Security Model (TSM) being
   used as the security model that is defined in [RFC5591].









































Hardaker                     Standards Track                    [Page 5]


RFC 6353              TLS Transport Model for SNMP             July 2011


 +---------------------------------------------------------------------+
 |                              Network                                |
 +---------------------------------------------------------------------+
     ^                     |            ^               |
     |Notifications        |Commands    |Commands       |Notifications
 +---|---------------------|-------+ +--|---------------|--------------+
 |   |                     V       | |  |               V              |
 | +------------+  +------------+  | | +-----------+   +----------+    |
 | |  (D)TLS    |  |  (D)TLS    |  | | | (D)TLS    |   | (D)TLS   |    |
 | |  (Client)  |  |  (Server)  |  | | | (Client)  |   | (Server) |    |
 | +------------+  +------------+  | | +-----------+   +----------+    |
 |       ^             ^           | |       ^              ^          |
 |       |             |           | |       |              |          |
 |       +-------------+           | |       +--------------+          |
 | +-----|------------+            | | +-----|------------+            |
 | |     V            |            | | |     V            |            |
 | | +--------+       |   +-----+  | | | +--------+       |   +-----+  |
 | | | TLS TM |<--------->|Cache|  | | | | TLS TM |<--------->|Cache|  |
 | | +--------+       |   +-----+  | | | +--------+       |   +-----+  |
 | |Transport Subsys. |      ^     | | |Transport Subsys. |      ^     |
 | +------------------+      |     | | +------------------+      |     |
 |    ^                      |     | |    ^                      |     |
 |    |                      +--+  | |    |                      +--+  |
 |    v                         |  | |    V                         |  |
 | +-----+ +--------+ +-------+ |  | | +-----+ +--------+ +-------+ |  |
 | |     | |Message | |Securi.| |  | | |     | |Message | |Securi.| |  |
 | |Disp.| |Proc.   | |Subsys.| |  | | |Disp.| |Proc.   | |Subsys.| |  |
 | |     | |Subsys. | |       | |  | | |     | |Subsys. | |       | |  |
 | |     | |        | |       | |  | | |     | |        | |       | |  |
 | |     | | +----+ | | +---+ | |  | | |     | | +----+ | | +---+ | |  |
 | |    <--->|v3MP|<--> |TSM|<--+  | | |    <--->|v3MP|<--->|TSM|<--+  |
 | |     | | +----+ | | +---+ |    | | |     | | +----+ | | +---+ |    |
 | |     | |        | |       |    | | |     | |        | |       |    |
 | +-----+ +--------+ +-------+    | | +-----+ +--------+ +-------+    |
 |    ^                            | |    ^                            |
 |    |                            | |    |                            |
 |    +-+------------+             | |    +-+----------+               |
 |      |            |             | |      |          |               |
 |      v            v             | |      v          V               |
 | +-------------+ +-------------+ | | +-------------+ +-------------+ |
 | |   COMMAND   | | NOTIFICAT.  | | | |  COMMAND    | | NOTIFICAT.  | |
 | |  RESPONDER  | | ORIGINATOR  | | | | GENERATOR   | | RECEIVER    | |
 | | application | | application | | | | application | | application | |
 | +-------------+ +-------------+ | | +-------------+ +-------------+ |
 |                     SNMP entity | |                     SNMP entity |
 +---------------------------------+ +---------------------------------+





Hardaker                     Standards Track                    [Page 6]


RFC 6353              TLS Transport Model for SNMP             July 2011


1.1.  Conventions

   For consistency with SNMP-related specifications, this document
   favors terminology as defined in STD 62, rather than favoring
   terminology that is consistent with non-SNMP specifications.  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 a 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.

   The terms "manager" and "agent" are not used in this document
   because, in the [RFC3411] architecture, all SNMP entities have the
   capability of acting as manager, agent, or both depending on the SNMP
   application types supported in the implementation.  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.

   Large portions of this document simultaneously refer to both TLS and
   DTLS when discussing TLSTM components that function equally with
   either protocol.  "(D)TLS" is used in these places to indicate that
   the statement applies to either or both protocols as appropriate.
   When a distinction between the protocols is needed, they are referred
   to independently through the use of "TLS" or "DTLS".  The Transport
   Model, however, is named "TLS Transport Model" and refers not to the
   TLS or DTLS protocol but to the specification in this document, which
   includes support for both TLS and DTLS.

   Throughout this document, the terms "client" and "server" are used to
   refer to the two ends of the (D)TLS transport connection.  The client
   actively opens the (D)TLS connection, and the server passively
   listens for the incoming (D)TLS connection.  An SNMP entity may act
   as a (D)TLS client or server or both, depending on the SNMP
   applications supported.

   The User-Based Security Model (USM) [RFC3414] is a mandatory-to-
   implement Security Model in STD 62.  While (D)TLS and USM frequently
   refer to a user, the terminology preferred in RFC 3411 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.



Hardaker                     Standards Track                    [Page 7]


RFC 6353              TLS Transport Model for SNMP             July 2011


   Throughout this document, the term "session" is used to refer to a
   secure association between two TLS Transport Models that permits the
   transmission of one or more SNMP messages within the lifetime of the
   session.  The (D)TLS protocols also have an internal notion of a
   session and although these two concepts of a session are related,
   when the term "session" is used this document is referring to the
   TLSTM's specific session and not directly to the (D)TLS protocol's
   session.

   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].

1.2.  Changes Since RFC 5953

   This document obsoletes [RFC5953].

   Since the publication of RFC 5953, a few editorial errata have been
   noted.  These errata are posted on the RFC Editor web site.  These
   errors have been corrected in this document.

   This document updates the references to RFC 3490 (IDNA 2003) to
   [RFC5890] (IDNA 2008), because RFC 3490 was obsoleted by RFC 5890.

   References to RFC 1033 were replaced with references to [RFC1123].

   Added informative reference to 5953.

   Updated MIB dates and revision date.

2.  The Transport Layer Security Protocol

   (D)TLS provides authentication, data message integrity, and privacy
   at the transport layer (see [RFC4347]).

   The primary goals of the TLS Transport Model are to provide privacy,
   peer identity authentication, and data integrity between two
   communicating SNMP entities.  The TLS and DTLS protocols provide a
   secure transport upon which the TLSTM is based.  Please refer to
   [RFC5246] and [RFC4347] for complete descriptions of the protocols.

3.  How the TLSTM Fits into the Transport Subsystem

   A transport model is a component of the Transport Subsystem.  The TLS
   Transport Model thus fits between the underlying (D)TLS transport
   layer and the Message Dispatcher [RFC3411] component of the SNMP
   engine.




Hardaker                     Standards Track                    [Page 8]


RFC 6353              TLS Transport Model for SNMP             July 2011


   The TLS Transport Model will establish a session between itself and
   the TLS Transport Model of another SNMP engine.  The sending
   transport model passes unencrypted and unauthenticated messages from
   the Dispatcher to (D)TLS to be encrypted and authenticated, and the
   receiving transport model accepts decrypted and authenticated/
   integrity-checked incoming messages from (D)TLS and passes them to
   the Dispatcher.

   After a TLS Transport Model session is established, SNMP messages can
   conceptually be sent through the session from one SNMP message
   Dispatcher to another SNMP Message Dispatcher.  If multiple SNMP
   messages are needed to be passed between two SNMP applications they
   MAY be passed through the same session.  A TLSTM implementation
   engine MAY choose to close the session to conserve resources.

   The TLS Transport Model of an SNMP engine will perform the
   translation between (D)TLS-specific security parameters and SNMP-
   specific, model-independent parameters.

































Hardaker                     Standards Track                    [Page 9]


RFC 6353              TLS Transport Model for SNMP             July 2011


   The diagram below depicts where the TLS Transport Model (shown as
   "(D)TLS TM") fits into the architecture described in RFC 3411 and the
   Transport Subsystem:

   +------------------------------+
   |    Network                   |
   +------------------------------+
      ^       ^              ^
      |       |              |
      v       v              v
   +-------------------------------------------------------------------+
   | +--------------------------------------------------+              |
   | |  Transport Subsystem                             |  +--------+  |
   | | +-----+ +-----+ +-------+             +-------+  |  |        |  |
   | | | UDP | | SSH | |(D)TLS |    . . .    | other |<--->| Cache  |  |
   | | |     | | TM  | | TM    |             |       |  |  |        |  |
   | | +-----+ +-----+ +-------+             +-------+  |  +--------+  |
   | +--------------------------------------------------+         ^    |
   |              ^                                               |    |
   |              |                                               |    |
   | Dispatcher   v                                               |    |
   | +--------------+ +---------------------+  +----------------+ |    |
   | | Transport    | | Message Processing  |  | Security       | |    |
   | | Dispatch     | | Subsystem           |  | Subsystem      | |    |
   | |              | |     +------------+  |  | +------------+ | |    |
   | |              | |  +->| v1MP       |<--->| | USM        | | |    |
   | |              | |  |  +------------+  |  | +------------+ | |    |
   | |              | |  |  +------------+  |  | +------------+ | |    |
   | |              | |  +->| v2cMP      |<--->| | Transport  | | |    |
   | | Message      | |  |  +------------+  |  | | Security   |<--+    |
   | | Dispatch    <---->|  +------------+  |  | | Model      | |      |
   | |              | |  +->| v3MP       |<--->| +------------+ |      |
   | |              | |  |  +------------+  |  | +------------+ |      |
   | | PDU Dispatch | |  |  +------------+  |  | | Other      | |      |
   | +--------------+ |  +->| otherMP    |<--->| | Model(s)   | |      |
   |              ^   |     +------------+  |  | +------------+ |      |
   |              |   +---------------------+  +----------------+      |
   |              v                                                    |
   |      +-------+-------------------------+---------------+          |
   |      ^                                 ^               ^          |
   |      |                                 |               |          |
   |      v                                 v               v          |









Hardaker                     Standards Track                   [Page 10]


RFC 6353              TLS Transport Model for SNMP             July 2011


   | +-------------+   +---------+   +--------------+  +-------------+ |
   | |   COMMAND   |   | ACCESS  |   | NOTIFICATION |  |    PROXY    | |
   | |  RESPONDER  |<->| CONTROL |<->|  ORIGINATOR  |  |  FORWARDER  | |
   | | application |   |         |   | applications |  | application | |
   | +-------------+   +---------+   +--------------+  +-------------+ |
   |      ^                                 ^                          |
   |      |                                 |                          |
   |      v                                 v                          |
   | +----------------------------------------------+                  |
   | |             MIB instrumentation              |      SNMP entity |
   +-------------------------------------------------------------------+

3.1.  Security Capabilities of This Model

3.1.1.  Threats

   The TLS Transport Model provides protection against the threats
   identified by the RFC 3411 architecture [RFC3411]:

   1.  Modification of Information - The modification threat is the
       danger that an unauthorized entity may alter in-transit SNMP
       messages generated on behalf of an authorized principal in such a
       way as to effect unauthorized management operations, including
       falsifying the value of an object.

       (D)TLS provides verification that the content of each received
       message has not been modified during its transmission through the
       network, data has not been altered or destroyed in an
       unauthorized manner, and data sequences have not been altered to
       an extent greater than can occur non-maliciously.

   2.  Masquerade - The masquerade threat is the danger that management
       operations unauthorized for a given principal may be attempted by
       assuming the identity of another principal that has the
       appropriate authorizations.

       The TLSTM verifies the identity of the (D)TLS server through the
       use of the (D)TLS protocol and X.509 certificates.  A TLS
       Transport Model implementation MUST support the authentication of
       both the server and the client.

   3.  Message stream modification - The re-ordering, delay, or replay
       of messages can and does occur through the natural operation of
       many connectionless transport services.  The message stream
       modification threat is the danger that messages may be
       maliciously re-ordered, delayed, or replayed to an extent that is
       greater than can occur through the natural operation of




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       connectionless transport services, in order to effect
       unauthorized management operations.

       (D)TLS provides replay protection with a Message Authentication
       Code (MAC) that includes a sequence number.  Since UDP provides
       no sequencing ability, DTLS uses a sliding window protocol with
       the sequence number used for replay protection (see [RFC4347]).

   4.  Disclosure - The disclosure threat is the danger of eavesdropping
       on the exchanges between SNMP engines.

       (D)TLS provides protection against the disclosure of information
       to unauthorized recipients or eavesdroppers by allowing for
       encryption of all traffic between SNMP engines.  A TLS Transport
       Model implementation MUST support message encryption to protect
       sensitive data from eavesdropping attacks.

   5.  Denial of Service - The RFC 3411 architecture [RFC3411] states
       that denial-of-service (DoS) attacks need not be addressed by an
       SNMP security protocol.  However, connectionless transports (like
       DTLS over UDP) are susceptible to a variety of DoS attacks
       because they are more vulnerable to spoofed IP addresses.  See
       Section 4.2 for details on how the cookie mechanism is used.
       Note, however, that this mechanism does not provide any defense
       against DoS attacks mounted from valid IP addresses.

   See Section 9 for more detail on the security considerations
   associated with the TLSTM and these security threats.

3.1.2.  Message Protection

   The RFC 3411 architecture recognizes three levels of security:

   o  without authentication and without privacy (noAuthNoPriv)

   o  with authentication but without privacy (authNoPriv)

   o  with authentication and with privacy (authPriv)

   The TLS Transport Model determines from (D)TLS the identity of the
   authenticated principal, the transport type, and the transport
   address associated with an incoming message.  The TLS Transport Model
   provides the identity and destination type and address to (D)TLS for
   outgoing messages.

   When an application requests a session for a message, it also
   requests a security level for that session.  The TLS Transport Model
   MUST ensure that the (D)TLS connection provides security at least as



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   high as the requested level of security.  How the security level is
   translated into the algorithms used to provide data integrity and
   privacy is implementation dependent.  However, the NULL integrity and
   encryption algorithms MUST NOT be used to fulfill security level
   requests for authentication or privacy.  Implementations MAY choose
   to force (D)TLS to only allow cipher_suites that provide both
   authentication and privacy to guarantee this assertion.

   If a suitable interface between the TLS Transport Model and the
   (D)TLS Handshake Protocol is implemented to allow the selection of
   security-level-dependent algorithms (for example, a security level to
   cipher_suites mapping table), then different security levels may be
   utilized by the application.

   The authentication, integrity, and privacy algorithms used by the
   (D)TLS Protocols may vary over time as the science of cryptography
   continues to evolve and the development of (D)TLS continues over
   time.  Implementers are encouraged to plan for changes in operator
   trust of particular algorithms.  Implementations SHOULD offer
   configuration settings for mapping algorithms to SNMPv3 security
   levels.

3.1.3.  (D)TLS Connections

   (D)TLS connections are opened by the TLS Transport Model during the
   elements of procedure for an outgoing SNMP message.  Since the sender
   of a message initiates the creation of a (D)TLS connection if needed,
   the (D)TLS connection will already exist for an incoming message.

   Implementations MAY choose to instantiate (D)TLS connections in
   anticipation of outgoing messages.  This approach might be useful to
   ensure that a (D)TLS connection to a given target can be established
   before it becomes important to send a message over the (D)TLS
   connection.  Of course, there is no guarantee that a pre-established
   session will still be valid when needed.

   DTLS connections, when used over UDP, are uniquely identified within
   the TLS Transport Model by the combination of transportDomain,
   transportAddress, tmSecurityName, and requestedSecurityLevel
   associated with each session.  Each unique combination of these
   parameters MUST have a locally chosen unique tlstmSessionID for each
   active session.  For further information, see Section 5.  TLS over
   TCP sessions, on the other hand, do not require a unique pairing of
   address and port attributes since their lower-layer protocols (TCP)
   already provide adequate session framing.  But they must still
   provide a unique tlstmSessionID for referencing the session.





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   The tlstmSessionID MUST NOT change during the entire duration of the
   session from the TLSTM's perspective, and MUST uniquely identify a
   single session.  As an implementation hint: note that the (D)TLS
   internal SessionID does not meet these requirements, since it can
   change over the life of the connection as seen by the TLSTM (for
   example, during renegotiation), and does not necessarily uniquely
   identify a TLSTM session (there can be multiple TLSTM sessions
   sharing the same D(TLS) internal SessionID).

3.2.  Security Parameter Passing

   For the (D)TLS server-side, (D)TLS-specific security parameters
   (i.e., cipher_suites, X.509 certificate fields, IP addresses, and
   ports) are translated by the TLS Transport Model into security
   parameters for the TLS Transport Model and security model (e.g.,
   tmSecurityLevel, tmSecurityName, transportDomain, transportAddress).
   The transport-related and (D)TLS-security-related information,
   including the authenticated identity, are stored in a cache
   referenced by tmStateReference.

   For the (D)TLS client side, the TLS Transport Model takes input
   provided by the Dispatcher in the sendMessage() Abstract Service
   Interface (ASI) and input from the tmStateReference cache.  The
   (D)TLS Transport Model converts that information into suitable
   security parameters for (D)TLS and establishes sessions as needed.

   The elements of procedure in Section 5 discuss these concepts in much
   greater detail.

3.3.  Notifications and Proxy

   (D)TLS connections may be initiated by (D)TLS clients on behalf of
   SNMP applications that initiate communications, such as command
   generators, notification originators, proxy forwarders.  Command
   generators are frequently operated by a human, but notification
   originators and proxy forwarders are usually unmanned automated
   processes.  The targets to whom notifications and proxied requests
   should be sent are typically determined and configured by a network
   administrator.

   The SNMP-TARGET-MIB module [RFC3413] contains objects for defining
   management targets, including transportDomain, transportAddress,
   securityName, securityModel, and securityLevel parameters, for
   notification originator, proxy forwarder, and SNMP-controllable
   command generator applications.  Transport domains and transport
   addresses are configured in the snmpTargetAddrTable, and the
   securityModel, securityName, and securityLevel parameters are
   configured in the snmpTargetParamsTable.  This document defines a MIB



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   module that extends the SNMP-TARGET-MIB's snmpTargetParamsTable to
   specify a (D)TLS client-side certificate to use for the connection.

   When configuring a (D)TLS target, the snmpTargetAddrTDomain and
   snmpTargetAddrTAddress parameters in snmpTargetAddrTable SHOULD be
   set to the snmpTLSTCPDomain or snmpDTLSUDPDomain object and an
   appropriate snmpTLSAddress value.  When used with the SNMPv3 message
   processing model, the snmpTargetParamsMPModel column of the
   snmpTargetParamsTable SHOULD be set to a value of 3.  The
   snmpTargetParamsSecurityName SHOULD be set to an appropriate
   securityName value, and the snmpTlstmParamsClientFingerprint
   parameter of the snmpTlstmParamsTable SHOULD be set to a value that
   refers to a locally held certificate (and the corresponding private
   key) to be used.  Other parameters, for example, cryptographic
   configuration such as which cipher_suites to use, must come from
   configuration mechanisms not defined in this document.

   The securityName defined in the snmpTargetParamsSecurityName column
   will be used by the access control model to authorize any
   notifications that need to be sent.

4.  Elements of the Model

   This section contains definitions required to realize the (D)TLS
   Transport Model defined by this document.

4.1.  X.509 Certificates

   (D)TLS can make use of X.509 certificates for authentication of both
   sides of the transport.  This section discusses the use of X.509
   certificates in the TLSTM.

   While (D)TLS supports multiple authentication mechanisms, this
   document only discusses X.509-certificate-based authentication; other
   forms of authentication are outside the scope of this specification.
   TLSTM implementations are REQUIRED to support X.509 certificates.

4.1.1.  Provisioning for the Certificate

   Authentication using (D)TLS will require that SNMP entities have
   certificates, either signed by trusted Certification Authorities
   (CAs), or self signed.  Furthermore, SNMP entities will most commonly
   need to be provisioned with root certificates that represent the list
   of trusted CAs that an SNMP entity can use for certificate
   verification.  SNMP entities SHOULD also be provisioned with an X.509
   certificate revocation mechanism which can be used to verify that a
   certificate has not been revoked.  Trusted public keys from either CA
   certificates and/or self-signed certificates MUST be installed into



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   the server through a trusted out-of-band mechanism and their
   authenticity MUST be verified before access is granted.

   Having received a certificate from a connecting TLSTM client, the
   authenticated tmSecurityName of the principal is derived using the
   snmpTlstmCertToTSNTable.  This table allows mapping of incoming
   connections to tmSecurityNames through defined transformations.  The
   transformations defined in the SNMP-TLS-TM-MIB include:

   o  Mapping a certificate's subjectAltName or CommonName components to
      a tmSecurityName, or

   o  Mapping a certificate's fingerprint value to a directly specified
      tmSecurityName

   As an implementation hint: implementations may choose to discard any
   connections for which no potential snmpTlstmCertToTSNTable mapping
   exists before performing certificate verification to avoid expending
   computational resources associated with certificate verification.

   Deployments SHOULD map the "subjectAltName" component of X.509
   certificates to the TLSTM specific tmSecurityNames.  The
   authenticated identity can be obtained by the TLS Transport Model by
   extracting the subjectAltName(s) from the peer's certificate.  The
   receiving application will then have an appropriate tmSecurityName
   for use by other SNMPv3 components like an access control model.

   An example of this type of mapping setup can be found in Appendix A.

   This tmSecurityName may be later translated from a TLSTM specific
   tmSecurityName to an SNMP engine securityName by the security model.
   A security model, like the TSM security model [RFC5591], may perform
   an identity mapping or a more complex mapping to derive the
   securityName from the tmSecurityName offered by the TLS Transport
   Model.

   The standard View-Based Access Control Model (VACM) access control
   model constrains securityNames to be 32 octets or less in length.  A
   TLSTM generated tmSecurityName, possibly in combination with a
   messaging or security model that increases the length of the
   securityName, might cause the securityName length to exceed 32
   octets.  For example, a 32-octet tmSecurityName derived from an IPv6
   address, paired with a TSM prefix, will generate a 36-octet
   securityName.  Such a securityName will not be able to be used with
   standard VACM or TARGET MIB modules.  Operators should be careful to
   select algorithms and subjectAltNames to avoid this situation.





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   A pictorial view of the complete transformation process (using the
   TSM security model for the example) is shown below:

    +-------------+     +-------+                   +-----+
    | Certificate |     |       |                   |     |
    |    Path     |     | TLSTM |  tmSecurityName   | TSM |
    | Validation  | --> |       | ----------------->|     |
    +-------------+     +-------+                   +-----+
                                                        |
                                                        | securityName
                                                        V
                                                    +-------------+
                                                    | application |
                                                    +-------------+

4.2.  (D)TLS Usage

   (D)TLS MUST negotiate a cipher_suite that uses X.509 certificates for
   authentication, and MUST authenticate both the client and the server.
   The mandatory-to-implement cipher_suite is specified in the TLS
   specification [RFC5246].

   TLSTM verifies the certificates when the connection is opened (see
   Section 5.3).  For this reason, TLS renegotiation with different
   certificates MUST NOT be done.  That is, implementations MUST either
   disable renegotiation completely (RECOMMENDED), or they MUST present
   the same certificate during renegotiation (and MUST verify that the
   other end presented the same certificate).

   For DTLS over UDP, each SNMP message MUST be placed in a single UDP
   datagram; it MAY be split to multiple DTLS records.  In other words,
   if a single datagram contains multiple DTLS application_data records,
   they are concatenated when received.  The TLSTM implementation SHOULD
   return an error if the SNMP message does not fit in the UDP datagram,
   and thus cannot be sent.

   For DTLS over UDP, the DTLS server implementation MUST support DTLS
   cookies ([RFC4347] already requires that clients support DTLS
   cookies).  Implementations are not required to perform the cookie
   exchange for every DTLS handshake; however, enabling it by default is
   RECOMMENDED.

   For DTLS, replay protection MUST be used.








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4.3.  SNMP Services

   This section describes the services provided by the TLS Transport
   Model with their inputs and outputs.  The services are between the
   Transport Model and the Dispatcher.

   The services are described as primitives of an abstract service
   interface (ASI) and the inputs and outputs are described as abstract
   data elements as they are passed in these abstract service
   primitives.

4.3.1.  SNMP Services for an Outgoing Message

   The Dispatcher passes the information to the TLS Transport Model
   using the ASI defined in the Transport Subsystem:

      statusInformation =
      sendMessage(
      IN   destTransportDomain           -- transport domain to be used
      IN   destTransportAddress          -- transport address to be used
      IN   outgoingMessage               -- the message to send
      IN   outgoingMessageLength         -- its length
      IN   tmStateReference              -- reference to transport state
       )

   The abstract data elements returned from or passed as parameters into
   the abstract service primitives are as follows:

   statusInformation:  An indication of whether the sending of the
      message was successful.  If not, it is an indication of the
      problem.

   destTransportDomain:  The transport domain for the associated
      destTransportAddress.  The Transport Model uses this parameter to
      determine the transport type of the associated
      destTransportAddress.  This document specifies the
      snmpTLSTCPDomain and the snmpDTLSUDPDomain transport domains.

   destTransportAddress:  The transport address of the destination TLS
      Transport Model in a format specified by the SnmpTLSAddress
      TEXTUAL-CONVENTION.

   outgoingMessage:  The outgoing message to send to (D)TLS for
      encapsulation and transmission.

   outgoingMessageLength:  The length of the outgoingMessage.





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   tmStateReference:  A reference used to pass model-specific and
      mechanism-specific parameters between the Transport Subsystem and
      transport-aware Security Models.

4.3.2.  SNMP Services for an Incoming Message

   The TLS Transport Model processes the received message from the
   network using the (D)TLS service and then passes it to the Dispatcher
   using the following ASI:

      statusInformation =
      receiveMessage(
      IN   transportDomain               -- origin transport domain
      IN   transportAddress              -- origin transport address
      IN   incomingMessage               -- the message received
      IN   incomingMessageLength         -- its length
      IN   tmStateReference              -- reference to transport state
       )

   The abstract data elements returned from or passed as parameters into
   the abstract service primitives are as follows:

   statusInformation:  An indication of whether the passing of the
      message was successful.  If not, it is an indication of the
      problem.

   transportDomain:  The transport domain for the associated
      transportAddress.  This document specifies the snmpTLSTCPDomain
      and the snmpDTLSUDPDomain transport domains.

   transportAddress:  The transport address of the source of the
      received message in a format specified by the SnmpTLSAddress
      TEXTUAL-CONVENTION.

   incomingMessage:  The whole SNMP message after being processed by
      (D)TLS.

   incomingMessageLength:  The length of the incomingMessage.

   tmStateReference:  A reference used to pass model-specific and
      mechanism-specific parameters between the Transport Subsystem and
      transport-aware Security Models.









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4.4.  Cached Information and References

   When performing SNMP processing, there are two levels of state
   information that may need to be retained: the immediate state linking
   a request-response pair, and potentially longer-term state relating
   to transport and security.  "Transport Subsystem for the Simple
   Network Management Protocol (SNMP)" [RFC5590] defines general
   requirements for caches and references.

4.4.1.  TLS Transport Model Cached Information

   The TLS Transport Model has specific responsibilities regarding the
   cached information.  See the Elements of Procedure in Section 5 for
   detailed processing instructions on the use of the tmStateReference
   fields by the TLS Transport Model.

4.4.1.1.  tmSecurityName

   The tmSecurityName MUST be a human-readable name (in snmpAdminString
   format) representing the identity that has been set according to the
   procedures in Section 5.  The tmSecurityName MUST be constant for all
   traffic passing through a single TLSTM session.  Messages MUST NOT be
   sent through an existing (D)TLS connection that was established using
   a different tmSecurityName.

   On the (D)TLS server side of a connection, the tmSecurityName is
   derived using the procedures described in Section 5.3.2 and the SNMP-
   TLS-TM-MIB's snmpTlstmCertToTSNTable DESCRIPTION clause.

   On the (D)TLS client side of a connection, the tmSecurityName is
   presented to the TLS Transport Model by the security model through
   the tmStateReference.  This tmSecurityName is typically a copy of or
   is derived from the securityName that was passed by application
   (possibly because of configuration specified in the SNMP-TARGET-MIB).
   The Security Model likely derived the tmSecurityName from the
   securityName presented to the Security Model by the application
   (possibly because of configuration specified in the SNMP-TARGET-MIB).

   Transport-Model-aware security models derive tmSecurityName from a
   securityName, possibly configured in MIB modules for notifications
   and access controls.  Transport Models SHOULD use predictable
   tmSecurityNames so operators will know what to use when configuring
   MIB modules that use securityNames derived from tmSecurityNames.  The
   TLSTM generates predictable tmSecurityNames based on the
   configuration found in the SNMP-TLS-TM-MIB's snmpTlstmCertToTSNTable
   and relies on the network operators to have configured this table
   appropriately.




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4.4.1.2.  tmSessionID

   The tmSessionID MUST be recorded per message at the time of receipt.
   When tmSameSecurity is set, the recorded tmSessionID can be used to
   determine whether the (D)TLS connection available for sending a
   corresponding outgoing message is the same (D)TLS connection as was
   used when receiving the incoming message (e.g., a response to a
   request).

4.4.1.3.  Session State

   The per-session state that is referenced by tmStateReference may be
   saved across multiple messages in a Local Configuration Datastore.
   Additional session/connection state information might also be stored
   in a Local Configuration Datastore.

5.  Elements of Procedure

   Abstract service interfaces have been defined by [RFC3411] and
   further augmented by [RFC5590] to describe the conceptual data flows
   between the various subsystems within an SNMP entity.  The TLSTM uses
   some of these conceptual data flows when communicating between
   subsystems.

   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 gets discarded, the
   message-state information should also be released.  If state
   information is available when a session is closed, the session state
   information should also be released.  Sensitive information, like
   cryptographic keys, should be overwritten appropriately prior to
   being released.

   An error indication in statusInformation will typically include the
   Object Identifier (OID) and value for an incremented error counter.
   This may be accompanied by the requested securityLevel and the
   tmStateReference.  Per-message context information is not accessible
   to Transport Models, so for the returned counter OID and value,
   contextEngine would be set to the local value of snmpEngineID and
   contextName to the default context for error counters.

5.1.  Procedures for an Incoming Message

   This section describes the procedures followed by the (D)TLS
   Transport Model when it receives a (D)TLS protected packet.  The
   required functionality is broken into two different sections.





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   Section 5.1.1 describes the processing required for de-multiplexing
   multiple DTLS connections, which is specifically needed for DTLS over
   UDP sessions.  It is assumed that TLS protocol implementations
   already provide appropriate message demultiplexing.

   Section 5.1.2 describes the transport processing required once the
   (D)TLS processing has been completed.  This will be needed for all
   (D)TLS-based connections.

5.1.1.  DTLS over UDP Processing for Incoming Messages

   Demultiplexing of incoming packets into separate DTLS sessions MUST
   be implemented.  For connection-oriented transport protocols, such as
   TCP, the transport protocol takes care of demultiplexing incoming
   packets to the right connection.  For DTLS over UDP, this
   demultiplexing will either need to be done within the DTLS
   implementation, if supported, or by the TLSTM implementation.

   Like TCP, DTLS over UDP uses the four-tuple <source IP, destination
   IP, source port, destination port> for identifying the connection
   (and relevant DTLS connection state).  This means that when
   establishing a new session, implementations MUST use a different UDP
   source port number for each active connection to a remote destination
   IP-address/port-number combination to ensure the remote entity can
   disambiguate between multiple connections.

   If demultiplexing received UDP datagrams to DTLS connection state is
   done by the TLSTM implementation (instead of the DTLS
   implementation), the steps below describe one possible method to
   accomplish this.

   The important output results from the steps in this process are the
   remote transport address, incomingMessage, incomingMessageLength, and
   the tlstmSessionID.

   1)  The TLS Transport Model examines the raw UDP message, in an
       implementation-dependent manner.

   2)  The TLS Transport Model queries the Local Configuration Datastore
       (LCD) (see [RFC3411], Section 3.4.2) using the transport
       parameters (source and destination IP addresses and ports) to
       determine if a session already exists.

       2a)  If a matching entry in the LCD does not exist, then the UDP
            packet is passed to the DTLS implementation for processing.
            If the DTLS implementation decides to continue with the
            connection and allocate state for it, it returns a new DTLS
            connection handle (an implementation dependent detail).  In



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            this case, TLSTM selects a new tlstmSessionId, and caches
            this and the DTLS connection handle as a new entry in the
            LCD (indexed by the transport parameters).  If the DTLS
            implementation returns an error or does not allocate
            connection state (which can happen with the stateless cookie
            exchange), processing stops.

       2b)  If a session does exist in the LCD, then its DTLS connection
            handle (an implementation dependent detail) and its
            tlstmSessionId is extracted from the LCD.  The UDP packet
            and the connection handle are passed to the DTLS
            implementation.  If the DTLS implementation returns success
            but does not return an incomingMessage and an
            incomingMessageLength, then processing stops (this is the
            case when the UDP datagram contained DTLS handshake
            messages, for example).  If the DTLS implementation returns
            an error, then processing stops.

   3)  Retrieve the incomingMessage and an incomingMessageLength from
       DTLS.  These results and the tlstmSessionID are used below in
       Section 5.1.2 to complete the processing of the incoming message.

5.1.2.  Transport Processing for Incoming SNMP Messages

   The procedures in this section describe how the TLS Transport Model
   should process messages that have already been properly extracted
   from the (D)TLS stream.  Note that care must be taken when processing
   messages originating from either TLS or DTLS to ensure they're
   complete and single.  For example, multiple SNMP messages can be
   passed through a single DTLS message and partial SNMP messages may be
   received from a TLS stream.  These steps describe the processing of a
   singular SNMP message after it has been delivered from the (D)TLS
   stream.

   1)  Determine the tlstmSessionID for the incoming message.  The
       tlstmSessionID MUST be a unique session identifier for this
       (D)TLS connection.  The contents and format of this identifier
       are implementation dependent as long as it is unique to the
       session.  A session identifier MUST NOT be reused until all
       references to it are no longer in use.  The tmSessionID is equal
       to the tlstmSessionID discussed in Section 5.1.1. tmSessionID
       refers to the session identifier when stored in the
       tmStateReference and tlstmSessionID refers to the session
       identifier when stored in the LCD.  They MUST always be equal
       when processing a given session's traffic.






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       If this is the first message received through this session, and
       the session does not have an assigned tlstmSessionID yet, then
       the snmpTlstmSessionAccepts counter is incremented and a
       tlstmSessionID for the session is created.  This will only happen
       on the server side of a connection because a client would have
       already assigned a tlstmSessionID during the openSession()
       invocation.  Implementations may have performed the procedures
       described in Section 5.3.2 prior to this point or they may
       perform them now, but the procedures described in Section 5.3.2
       MUST be performed before continuing beyond this point.

   2)  Create a tmStateReference cache for the subsequent reference and
       assign the following values within it:

       tmTransportDomain  = snmpTLSTCPDomain or snmpDTLSUDPDomain as
          appropriate.

       tmTransportAddress  = The address from which the message
          originated.

       tmSecurityLevel  = The derived tmSecurityLevel for the session,
          as discussed in Sections 3.1.2 and 5.3.

       tmSecurityName  = The derived tmSecurityName for the session as
          discussed in Section 5.3.  This value MUST be constant during
          the lifetime of the session.

       tmSessionID  = The tlstmSessionID described in step 1 above.

   3)  The incomingMessage and incomingMessageLength are assigned values
       from the (D)TLS processing.

   4)  The TLS Transport Model passes the transportDomain,
       transportAddress, incomingMessage, and incomingMessageLength to
       the Dispatcher using the receiveMessage ASI:

      statusInformation =
      receiveMessage(
      IN   transportDomain     -- snmpTLSTCPDomain or snmpDTLSUDPDomain,
      IN   transportAddress    -- address for the received message
      IN   incomingMessage        -- the whole SNMP message from (D)TLS
      IN   incomingMessageLength  -- the length of the SNMP message
      IN   tmStateReference    -- transport info
       )







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5.2.  Procedures for an Outgoing SNMP Message

   The Dispatcher sends a message to the TLS Transport Model using the
   following ASI:

      statusInformation =
      sendMessage(
      IN   destTransportDomain           -- transport domain to be used
      IN   destTransportAddress          -- transport address to be used
      IN   outgoingMessage               -- the message to send
      IN   outgoingMessageLength         -- its length
      IN   tmStateReference              -- transport info
      )

   This section describes the procedure followed by the TLS Transport
   Model whenever it is requested through this ASI to send a message.

   1)  If tmStateReference does not refer to a cache containing values
       for tmTransportDomain, tmTransportAddress, tmSecurityName,
       tmRequestedSecurityLevel, and tmSameSecurity, then increment the
       snmpTlstmSessionInvalidCaches counter, discard the message, and
       return the error indication in the statusInformation.  Processing
       of this message stops.

   2)  Extract the tmSessionID, tmTransportDomain, tmTransportAddress,
       tmSecurityName, tmRequestedSecurityLevel, and tmSameSecurity
       values from the tmStateReference.  Note: the tmSessionID value
       may be undefined if no session exists yet over which the message
       can be sent.

   3)  If tmSameSecurity is true and tmSessionID is either undefined or
       refers to a session that is no longer open, then increment the
       snmpTlstmSessionNoSessions counter, discard the message, and
       return the error indication in the statusInformation.  Processing
       of this message stops.

   4)  If tmSameSecurity is false and tmSessionID refers to a session
       that is no longer available, then an implementation SHOULD open a
       new session, using the openSession() ASI (described in greater
       detail in step 5b).  Instead of opening a new session an
       implementation MAY return an snmpTlstmSessionNoSessions error to
       the calling module and stop the processing of the message.

   5)  If tmSessionID is undefined, then use tmTransportDomain,
       tmTransportAddress, tmSecurityName, and tmRequestedSecurityLevel
       to see if there is a corresponding entry in the LCD suitable to
       send the message over.




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       5a)  If there is a corresponding LCD entry, then this session
            will be used to send the message.

       5b)  If there is no corresponding LCD entry, then open a session
            using the openSession() ASI (discussed further in
            Section 5.3.1).  Implementations MAY wish to offer message
            buffering to prevent redundant openSession() calls for the
            same cache entry.  If an error is returned from
            openSession(), then discard the message, discard the
            tmStateReference, increment the snmpTlstmSessionOpenErrors,
            return an error indication to the calling module, and stop
            the processing of the message.

   6)  Using either the session indicated by the tmSessionID (if there
       was one) or the session resulting from a previous step (4 or 5),
       pass the outgoingMessage to (D)TLS for encapsulation and
       transmission.

5.3.  Establishing or Accepting a Session

   Establishing a (D)TLS connection as either a client or a server
   requires slightly different processing.  The following two sections
   describe the necessary processing steps.

5.3.1.  Establishing a Session as a Client

   The TLS Transport Model provides the following primitive for use by a
   client to establish a new (D)TLS connection:

   statusInformation =           -- errorIndication or success
   openSession(
   IN   tmStateReference         -- transport information to be used
   OUT  tmStateReference         -- transport information to be used
   IN   maxMessageSize           -- of the sending SNMP entity
   )

   The following describes the procedure to follow when establishing an
   SNMP over a (D)TLS connection between SNMP engines for exchanging
   SNMP messages.  This process is followed by any SNMP client's engine
   when establishing a session for subsequent use.

   This procedure MAY be done automatically for an SNMP application that
   initiates a transaction, such as a command generator, a notification
   originator, or a proxy forwarder.

   1)  The snmpTlstmSessionOpens counter is incremented.





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   2)  The client selects the appropriate certificate and cipher_suites
       for the key agreement based on the tmSecurityName and the
       tmRequestedSecurityLevel for the session.  For sessions being
       established as a result of an SNMP-TARGET-MIB based operation,
       the certificate will potentially have been identified via the
       snmpTlstmParamsTable mapping and the cipher_suites will have to
       be taken from a system-wide or implementation-specific
       configuration.  If no row in the snmpTlstmParamsTable exists,
       then implementations MAY choose to establish the connection using
       a default client certificate available to the application.
       Otherwise, the certificate and appropriate cipher_suites will
       need to be passed to the openSession() ASI as supplemental
       information or configured through an implementation-dependent
       mechanism.  It is also implementation-dependent and possibly
       policy-dependent how tmRequestedSecurityLevel will be used to
       influence the security capabilities provided by the (D)TLS
       connection.  However this is done, the security capabilities
       provided by (D)TLS MUST be at least as high as the level of
       security indicated by the tmRequestedSecurityLevel parameter.
       The actual security level of the session is reported in the
       tmStateReference cache as tmSecurityLevel.  For (D)TLS to provide
       strong authentication, each principal acting as a command
       generator SHOULD have its own certificate.

   3)  Using the destTransportDomain and destTransportAddress values,
       the client will initiate the (D)TLS handshake protocol to
       establish session keys for message integrity and encryption.

       If the attempt to establish a session is unsuccessful, then
       snmpTlstmSessionOpenErrors is incremented, an error indication is
       returned, and processing stops.  If the session failed to open
       because the presented server certificate was unknown or invalid,
       then the snmpTlstmSessionUnknownServerCertificate or
       snmpTlstmSessionInvalidServerCertificates MUST be incremented and
       an snmpTlstmServerCertificateUnknown or
       snmpTlstmServerInvalidCertificate notification SHOULD be sent as
       appropriate.  Reasons for server certificate invalidation
       include, but are not limited to, cryptographic validation
       failures and an unexpected presented certificate identity.

   4)  The (D)TLS client MUST then verify that the (D)TLS server's
       presented certificate is the expected certificate.  The (D)TLS
       client MUST NOT transmit SNMP messages until the server
       certificate has been authenticated, the client certificate has
       been transmitted, and the TLS connection has been fully
       established.





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       If the connection is being established from a configuration based
       on SNMP-TARGET-MIB configuration, then the snmpTlstmAddrTable
       DESCRIPTION clause describes how the verification is done (using
       either a certificate fingerprint, or an identity authenticated
       via certification path validation).

       If the connection is being established for reasons other than
       configuration found in the SNMP-TARGET-MIB, then configuration
       and procedures outside the scope of this document should be
       followed.  Configuration mechanisms SHOULD be similar in nature
       to those defined in the snmpTlstmAddrTable to ensure consistency
       across management configuration systems.  For example, a command-
       line tool for generating SNMP GETs might support specifying
       either the server's certificate fingerprint or the expected host
       name as a command-line argument.

   5)  (D)TLS provides assurance that the authenticated identity has
       been signed by a trusted configured Certification Authority.  If
       verification of the server's certificate fails in any way (for
       example, because of failures in cryptographic verification or the
       presented identity did not match the expected named entity), then
       the session establishment MUST fail, and the
       snmpTlstmSessionInvalidServerCertificates object is incremented.
       If the session cannot be opened for any reason at all, including
       cryptographic verification failures and snmpTlstmCertToTSNTable
       lookup failures, then the snmpTlstmSessionOpenErrors counter is
       incremented and processing stops.

   6)  The TLSTM-specific session identifier (tlstmSessionID) is set in
       the tmSessionID of the tmStateReference passed to the TLS
       Transport Model to indicate that the session has been established
       successfully and to point to a specific (D)TLS connection for
       future use.  The tlstmSessionID is also stored in the LCD for
       later lookup during processing of incoming messages
       (Section 5.1.2).

5.3.2.  Accepting a Session as a Server

   A (D)TLS server should accept new session connections from any client
   for which it is able to verify the client's credentials.  This is
   done by authenticating the client's presented certificate through a
   certificate path validation process (e.g., [RFC5280]) or through
   certificate fingerprint verification using fingerprints configured in
   the snmpTlstmCertToTSNTable.  Afterward, the server will determine
   the identity of the remote entity using the following procedures.






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   The (D)TLS server identifies the authenticated identity from the
   (D)TLS client's principal certificate using configuration information
   from the snmpTlstmCertToTSNTable mapping table.  The (D)TLS server
   MUST request and expect a certificate from the client and MUST NOT
   accept SNMP messages over the (D)TLS connection until the client has
   sent a certificate and it has been authenticated.  The resulting
   derived tmSecurityName is recorded in the tmStateReference cache as
   tmSecurityName.  The details of the lookup process are fully
   described in the DESCRIPTION clause of the snmpTlstmCertToTSNTable
   MIB object.  If any verification fails in any way (for example,
   because of failures in cryptographic verification or because of the
   lack of an appropriate row in the snmpTlstmCertToTSNTable), then the
   session establishment MUST fail, and the
   snmpTlstmSessionInvalidClientCertificates object is incremented.  If
   the session cannot be opened for any reason at all, including
   cryptographic verification failures, then the
   snmpTlstmSessionOpenErrors counter is incremented and processing
   stops.

   Servers that wish to support multiple principals at a particular port
   SHOULD make use of a (D)TLS extension that allows server-side
   principal selection like the Server Name Indication extension defined
   in Section 3.1 of [RFC4366].  Supporting this will allow, for
   example, sending notifications to a specific principal at a given TCP
   or UDP port.

5.4.  Closing a Session

   The TLS Transport Model provides the following primitive to close a
   session:

   statusInformation =
   closeSession(
   IN  tmSessionID        -- session ID of the session to be closed
   )

   The following describes the procedure to follow to close a session
   between a client and server.  This process is followed by any SNMP
   engine closing the corresponding SNMP session.

   1)  Increment either the snmpTlstmSessionClientCloses or the
       snmpTlstmSessionServerCloses counter as appropriate.

   2)  Look up the session using the tmSessionID.

   3)  If there is no open session associated with the tmSessionID, then
       closeSession processing is completed.




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   4)  Have (D)TLS close the specified connection.  This MUST include
       sending a close_notify TLS Alert to inform the other side that
       session cleanup may be performed.

6.  MIB Module Overview

   This MIB module provides management of the TLS Transport Model.  It
   defines needed textual conventions, statistical counters,
   notifications, and configuration infrastructure necessary for session
   establishment.  Example usage of the configuration tables can be
   found in Appendix A.

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 module can be
   found summarized at http://www.ops.ietf.org/mib-common-tcs.html.

   This module defines the following new Textual Conventions:

   o  A new TransportAddress format for describing (D)TLS connection
      addressing requirements.

   o  A certificate fingerprint allowing MIB module objects to
      generically refer to a stored X.509 certificate using a
      cryptographic hash as a reference pointer.

6.3.  Statistical Counters

   The SNMP-TLS-TM-MIB defines counters that provide network management
   stations with information about session usage and potential errors
   that a device may be experiencing.

6.4.  Configuration Tables

   The SNMP-TLS-TM-MIB defines configuration tables that an
   administrator can use for configuring a device for sending and
   receiving SNMP messages over (D)TLS.  In particular, there are MIB
   tables that extend the SNMP-TARGET-MIB for configuring (D)TLS
   certificate usage and a MIB table for mapping incoming (D)TLS client
   certificates to SNMPv3 tmSecurityNames.




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6.4.1.  Notifications

   The SNMP-TLS-TM-MIB defines notifications to alert management
   stations when a (D)TLS connection fails because a server's presented
   certificate did not meet an expected value
   (snmpTlstmServerCertificateUnknown) or because cryptographic
   validation failed (snmpTlstmServerInvalidCertificate).

6.5.  Relationship to Other MIB Modules

   Some management objects defined in other MIB modules are applicable
   to an entity implementing the TLS Transport Model.  In particular, it
   is assumed that an entity implementing the SNMP-TLS-TM-MIB will
   implement the SNMPv2-MIB [RFC3418], the SNMP-FRAMEWORK-MIB [RFC3411],
   the SNMP-TARGET-MIB [RFC3413], the SNMP-NOTIFICATION-MIB [RFC3413],
   and the SNMP-VIEW-BASED-ACM-MIB [RFC3415].

   The SNMP-TLS-TM-MIB module contained in this document is for managing
   TLS Transport Model information.

6.5.1.  MIB Modules Required for IMPORTS

   The SNMP-TLS-TM-MIB module imports items from SNMPv2-SMI [RFC2578],
   SNMPv2-TC [RFC2579], SNMP-FRAMEWORK-MIB [RFC3411], SNMP-TARGET-MIB
   [RFC3413], and SNMPv2-CONF [RFC2580].

7.  MIB Module Definition

SNMP-TLS-TM-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE,
    OBJECT-IDENTITY, mib-2, snmpDomains,
    Counter32, Unsigned32, Gauge32, NOTIFICATION-TYPE
      FROM SNMPv2-SMI                 -- RFC 2578 or any update thereof
    TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType,
    AutonomousType
      FROM SNMPv2-TC                  -- RFC 2579 or any update thereof
    MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
      FROM SNMPv2-CONF                -- RFC 2580 or any update thereof
    SnmpAdminString
      FROM SNMP-FRAMEWORK-MIB         -- RFC 3411 or any update thereof
    snmpTargetParamsName, snmpTargetAddrName
      FROM SNMP-TARGET-MIB            -- RFC 3413 or any update thereof
    ;

snmpTlstmMIB MODULE-IDENTITY
    LAST-UPDATED "201107190000Z"



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    ORGANIZATION "ISMS Working Group"
    CONTACT-INFO "WG-EMail:   isms@lists.ietf.org
                  Subscribe:  isms-request@lists.ietf.org

                  Chairs:
                     Juergen Schoenwaelder
                     Jacobs University Bremen
                     Campus Ring 1
                     28725 Bremen
                     Germany
                     +49 421 200-3587
                     j.schoenwaelder@jacobs-university.de

                     Russ Mundy
                     SPARTA, Inc.
                     7110 Samuel Morse Drive
                     Columbia, MD  21046
                     USA

                  Editor:
                     Wes Hardaker
                     SPARTA, Inc.
                     P.O. Box 382
                     Davis, CA  95617
                     USA
                     ietf@hardakers.net
                  "

    DESCRIPTION  "
        The TLS Transport Model MIB

        Copyright (c) 2010-2011 IETF Trust and the persons identified
        as authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info)."

       REVISION     "201107190000Z"
       DESCRIPTION  "This version of this MIB module is part of
                     RFC 6353; see the RFC itself for full legal
                     notices.  The only change was to introduce
                     new wording to reflect require changes for
                     IDNA addresses in the SnmpTLSAddress TC."




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       REVISION     "201005070000Z"
       DESCRIPTION  "This version of this MIB module is part of
                     RFC 5953; see the RFC itself for full legal
                     notices."

    ::= { mib-2 198 }

-- ************************************************
-- subtrees of the SNMP-TLS-TM-MIB
-- ************************************************

snmpTlstmNotifications OBJECT IDENTIFIER ::= { snmpTlstmMIB 0 }
snmpTlstmIdentities    OBJECT IDENTIFIER ::= { snmpTlstmMIB 1 }
snmpTlstmObjects       OBJECT IDENTIFIER ::= { snmpTlstmMIB 2 }
snmpTlstmConformance   OBJECT IDENTIFIER ::= { snmpTlstmMIB 3 }

-- ************************************************
-- snmpTlstmObjects - Objects
-- ************************************************

snmpTLSTCPDomain OBJECT-IDENTITY
    STATUS      current
    DESCRIPTION
        "The SNMP over TLS via TCP transport domain.  The
        corresponding transport address is of type SnmpTLSAddress.

        The securityName prefix to be associated with the
        snmpTLSTCPDomain is 'tls'.  This prefix may be used by
        security models or other components to identify which secure
        transport infrastructure authenticated a securityName."
    REFERENCE
      "RFC 2579: Textual Conventions for SMIv2"
    ::= { snmpDomains 8 }

snmpDTLSUDPDomain OBJECT-IDENTITY
    STATUS      current
    DESCRIPTION
        "The SNMP over DTLS via UDP transport domain.  The
        corresponding transport address is of type SnmpTLSAddress.

        The securityName prefix to be associated with the
        snmpDTLSUDPDomain is 'dtls'.  This prefix may be used by
        security models or other components to identify which secure
        transport infrastructure authenticated a securityName."
    REFERENCE
      "RFC 2579: Textual Conventions for SMIv2"
    ::= { snmpDomains 9 }




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SnmpTLSAddress ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "1a"
    STATUS       current
    DESCRIPTION
        "Represents an IPv4 address, an IPv6 address, or a
         US-ASCII-encoded hostname and port number.

        An IPv4 address must be in dotted decimal format followed by a
        colon ':' (US-ASCII character 0x3A) and a decimal port number
        in US-ASCII.

        An IPv6 address must be a colon-separated format (as described
        in RFC 5952), surrounded by square brackets ('[', US-ASCII
        character 0x5B, and ']', US-ASCII character 0x5D), followed by
        a colon ':' (US-ASCII character 0x3A) and a decimal port number
        in US-ASCII.

        A hostname is always in US-ASCII (as per RFC 1123);
        internationalized hostnames are encoded as A-labels as specified
        in  RFC 5890.  The hostname is followed by a
        colon ':' (US-ASCII character 0x3A) and a decimal port number
        in US-ASCII.  The name SHOULD be fully qualified whenever
        possible.

        Values of this textual convention may not be directly usable
        as transport-layer addressing information, and may require
        run-time resolution.  As such, applications that write them
        must be prepared for handling errors if such values are not
        supported, or cannot be resolved (if resolution occurs at the
        time of the management operation).

        The DESCRIPTION clause of TransportAddress objects that may
        have SnmpTLSAddress values must fully describe how (and
        when) such names are to be resolved to IP addresses and vice
        versa.

        This textual convention SHOULD NOT be used directly in object
        definitions since it restricts addresses to a specific
        format.  However, if it is used, it MAY be used either on its
        own or in conjunction with TransportAddressType or
        TransportDomain as a pair.

        When this textual convention is used as a syntax of an index
        object, there may be issues with the limit of 128
        sub-identifiers specified in SMIv2 (STD 58).  It is RECOMMENDED
        that all MIB documents using this textual convention make
        explicit any limitations on index component lengths that
        management software must observe.  This may be done either by



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        including SIZE constraints on the index components or by
        specifying applicable constraints in the conceptual row
        DESCRIPTION clause or in the surrounding documentation."
    REFERENCE
      "RFC 1123: Requirements for Internet Hosts - Application and
                 Support
       RFC 5890: Internationalized Domain Names for Applications (IDNA):
                 Definitions and Document Framework
       RFC 5952: A Recommendation for IPv6 Address Text Representation
      "
    SYNTAX       OCTET STRING (SIZE (1..255))

SnmpTLSFingerprint ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "1x:1x"
    STATUS       current
    DESCRIPTION
       "A fingerprint value that can be used to uniquely reference
       other data of potentially arbitrary length.

       An SnmpTLSFingerprint value is composed of a 1-octet hashing
       algorithm identifier followed by the fingerprint value.  The
       octet value encoded is taken from the IANA TLS HashAlgorithm
       Registry (RFC 5246).  The remaining octets are filled using the
       results of the hashing algorithm.

       This TEXTUAL-CONVENTION allows for a zero-length (blank)
       SnmpTLSFingerprint value for use in tables where the
       fingerprint value may be optional.  MIB definitions or
       implementations may refuse to accept a zero-length value as
       appropriate."
       REFERENCE "RFC 5246: The Transport Layer
                  Security (TLS) Protocol Version 1.2
                  http://www.iana.org/assignments/tls-parameters/
       "
    SYNTAX OCTET STRING (SIZE (0..255))

-- Identities for use in the snmpTlstmCertToTSNTable

snmpTlstmCertToTSNMIdentities OBJECT IDENTIFIER
    ::= { snmpTlstmIdentities 1 }

snmpTlstmCertSpecified OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "Directly specifies the tmSecurityName to be used for
                  this certificate.  The value of the tmSecurityName
                  to use is specified in the snmpTlstmCertToTSNData
                  column.  The snmpTlstmCertToTSNData column must
                  contain a non-zero length SnmpAdminString compliant



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                  value or the mapping described in this row must be
                  considered a failure."
    ::= { snmpTlstmCertToTSNMIdentities 1 }

snmpTlstmCertSANRFC822Name OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "Maps a subjectAltName's rfc822Name to a
                  tmSecurityName.  The local part of the rfc822Name is
                  passed unaltered but the host-part of the name must
                  be passed in lowercase.  This mapping results in a
                  1:1 correspondence between equivalent subjectAltName
                  rfc822Name values and tmSecurityName values except
                  that the host-part of the name MUST be passed in
                  lowercase.

                  Example rfc822Name Field:  FooBar@Example.COM
                  is mapped to tmSecurityName: FooBar@example.com."
    ::= { snmpTlstmCertToTSNMIdentities 2 }

snmpTlstmCertSANDNSName OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "Maps a subjectAltName's dNSName to a
                  tmSecurityName after first converting it to all
                  lowercase (RFC 5280 does not specify converting to
                  lowercase so this involves an extra step).  This
                  mapping results in a 1:1 correspondence between
                  subjectAltName dNSName values and the tmSecurityName
                  values."
    REFERENCE "RFC 5280 - Internet X.509 Public Key Infrastructure
                         Certificate and Certificate Revocation
                         List (CRL) Profile."
    ::= { snmpTlstmCertToTSNMIdentities 3 }

snmpTlstmCertSANIpAddress OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "Maps a subjectAltName's iPAddress to a
                  tmSecurityName by transforming the binary encoded
                  address as follows:

                  1) for IPv4, the value is converted into a
                     decimal-dotted quad address (e.g., '192.0.2.1').

                  2) for IPv6 addresses, the value is converted into a
                     32-character all lowercase hexadecimal string
                     without any colon separators.






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                  This mapping results in a 1:1 correspondence between
                  subjectAltName iPAddress values and the
                  tmSecurityName values.

                  The resulting length of an encoded IPv6 address is
                  the maximum length supported by the View-Based
                  Access Control Model (VACM).  Using both the
                  Transport Security Model's support for transport
                  prefixes (see the SNMP-TSM-MIB's
                  snmpTsmConfigurationUsePrefix object for details)
                  will result in securityName lengths that exceed what
                  VACM can handle."
    ::= { snmpTlstmCertToTSNMIdentities 4 }

snmpTlstmCertSANAny OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "Maps any of the following fields using the
                  corresponding mapping algorithms:

                  |------------+----------------------------|
                  | Type       | Algorithm                  |
                  |------------+----------------------------|
                  | rfc822Name | snmpTlstmCertSANRFC822Name |
                  | dNSName    | snmpTlstmCertSANDNSName    |
                  | iPAddress  | snmpTlstmCertSANIpAddress  |
                  |------------+----------------------------|

                  The first matching subjectAltName value found in the
                  certificate of the above types MUST be used when
                  deriving the tmSecurityName.  The mapping algorithm
                  specified in the 'Algorithm' column MUST be used to
                  derive the tmSecurityName.

                  This mapping results in a 1:1 correspondence between
                  subjectAltName values and tmSecurityName values.  The
                  three sub-mapping algorithms produced by this
                  combined algorithm cannot produce conflicting
                  results between themselves."
    ::= { snmpTlstmCertToTSNMIdentities 5 }

snmpTlstmCertCommonName OBJECT-IDENTITY
    STATUS        current

    DESCRIPTION  "Maps a certificate's CommonName to a tmSecurityName
                  after converting it to a UTF-8 encoding.  The usage
                  of CommonNames is deprecated and users are
                  encouraged to use subjectAltName mapping methods
                  instead.  This mapping results in a 1:1



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                  correspondence between certificate CommonName values
                  and tmSecurityName values."
    ::= { snmpTlstmCertToTSNMIdentities 6 }

-- The snmpTlstmSession Group

snmpTlstmSession           OBJECT IDENTIFIER ::= { snmpTlstmObjects 1 }

snmpTlstmSessionOpens  OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
       "The number of times an openSession() request has been executed
       as a (D)TLS client, regardless of whether it succeeded or
       failed."
    ::= { snmpTlstmSession 1 }

snmpTlstmSessionClientCloses  OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times a closeSession() request has been
        executed as a (D)TLS client, regardless of whether it
        succeeded or failed."
    ::= { snmpTlstmSession 2 }

snmpTlstmSessionOpenErrors  OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an openSession() request failed to open a
        session as a (D)TLS client, for any reason."
    ::= { snmpTlstmSession 3 }

snmpTlstmSessionAccepts  OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
       "The number of times a (D)TLS server has accepted a new
       connection from a client and has received at least one SNMP
       message through it."
    ::= { snmpTlstmSession 4 }





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snmpTlstmSessionServerCloses  OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times a closeSession() request has been
        executed as a (D)TLS server, regardless of whether it
        succeeded or failed."
    ::= { snmpTlstmSession 5 }

snmpTlstmSessionNoSessions  OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an outgoing message was dropped because
        the session associated with the passed tmStateReference was no
        longer (or was never) available."
    ::= { snmpTlstmSession 6 }

snmpTlstmSessionInvalidClientCertificates OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an incoming session was not established
        on a (D)TLS server because the presented client certificate
        was invalid.  Reasons for invalidation include, but are not
        limited to, cryptographic validation failures or lack of a
        suitable mapping row in the snmpTlstmCertToTSNTable."
    ::= { snmpTlstmSession 7 }

snmpTlstmSessionUnknownServerCertificate OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an outgoing session was not established
         on a (D)TLS client because the server certificate presented
         by an SNMP over (D)TLS server was invalid because no
         configured fingerprint or Certification Authority (CA) was
         acceptable to validate it.
         This may result because there was no entry in the
         snmpTlstmAddrTable or because no path could be found to a
         known CA."
    ::= { snmpTlstmSession 8 }





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snmpTlstmSessionInvalidServerCertificates OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an outgoing session was not established
         on a (D)TLS client because the server certificate presented
         by an SNMP over (D)TLS server could not be validated even if
         the fingerprint or expected validation path was known.  That
         is, a cryptographic validation error occurred during
         certificate validation processing.

        Reasons for invalidation include, but are not
        limited to, cryptographic validation failures."
    ::= { snmpTlstmSession 9 }

snmpTlstmSessionInvalidCaches OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of outgoing messages dropped because the
        tmStateReference referred to an invalid cache."
    ::= { snmpTlstmSession 10 }

-- Configuration Objects

snmpTlstmConfig             OBJECT IDENTIFIER ::= { snmpTlstmObjects 2 }

-- Certificate mapping

snmpTlstmCertificateMapping OBJECT IDENTIFIER ::= { snmpTlstmConfig 1 }

snmpTlstmCertToTSNCount OBJECT-TYPE
    SYNTAX      Gauge32
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "A count of the number of entries in the
        snmpTlstmCertToTSNTable."
    ::= { snmpTlstmCertificateMapping 1 }

snmpTlstmCertToTSNTableLastChanged OBJECT-TYPE
    SYNTAX      TimeStamp
    MAX-ACCESS  read-only
    STATUS      current





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    DESCRIPTION
        "The value of sysUpTime.0 when the snmpTlstmCertToTSNTable was
        last modified through any means, or 0 if it has not been
        modified since the command responder was started."
    ::= { snmpTlstmCertificateMapping 2 }

snmpTlstmCertToTSNTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF SnmpTlstmCertToTSNEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "This table is used by a (D)TLS server to map the (D)TLS
        client's presented X.509 certificate to a tmSecurityName.

        On an incoming (D)TLS/SNMP connection, the client's presented
        certificate must either be validated based on an established
        trust anchor, or it must directly match a fingerprint in this
        table.  This table does not provide any mechanisms for
        configuring the trust anchors; the transfer of any needed
        trusted certificates for path validation is expected to occur
        through an out-of-band transfer.

        Once the certificate has been found acceptable (either by path
        validation or directly matching a fingerprint in this table),
        this table is consulted to determine the appropriate
        tmSecurityName to identify with the remote connection.  This
        is done by considering each active row from this table in
        prioritized order according to its snmpTlstmCertToTSNID value.
        Each row's snmpTlstmCertToTSNFingerprint value determines
        whether the row is a match for the incoming connection:

            1) If the row's snmpTlstmCertToTSNFingerprint value
               identifies the presented certificate, then consider the
               row as a successful match.

            2) If the row's snmpTlstmCertToTSNFingerprint value
               identifies a locally held copy of a trusted CA
               certificate and that CA certificate was used to
               validate the path to the presented certificate, then
               consider the row as a successful match.

        Once a matching row has been found, the
        snmpTlstmCertToTSNMapType value can be used to determine how
        the tmSecurityName to associate with the session should be
        determined.  See the snmpTlstmCertToTSNMapType column's
        DESCRIPTION for details on determining the tmSecurityName
        value.  If it is impossible to determine a tmSecurityName from
        the row's data combined with the data presented in the



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        certificate, then additional rows MUST be searched looking for
        another potential match.  If a resulting tmSecurityName mapped
        from a given row is not compatible with the needed
        requirements of a tmSecurityName (e.g., VACM imposes a
        32-octet-maximum length and the certificate derived
        securityName could be longer), then it must be considered an
        invalid match and additional rows MUST be searched looking for
        another potential match.

        If no matching and valid row can be found, the connection MUST
        be closed and SNMP messages MUST NOT be accepted over it.

        Missing values of snmpTlstmCertToTSNID are acceptable and
        implementations should continue to the next highest numbered
        row.  It is recommended that administrators skip index values
        to leave room for the insertion of future rows (for example,
        use values of 10 and 20 when creating initial rows).

        Users are encouraged to make use of certificates with
        subjectAltName fields that can be used as tmSecurityNames so
        that a single root CA certificate can allow all child
        certificate's subjectAltName to map directly to a
        tmSecurityName via a 1:1 transformation.  However, this table
        is flexible to allow for situations where existing deployed
        certificate infrastructures do not provide adequate
        subjectAltName values for use as tmSecurityNames.
        Certificates may also be mapped to tmSecurityNames using the
        CommonName portion of the Subject field.  However, the usage
        of the CommonName field is deprecated and thus this usage is
        NOT RECOMMENDED.  Direct mapping from each individual
        certificate fingerprint to a tmSecurityName is also possible
        but requires one entry in the table per tmSecurityName and
        requires more management operations to completely configure a
        device."
    ::= { snmpTlstmCertificateMapping 3 }

snmpTlstmCertToTSNEntry OBJECT-TYPE
    SYNTAX      SnmpTlstmCertToTSNEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A row in the snmpTlstmCertToTSNTable that specifies a mapping
        for an incoming (D)TLS certificate to a tmSecurityName to use
        for a connection."
    INDEX   { snmpTlstmCertToTSNID }
    ::= { snmpTlstmCertToTSNTable 1 }





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SnmpTlstmCertToTSNEntry ::= SEQUENCE {
    snmpTlstmCertToTSNID           Unsigned32,
    snmpTlstmCertToTSNFingerprint  SnmpTLSFingerprint,
    snmpTlstmCertToTSNMapType      AutonomousType,
    snmpTlstmCertToTSNData         OCTET STRING,
    snmpTlstmCertToTSNStorageType  StorageType,
    snmpTlstmCertToTSNRowStatus    RowStatus
}

snmpTlstmCertToTSNID OBJECT-TYPE
    SYNTAX      Unsigned32 (1..4294967295)
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A unique, prioritized index for the given entry.  Lower
        numbers indicate a higher priority."
    ::= { snmpTlstmCertToTSNEntry 1 }

snmpTlstmCertToTSNFingerprint OBJECT-TYPE
    SYNTAX      SnmpTLSFingerprint (SIZE(1..255))
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "A cryptographic hash of an X.509 certificate.  The results of
        a successful matching fingerprint to either the trusted CA in
        the certificate validation path or to the certificate itself
        is dictated by the snmpTlstmCertToTSNMapType column."
    ::= { snmpTlstmCertToTSNEntry 2 }

snmpTlstmCertToTSNMapType OBJECT-TYPE
    SYNTAX      AutonomousType
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "Specifies the mapping type for deriving a tmSecurityName from
        a certificate.  Details for mapping of a particular type SHALL
        be specified in the DESCRIPTION clause of the OBJECT-IDENTITY
        that describes the mapping.  If a mapping succeeds it will
        return a tmSecurityName for use by the TLSTM model and
        processing stops.

        If the resulting mapped value is not compatible with the
        needed requirements of a tmSecurityName (e.g., VACM imposes a
        32-octet-maximum length and the certificate derived
        securityName could be longer), then future rows MUST be
        searched for additional snmpTlstmCertToTSNFingerprint matches
        to look for a mapping that succeeds.




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        Suitable values for assigning to this object that are defined
        within the SNMP-TLS-TM-MIB can be found in the
        snmpTlstmCertToTSNMIdentities portion of the MIB tree."
    DEFVAL { snmpTlstmCertSpecified }
    ::= { snmpTlstmCertToTSNEntry 3 }

snmpTlstmCertToTSNData OBJECT-TYPE
    SYNTAX      OCTET STRING (SIZE(0..1024))
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "Auxiliary data used as optional configuration information for
        a given mapping specified by the snmpTlstmCertToTSNMapType
        column.  Only some mapping systems will make use of this
        column.  The value in this column MUST be ignored for any
        mapping type that does not require data present in this
        column."
    DEFVAL { "" }
    ::= { snmpTlstmCertToTSNEntry 4 }

snmpTlstmCertToTSNStorageType OBJECT-TYPE
    SYNTAX       StorageType
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION
        "The storage type for this conceptual row.  Conceptual rows
        having the value 'permanent' need not allow write-access to
        any columnar objects in the row."
    DEFVAL      { nonVolatile }
    ::= { snmpTlstmCertToTSNEntry 5 }

snmpTlstmCertToTSNRowStatus OBJECT-TYPE
    SYNTAX      RowStatus
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "The status of this conceptual row.  This object may be used
        to create or remove rows from this table.

        To create a row in this table, an administrator must set this
        object to either createAndGo(4) or createAndWait(5).

        Until instances of all corresponding columns are appropriately
        configured, the value of the corresponding instance of the
        snmpTlstmParamsRowStatus column is notReady(3).

        In particular, a newly created row cannot be made active until
        the corresponding snmpTlstmCertToTSNFingerprint,



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        snmpTlstmCertToTSNMapType, and snmpTlstmCertToTSNData columns
        have been set.

        The following objects may not be modified while the
        value of this object is active(1):
            - snmpTlstmCertToTSNFingerprint
            - snmpTlstmCertToTSNMapType
            - snmpTlstmCertToTSNData
        An attempt to set these objects while the value of
        snmpTlstmParamsRowStatus is active(1) will result in
        an inconsistentValue error."
    ::= { snmpTlstmCertToTSNEntry 6 }

-- Maps tmSecurityNames to certificates for use by the SNMP-TARGET-MIB

snmpTlstmParamsCount OBJECT-TYPE
    SYNTAX      Gauge32
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "A count of the number of entries in the snmpTlstmParamsTable."
    ::= { snmpTlstmCertificateMapping 4 }

snmpTlstmParamsTableLastChanged OBJECT-TYPE
    SYNTAX      TimeStamp
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "The value of sysUpTime.0 when the snmpTlstmParamsTable
        was last modified through any means, or 0 if it has not been
        modified since the command responder was started."
    ::= { snmpTlstmCertificateMapping 5 }

snmpTlstmParamsTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF SnmpTlstmParamsEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "This table is used by a (D)TLS client when a (D)TLS
        connection is being set up using an entry in the
        SNMP-TARGET-MIB.  It extends the SNMP-TARGET-MIB's
        snmpTargetParamsTable with a fingerprint of a certificate to
        use when establishing such a (D)TLS connection."
    ::= { snmpTlstmCertificateMapping 6 }

snmpTlstmParamsEntry OBJECT-TYPE
    SYNTAX      SnmpTlstmParamsEntry
    MAX-ACCESS  not-accessible



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    STATUS      current
    DESCRIPTION
        "A conceptual row containing a fingerprint hash of a locally
        held certificate for a given snmpTargetParamsEntry.  The
        values in this row should be ignored if the connection that
        needs to be established, as indicated by the SNMP-TARGET-MIB
        infrastructure, is not a certificate and (D)TLS based
        connection.  The connection SHOULD NOT be established if the
        certificate fingerprint stored in this entry does not point to
        a valid locally held certificate or if it points to an
        unusable certificate (such as might happen when the
        certificate's expiration date has been reached)."
    INDEX    { IMPLIED snmpTargetParamsName }
    ::= { snmpTlstmParamsTable 1 }

SnmpTlstmParamsEntry ::= SEQUENCE {
    snmpTlstmParamsClientFingerprint SnmpTLSFingerprint,
    snmpTlstmParamsStorageType       StorageType,
    snmpTlstmParamsRowStatus         RowStatus
}

snmpTlstmParamsClientFingerprint OBJECT-TYPE
    SYNTAX      SnmpTLSFingerprint
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "This object stores the hash of the public portion of a
        locally held X.509 certificate.  The X.509 certificate, its
        public key, and the corresponding private key will be used
        when initiating a (D)TLS connection as a (D)TLS client."
    ::= { snmpTlstmParamsEntry 1 }

snmpTlstmParamsStorageType OBJECT-TYPE
    SYNTAX       StorageType
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION
        "The storage type for this conceptual row.  Conceptual rows
        having the value 'permanent' need not allow write-access to
        any columnar objects in the row."
    DEFVAL      { nonVolatile }
    ::= { snmpTlstmParamsEntry 2 }

snmpTlstmParamsRowStatus OBJECT-TYPE
    SYNTAX      RowStatus
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION



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        "The status of this conceptual row.  This object may be used
        to create or remove rows from this table.

        To create a row in this table, an administrator must set this
        object to either createAndGo(4) or createAndWait(5).

        Until instances of all corresponding columns are appropriately
        configured, the value of the corresponding instance of the
        snmpTlstmParamsRowStatus column is notReady(3).

        In particular, a newly created row cannot be made active until
        the corresponding snmpTlstmParamsClientFingerprint column has
        been set.

        The snmpTlstmParamsClientFingerprint object may not be modified
        while the value of this object is active(1).

        An attempt to set these objects while the value of
        snmpTlstmParamsRowStatus is active(1) will result in
        an inconsistentValue error."
    ::= { snmpTlstmParamsEntry 3 }

snmpTlstmAddrCount OBJECT-TYPE
    SYNTAX      Gauge32
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "A count of the number of entries in the snmpTlstmAddrTable."
    ::= { snmpTlstmCertificateMapping 7 }

snmpTlstmAddrTableLastChanged OBJECT-TYPE
    SYNTAX      TimeStamp
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "The value of sysUpTime.0 when the snmpTlstmAddrTable
        was last modified through any means, or 0 if it has not been
        modified since the command responder was started."
    ::= { snmpTlstmCertificateMapping 8 }

snmpTlstmAddrTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF SnmpTlstmAddrEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "This table is used by a (D)TLS client when a (D)TLS
        connection is being set up using an entry in the
        SNMP-TARGET-MIB.  It extends the SNMP-TARGET-MIB's



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        snmpTargetAddrTable so that the client can verify that the
        correct server has been reached.  This verification can use
        either a certificate fingerprint, or an identity
        authenticated via certification path validation.

        If there is an active row in this table corresponding to the
        entry in the SNMP-TARGET-MIB that was used to establish the
        connection, and the row's snmpTlstmAddrServerFingerprint
        column has non-empty value, then the server's presented
        certificate is compared with the
        snmpTlstmAddrServerFingerprint value (and the
        snmpTlstmAddrServerIdentity column is ignored).  If the
        fingerprint matches, the verification has succeeded.  If the
        fingerprint does not match, then the connection MUST be
        closed.

        If the server's presented certificate has passed
        certification path validation [RFC5280] to a configured
        trust anchor, and an active row exists with a zero-length
        snmpTlstmAddrServerFingerprint value, then the
        snmpTlstmAddrServerIdentity column contains the expected
        host name.  This expected host name is then compared against
        the server's certificate as follows:

          - Implementations MUST support matching the expected host
          name against a dNSName in the subjectAltName extension
          field and MAY support checking the name against the
          CommonName portion of the subject distinguished name.

          - The '*' (ASCII 0x2a) wildcard character is allowed in the
          dNSName of the subjectAltName extension (and in common
          name, if used to store the host name), but only as the
          left-most (least significant) DNS label in that value.
          This wildcard matches any left-most DNS label in the
          server name.  That is, the subject *.example.com matches
          the server names a.example.com and b.example.com, but does
          not match example.com or a.b.example.com.  Implementations
          MUST support wildcards in certificates as specified above,
          but MAY provide a configuration option to disable them.

          - If the locally configured name is an internationalized
          domain name, conforming implementations MUST convert it to
          the ASCII Compatible Encoding (ACE) format for performing
          comparisons, as specified in Section 7 of [RFC5280].

        If the expected host name fails these conditions then the
        connection MUST be closed.




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        If there is no row in this table corresponding to the entry
        in the SNMP-TARGET-MIB and the server can be authorized by
        another, implementation-dependent means, then the connection
        MAY still proceed."

    ::= { snmpTlstmCertificateMapping 9 }

snmpTlstmAddrEntry OBJECT-TYPE
    SYNTAX      SnmpTlstmAddrEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A conceptual row containing a copy of a certificate's
        fingerprint for a given snmpTargetAddrEntry.  The values in
        this row should be ignored if the connection that needs to be
        established, as indicated by the SNMP-TARGET-MIB
        infrastructure, is not a (D)TLS based connection.  If an
        snmpTlstmAddrEntry exists for a given snmpTargetAddrEntry, then
        the presented server certificate MUST match or the connection
        MUST NOT be established.  If a row in this table does not
        exist to match an snmpTargetAddrEntry row, then the connection
        SHOULD still proceed if some other certificate validation path
        algorithm (e.g., RFC 5280) can be used."
    INDEX    { IMPLIED snmpTargetAddrName }
    ::= { snmpTlstmAddrTable 1 }

SnmpTlstmAddrEntry ::= SEQUENCE {
    snmpTlstmAddrServerFingerprint    SnmpTLSFingerprint,
    snmpTlstmAddrServerIdentity       SnmpAdminString,
    snmpTlstmAddrStorageType          StorageType,
    snmpTlstmAddrRowStatus            RowStatus
}

snmpTlstmAddrServerFingerprint OBJECT-TYPE
    SYNTAX      SnmpTLSFingerprint
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "A cryptographic hash of a public X.509 certificate.  This
        object should store the hash of the public X.509 certificate
        that the remote server should present during the (D)TLS
        connection setup.  The fingerprint of the presented
        certificate and this hash value MUST match exactly or the
        connection MUST NOT be established."
    DEFVAL { "" }
    ::= { snmpTlstmAddrEntry 1 }





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snmpTlstmAddrServerIdentity OBJECT-TYPE
    SYNTAX      SnmpAdminString
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "The reference identity to check against the identity
        presented by the remote system."
    DEFVAL { "" }
    ::= { snmpTlstmAddrEntry 2 }

snmpTlstmAddrStorageType OBJECT-TYPE
    SYNTAX       StorageType
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION
        "The storage type for this conceptual row.  Conceptual rows
        having the value 'permanent' need not allow write-access to
        any columnar objects in the row."
    DEFVAL      { nonVolatile }
    ::= { snmpTlstmAddrEntry 3 }


snmpTlstmAddrRowStatus OBJECT-TYPE
    SYNTAX      RowStatus
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "The status of this conceptual row.  This object may be used
        to create or remove rows from this table.

        To create a row in this table, an administrator must set this
        object to either createAndGo(4) or createAndWait(5).

        Until instances of all corresponding columns are
        appropriately configured, the value of the
        corresponding instance of the snmpTlstmAddrRowStatus
        column is notReady(3).

        In particular, a newly created row cannot be made active until
        the corresponding snmpTlstmAddrServerFingerprint column has been
        set.

        Rows MUST NOT be active if the snmpTlstmAddrServerFingerprint
        column is blank and the snmpTlstmAddrServerIdentity is set to
        '*' since this would insecurely accept any presented
        certificate.





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        The snmpTlstmAddrServerFingerprint object may not be modified
        while the value of this object is active(1).

        An attempt to set these objects while the value of
        snmpTlstmAddrRowStatus is active(1) will result in
        an inconsistentValue error."
    ::= { snmpTlstmAddrEntry 4 }

-- ************************************************
--  snmpTlstmNotifications - Notifications Information
-- ************************************************

snmpTlstmServerCertificateUnknown NOTIFICATION-TYPE
    OBJECTS { snmpTlstmSessionUnknownServerCertificate }
    STATUS  current
    DESCRIPTION
        "Notification that the server certificate presented by an SNMP
         over (D)TLS server was invalid because no configured
         fingerprint or CA was acceptable to validate it.  This may be
         because there was no entry in the snmpTlstmAddrTable or
         because no path could be found to known Certification
         Authority.

         To avoid notification loops, this notification MUST NOT be
         sent to servers that themselves have triggered the
         notification."
    ::= { snmpTlstmNotifications 1 }

snmpTlstmServerInvalidCertificate NOTIFICATION-TYPE
    OBJECTS { snmpTlstmAddrServerFingerprint,
              snmpTlstmSessionInvalidServerCertificates}
    STATUS  current
    DESCRIPTION
        "Notification that the server certificate presented by an SNMP
         over (D)TLS server could not be validated even if the
         fingerprint or expected validation path was known.  That is, a
         cryptographic validation error occurred during certificate
         validation processing.

         To avoid notification loops, this notification MUST NOT be
         sent to servers that themselves have triggered the
         notification."
    ::= { snmpTlstmNotifications 2 }

-- ************************************************
-- snmpTlstmCompliances - Conformance Information
-- ************************************************




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snmpTlstmCompliances OBJECT IDENTIFIER ::= { snmpTlstmConformance 1 }

snmpTlstmGroups OBJECT IDENTIFIER ::= { snmpTlstmConformance 2 }

-- ************************************************
-- Compliance statements
-- ************************************************

snmpTlstmCompliance MODULE-COMPLIANCE
    STATUS      current
    DESCRIPTION
        "The compliance statement for SNMP engines that support the
        SNMP-TLS-TM-MIB"
    MODULE
        MANDATORY-GROUPS { snmpTlstmStatsGroup,
                           snmpTlstmIncomingGroup,
                           snmpTlstmOutgoingGroup,
                           snmpTlstmNotificationGroup }
    ::= { snmpTlstmCompliances 1 }

-- ************************************************
-- Units of conformance
-- ************************************************
snmpTlstmStatsGroup OBJECT-GROUP
    OBJECTS {
        snmpTlstmSessionOpens,
        snmpTlstmSessionClientCloses,
        snmpTlstmSessionOpenErrors,
        snmpTlstmSessionAccepts,
        snmpTlstmSessionServerCloses,
        snmpTlstmSessionNoSessions,
        snmpTlstmSessionInvalidClientCertificates,
        snmpTlstmSessionUnknownServerCertificate,
        snmpTlstmSessionInvalidServerCertificates,
        snmpTlstmSessionInvalidCaches
    }
    STATUS      current
    DESCRIPTION
        "A collection of objects for maintaining
        statistical information of an SNMP engine that
        implements the SNMP TLS Transport Model."
    ::= { snmpTlstmGroups 1 }

snmpTlstmIncomingGroup OBJECT-GROUP
    OBJECTS {
        snmpTlstmCertToTSNCount,
        snmpTlstmCertToTSNTableLastChanged,
        snmpTlstmCertToTSNFingerprint,



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        snmpTlstmCertToTSNMapType,
        snmpTlstmCertToTSNData,
        snmpTlstmCertToTSNStorageType,
        snmpTlstmCertToTSNRowStatus
    }
    STATUS      current
    DESCRIPTION
        "A collection of objects for maintaining
        incoming connection certificate mappings to
        tmSecurityNames of an SNMP engine that implements the
        SNMP TLS Transport Model."
    ::= { snmpTlstmGroups 2 }

snmpTlstmOutgoingGroup OBJECT-GROUP
    OBJECTS {
        snmpTlstmParamsCount,
        snmpTlstmParamsTableLastChanged,
        snmpTlstmParamsClientFingerprint,
        snmpTlstmParamsStorageType,
        snmpTlstmParamsRowStatus,
        snmpTlstmAddrCount,
        snmpTlstmAddrTableLastChanged,
        snmpTlstmAddrServerFingerprint,
        snmpTlstmAddrServerIdentity,
        snmpTlstmAddrStorageType,
        snmpTlstmAddrRowStatus
    }
    STATUS      current
    DESCRIPTION
        "A collection of objects for maintaining
        outgoing connection certificates to use when opening
        connections as a result of SNMP-TARGET-MIB settings."
    ::= { snmpTlstmGroups 3 }

snmpTlstmNotificationGroup NOTIFICATION-GROUP
    NOTIFICATIONS {
        snmpTlstmServerCertificateUnknown,
        snmpTlstmServerInvalidCertificate
    }
    STATUS current
    DESCRIPTION
        "Notifications"
    ::= { snmpTlstmGroups 4 }

END






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8.  Operational Considerations

   This section discusses various operational aspects of deploying
   TLSTM.

8.1.  Sessions

   A session is discussed throughout this document as meaning a security
   association between two TLSTM instances.  State information for the
   sessions are maintained in each TLSTM implementation and this
   information is created and destroyed as sessions are opened and
   closed.  A "broken" session (one side up and one side down) can
   result if one side of a session is brought down abruptly (i.e.,
   reboot, power outage, etc.).  Whenever possible, implementations
   SHOULD provide graceful session termination through the use of TLS
   disconnect messages.  Implementations SHOULD also have a system in
   place for detecting "broken" sessions through the use of heartbeats
   [HEARTBEAT] or other detection mechanisms.

   Implementations SHOULD limit the lifetime of established sessions
   depending on the algorithms used for generation of the master session
   secret, the privacy and integrity algorithms used to protect
   messages, the environment of the session, the amount of data
   transferred, and the sensitivity of the data.

8.2.  Notification Receiver Credential Selection

   When an SNMP engine needs to establish an outgoing session for
   notifications, the snmpTargetParamsTable includes an entry for the
   snmpTargetParamsSecurityName of the target.  Servers that wish to
   support multiple principals at a particular port SHOULD make use of
   the Server Name Indication extension defined in Section 3.1 of
   [RFC4366].  Without the Server Name Indication the receiving SNMP
   engine (server) will not know which (D)TLS certificate to offer to
   the client so that the tmSecurityName identity-authentication will be
   successful.

   Another solution is to maintain a one-to-one mapping between
   certificates and incoming ports for notification receivers.  This can
   be handled at the notification originator by configuring the
   snmpTargetAddrTable (snmpTargetAddrTDomain and
   snmpTargetAddrTAddress) and requiring the receiving SNMP engine to
   monitor multiple incoming static ports based on which principals are
   capable of receiving notifications.

   Implementations MAY also choose to designate a single Notification
   Receiver Principal to receive all incoming notifications or select an




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   implementation specific method of selecting a server certificate to
   present to clients.

8.3.  contextEngineID Discovery

   SNMPv3 requires that an application know the identifier
   (snmpEngineID) of the remote SNMP protocol engine in order to
   retrieve or manipulate objects maintained on the remote SNMP entity.

   [RFC5343] introduces a well-known localEngineID and a discovery
   mechanism that can be used to learn the snmpEngineID of a remote SNMP
   protocol engine.  Implementations are RECOMMENDED to support and use
   the contextEngineID discovery mechanism defined in [RFC5343].

8.4.  Transport Considerations

   This document defines how SNMP messages can be transmitted over the
   TLS- and DTLS-based protocols.  Each of these protocols is
   additionally based on other transports (TCP and UDP).  These two base
   protocols also have operational considerations that must be taken
   into consideration when selecting a (D)TLS-based protocol to use such
   as its performance in degraded or limited networks.  It is beyond the
   scope of this document to summarize the characteristics of these
   transport mechanisms.  Please refer to the base protocol documents
   for details on messaging considerations with respect to MTU size,
   fragmentation, performance in lossy networks, etc.

9.  Security Considerations

   This document describes a transport model that permits SNMP to
   utilize (D)TLS security services.  The security threats and how the
   (D)TLS transport model mitigates these threats are covered in detail
   throughout this document.  Security considerations for DTLS are
   covered in [RFC4347] and security considerations for TLS are
   described in Section 11 and Appendices D, E, and F of TLS 1.2
   [RFC5246].  When run over a connectionless transport such as UDP,
   DTLS is more vulnerable to denial-of-service attacks from spoofed IP
   addresses; see Section 4.2 for details how the cookie exchange is
   used to address this issue.

9.1.  Certificates, Authentication, and Authorization

   Implementations are responsible for providing a security certificate
   installation and configuration mechanism.  Implementations SHOULD
   support certificate revocation lists.

   (D)TLS provides for authentication of the identity of both the (D)TLS
   server and the (D)TLS client.  Access to MIB objects for the



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   authenticated principal MUST be enforced by an access control
   subsystem (e.g., the VACM).

   Authentication of the command generator principal's identity is
   important for use with the SNMP access control subsystem to ensure
   that only authorized principals have access to potentially sensitive
   data.  The authenticated identity of the command generator
   principal's certificate is mapped to an SNMP model-independent
   securityName for use with SNMP access control.

   The (D)TLS handshake only provides assurance that the certificate of
   the authenticated identity has been signed by a configured accepted
   Certification Authority.  (D)TLS has no way to further authorize or
   reject access based on the authenticated identity.  An Access Control
   Model (such as the VACM) provides access control and authorization of
   a command generator's requests to a command responder and a
   notification receiver's authorization to receive Notifications from a
   notification originator.  However, to avoid man-in-the-middle
   attacks, both ends of the (D)TLS-based connection MUST check the
   certificate presented by the other side against what was expected.
   For example, command generators must check that the command responder
   presented and authenticated itself with an X.509 certificate that was
   expected.  Not doing so would allow an impostor, at a minimum, to
   present false data, receive sensitive information, and/or provide a
   false belief that configuration was actually received and acted upon.
   Authenticating and verifying the identity of the (D)TLS server and
   the (D)TLS client for all operations ensures the authenticity of the
   SNMP engine that provides MIB data.

   The instructions found in the DESCRIPTION clause of the
   snmpTlstmCertToTSNTable object must be followed exactly.  It is also
   important that the rows of the table be searched in prioritized order
   starting with the row containing the lowest numbered
   snmpTlstmCertToTSNID value.

9.2.  (D)TLS Security Considerations

   This section discusses security considerations specific to the usage
   of (D)TLS.

9.2.1.  TLS Version Requirements

   Implementations of TLS typically support multiple versions of the
   Transport Layer Security protocol as well as the older Secure Sockets
   Layer (SSL) protocol.  Because of known security vulnerabilities,
   TLSTM clients and servers MUST NOT request, offer, or use SSL 2.0.
   See Appendix E.2 of [RFC5246] for further details.




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9.2.2.  Perfect Forward Secrecy

   The use of Perfect Forward Secrecy is RECOMMENDED and can be provided
   by (D)TLS with appropriately selected cipher_suites, as discussed in
   Appendix F of [RFC5246].

9.3.  Use with SNMPv1/SNMPv2c Messages

   The SNMPv1 and SNMPv2c message processing described in [RFC3584] (BCP
   74) always selects the SNMPv1 or SNMPv2c Security Models,
   respectively.  Both of these and the User-based Security Model
   typically used with SNMPv3 derive the securityName and securityLevel
   from the SNMP message received, even when the message was received
   over a secure transport.  Access control decisions are therefore made
   based on the contents of the SNMP message, rather than using the
   authenticated identity and securityLevel provided by the TLS
   Transport Model.  It is RECOMMENDED that only SNMPv3 messages using
   the Transport Security Model (TSM) or another secure-transport aware
   security model be sent over the TLSTM transport.

   Using a non-transport-aware Security Model with a secure Transport
   Model is NOT RECOMMENDED.  See [RFC5590], Section 7.1 for additional
   details on the coexistence of security-aware transports and non-
   transport-aware security models.

9.4.  MIB Module Security

   There are a number of management objects defined in this MIB module
   with a MAX-ACCESS clause of read-write and/or read-create.  Such
   objects may be considered sensitive or vulnerable in some network
   environments.  The support for SET operations in a non-secure
   environment without proper protection can have a negative effect on
   network operations.  These are the tables and objects and their
   sensitivity/vulnerability:

   o  The snmpTlstmParamsTable can be used to change the outgoing X.509
      certificate used to establish a (D)TLS connection.  Modifications
      to objects in this table need to be adequately authenticated since
      modifying the values in this table will have profound impacts to
      the security of outbound connections from the device.  Since
      knowledge of authorization rules and certificate usage mechanisms
      may be considered sensitive, protection from disclosure of the
      SNMP traffic via encryption is also highly recommended.

   o  The snmpTlstmAddrTable can be used to change the expectations of
      the certificates presented by a remote (D)TLS server.
      Modifications to objects in this table need to be adequately
      authenticated since modifying the values in this table will have



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      profound impacts to the security of outbound connections from the
      device.  Since knowledge of authorization rules and certificate
      usage mechanisms may be considered sensitive, protection from
      disclosure of the SNMP traffic via encryption is also highly
      recommended.

   o  The snmpTlstmCertToTSNTable is used to specify the mapping of
      incoming X.509 certificates to tmSecurityNames, which eventually
      get mapped to an SNMPv3 securityName.  Modifications to objects in
      this table need to be adequately authenticated since modifying the
      values in this table will have profound impacts to the security of
      incoming connections to the device.  Since knowledge of
      authorization rules and certificate usage mechanisms may be
      considered sensitive, protection from disclosure of the SNMP
      traffic via encryption is also highly recommended.  When this
      table contains a significant number of rows it may affect the
      system performance when accepting new (D)TLS connections.

   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  This MIB contains a collection of counters that monitor the (D)TLS
      connections being established with a device.  Since knowledge of
      connection and certificate usage mechanisms may be considered
      sensitive, protection from disclosure of the SNMP traffic via
      encryption is highly recommended.

   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 SNMPv3 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



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   the objects only to those principals (users) that have legitimate
   rights to indeed GET or SET (change/create/delete) them.

10.  IANA Considerations

   IANA has assigned:

   1.  Two TCP/UDP port numbers from the "Registered Ports" range of the
       Port Numbers registry, with the following keywords:

     Keyword         Decimal      Description       References
     -------         -------      -----------       ----------
     snmptls         10161/tcp    SNMP-TLS          [RFC6353]
     snmpdtls        10161/udp    SNMP-DTLS         [RFC6353]
     snmptls-trap    10162/tcp    SNMP-Trap-TLS     [RFC6353]
     snmpdtls-trap   10162/udp    SNMP-Trap-DTLS    [RFC6353]

   These are the default ports for receipt of SNMP command messages
   (snmptls and snmpdtls) and SNMP notification messages (snmptls-trap
   and snmpdtls-trap) over a TLS Transport Model as defined in this
   document.

   2.  An SMI number (8) under snmpDomains for the snmpTLSTCPDomain
       object identifier

   3.  An SMI number (9) under snmpDomains for the snmpDTLSUDPDomain
       object identifier

   4.  An SMI number (198) under mib-2, for the MIB module in this
       document

   5.  "tls" as the corresponding prefix for the snmpTLSTCPDomain in the
       SNMP Transport Domains registry

   6.  "dtls" as the corresponding prefix for the snmpDTLSUDPDomain in
       the SNMP Transport Domains registry

11.  Acknowledgements

   This document closely follows and copies the Secure Shell Transport
   Model for SNMP documented by David Harrington and Joseph Salowey in
   [RFC5592].

   This document was reviewed by the following people who helped provide
   useful comments (in alphabetical order): Andy Donati, Pasi Eronen,
   David Harrington, Jeffrey Hutzelman, Alan Luchuk, Michael Peck, Tom
   Petch, Randy Presuhn, Ray Purvis, Peter Saint-Andre, Joseph Salowey,
   Juergen Schoenwaelder, Dave Shield, and Robert Story.



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   This work was supported in part by the United States Department of
   Defense.  Large portions of this document are based on work by
   General Dynamics C4 Systems and the following individuals: Brian
   Baril, Kim Bryant, Dana Deluca, Dan Hanson, Tim Huemiller, John
   Holzhauer, Colin Hoogeboom, Dave Kornbau, Chris Knaian, Dan Knaul,
   Charles Limoges, Steve Moccaldi, Gerardo Orlando, and Brandon Yip.

12.  References

12.1.  Normative References

   [RFC1123]    Braden, R., "Requirements for Internet Hosts -
                Application and Support", STD 3, RFC 1123, October 1989.

   [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.

   [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.

   [RFC3415]    Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
                Access Control Model (VACM) for the Simple Network
                Management Protocol (SNMP)", STD 62, RFC 3415,
                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.

   [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.

   [RFC4347]    Rescorla, E. and N. Modadugu, "Datagram Transport Layer
                Security", RFC 4347, April 2006.

   [RFC4366]    Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen,
                J., and T. Wright, "Transport Layer Security (TLS)
                Extensions", RFC 4366, April 2006.

   [RFC5246]    Dierks, T. and E. Rescorla, "The Transport Layer
                Security (TLS) Protocol Version 1.2", RFC 5246,
                August 2008.

   [RFC5280]    Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
                Housley, R., and W. Polk, "Internet X.509 Public Key
                Infrastructure Certificate and Certificate Revocation
                List (CRL) Profile", RFC 5280, May 2008.

   [RFC5590]    Harrington, D. and J. Schoenwaelder, "Transport
                Subsystem for the Simple Network Management Protocol
                (SNMP)", RFC 5590, June 2009.

   [RFC5591]    Harrington, D. and W. Hardaker, "Transport Security
                Model for the Simple Network Management Protocol
                (SNMP)", RFC 5591, June 2009.

   [RFC5952]    Kawamura, S. and M. Kawashima, "A Recommendation for
                IPv6 Address Text Representation", RFC 5952,
                August 2010.

12.2.  Informative References

   [HEARTBEAT]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
                Layer Security (TLS) and Datagram Transport Layer
                Security (DTLS) Heartbeat Extension", Work in Progress,
                July 2011.

   [RFC3410]    Case, J., Mundy, R., Partain, D., and B. Stewart,
                "Introduction and Applicability Statements for Internet-
                Standard Management Framework", RFC 3410, December 2002.




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   [RFC5343]    Schoenwaelder, J., "Simple Network Management Protocol
                (SNMP) Context EngineID Discovery", RFC 5343,
                September 2008.

   [RFC5592]    Harrington, D., Salowey, J., and W. Hardaker, "Secure
                Shell Transport Model for the Simple Network Management
                Protocol (SNMP)", RFC 5592, June 2009.

   [RFC5890]    Klensin, J., "Internationalized Domain Names for
                Applications (IDNA): Definitions and Document
                Framework", RFC 5890, August 2010.

   [RFC5953]    Hardaker, W., "Transport Layer Security (TLS) Transport
                Model for the Simple Network Management Protocol
                (SNMP)", RFC 5953, August 2010.




































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Appendix A.  Target and Notification Configuration Example

   The following sections describe example configuration for the SNMP-
   TLS-TM-MIB, the SNMP-TARGET-MIB, the NOTIFICATION-MIB, and the SNMP-
   VIEW-BASED-ACM-MIB.

A.1.  Configuring a Notification Originator

   The following row adds the "Joe Cool" user to the "administrators"
   group:

       vacmSecurityModel              = 4 (TSM)
       vacmSecurityName               = "Joe Cool"
       vacmGroupName                  = "administrators"
       vacmSecurityToGroupStorageType = 3 (nonVolatile)
       vacmSecurityToGroupStatus      = 4 (createAndGo)

   The following row configures the snmpTlstmAddrTable to use
   certificate path validation and to require the remote notification
   receiver to present a certificate for the "server.example.org"
   identity.

       snmpTargetAddrName             =  "toNRAddr"
       snmpTlstmAddrServerFingerprint =  ""
       snmpTlstmAddrServerIdentity    =  "server.example.org"
       snmpTlstmAddrStorageType       =  3         (nonVolatile)
       snmpTlstmAddrRowStatus         =  4         (createAndGo)

   The following row configures the snmpTargetAddrTable to send
   notifications using TLS/TCP to the snmptls-trap port at 192.0.2.1:

       snmpTargetAddrName              = "toNRAddr"
       snmpTargetAddrTDomain           = snmpTLSTCPDomain
       snmpTargetAddrTAddress          = "192.0.2.1:10162"
       snmpTargetAddrTimeout           = 1500
       snmpTargetAddrRetryCount        = 3
       snmpTargetAddrTagList           = "toNRTag"
       snmpTargetAddrParams            = "toNR"     (MUST match below)
       snmpTargetAddrStorageType       = 3          (nonVolatile)
       snmpTargetAddrRowStatus         = 4          (createAndGo)











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   The following row configures the snmpTargetParamsTable to send the
   notifications to "Joe Cool", using authPriv SNMPv3 notifications
   through the TransportSecurityModel [RFC5591]:

       snmpTargetParamsName            = "toNR"     (must match above)
       snmpTargetParamsMPModel         = 3 (SNMPv3)
       snmpTargetParamsSecurityModel   = 4 (TransportSecurityModel)
       snmpTargetParamsSecurityName    = "Joe Cool"
       snmpTargetParamsSecurityLevel   = 3          (authPriv)
       snmpTargetParamsStorageType     = 3          (nonVolatile)
       snmpTargetParamsRowStatus       = 4          (createAndGo)

A.2.  Configuring TLSTM to Utilize a Simple Derivation of tmSecurityName

   The following row configures the snmpTlstmCertToTSNTable to map a
   validated client certificate, referenced by the client's public X.509
   hash fingerprint, to a tmSecurityName using the subjectAltName
   component of the certificate.

       snmpTlstmCertToTSNID          = 1
                                       (chosen by ordering preference)
       snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint)
       snmpTlstmCertToTSNMapType     = snmpTlstmCertSANAny
       snmpTlstmCertToTSNData        = ""  (not used)
       snmpTlstmCertToTSNStorageType = 3   (nonVolatile)
       snmpTlstmCertToTSNRowStatus   = 4   (createAndGo)

   This type of configuration should only be used when the naming
   conventions of the (possibly multiple) Certification Authorities are
   well understood, so two different principals cannot inadvertently be
   identified by the same derived tmSecurityName.

A.3.  Configuring TLSTM to Utilize Table-Driven Certificate Mapping

   The following row configures the snmpTlstmCertToTSNTable to map a
   validated client certificate, referenced by the client's public X.509
   hash fingerprint, to the directly specified tmSecurityName of "Joe
   Cool".

       snmpTlstmCertToTSNID           = 2
                                        (chosen by ordering preference)
       snmpTlstmCertToTSNFingerprint  = HASH (appropriate fingerprint)
       snmpTlstmCertToTSNMapType      = snmpTlstmCertSpecified
       snmpTlstmCertToTSNSecurityName = "Joe Cool"
       snmpTlstmCertToTSNStorageType  = 3  (nonVolatile)
       snmpTlstmCertToTSNRowStatus    = 4  (createAndGo)





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Author's Address

   Wes Hardaker
   SPARTA, Inc.
   P.O. Box 382
   Davis, CA  95617
   USA

   Phone: +1 530 792 1913
   EMail: ietf@hardakers.net









































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