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Versions: (draft-hardaker-isms-dtls-tm) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 5953

ISMS                                                         W. Hardaker
Internet-Draft                                              Sparta, Inc.
Intended status: Standards Track                       December 30, 2009
Expires: July 3, 2010


        Transport Layer Security (TLS) Transport Model for SNMP
                     draft-ietf-isms-dtls-tm-04.txt

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 a
   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 sending of SNMP
   messages over TLS/TCP, DTLS/UDP and DTLS/SCTP.  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 or SCTP) 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 Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at



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   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 3, 2010.

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
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   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
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   Without obtaining an adequate license from the person(s) controlling
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   it for publication as an RFC or to translate it into languages other
   than English.


















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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  7
   2.  The Transport Layer Security Protocol  . . . . . . . . . . . .  8
   3.  How the TLSTM fits into the Transport Subsystem  . . . . . . .  9
     3.1.  Security Capabilities of this Model  . . . . . . . . . . . 10
       3.1.1.  Threats  . . . . . . . . . . . . . . . . . . . . . . . 10
       3.1.2.  Message Protection . . . . . . . . . . . . . . . . . . 12
       3.1.3.  (D)TLS Sessions  . . . . . . . . . . . . . . . . . . . 13
     3.2.  Security Parameter Passing . . . . . . . . . . . . . . . . 13
     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.  Messages . . . . . . . . . . . . . . . . . . . . . . . . . 16
     4.3.  SNMP Services  . . . . . . . . . . . . . . . . . . . . . . 16
       4.3.1.  SNMP Services for an Outgoing Message  . . . . . . . . 17
       4.3.2.  SNMP Services for an Incoming Message  . . . . . . . . 18
     4.4.  Cached Information and References  . . . . . . . . . . . . 18
       4.4.1.  TLS Transport Model Cached Information . . . . . . . . 19
         4.4.1.1.  tmSecurityName . . . . . . . . . . . . . . . . . . 19
         4.4.1.2.  tmSessionID  . . . . . . . . . . . . . . . . . . . 19
         4.4.1.3.  Session State  . . . . . . . . . . . . . . . . . . 19
   5.  Elements of Procedure  . . . . . . . . . . . . . . . . . . . . 20
     5.1.  Procedures for an Incoming Message . . . . . . . . . . . . 20
       5.1.1.  DTLS Processing for Incoming Messages  . . . . . . . . 20
       5.1.2.  Transport Processing for Incoming SNMP Messages  . . . 22
     5.2.  Procedures for an Outgoing SNMP Message  . . . . . . . . . 23
     5.3.  Establishing a Session . . . . . . . . . . . . . . . . . . 24
     5.4.  Closing a Session  . . . . . . . . . . . . . . . . . . . . 27
   6.  MIB Module Overview  . . . . . . . . . . . . . . . . . . . . . 28
     6.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 28
     6.2.  Textual Conventions  . . . . . . . . . . . . . . . . . . . 28
     6.3.  Statistical Counters . . . . . . . . . . . . . . . . . . . 28
     6.4.  Configuration Tables . . . . . . . . . . . . . . . . . . . 28
       6.4.1.  Notifications  . . . . . . . . . . . . . . . . . . . . 29
     6.5.  Relationship to Other MIB Modules  . . . . . . . . . . . . 29
       6.5.1.  MIB Modules Required for IMPORTS . . . . . . . . . . . 29
   7.  MIB Module Definition  . . . . . . . . . . . . . . . . . . . . 29
   8.  Operational Considerations . . . . . . . . . . . . . . . . . . 51
     8.1.  Sessions . . . . . . . . . . . . . . . . . . . . . . . . . 51
     8.2.  Notification Receiver Credential Selection . . . . . . . . 51
     8.3.  contextEngineID Discovery  . . . . . . . . . . . . . . . . 52
     8.4.  Transport Considerations . . . . . . . . . . . . . . . . . 52
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 52
     9.1.  Certificates, Authentication, and Authorization  . . . . . 53
     9.2.  Use with SNMPv1/SNMPv2c Messages . . . . . . . . . . . . . 53



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     9.3.  MIB Module Security  . . . . . . . . . . . . . . . . . . . 54
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 55
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 57
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 57
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 57
     12.2. Informative References . . . . . . . . . . . . . . . . . . 58
   Appendix A.  (D)TLS Overview . . . . . . . . . . . . . . . . . . . 59
     A.1.  The (D)TLS Record Protocol . . . . . . . . . . . . . . . . 60
     A.2.  The (D)TLS Handshake Protocol  . . . . . . . . . . . . . . 60
   Appendix B.  PKIX Certificate Infrastructure . . . . . . . . . . . 61
   Appendix C.  Target and Notificaton Configuration Example  . . . . 62
     C.1.  Configuring the Notification Generator . . . . . . . . . . 63
     C.2.  Configuring the Command Responder  . . . . . . . . . . . . 63
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 64





































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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 or SCTP) 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, DTLS/UDP and DTLS/
   SCTP.

   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].

   The diagram shown below gives a conceptual overview of two SNMP
   entities communicating using the TLS Transport Model.  One entity
   contains a command responder and notification originator application,
   and the other a command generator and notification responder
   application.  It should be understood that this particular mix of



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   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 which is defined in [RFC5591].


 +----------------------------------------------------------------+
 |                              Network                           |
 +----------------------------------------------------------------+
     ^                     |             ^               |
     |Notifications        |Commands     |Commands       |Notifications
 +---|---------------------|--------+ +--|---------------|-------------+
 |   |                     V        | |  |               V             |
 | +------------+  +------------+   | | +-----------+   +----------+   |
 | |  (D)TLS    |  |  (D)TLS    |   | | | (D)TLS    |   | (D)TLS   |   |
 | |   Service  |  |   Service  |   | | |  Service  |   |  Service |   |
 | |   (Client) |  |   (Server) |   | | |  (Client) |   |  (Server)|   |
 | +------------+  +------------+   | | +-----------+   +----------+   |
 |          ^          ^            | |       ^              ^         |
 |          |          |            | |       |              |         |
 |       +--+----------+            | |     +-+--------------+         |
 | +-----|---------+----+           | | +---|--------+----+            |
 | |     V         |LCD | +-------+ | | |   V        |LCD | +--------+ |
 | | +------+      +----+ |       | | | | +------+   +----+ |        | |
 | | | TLS  | <---------->| Cache | | | | | TLS  |    <---->| Cache  | |
 | | |  TM  |           | |       | | | | |  TM  |        | |        | |
 | | +------+           | +-------+ | | | +------+        | +--------+ |
 | |Transport Subsystem |    ^      | | |Transport Sub.   |      ^     |
 | +--------------------+    |      | | +-----------------+      |     |
 |    ^                      +----+ | |    ^                     |     |
 |    |                           | | |    |                     |     |
 |    v                           | | |    V                     |     |
 | +-------+ +----------+ +-----+ | | | +-----+ +------+ +-----+ |     |
 | |       | |Message   | |Sec. | | | | |     | |  MP  | |Sec. | |     |
 | | Disp. | |Processing| |Sub- | | | | |Disp.| | Sub- | |Sub- | |     |
 | |       | |Subsystem | |sys. | | | | |     | |system| |sys. | |     |
 | |       | |          | |     | | | | |     | |      | |     | |     |
 | |       | |          | |+---+| | | | |     | |      | |+---+| |     |
 | |       | | +-----+  | ||   || | | | |     | |+----+| ||   || |     |
 | |      <--->|v3MP |<-->||TSM|<-+ | | |    <-->|v3MP|<->|TSM|<-+     |
 | |       | | +-----+  | ||   ||   | | |     | |+----+| ||   ||       |
 | +-------+ |          | |+---+|   | | +-----+ |      | |+---+|       |
 |    ^      |          | |     |   | |    ^    |      | |     |       |
 |    |      +----------+ +-----+   | |    |    +------+ +-----+       |
 |    +-+------------+              | |  +-+------------+              |
 |      ^            ^              | |  ^              ^              |
 |      |            |              | |  |              |              |
 |      v            v              | |  V              V              |
 | +-------------+ +--------------+ | | +-----------+ +--------------+ |



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 | |   COMMAND   | | NOTIFICATION | | | |  COMMAND  | | NOTIFICATION | |
 | |  RESPONDER  | |  ORIGINATOR  | | | | GENERATOR | |   RECEIVER   | |
 | | application | | application  | | | |application| | application  | |
 | +-------------+ +--------------+ | | +-----------+ +--------------+ |
 |                      SNMP entity | |                    SNMP entity |
 +----------------------------------+ +--------------------------------+

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 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
   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.

   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 [RFC3411], all SNMP entities
   have the capability of acting in either manager or agent or in both
   roles 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



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   Model, however, is named "TLS Transport Model" and refers not to the
   TLS or DTLS protocol but to the standard defined 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.  Either SNMP entity may
   act as client or as server.

   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 RFC3411 and in this
   memo is "principal".  A principal is the "who" on whose behalf
   services are provided or processing takes place.  A principal can be,
   among other things, an individual acting in a particular role; a set
   of individuals, with each acting in a particular role; an application
   or a set of applications, or a combination of these within an
   administrative domain.

   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,
   this document (unless otherwise specified) is referring to 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].


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.  An overview of
   (D)TLS can be found in section Appendix A.  Please refer to [RFC5246]
   and [RFC4347] for complete descriptions of the protocols.







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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 and the Transport Subsystem.

   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 a (D)TLS 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.

   The diagram below depicts where the TLS Transport Model fits into the
   architecture described in RFC3411 and the Transport Subsystem:


   +------------------------------+
   |    Network                   |
   +------------------------------+
      ^       ^              ^
      |       |              |
      v       v              v
   +-------------------------------------------------------------------+
   | +--------------------------------------------------+              |
   | |  Transport Subsystem                             |  +--------+  |
   | | +-----+ +-----+ +-------+             +-------+  |  |        |  |
   | | | UDP | | SSH | |(D)TLS |    . . .    | other |<--->| Cache  |  |
   | | |     | | TM  | | TM    |             |       |  |  |        |  |
   | | +-----+ +-----+ +-------+             +-------+  |  +--------+  |
   | +--------------------------------------------------+         ^    |
   |              ^                                               |    |
   |              |                                               |    |
   | Dispatcher   v                                               |    |
   | +--------------+ +---------------------+  +----------------+ |    |



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   | | 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 |
   +-------------------------------------------------------------------+

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



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       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 provides for verification of the identity of the (D)TLS
       server through the use of the (D)TLS protocol and the X.509
       certificates.  The TLS Transport Model MUST support
       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 which is
       greater than can occur through the natural operation of
       connectionless transport services, in order to effect
       unauthorized management operations.

       (D)TLS provides replay protection with a MAC that includes a
       sequence number.  Since UDP provides no sequencing ability DTLS
       uses a sliding window protocol with the sequence number 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.  The TLS
       Transport Model SHOULD support the 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, datagram-based security
       protocols like DTLS are susceptible to a variety of denial of
       service attacks because it is more vulnerable to spoofed
       messages.

       In order to counter these attacks, DTLS borrows the stateless
       cookie technique used by Photuris [RFC2522] and IKEv2 [RFC4306]
       and is described fully in section 4.2.1 of [RFC4347].  This
       mechanism, though, does not provide any defense against denial of
       service attacks mounted from valid IP addresses.  DTLS Transport



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       Model server implementations MUST support DTLS cookies.

       Implementations are not required to perform the stateless cookie
       exchange for every DTLS handshake, but in environments where an
       overload on server side resources is detectable by the
       implementation it is RECOMMENDED that the cookie exchange is
       utilized by the implementation.

   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, and the type and 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, through the
   cache, the application requests a security level for that session.
   The TLS Transport Model MUST ensure that the (D)TLS session provides
   security at least as 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



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   trust of particular algorithms.  Implementations should offer
   configuration settings for mapping algorithms to SNMPv3 security
   levels.

3.1.3.  (D)TLS Sessions

   (D)TLS sessions 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 session if needed,
   the (D)TLS session will already exist for an incoming message.

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

   DTLS sessions, 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
   associated for active sessions.  For further information see
   Section 5.  TLS and DTLS over SCTP sessions, on the other hand, do
   not require a unique pairing of address and port attributes since
   their lower layer protocols (TCP and SCTP) already provide adequate
   session framing.  But they must still provide a unique tlstmSessionID
   for referencing the session.

   The tlstmSessionID MAY be the same as the (D)TLS internal SessionID
   but caution must be exercised since the (D)TLS internal SessionID may
   change over the life of the connection as seen by the TLSTM (for
   example during renegotiation).  The tlstmSessionID identifier MUST
   NOT change during the entire duration of the connection from the
   TLSTM's perspective.

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 address and port)
   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.




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   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 sessions may be initiated by (D)TLS clients on behalf of SNMP
   appplications 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 is 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 generator, 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
   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, snmpDTLSUDPDomain, or snmpDTLSSCTPDomain
   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 tlstmParamsClientFingerprint parameter of
   the tlstmParamsTable should be set a value that refers to a locally
   held certificate to be used.  Other parameters, for example
   cryptographic configuration such as 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.





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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.  A brief overview of X.509 certificate
   infrastructure can be found in Appendix B.

   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.  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 are
   provisioned with certificates, which are signed by trusted
   certificate authorities (possibly the certificate itself).
   Furthermore, SNMP entities will most commonly need to be provisioned
   with root certificates which represent the list of trusted
   certificate authorities that an SNMP entity can use for certificate
   verification.  SNMP entities SHOULD also be provisioned with a 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
   through a trusted out of band mechanism into the server and its
   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
   tlstmCertToTSNTable.  This table allows mapping of incoming
   connections to tmSecurityNames through defined transformations.  The
   transformations defined in the TLSTM-MIB include:

   o  Mapping a certificate's fingerprint type and value to a directly
      specified tmSecurityName, or

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

   Implementations MAY choose to discard any connections for which no
   potential tlstmCertToTSNTable mapping exists before performing
   certificate verification to avoid expending computational resources



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   associated with certificate verification.

   Enterprise configurations are encouraged to map a "subjectAltName"
   component of the X.509 certificate to the TLSTM specific
   tmSecurityName.  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 C.

   This tmSecurityName may be later translated from a TLSTM specific
   tmSecurityName to a 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.

   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  | --> |       | --> |                | --> |     |
   +-------------+     +-------+     +----------------+     +-----+
                                                               |
                                                               V
                               +-------------+     +--------------+
                               | application | <-- | securityName |
                               +-------------+     +--------------+

4.2.  Messages

   As stated in Section 4.1.1 of [RFC4347], each DTLS record must fit
   within a single DTLS datagram.  The TLSTM SHOULD prohibit SNMP
   messages from being sent that exceeds the maximum DTLS message size.
   The TLSTM implementation SHOULD return an error when the DTLS message
   size would be exceeded and the message won't be sent.

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



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   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 passing 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 snmpTLSDomain,
      the snmpDTLSUDPDomain and the snmpDTLSSCTPDomain" 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.

   outgoingMessageLength:  The length of the outgoingMessage field.

   tmStateReference:  A handle/reference to tmState to be used when
      securing outgoing messages.








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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 snmpTLSDomain, the
      snmpDTLSUDPDomain and the snmpDTLSSCTPDomain" 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 and removed of the (D)TLS transport layer data.

   incomingMessageLength:  The length of the incomingMessage field.

   tmStateReference:  A handle/reference to tmSecurityData to be used by
      the security model.

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" [RFC5590] defines general requirements
   for caches and references.




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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 an TLSTM session.  Messages MUST NOT be sent
   through an existing (D)TLS session 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 and the TLSTM-
   MIB's tlstmCertToTSNTable DESCRIPTION clause.

   On the (D)TLS client side of a connection the tmSecurityName is
   presented to the TLS Transport Model by the application (possibly
   because of configuration specified in the SNMP-TARGET-MIB).

   The securityName MAY be derived from the tmSecurityName by a Security
   Model and MAY be used to configure notifications and access controls
   in MIB modules.  Transport Models SHOULD generate a predictable
   tmSecurityName so operators will know what to use when configuring
   MIB modules that use securityNames derived from tmSecurityNames.

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 session available for sending a
   corresponding outgoing message is the same (D)TLS session 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.







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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 first 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
   steps are broken into two different sections.  Section 5.1.1
   describes the needed steps for de-multiplexing multiple DTLS
   sessions, which is specifically needed for DTLS over UDP sessions.
   Section 5.1.2 describes the steps specific to transport processing
   once the (D)TLS processing has been completed.  It is assumed that
   TLS and DTLS/SCP protocol implementations already provide appropriate
   message demultiplexing and only the processing steps in Section 5.1.2
   are needed.

5.1.1.  DTLS Processing for Incoming Messages

   DTLS over UDP is significantly different in terms of session handling
   than when TLS or DTLS is run over session based streaming protocols
   like TCP or SCTP.  Specifically, the DTLS protocol, when run over
   UDP, does not have a session identifier that allows implementations
   to determine through which session a packet arrived.  It is always
   critical, however, that implementations be able to derive a
   tlstmSessionID from any session demultiplexing process.  When
   establishing a new session implementations MUST use a different UDP



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   source port number for each connection to a remote destination IP-
   address/port-number combination to ensure the remote entity can
   easily disambiguate between multiple sessions from a host to the same
   port on a server.

   A process for demultiplexing multiple DTLS sessions arriving over UDP
   must be incorporated into the procedures for processing an incoming
   message.  The steps in this section describe one possible method to
   accomplish this, although any implementation-dependent method should
   be suitable as long as the results are deterministic.  The important
   output results from the steps in this process are the
   transportDomain, the transportAddress, the wholeMessage, the
   wholeMessageLength, and a unique implementation-dependent session
   identifier (tlstmSessionID).

   This demultiplexing procedure assumes that upon session establishment
   an entry in a local transport mapping table is created in the
   Transport Model's Local Configuration Datastore (LCD).  The transport
   mapping table's entry should map a unique combination of the remote
   address, remote port number, local address and local port number to
   an implementation-dependent tlstmSessionID.

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

   2)  The TLS Transport Model queries the LCD using the transport
       parameters (source and destination addresses and ports) to
       determine if a session already exists and its tlstmSessionID.

       If a matching entry in the LCD does not exist then the message is
       passed to DTLS for processing without a corresponding
       tlstmSessionID.  The incoming packet may result in a new session
       being established if the receiving entity is acting as a DTLS
       server.  If DTLS returns success then stop processing of this
       message.  If DTLS returns an error then increment the
       snmpTlstmSessionNoSessions counter and stop processing the
       message.

       Note that an entry would already exist if the client and server's
       session establishment procedures had been successfully completed
       previously (as described both above and in Section 5.3) even if
       no message had yet been sent through the newly established
       session.  An entry may not exist, however, if a message not
       intended the SNMP entity was routed to it by mistake.  An entry
       might also be missing because of a "broken" session (see
       operational considerations).





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   3)  Retrieve the tlstmSessionID from the LCD.

   4)  The UDP packet and the tlstmSessionID are passed to DTLS for
       integrity checking and decryption.

       If the message fails integrity checks or other (D)TLS security
       processing then increment the tlstmDTLSProtectionErrors counter,
       discard and stop processing the message.

   5)  (D)TLS should return an incomingMessage and an
       incomingMessageLength.  These results and the tlstmSessionID are
       used below in the 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.

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

   tmTransportDomain  = snmpTLSTCPDomain, snmpDTLSUDPDomain or
      snmpDTLSSCTPDomain as appropriate.

   tmTransportAddress  = The address the message originated from.

   tmSecurityLevel  = The derived tmSecurityLevel for the session, as
      discussed in Section 3.1.2 and Section 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 (D)TLS session.

   tmSessionID  = The tlstmSessionID, which 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



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      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.

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

   The TLS Transport Model passes the transportDomain, transportAddress,
   wholeMessage, and wholeMessageLength to the Dispatcher using the
   receiveMessage ASI:

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

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.






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   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 either tmSessionID is 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 4b).  Instead of opening a new session an
       implementation MAY return a snmpTlstmSessionNoSessions error to
       the calling module and stop 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.

       4a)  If there is a corresponding LCD entry, then this session
            will be used to send the message.

       4b)  If there is not a corresponding LCD entry, then open a
            session using the openSession() ASI (discussed further in
            Section 5.3).  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
            tmStateReferenc, increment the snmpTlstmSessionOpenErrors,
            return an error indication to the calling module and stop
            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 (3 or 4),
       pass the outgoingMessage to (D)TLS for encapsulation and
       transmission.

5.3.  Establishing a Session

   The TLS Transport Model provides the following primitive to establish
   a new (D)TLS session:





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   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 a
   SNMP over (D)TLS session between SNMP engines for exchanging SNMP
   messages.  This process is followed by any SNMP engine establishing a
   session for subsequent use.

   This 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 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 a SNMP-TARGET-MIB based operation, the
       certificate will potentially have been identified via the
       tlstmParamsTable mapping and the cipher_suites will have to be
       taken from system-wide or implementation-specific configuration.
       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
       session.  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.

   2)  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
       a tlstmServerCertificateUnknown or tlstmServerInvalidCertificate



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       notification SHOULD be sent as appropriate.  Reasons for server
       certificate invalidation includes, but is not limited to,
       cryptographic validation failures and an unexpected presented
       certificate identity.

   3)  Once a (D)TLS secured session is established and both sides have
       verified the authenticity of the peer's certificate (e.g.
       [RFC5280]) then each side will determine and/or check the
       identity of the remote entity using the procedures described
       below.

       a)  The (D)TLS server side of the connection identifies the
           authenticated identity from the (D)TLS client's principal
           certificate using configuration information from the
           tlstmCertToTSNTable 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 session 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 tlstmCertToTSNTable 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 tlstmCertToTSNTable) then the session
           establishment MUST fail, the
           snmpTlstmSessionInvalidClientCertificates object is
           incremented and processing stops.

       b)  The (D)TLS client side of the connection MUST verify that
           authenticated identity of 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 and the client certificate has been
           transmitted.

           If the connection is being established from configuration
           based on SNMP-TARGET-MIB configuration then the procedures in
           the tlstmAddrTable DESCRIPTION clause should be followed to
           determine if the presented identity matches the expectations
           of the configuration.  Path validation procedures (like those
           defined in [RFC5280]) MUST be followed.  If a server identity
           name has been configured in the tlstmAddrServerIdentity
           column then this reference identity must be compared against
           the presented identity (for example using procedures
           described in [I-D.saintandre-tls-server-id-check]).

           If the connection is being established for other reasons then



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           configuration and procedures outside the scope of this
           document should be followed.

           (D)TLS provides assurance that the authenticated identity has
           been signed by a trusted configured certificate 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, the snmpTlstmSessionInvalidServerCertificates object is
           incremented and processing stops.

   4)  The TLSTM-specific session identifier (tlstmSessionID) is set in
       the sessionID 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 session for future
       use.

   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].  Supporting this will allow, for example,
   sending notifications to a specific principal at a given TCP, UDP or
   SCTP 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 the snmpTlstmSessionCloses counter.

   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 session.  This SHOULD 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 C.

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  New TransportDomain and TransportAddress formats 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 TLSTM-MIB defines some counters that can provide network managers
   with information about (D)TLS session usage and potential errors that
   a MIB-instrumented device may be experiencing.

6.4.  Configuration Tables

   The TLSTM-MIB defines configuration tables that a manager can use for
   configuring a MIB-instrumented 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 securityNames.



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6.4.1.  Notifications

   The TLSTM-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 (tlstmServerCertificateUnknown) or
   because cryptographic validation failed
   (tlstmServerInvalidCertificate).

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 TLSTM-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 TLSTM-MIB module contained in this document is for managing TLS
   Transport Model information.

6.5.1.  MIB Modules Required for IMPORTS

   The TLSTM-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


TLSTM-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE,
    OBJECT-IDENTITY, snmpModules, snmpDomains,
    Counter32, Unsigned32, NOTIFICATION-TYPE
      FROM SNMPv2-SMI
    TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType,
    AutonomousType
      FROM SNMPv2-TC
    MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
      FROM SNMPv2-CONF
    SnmpAdminString
      FROM SNMP-FRAMEWORK-MIB
    snmpTargetParamsName, snmpTargetAddrName
      FROM SNMP-TARGET-MIB
    ;




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tlstmMIB MODULE-IDENTITY
    LAST-UPDATED "200912300000Z"
    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

                  Co-editors:
                     Wes Hardaker
                     Sparta, Inc.
                     P.O. Box 382
                     Davis, CA  95617
                     USA
                     ietf@hardakers.net
                  "

    DESCRIPTION  "
        The TLS Transport Model MIB

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

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

-- NOTE to RFC editor: replace XXXX with actual RFC number
--                     for this document and remove this note



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       REVISION     "200912300000Z"
       DESCRIPTION  "The initial version, published in RFC XXXX."
-- NOTE to RFC editor: replace XXXX with actual RFC number
--                     for this document and remove this note

    ::= { snmpModules xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and
--          remove this note

-- ************************************************
-- subtrees of the TLSTM-MIB
-- ************************************************

tlstmNotifications OBJECT IDENTIFIER ::= { tlstmMIB 0 }
tlstmIdentities    OBJECT IDENTIFIER ::= { tlstmMIB 1 }
tlstmObjects       OBJECT IDENTIFIER ::= { tlstmMIB 2 }
tlstmConformance   OBJECT IDENTIFIER ::= { tlstmMIB 3 }

-- ************************************************
-- tlstmObjects - Objects
-- ************************************************

snmpTLSTCPDomain OBJECT-IDENTITY
    STATUS      current
    DESCRIPTION
        "The SNMP over TLS 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."

    ::= { snmpDomains xx }


-- RFC Ed.: replace xx with IANA-assigned number and
--          remove this note

-- RFC Ed.: replace 'tls' with the actual IANA assigned prefix string
--          if 'tls' is not assigned to this document.

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




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        The securityName prefix to be associated with the
        snmpDTLSUDPDomain is 'dudp'.  This prefix may be used by
        security models or other components to identify which secure
        transport infrastructure authenticated a securityName."

    ::= { snmpDomains yy }


-- RFC Ed.: replace yy with IANA-assigned number and
--          remove this note

-- RFC Ed.: replace 'dudp' with the actual IANA assigned prefix string
--          if 'dtls' is not assigned to this document.

snmpDTLSSCTPDomain OBJECT-IDENTITY
    STATUS      current
    DESCRIPTION
        "The SNMP over DTLS/SCTP transport domain. The corresponding
        transport address is of type SnmpTLSAddress.

        The securityName prefix to be associated with the
        snmpDTLSSCTPDomain is 'dsct'.  This prefix may be used by
        security models or other components to identify which secure
        transport infrastructure authenticated a securityName."

    ::= { snmpDomains zz }


-- RFC Ed.: replace zz with IANA-assigned number and
--          remove this note

-- RFC Ed.: replace 'dsct' with the actual IANA assigned prefix string
--          if 'dtls' is not assigned to this document.

SnmpTLSAddress ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "1a"
    STATUS       current
    DESCRIPTION
        "Represents a IPv4 address, an IPv6 address or an 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, surrounded
        by square brackets ('[', US-ASCII character 0x5B, and ']',
        US-ASCII character 0x5D), followed by a colon ':' (US-ASCII



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        character 0x3A) and a decimal port number in US-ASCII.

        A hostname is always in US-ASCII (as per RFC1033);
        internationalized hostnames are encoded in US-ASCII as
        specified in RFC 3490.  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
        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 1033: DOMAIN ADMINISTRATORS OPERATIONS GUIDE
       RFC 3490: Internationalizing Domain Names in Applications
       RFC 3986: Uniform Resource Identifier (URI): Generic Syntax
       RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
      "
    SYNTAX       OCTET STRING (SIZE (1..255))

Fingerprint ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "1x:254x"
    STATUS       current
    DESCRIPTION



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       "A Fingerprint value that can be used to uniquely reference
       other data of potentially arbitrary length.

       A Fingerprint 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
       (RFC5246).  The remaining octets are filled using the results
       of the hashing algorithm.

       This TEXTUAL-CONVENTION allows for a zero-length (blank)
       Fingerprint 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
      "
    SYNTAX       OCTET STRING (SIZE (0..255))

-- Identities

tlstmCertToTSNMIdentities    OBJECT IDENTIFIER ::= { tlstmIdentities 1 }

tlstmCertSpecified 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 tlstmCertToTSNData column.
                  The column must contain a SnmpAdminString compliant
                  value or contains a zero length string then the
                  mapping will be considered a failure."
    ::= { tlstmCertToTSNMIdentities 1 }

tlstmCertSANRFC822Name 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 lower case.

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

tlstmCertSANDNSName OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "Maps a subjectAltName's dNSName to a
                  tmSecurityName by directly passing the value without
                  any transformations."



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    ::= { tlstmCertToTSNMIdentities 3 }

tlstmCertSANIpAddress 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 hexadecimal string without any colon
                     separators.

                     Note that the resulting length is the maximum
                     length supported by the View-Based Access Control
                     Model (VACM).  Note that 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."
    ::= { tlstmCertToTSNMIdentities 4 }

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

                  |------------+------------------------|
                  | Type       | Algorithm              |
                  |------------+------------------------|
                  | rfc822Name | tlstmCertSANRFC822Name |
                  | dNSName    | tlstmCertSANDNSName    |
                  | ipAddress  | tlstmCertSANIpAddress  |
                  |------------+------------------------|

                  The first matching subjectAltName value found in the
                  certificate any of the above types MUST be used when
                  deriving the tmSecurityName."
    ::= { tlstmCertToTSNMIdentities 5 }

tlstmCertCommonName OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "Maps a certificate's CommonName to a
                  tmSecurityName by directly passing the value without



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                  any transformations."
    ::= { tlstmCertToTSNMIdentities 6 }

-- The snmpTlstmSession Group

snmpTlstmSession           OBJECT IDENTIFIER ::= { tlstmObjects 1 }

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

snmpTlstmSessionCloses  OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times a closeSession() request has been
        executed as an (D)TLS client, 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 }

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 4 }

snmpTlstmSessionInvalidClientCertificates OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current



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    DESCRIPTION
        "The number of times an incoming session was not established
        on an (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 tlstmCertToTSNTable."
    ::= { snmpTlstmSession 5 }

snmpTlstmSessionUnknownServerCertificate OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an outgoing session was not established
         on an (D)TLS client because the server certificate presented
         by a SNMP over (D)TLS server was invalid because no
         configured fingerprint or CA was acceptable to validate it.
         This may result because there was no entry in the
         tlstmAddrTable or because no path could be found to known
         certificate authority."
    ::= { snmpTlstmSession 6 }

snmpTlstmSessionInvalidServerCertificates OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an outgoing session was not established
         on an (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.  I.E.,
         a cryptographic validation occurred during certificate
         validation processing.

        Reasons for invalidation include, but are not
        limited to, cryptographic validation failures."
    ::= { snmpTlstmSession 7 }

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 8 }

tlstmTLSProtectionErrors OBJECT-TYPE



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    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times (D)TLS processing resulted in a message
        being discarded because it failed its integrity test,
        decryption processing or other (D)TLS processing."
    ::= { snmpTlstmSession 9 }


-- Configuration Objects

tlstmConfig          OBJECT IDENTIFIER ::= { tlstmObjects 2 }

-- Certificate mapping

tlstmCertificateMapping    OBJECT IDENTIFIER ::= { tlstmConfig 1 }

tlstmCertToTSNCount OBJECT-TYPE
    SYNTAX      Unsigned32
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "A count of the number of entries in the tlstmCertToTSNTable"
    ::= { tlstmCertificateMapping 1 }

tlstmCertToTSNTableLastChanged OBJECT-TYPE
    SYNTAX      TimeStamp
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "The value of sysUpTime.0 when the tlstmCertToTSNTable
        was last modified through any means, or 0 if it has not been
        modified since the command responder was started."
    ::= { tlstmCertificateMapping 2 }

tlstmCertToTSNTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF TlstmCertToTSNEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A table listing the X.509 certificates known to the entity
        and the associated method for determining the SNMPv3 security
        name from a certificate.

        On an incoming (D)TLS/SNMP connection the client's presented
        certificate must be examined and validated based on an
        established trusted path from a CA certificate or self-signed



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        public certificate (e.g. RFC5280).  This table provides a
        mapping from a validated certificate to a tmSecurityName.
        This table does not provide any mechanisms for uploading
        trusted certificates; the transfer of any needed trusted
        certificates for path validation is expected to occur through
        an out-of-band transfer.

        Once the authenticity of a certificate has been verified, 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 tlstmCertToTSNID value.  Each row's
        tlstmCertToTSNFingerprint value determines whether the row is a
        match for the incoming connection:

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

            2) If the row's tlstmCertToTSNFingerprint value identifies
               a locally held copy of a trusted CA certificate and
               that CA certificated 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 tlstmCertToTSNMapType
        value can be used to determine how the tmSecurityName to
        associate with the session should be determined.  See the
        tlstmCertToTSNMapType 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 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.

        Missing values of tlstmCertToTSNID are acceptable and
        implementations should continue to the next highest numbered
        row.  E.G., the table may legally contain only two rows with
        tlstmCertToTSNID values of 10 and 20.

        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



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        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 but usage of the CommonName field is deprecated.
        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."
    ::= { tlstmCertificateMapping 3 }

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

TlstmCertToTSNEntry ::= SEQUENCE {
    tlstmCertToTSNID           Unsigned32,
    tlstmCertToTSNFingerprint  Fingerprint,
    tlstmCertToTSNMapType      AutonomousType,
    tlstmCertToTSNData         OCTET STRING,
    tlstmCertToTSNStorageType  StorageType,
    tlstmCertToTSNRowStatus    RowStatus
}

tlstmCertToTSNID OBJECT-TYPE
    SYNTAX      Unsigned32 (1..4294967295)
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A unique, prioritized index for the given entry."
    ::= { tlstmCertToTSNEntry 1 }

tlstmCertToTSNFingerprint OBJECT-TYPE
    SYNTAX      Fingerprint (SIZE(1..255))
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "A cryptographic hash of a X.509 certificate.  The results of
        a successful matching fingerprint to either the trusted CA in



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        the certificate validation path or to the certificate itself
        is dictated by the tlstmCertToTSNMapType column."
    ::= { tlstmCertToTSNEntry 2 }

tlstmCertToTSNMapType 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 tlstmCertToTSNFingerprint matches to
        look for a mapping that succeeds."
    DEFVAL { tlstmCertSpecified }
    ::= { tlstmCertToTSNEntry 3 }

tlstmCertToTSNData OBJECT-TYPE
    SYNTAX      OCTET STRING (SIZE(0..1024))
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "Axillary data used as optional configuration information for
        a given mapping specified by the tlstmCertToTSNMapType 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 { "" }
    ::= { tlstmCertToTSNEntry 4 }

tlstmCertToTSNStorageType 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 }
    ::= { tlstmCertToTSNEntry 5 }



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tlstmCertToTSNRowStatus 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, a manager 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
        tlstmParamsRowStatus column is 'notReady'.

        In particular, a newly created row cannot be made active until
        the corresponding tlstmCertToTSNFingerprint,
        tlstmCertToTSNMapType, and tlstmCertToTSNData columns have been
        set.

        The following objects may not be modified while the
        value of this object is active(1):
            - tlstmCertToTSNFingerprint
            - tlstmCertToTSNMapType
            - tlstmCertToTSNData
        An attempt to set these objects while the value of
        tlstmParamsRowStatus is active(1) will result in
        an inconsistentValue error."
    ::= { tlstmCertToTSNEntry 6 }

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

tlstmParamsCount OBJECT-TYPE
    SYNTAX      Unsigned32
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "A count of the number of entries in the tlstmParamsTable"
    ::= { tlstmCertificateMapping 4 }

tlstmParamsTableLastChanged OBJECT-TYPE
    SYNTAX      TimeStamp
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "The value of sysUpTime.0 when the tlstmParamsTable
        was last modified through any means, or 0 if it has not been
        modified since the command responder was started."



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    ::= { tlstmCertificateMapping 5 }

tlstmParamsTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF TlstmParamsEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "This table extends the SNMP-TARGET-MIB's
        snmpTargetParamsTable with an additional (D)TLS client-side
        certificate fingerprint identifier to use when establishing
        new (D)TLS connections."
    ::= { tlstmCertificateMapping 6 }

tlstmParamsEntry OBJECT-TYPE
    SYNTAX      TlstmParamsEntry
    MAX-ACCESS  not-accessible
    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 }
    ::= { tlstmParamsTable 1 }

TlstmParamsEntry ::= SEQUENCE {
    tlstmParamsClientFingerprint Fingerprint,
    tlstmParamsStorageType       StorageType,
    tlstmParamsRowStatus         RowStatus
}

tlstmParamsClientFingerprint OBJECT-TYPE
    SYNTAX      Fingerprint
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "A cryptographic hash of a X.509 certificate.  This object
        should store the hash of a locally held X.509 certificate that
        should be used when initiating a (D)TLS connection as a (D)TLS
        client."
    ::= { tlstmParamsEntry 1 }




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tlstmParamsStorageType 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 }
    ::= { tlstmParamsEntry 2 }


tlstmParamsRowStatus 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, a manager 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
        tlstmParamsRowStatus column is 'notReady'.

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

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

        An attempt to set these objects while the value of
        tlstmParamsRowStatus is active(1) will result in
        an inconsistentValue error.

        If this row is deleted it has no effect on the corresponding
        row in the targetParamsTable.

        If the corresponding row in the targetParamsTable is deleted
        then this row must be automatically removed."
    ::= { tlstmParamsEntry 3 }

-- Lists expected certificate fingerprints to be presented by a DTLS
-- server




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tlstmAddrCount OBJECT-TYPE
    SYNTAX      Unsigned32
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "A count of the number of entries in the tlstmAddrTable"
    ::= { tlstmCertificateMapping 7 }

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

tlstmAddrTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF TlstmAddrEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "This table extends the SNMP-TARGET-MIB's snmpTargetAddrTable
        with an expected (D)TLS server-side certificate identifier to
        expect when establishing a new (D)TLS connections.  If a
        matching row in this table exists and the row is active then
        the fingerprint identifier from the tlstmAddrServerFingerprint
        columnshould be compared against the fingerprint of the
        certificate being presented by the server.  If the fingerprint
        of the certificate presented by the server does not match the
        tlstmAddrServerFingerprint column's value then the connection
        MUST NOT be established.

        If a matching row exists with a zero-length
        tlstmAddrServerFingerprint value and the certificate can still
        be validated through another certificate validation path
        (e.g. RFC5280) then the server's presented identity should be
        checked against the value of the tlstmAddrServerIdentity
        column.  If the server's identity does not match the reference
        identity found in the tlstmAddrServerIdentity column then the
        connection MUST NOT be established.  A tlstmAddrServerIdentity
        may contain a '*' to match any server's identity or may
        contain a '*.' prefix to match any server identity from a
        given domain (e.g. '*.example.com').

        If no matching row exists in this table then the connection
        SHOULD still proceed if another certificate validation path



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        algorithm (e.g. RFC5280) can be followed to a configured trust
        anchor."
    ::= { tlstmCertificateMapping 9 }

tlstmAddrEntry OBJECT-TYPE
    SYNTAX      TlstmAddrEntry
    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
        tlstmAddrEntry 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 a snmpTargetAddrEntry row then the connection SHOULD
        still proceed if some other certificate validation path
        algorithm (e.g. RFC5280) can be followed to a configured trust
        anchor."
    INDEX    { IMPLIED snmpTargetAddrName }
    ::= { tlstmAddrTable 1 }

TlstmAddrEntry ::= SEQUENCE {
    tlstmAddrServerFingerprint    Fingerprint,
    tlstmAddrServerIdentity       SnmpAdminString,
    tlstmAddrStorageType          StorageType,
    tlstmAddrRowStatus            RowStatus
}

tlstmAddrServerFingerprint OBJECT-TYPE
    SYNTAX      Fingerprint
    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 { "" }
    ::= { tlstmAddrEntry 1 }

tlstmAddrServerIdentity OBJECT-TYPE
    SYNTAX      SnmpAdminString
    MAX-ACCESS  read-create



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    STATUS      current
    DESCRIPTION
        "The reference identity to check against the identity
        presented by the remote system.  A single ASCII '*' character
        (ASCII code 0x2a) may be used as a wildcard string and will
        match any presented server identity.  A '*.' prefix may also
        be used to match any identity within a given domain
        (e.g. '*.example.com' will match both 'foo.example.com' and
        'bar.example.com')."
    REFERENCE "draft-saintandre-tls-server-id-check"
    DEFVAL { "*" }
    ::= { tlstmAddrEntry 2 }

tlstmAddrStorageType 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 }
    ::= { tlstmAddrEntry 3 }


tlstmAddrRowStatus 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, a manager 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 tlstmAddrRowStatus
        column is 'notReady'.

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

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



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        An attempt to set these objects while the value of
        tlstmAddrRowStatus is active(1) will result in
        an inconsistentValue error.

        If this row is deleted it has no effect on the corresponding
        row in the targetAddrTable.

        If the corresponding row in the targetAddrTable is deleted
        then this row must be automatically removed."
    ::= { tlstmAddrEntry 4 }


-- ************************************************
--  tlstmNotifications - Notifications Information
-- ************************************************

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

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

tlstmServerInvalidCertificate NOTIFICATION-TYPE
    OBJECTS { tlstmAddrServerFingerprint,
              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.  I.E., a
         cryptographic validation occurred during certificate
         validation processing.

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




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-- ************************************************
-- tlstmCompliances - Conformance Information
-- ************************************************

tlstmCompliances OBJECT IDENTIFIER ::= { tlstmConformance 1 }

tlstmGroups OBJECT IDENTIFIER ::= { tlstmConformance 2 }



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

tlstmCompliance MODULE-COMPLIANCE
    STATUS      current
    DESCRIPTION
        "The compliance statement for SNMP engines that support the
        TLSTM-MIB"
    MODULE
        MANDATORY-GROUPS { tlstmStatsGroup,
                           tlstmIncomingGroup,
                           tlstmOutgoingGroup,
                           tlstmNotificationGroup }
    ::= { tlstmCompliances 1 }

-- ************************************************
-- Units of conformance
-- ************************************************
tlstmStatsGroup OBJECT-GROUP
    OBJECTS {
        snmpTlstmSessionOpens,
        snmpTlstmSessionCloses,
        snmpTlstmSessionOpenErrors,
        snmpTlstmSessionNoSessions,
        snmpTlstmSessionInvalidClientCertificates,
        snmpTlstmSessionUnknownServerCertificate,
        snmpTlstmSessionInvalidServerCertificates,
        snmpTlstmSessionInvalidCaches,
        tlstmTLSProtectionErrors
    }
    STATUS      current
    DESCRIPTION
        "A collection of objects for maintaining
        statistical information of an SNMP engine which
        implements the SNMP TLS Transport Model."
    ::= { tlstmGroups 1 }




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tlstmIncomingGroup OBJECT-GROUP
    OBJECTS {
        tlstmCertToTSNCount,
        tlstmCertToTSNTableLastChanged,
        tlstmCertToTSNFingerprint,
        tlstmCertToTSNMapType,
        tlstmCertToTSNData,
        tlstmCertToTSNStorageType,
        tlstmCertToTSNRowStatus
    }
    STATUS      current
    DESCRIPTION
        "A collection of objects for maintaining
        incoming connection certificate mappings to
        tmSecurityNames of an SNMP engine which implements the
        SNMP TLS Transport Model."
    ::= { tlstmGroups 2 }

tlstmOutgoingGroup OBJECT-GROUP
    OBJECTS {
        tlstmParamsCount,
        tlstmParamsTableLastChanged,
        tlstmParamsClientFingerprint,
        tlstmParamsStorageType,
        tlstmParamsRowStatus,
        tlstmAddrCount,
        tlstmAddrTableLastChanged,
        tlstmAddrServerFingerprint,
        tlstmAddrServerIdentity,
        tlstmAddrStorageType,
        tlstmAddrRowStatus
    }
    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."
    ::= { tlstmGroups 3 }

tlstmNotificationGroup NOTIFICATION-GROUP
    NOTIFICATIONS {
        tlstmServerCertificateUnknown,
        tlstmServerInvalidCertificate
    }
    STATUS current
    DESCRIPTION
        "Notifications"
    ::= { tlstmGroups 4 }



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END


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 the (D)TLS client and the (D)TLS server.  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 disconnect messages.  Implementations SHOULD also have a
   system in place for detecting "broken" sessions through the use of
   heartbeats [I-D.seggelmann-tls-dtls-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.



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   Implementations MAY also choose to designate a single Notification
   Receiver Principal to receive all incoming notifications or select an
   implementation specific method of selecting a server certificate to
   present to clients.

8.3.  contextEngineID Discovery

   Most command responders have contextEngineIDs that are identical to
   the USM securityEngineID.  USM provides a discovery service that
   allows command generators to determine a securityEngineID and thus a
   default contextEngineID to use.  Because the TLS Transport Model does
   not make use of a securityEngineID, it may be difficult for command
   generators to discover a suitable default contextEngineID.
   Implementations should consider offering another engineID discovery
   mechanism to continue providing Command Generators with a suitable
   contextEngineID mechanism.  A recommended discovery solution is
   documented 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 are
   additionally based on other transports (TCP, UDP and SCTP).  These
   three 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].  DTLS adds to the security considerations of TLS only
   because it is more vulnerable to denial of service attacks.  A random
   cookie exchange was added to the handshake to prevent anonymous
   denial of service attacks.  RFC 4347 recommends that the cookie
   exchange is utilized for all handshakes and therefore this
   specification also RECOMMENDEDs that implementers also support this
   cookie exchange.




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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
   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 an configured accepted
   Certificate 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 responder'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 a 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
   tlstmCertToTSNTable 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 tlstmCertToTSNID
   value.

9.2.  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



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   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.

9.3.  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 tlstmParamsTable can be used to change the outgoing X.509
      certificate used to establish a (D)TLS connection.  Modification
      to objects in this table need to be adequately authenticated since
      modification to 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 tlstmAddrTable can be used to change the expectations of the
      certificates presented by a remote (D)TLS server.  Modification to
      objects in this table need to be adequately authenticated since
      modification to 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 tlstmCertToTSNTable is used to specify the mapping of incoming
      X.509 certificates to tmSecurityNames which eventually get mapped
      to a SNMPv3 securityName.  Modification to objects in this table
      need to be adequately authenticated since modification to 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.

   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



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


10.  IANA Considerations

   IANA is requested to assign:

   1.   a TCP port number above 1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for receipt of SNMP command messages over a
        TLS Transport Model as defined in this document,

   2.   a TCP port number above 1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for receipt of SNMP notification messages
        over a TLS Transport Model as defined in this document,

   3.   a UDP port number above 1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for receipt of SNMP command messages over a



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        DTLS/UDP connection as defined in this document,

   4.   a UDP port number above 1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for receipt of SNMP notification messages
        over a DTLS/UDP connection as defined in this document,

   5.   a SCTP port number above 1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for receipt of SNMP command messages over a
        DTLS/SCTP connection as defined in this document,

   6.   a SCTP port number above 1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for receipt of SNMP notification messages
        over a DTLS/SCTP connection as defined in this document,

   7.   an SMI number under snmpDomains for the snmpTLSTCPDomain object
        identifier,

   8.   an SMI number under snmpDomains for the snmpDTLSUDPDomain object
        identifier,

   9.   an SMI number under snmpDomains for the snmpDTLSSCTPDomain
        object identifier,

   10.  a SMI number under snmpModules, for the MIB module in this
        document,

   11.  "tls" as the corresponding prefix for the snmpTLSTCPDomain in
        the SNMP Transport Model registry,

   12.  "dudp" as the corresponding prefix for the snmpDTLSUDPDomain in
        the SNMP Transport Model registry,

   13.  "dsct" as the corresponding prefix for the snmpDTLSSCTPDomain in
        the SNMP Transport Model registry;

   If possible, IANA is requested to use matching port numbers for all
   assignments for SNMP Commands being sent over TLS, DTLS/UDP, DTLS/
   SCTP.

   If possible, IANA is requested to use matching port numbers for all
   assignments for SNMP Notifications being sent over TLS, DTLS/UDP,
   DTLS/SCTP.

   Editor's note: this section should be replaced with appropriate
   descriptive assignment text after IANA assignments are made and prior



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   to publication.


11.  Acknowledgements

   This document closely follows and copies the Secure Shell Transport
   Model for SNMP defined by David Harrington and Joseph Salowey in
   [RFC5292].

   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, Tom Petch, Randy
   Presuhn, Ray Purvis, Joseph Salowey, Jurgen Schonwalder, Dave Shield.

   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

   [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,



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              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.

   [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.

   [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.

12.2.  Informative References

   [RFC2522]  Karn, P. and W. Simpson, "Photuris: Session-Key Management
              Protocol", RFC 2522, March 1999.

   [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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   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

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

   [RFC5292]  Chen, E. and S. Sangli, "Address-Prefix-Based Outbound
              Route Filter for BGP-4", RFC 5292, August 2008.

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

   [I-D.saintandre-tls-server-id-check]
              Saint-Andre, P., Zeilenga, K., Hodges, J., and B. Morgan,
              "Best Practices for Checking of Server Identities in the
              Context of Transport Layer Security (TLS)".

   [I-D.seggelmann-tls-dtls-heartbeat]
              Seggelmann, R., Tuexen, M., and M. Williams, "Transport
              Layer Security and Datagram Transport Layer Security
              Heartbeat Extension".

   [AES]      National Institute of Standards, "Specification for the
              Advanced Encryption Standard (AES)".

   [DES]      National Institute of Standards, "American National
              Standard for Information Systems-Data Link Encryption".

   [DSS]      National Institute of Standards, "Digital Signature
              Standard".

   [RSA]      Rivest, R., Shamir, A., and L. Adleman, "A Method for
              Obtaining Digital Signatures and Public-Key
              Cryptosystems".

   [X509]     , ITU., "INFORMATION TECHNOLOGY  OPEN SYSTEMS
              INTERCONNECTION  THE DIRECTORY: PUBLIC-KEY AND ATTRIBUTE
              CERTIFICATE FRAMEWORKS".


Appendix A.  (D)TLS Overview

   The (D)TLS protocol is composed of two layers: the (D)TLS Record
   Protocol and the (D)TLS Handshake Protocol.  The following
   subsections provide an overview of these two layers.  Please refer to
   [RFC4347] for a complete description of the protocol.



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A.1.  The (D)TLS Record Protocol

   At the lowest layer, layered on top of the transport control protocol
   or a datagram transport protocol (e.g.  UDP or SCTP) is the (D)TLS
   Record Protocol.

   The (D)TLS Record Protocol provides security that has three basic
   properties:

   o  The session can be confidential.  Symmetric cryptography is used
      for data encryption (e.g., [AES], [DES] etc.).  The keys for this
      symmetric encryption are generated uniquely for each session and
      are based on a secret negotiated by another protocol (such as the
      (D)TLS Handshake Protocol).  The Record Protocol can also be used
      without encryption.

   o  Messages can have data integrity.  Message transport includes a
      message integrity check using a keyed MAC.  Secure hash functions
      (e.g., SHA, MD5, etc.) are used for MAC computations.  The Record
      Protocol can operate without a MAC, but is generally only used in
      this mode while another protocol is using the Record Protocol as a
      transport for negotiating security parameters.

   o  Messages are protected against replay.  (D)TLS uses explicit
      sequence numbers and integrity checks.  DTLS uses a sliding window
      to protect against replay of messages within a session.

   (D)TLS also provides protection against replay of entire sessions.
   In a properly-implemented keying material exchange, both sides will
   generate new random numbers for each exchange.  This results in
   different encryption and integrity keys for every session.

A.2.  The (D)TLS Handshake Protocol

   The (D)TLS Record Protocol is used for encapsulation of various
   higher-level protocols.  One such encapsulated protocol, the (D)TLS
   Handshake Protocol, allows the server and client to authenticate each
   other and to negotiate an integrity algorithm, an encryption
   algorithm and cryptographic keys before the application protocol
   transmits or receives its first octet of data.  Only the (D)TLS
   client can initiate the handshake protocol.  The (D)TLS Handshake
   Protocol provides security that has four basic properties:

   o  The peer's identity can be authenticated using asymmetric (public
      key) cryptography (e.g., RSA [RSA], DSS [DSS], etc.).  This
      authentication can be made optional, but is generally required by
      at least one of the peers.




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      (D)TLS supports three authentication modes: authentication of both
      the server and the client, server authentication with an
      unauthenticated client, and total anonymity.  For authentication
      of both entities, each entity provides a valid certificate chain
      leading to an acceptable certificate authority.  Each entity is
      responsible for verifying that the other's certificate is valid
      and has not expired or been revoked.  See
      [I-D.saintandre-tls-server-id-check] for further details on
      standardized processing when checking server certificate
      identities.

   o  The negotiation of a shared secret is secure: the negotiated
      secret is unavailable to eavesdroppers, and for any authenticated
      handshake the secret cannot be obtained, even by an attacker who
      can place himself in the middle of the session.

   o  The negotiation is not vulnerable to malicious modification: it is
      infeasible for an attacker to modify negotiation communication
      without being detected by the parties to the communication.

   o  DTLS uses a stateless cookie exchange to protect against anonymous
      denial of service attacks and has retransmission timers, sequence
      numbers, and counters to handle message loss, reordering, and
      fragmentation.


Appendix B.  PKIX Certificate Infrastructure

   Users of a public key from a PKIX / X.509 certificate can be be
   confident that the associated private key is owned by the correct
   remote subject (person or system) with which an encryption or digital
   signature mechanism will be used.  This confidence is obtained
   through the use of public key certificates, which are data structures
   that bind public key values to subjects.  The binding is asserted by
   having a trusted CA digitally sign each certificate.  The CA may base
   this assertion upon technical means (i.e., proof of possession
   through a challenge-response protocol), presentation of the private
   key, or on an assertion by the subject.  A certificate has a limited
   valid lifetime which is indicated in its signed contents.  Because a
   certificate's signature and timeliness can be independently checked
   by a certificate-using client, certificates can be distributed via
   untrusted communications and server systems, and can be cached in
   unsecured storage in certificate-using systems.

   ITU-T X.509 (formerly CCITT X.509) or ISO/IEC/ITU 9594-8 [X509],
   which was first published in 1988 as part of the X.500 Directory
   recommendations, defines a standard certificate format which is a
   certificate which binds a subject (principal) to a public key value.



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   This was later further expanded and documented in [RFC5280].

   A X.509 certificate is a sequence of three required fields:

   tbsCertificate:  The tbsCertificate field contains the names of the
      subject and issuer, a public key associated with the subject, a
      validity period, and other associated information.  This field may
      also contain extension components.

   signatureAlgorithm:  The signatureAlgorithm field contains the
      identifier for the cryptographic algorithm used by the certificate
      authority (CA) to sign this certificate.

   signatureValue:  The signatureValue field contains a digital
      signature computed by the CA upon the ASN.1 DER encoded
      tbsCertificate field.  The ASN.1 DER encoded tbsCertificate is
      used as the input to the signature function.  This signature value
      is then ASN.1 DER encoded as a BIT STRING and included in the
      Certificate's signature field.  By generating this signature, the
      CA certifies the validity of the information in the tbsCertificate
      field.  In particular, the CA certifies the binding between the
      public key material and the subject of the certificate.

   The basic X.509 authentication procedure is as follows: A system is
   initialized with a number of root certificates that contain the
   public keys of a number of trusted CAs.  When a system receives a
   X.509 certificate, signed by one of those CAs, the certificate has to
   be verified.  It first checks the signatureValue field by using the
   public key of the corresponding trusted CA.  Then it compares the
   digest of the received certificate with a digest of the
   tbsCertificate field.  If they match, then the subject in the
   tbsCertificate field is authenticated.


Appendix C.  Target and Notificaton Configuration Example

   Configuring the SNMP-TARGET-MIB and NOTIFICATION-MIB along with
   access control settings for the SNMP-VIEW-BASED-ACM-MIB can be a
   daunting task without an example to follow.  The following section
   describes an example of what pieces must be in place to accomplish
   this configuration.

   The isAccessAllowed() ASI requires configuration to exist in the
   following SNMP-VIEW-BASED-ACM-MIB tables:

      vacmSecurityToGroupTable
      vacmAccessTable
      vacmViewTreeFamilyTable



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   The only table that needs to be discussed as particularly different
   here is the vacmSecurityToGroupTable.  This table is indexed by both
   the SNMPv3 security model and the security name.  The security model,
   when TLSTM is in use, should be set to the value of 4, corresponding
   to the TSM [RFC5591].  An example vacmSecurityToGroupTable row might
   be filled out as follows (using a single SNMP SET request):


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

   This example will assume that the "administrators" group has been
   given proper permissions via rows in the vacmAccessTable and
   vacmViewTreeFamilyTable.

   Depending on whether this VACM configuration is for a Command
   Responder or a command generator the security name "blueberry" will
   come from a few different locations.

C.1.  Configuring the Notification Generator

   For notification generators performing authorization checks, the
   server's certificate must be verified against the expected
   certificate before proceeding to send the notification.  The expected
   certificate from the server may be listed in the tlstmAddrTable or
   may be determined through other X.509 path validation mechanisms.
   The securityName to use for VACM authorization checks is set by the
   SNMP-TARGET-MIB's snmpTargetParamsSecurityName column.

   The certificate that the notification generator should present to the
   server is taken from the tlstmParamsClientFingerprint column from the
   appropriate entry in the tlstmParamsTable table.

C.2.  Configuring the Command Responder

   For command responder applications, the vacmSecurityName "blueberry"
   value is a value that derived from an incoming (D)TLS session.  The
   mapping from a recevied (D)TLS client certificate to a tmSecurityName
   is done with the tlstmCertToTSNTable.  The certificates must be
   loaded into the device so that a tlstmCertToTSNEntry may refer to it.
   As an example, consider the following entry which will provide a
   mapping from a client's public X.509's hash fingerprint directly to
   the "blueberry" tmSecurityName:





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     tlstmCertToTSNID           = 1      (chosen by ordering preference)
     tlstmCertToTSNFingerprint  = HASH   (appropriate fingerprint)
     tlstmCertToTSNMapType      = 1      (specified)
     tlstmCertToTSNSecurityName = "blueberry"
     tlstmCertToTSNStorageType  = 3      (nonVolatile)
     tlstmCertToTSNRowStatus    = 4      (createAndGo)

   The above is an example of how to map a particular certificate to a
   particular tmSecurityName.  It is recommended, however, that users
   make use of direct subjectAltName or CommonName mappings where
   possible as it provides a more scalable approach to certificate
   management.  This entry provides an example of using a subjectAltName
   mapping:

     tlstmCertToTSNID          = 1       (chosen by ordering preference)
     tlstmCertToTSNFingerprint = HASH    (appropriate fingerprint)
     tlstmCertToTSNMapType     = 2       (bySubjectAltName)
     tlstmCertToTSNSANType     = 1       (any)
     tlstmCertToTSNStorageType = 3       (nonVolatile)
     tlstmCertToTSNRowStatus   = 4       (createAndGo)

   The above entry indicates the subjectAltName field for certificates
   created by an issuing certificate with a corresponding fingerprint
   will be trusted to always produce common names that are directly one-
   to-one mappable into tmSecurityNames.  This type of configuration
   should only be used when the certificate authorities naming
   conventions are carefully controlled.

   In the example, if the incoming (D)TLS client provided certificate
   contained a subjectAltName where the first listed subjectAltName in
   the extension is the rfc822Name of "blueberry@example.com", the
   certificate was signed by a certificate matching the
   tlstmCertToTSNFingerprint value and the CA's certificate was properly
   installed on the device then the string "blueberry@example.com" would
   be used as the tmSecurityName for the session.


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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