path: root/doc/rfc/rfc5953.txt

Internet Engineering Task Force (IETF)                       W. Hardaker
Request for Comments: 5953                                  SPARTA, Inc.
Category: Standards Track                                    August 2010
ISSN: 2070-1721


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

Abstract

   This document describes a Transport Model for the Simple Network
   Management Protocol (SNMP), that uses either the Transport Layer
   Security protocol or the Datagram Transport Layer Security (DTLS)
   protocol.  The TLS and DTLS protocols provide authentication and
   privacy services for SNMP applications.  This document describes how
   the TLS Transport Model (TLSTM) implements the needed features of 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 the sending of SNMP
   messages over TLS/TCP and DTLS/UDP.  The TLS mode can make use of
   TCP's improved support for larger packet sizes and the DTLS mode
   provides potentially superior operation in environments where a
   connectionless (e.g., UDP) transport is preferred.  Both TLS and DTLS
   integrate well into existing public keying infrastructures.

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

Status of This Memo

   This is an Internet Standards Track document.

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

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5953.






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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

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

Table of Contents

   1. Introduction ....................................................4
      1.1. Conventions ................................................7
   2. The Transport Layer Security Protocol ...........................8
   3. How the TLSTM Fits into the Transport Subsystem .................8
      3.1. Security Capabilities of this Model .......................10
           3.1.1. Threats ............................................10
           3.1.2. Message Protection .................................11
           3.1.3. (D)TLS Connections .................................12
      3.2. Security Parameter Passing ................................13
      3.3. Notifications and Proxy ...................................13
   4. Elements of the Model ..........................................14
      4.1. X.509 Certificates ........................................14
           4.1.1. Provisioning for the Certificate ...................14
      4.2. (D)TLS Usage ..............................................16
      4.3. SNMP Services .............................................17
           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 .........................19
           4.4.1. TLS Transport Model Cached Information .............19



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                  4.4.1.1. tmSecurityName ............................19
                  4.4.1.2. tmSessionID ...............................20
                  4.4.1.3. Session State .............................20
   5. Elements of Procedure ..........................................20
      5.1. Procedures for an Incoming Message ........................20
           5.1.1. DTLS over UDP Processing for Incoming Messages .....21
           5.1.2. Transport Processing for Incoming SNMP Messages ....22
      5.2. Procedures for an Outgoing SNMP Message ...................24
      5.3. Establishing or Accepting a Session .......................25
           5.3.1. Establishing a Session as a Client .................25
           5.3.2. Accepting a Session as a Server ....................27
      5.4. Closing a Session .........................................28
   6. MIB Module Overview ............................................29
      6.1. Structure of the MIB Module ...............................29
      6.2. Textual Conventions .......................................29
      6.3. Statistical Counters ......................................29
      6.4. Configuration Tables ......................................29
           6.4.1. Notifications ......................................30
      6.5. Relationship to Other MIB Modules .........................30
           6.5.1. MIB Modules Required for IMPORTS ...................30
   7. MIB Module Definition ..........................................30
   8. Operational Considerations .....................................53
      8.1. Sessions ..................................................53
      8.2. Notification Receiver Credential Selection ................54
      8.3. contextEngineID Discovery .................................54
      8.4. Transport Considerations ..................................55
   9. Security Considerations ........................................55
      9.1. Certificates, Authentication, and Authorization ...........55
      9.2. (D)TLS Security Considerations ............................56
           9.2.1. TLS Version Requirements ...........................56
           9.2.2. Perfect Forward Secrecy ............................56
      9.3. Use with SNMPv1/SNMPv2c Messages ..........................56
      9.4. MIB Module Security .......................................57
   10. IANA Considerations ...........................................58
   11. Acknowledgements ..............................................59
   12. References ....................................................60
      12.1. Normative References .....................................60
      12.2. Informative References ...................................61
   Appendix A.  Target and Notification Configuration Example ........63
     A.1.  Configuring a Notification Originator .....................63
     A.2.  Configuring TLSTM to Utilize a Simple Derivation of
           tmSecurityName ............................................64
     A.3.  Configuring TLSTM to Utilize Table-Driven Certificate
           Mapping ...................................................64







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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) transport is
   preferred and in environments where large quantities of data need to
   be sent (e.g., over a TCP-based stream).  Both TLS and DTLS integrate
   well into existing public keying infrastructures.  This document
   supports sending of SNMP messages over TLS/TCP and DTLS/UDP.

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

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  MIB objects are generally
   accessed through the Simple Network Management Protocol (SNMP).
   Objects in the MIB are defined using the mechanisms defined in the
   Structure of Management Information (SMI).  This memo specifies a MIB
   module that is compliant to the SMIv2, which is described in STD 58:
   [RFC2578], [RFC2579], and [RFC2580].










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

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









































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





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1.1.  Conventions

   For consistency with SNMP-related specifications, this document
   favors terminology as defined in STD 62, rather than favoring
   terminology that is consistent with non-SNMP specifications.  This is
   consistent with the IESG decision to not require the SNMPv3
   terminology be modified to match the usage of other non-SNMP
   specifications when SNMPv3 was advanced to a Full Standard.

   "Authentication" in this document typically refers to the English
   meaning of "serving to prove the authenticity of" the message, not
   data source authentication or peer identity authentication.

   The terms "manager" and "agent" are not used in this document
   because, in the [RFC3411] architecture, all SNMP entities have the
   capability of acting as manager, agent, or both depending on the SNMP
   application types supported in the implementation.  Where distinction
   is required, the application names of command generator, command
   responder, notification originator, notification receiver, and proxy
   forwarder are used.  See "SNMP Applications" [RFC3413] for further
   information.

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

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

   The User-Based Security Model (USM) [RFC3414] is a mandatory-to-
   implement Security Model in STD 62.  While (D)TLS and USM frequently
   refer to a user, the terminology preferred in RFC 3411 and in this
   memo is "principal".  A principal is the "who" on whose behalf
   services are provided or processing takes place.  A principal can be,
   among other things, an individual acting in a particular role; a set
   of individuals, with each acting in a particular role; an application
   or a set of applications, or a combination of these within an
   administrative domain.



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

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

2.  The Transport Layer Security Protocol

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

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

3.  How the TLSTM Fits into the Transport Subsystem

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

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

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






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   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 (shown as
   "(D)TLS TM") fits into the architecture described in RFC 3411 and the
   Transport Subsystem:

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





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

3.1.  Security Capabilities of this Model

3.1.1.  Threats

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

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

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

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

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

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





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

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

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

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

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

3.1.2.  Message Protection

   The RFC 3411 architecture recognizes three levels of security:

   o  without authentication and without privacy (noAuthNoPriv)

   o  with authentication but without privacy (authNoPriv)

   o  with authentication and with privacy (authPriv)

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






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   When an application requests a session for a message, it also
   requests a security level for that session.  The TLS Transport Model
   MUST ensure that the (D)TLS connection provides security at least as
   high as the requested level of security.  How the security level is
   translated into the algorithms used to provide data integrity and
   privacy is implementation dependent.  However, the NULL integrity and
   encryption algorithms MUST NOT be used to fulfill security level
   requests for authentication or privacy.  Implementations MAY choose
   to force (D)TLS to only allow cipher_suites that provide both
   authentication and privacy to guarantee this assertion.

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

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

3.1.3.  (D)TLS Connections

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

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

   DTLS connections, when used over UDP, are uniquely identified within
   the TLS Transport Model by the combination of transportDomain,
   transportAddress, tmSecurityName, and requestedSecurityLevel
   associated with each session.  Each unique combination of these
   parameters MUST have a locally chosen unique tlstmSessionID for each
   active session.  For further information, see Section 5.  TLS over
   TCP sessions, on the other hand, do not require a unique pairing of





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   address and port attributes since their lower-layer protocols (TCP)
   already provide adequate session framing.  But they must still
   provide a unique tlstmSessionID for referencing the session.

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

3.2.  Security Parameter Passing

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

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

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

3.3.  Notifications and Proxy

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



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

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

4.  Elements of the Model

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

4.1.  X.509 Certificates

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

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

4.1.1.  Provisioning for the Certificate

   Authentication using (D)TLS will require that SNMP entities have
   certificates, either signed by trusted Certification Authorities
   (CAs), or self signed.  Furthermore, SNMP entities will most commonly
   need to be provisioned with root certificates that represent the list
   of trusted CAs that an SNMP entity can use for certificate



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

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

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

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

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

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

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

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

   The standard View-Based Access Control Model (VACM) access control
   model constrains securityNames to be 32 octets or less in length.  A
   TLSTM generated tmSecurityName, possibly in combination with a
   messaging or security model that increases the length of the
   securityName, might cause the securityName length to exceed 32
   octets.  For example, a 32-octet tmSecurityName derived from an IPv6
   address, paired with a TSM prefix, will generate a 36-octet




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   securityName.  Such a securityName will not be able to be used with
   standard VACM or TARGET MIB modules.  Operators should be careful to
   select algorithms and subjectAltNames to avoid this situation.

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

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

4.2.  (D)TLS Usage

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

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

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

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

   For DTLS, replay protection MUST be used.




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4.3.  SNMP Services

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

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

4.3.1.  SNMP Services for an Outgoing Message

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

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

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

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

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

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

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

   outgoingMessageLength:  The length of the outgoingMessage.





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

4.3.2.  SNMP Services for an Incoming Message

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

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

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

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

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

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

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

   incomingMessageLength:  The length of the incomingMessage.

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









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4.4.  Cached Information and References

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

4.4.1.  TLS Transport Model Cached Information

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

4.4.1.1.  tmSecurityName

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

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

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

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




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4.4.1.2.  tmSessionID

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

4.4.1.3.  Session State

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

5.  Elements of Procedure

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

   To simplify the elements of procedure, the release of state
   information is not always explicitly specified.  As a general rule,
   if state information is available when a message gets discarded, the
   message-state information should also be released.  If state
   information is available when a session is closed, the session state
   information should also be released.  Sensitive information, like
   cryptographic keys, should be overwritten appropriately prior to
   being released.

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

5.1.  Procedures for an Incoming Message

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





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

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

5.1.1.  DTLS over UDP Processing for Incoming Messages

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

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

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

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

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

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

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



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

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

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

5.1.2.  Transport Processing for Incoming SNMP Messages

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

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






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

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

       tmTransportDomain  = snmpTLSTCPDomain or snmpDTLSUDPDomain as
          appropriate.

       tmTransportAddress  = The address from which the message
          originated.

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

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

       tmSessionID  = The tlstmSessionID described in step 1 above.

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

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

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







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5.2.  Procedures for an Outgoing SNMP Message

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

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

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

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

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

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

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

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




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

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

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

5.3.  Establishing or Accepting a Session

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

5.3.1.  Establishing a Session as a Client

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


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

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

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

   1)  The snmpTlstmSessionOpens counter is incremented.




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

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

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

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





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

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

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

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

5.3.2.  Accepting a Session as a Server

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






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

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

5.4.  Closing a Session

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

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

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

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

   2)  Look up the session using the tmSessionID.

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




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

6.  MIB Module Overview

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

6.1.  Structure of the MIB Module

   Objects in this MIB module are arranged into subtrees.  Each subtree
   is organized as a set of related objects.  The overall structure and
   assignment of objects to their subtrees, and the intended purpose of
   each subtree, is shown below.

6.2.  Textual Conventions

   Generic and Common Textual Conventions used in this module can be
   found summarized at http://www.ops.ietf.org/mib-common-tcs.html.

   This module defines the following new Textual Conventions:

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

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

6.3.  Statistical Counters

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

6.4.  Configuration Tables

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




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6.4.1.  Notifications

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

6.5.  Relationship to Other MIB Modules

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

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

6.5.1.  MIB Modules Required for IMPORTS

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

7.  MIB Module Definition

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

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






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snmpTlstmMIB MODULE-IDENTITY
    LAST-UPDATED "201005070000Z"
    ORGANIZATION "ISMS Working Group"
    CONTACT-INFO "WG-EMail:   isms@lists.ietf.org
                  Subscribe:  isms-request@lists.ietf.org

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

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

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

    DESCRIPTION  "
        The TLS Transport Model MIB

        Copyright (c) 2010 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)."

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




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    ::= { mib-2 198 }

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

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

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

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

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

    ::= { snmpDomains 8 }

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

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

    ::= { snmpDomains 9 }







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

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

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

        A hostname is always in US-ASCII (as per [RFC1033]);
        internationalized hostnames are encoded in US-ASCII as domain
        names after transformation via the ToASCII operation specified
        in [RFC3490].  The ToASCII operation MUST be performed with the
        UseSTD3ASCIIRules flag set.  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



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        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 5952: A Recommendation for IPv6 Address Text Representation
      "
    SYNTAX       OCTET STRING (SIZE (1..255))

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

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

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

-- Identities for use in the snmpTlstmCertToTSNTable

snmpTlstmCertToTSNMIdentities OBJECT IDENTIFIER
    ::= { snmpTlstmIdentities 1 }

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



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                  contain a non-zero length SnmpAdminString compliant
                  value or the mapping described in this row must be
                  considered a failure."
    ::= { snmpTlstmCertToTSNMIdentities 1 }

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

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

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

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


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

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




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

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

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

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

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

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

snmpTlstmCertCommonName OBJECT-IDENTITY
    STATUS        current

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




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                  instead.  This mapping results in a 1:1
                  correspondence between certificate CommonName values
                  and tmSecurityName values."
    ::= { snmpTlstmCertToTSNMIdentities 6 }

-- The snmpTlstmSession Group

snmpTlstmSession           OBJECT IDENTIFIER ::= { snmpTlstmObjects 1 }

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

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

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

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




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

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

snmpTlstmSessionInvalidClientCertificates OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an incoming session was not established
        on 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 snmpTlstmCertToTSNTable."
    ::= { snmpTlstmSession 7 }

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





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

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

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

-- Configuration Objects

snmpTlstmConfig             OBJECT IDENTIFIER ::= { snmpTlstmObjects 2 }

-- Certificate mapping

snmpTlstmCertificateMapping OBJECT IDENTIFIER ::= { snmpTlstmConfig 1 }

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










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

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

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

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

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

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

        Once a matching row has been found, the
        snmpTlstmCertToTSNMapType value can be used to determine how
        the tmSecurityName to associate with the session should be



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        determined.  See the snmpTlstmCertToTSNMapType column's
        DESCRIPTION for details on determining the tmSecurityName
        value.  If it is impossible to determine a tmSecurityName from
        the row's data combined with the data presented in the
        certificate, then additional rows MUST be searched looking for
        another potential match.  If a resulting tmSecurityName mapped
        from a given row is not compatible with the needed
        requirements of a tmSecurityName (e.g., VACM imposes a
        32-octet-maximum length and the certificate derived
        securityName could be longer), then it must be considered an
        invalid match and additional rows MUST be searched looking for
        another potential match.

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

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

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

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



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    INDEX   { snmpTlstmCertToTSNID }
    ::= { snmpTlstmCertToTSNTable 1 }

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

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

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

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

        If the resulting mapped value is not compatible with the
        needed requirements of a tmSecurityName (e.g., VACM imposes a
        32-octet-maximum length and the certificate derived




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        securityName could be longer), then future rows MUST be
        searched for additional snmpTlstmCertToTSNFingerprint matches
        to look for a mapping that succeeds.

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

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

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

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

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






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

        In particular, a newly created row cannot be made active until
        the corresponding snmpTlstmCertToTSNFingerprint,
        snmpTlstmCertToTSNMapType, and snmpTlstmCertToTSNData columns
        have been set.

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

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

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

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













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

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

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

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





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


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

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

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

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

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

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

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





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

snmpTlstmAddrTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF SnmpTlstmAddrEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "This table is used by a (D)TLS client when a (D)TLS
        connection is being set up using an entry in the
        SNMP-TARGET-MIB.  It extends the SNMP-TARGET-MIB's
        snmpTargetAddrTable so that the client can verify that the
        correct server has been reached.  This verification can use
        either a certificate fingerprint, or an identity
        authenticated via certification path validation.

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

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

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





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

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

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

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

    ::= { snmpTlstmCertificateMapping 9 }

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







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

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

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

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


snmpTlstmAddrRowStatus OBJECT-TYPE
    SYNTAX      RowStatus
    MAX-ACCESS  read-create
    STATUS      current




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

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

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

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

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

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

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


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

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







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

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

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

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

snmpTlstmCompliances OBJECT IDENTIFIER ::= { snmpTlstmConformance 1 }

snmpTlstmGroups OBJECT IDENTIFIER ::= { snmpTlstmConformance 2 }



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

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





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

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

snmpTlstmOutgoingGroup OBJECT-GROUP
    OBJECTS {
        snmpTlstmParamsCount,
        snmpTlstmParamsTableLastChanged,
        snmpTlstmParamsClientFingerprint,
        snmpTlstmParamsStorageType,
        snmpTlstmParamsRowStatus,



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

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

END

8.  Operational Considerations

   This section discusses various operational aspects of deploying
   TLSTM.

8.1.  Sessions

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







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

8.2.  Notification Receiver Credential Selection

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

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

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

8.3.  contextEngineID Discovery

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

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










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

9.  Security Considerations

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

9.1.  Certificates, Authentication, and Authorization

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

   (D)TLS provides for authentication of the identity of both the (D)TLS
   server and the (D)TLS client.  Access to MIB objects for the
   authenticated principal MUST be enforced by an access control
   subsystem (e.g., the VACM).

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

   The (D)TLS handshake only provides assurance that the certificate of
   the authenticated identity has been signed by a configured accepted
   Certification Authority.  (D)TLS has no way to further authorize or
   reject access based on the authenticated identity.  An Access Control



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   Model (such as the VACM) provides access control and authorization of
   a command generator's requests to a command responder and a
   notification receiver's authorization to receive Notifications from a
   notification originator.  However, to avoid man-in-the-middle
   attacks, both ends of the (D)TLS-based connection MUST check the
   certificate presented by the other side against what was expected.
   For example, command generators must check that the command responder
   presented and authenticated itself with 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
   snmpTlstmCertToTSNTable object must be followed exactly.  It is also
   important that the rows of the table be searched in prioritized order
   starting with the row containing the lowest numbered
   snmpTlstmCertToTSNID value.

9.2.  (D)TLS Security Considerations

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

9.2.1.  TLS Version Requirements

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

9.2.2.  Perfect Forward Secrecy

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

9.3.  Use with SNMPv1/SNMPv2c Messages

   The SNMPv1 and SNMPv2c message processing described in [RFC3584] (BCP
   74) always selects the SNMPv1 or SNMPv2c Security Models,
   respectively.  Both of these and the User-based Security Model
   typically used with SNMPv3 derive the securityName and securityLevel
   from the SNMP message received, even when the message was received
   over a secure transport.  Access control decisions are therefore made



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   based on the contents of the SNMP message, rather than using the
   authenticated identity and securityLevel provided by the TLS
   Transport Model.  It is RECOMMENDED that only SNMPv3 messages using
   the Transport Security Model (TSM) or another secure-transport aware
   security model be sent over the TLSTM transport.

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

9.4.  MIB Module Security

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

   o  The snmpTlstmParamsTable can be used to change the outgoing X.509
      certificate used to establish a (D)TLS connection.  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 snmpTlstmAddrTable 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 snmpTlstmCertToTSNTable 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



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      traffic via encryption is also highly recommended.  When this
      table contains a significant number of rows it may affect the
      system performance when accepting new (D)TLS connections.

   Some of the readable objects in this MIB module (i.e., objects with a
   MAX-ACCESS other than not-accessible) may be considered sensitive or
   vulnerable in some network environments.  It is thus important to
   control even GET and/or NOTIFY access to these objects and possibly
   to even encrypt the values of these objects when sending them over
   the network via SNMP.  These are the tables and objects and their
   sensitivity/vulnerability:

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

   SNMP versions prior to SNMPv3 did not include adequate security.
   Even if the network itself is secure (for example, by using IPsec),
   even then, there is no control as to who on the secure network is
   allowed to access and GET/SET (read/change/create/delete) the objects
   in this MIB module.

   It is RECOMMENDED that implementers consider the security features as
   provided by the SNMPv3 framework (see [RFC3410], Section 8),
   including full support for the SNMPv3 cryptographic mechanisms (for
   authentication and privacy).

   Further, deployment of SNMP versions prior to SNMPv3 is NOT
   RECOMMENDED.  Instead, it is RECOMMENDED to deploy SNMPv3 and to
   enable cryptographic security.  It is then a customer/operator
   responsibility to ensure that the SNMP entity giving access to an
   instance of this MIB module is properly configured to give access to
   the objects only to those principals (users) that have legitimate
   rights to indeed GET or SET (change/create/delete) them.

10.  IANA Considerations

   IANA has assigned:

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








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     Keyword         Decimal      Description       References
     -------         -------      -----------       ----------
     snmptls         10161/tcp    SNMP-TLS          [RFC5953]
     snmpdtls        10161/udp    SNMP-DTLS         [RFC5953]
     snmptls-trap    10162/tcp    SNMP-Trap-TLS     [RFC5953]
     snmpdtls-trap   10162/udp    SNMP-Trap-DTLS    [RFC5953]

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

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

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

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

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

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

11.  Acknowledgements

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

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

   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.






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12.  References

12.1.  Normative References

   [RFC1033]    Lottor, M., "Domain administrators operations guide",
                RFC 1033, November 1987.

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

   [RFC2578]    McCloghrie, K., Ed., Perkins, D., Ed., and J.
                Schoenwaelder, Ed., "Structure of Management Information
                Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

   [RFC2579]    McCloghrie, K., Ed., Perkins, D., Ed., and J.
                Schoenwaelder, Ed., "Textual Conventions for SMIv2",
                STD 58, RFC 2579, April 1999.

   [RFC2580]    McCloghrie, K., Perkins, D., and J. Schoenwaelder,
                "Conformance Statements for SMIv2", STD 58, RFC 2580,
                April 1999.

   [RFC3411]    Harrington, D., Presuhn, R., and B. Wijnen, "An
                Architecture for Describing Simple Network Management
                Protocol (SNMP) Management Frameworks", STD 62,
                RFC 3411, December 2002.

   [RFC3413]    Levi, D., Meyer, P., and B. Stewart, "Simple Network
                Management Protocol (SNMP) Applications", STD 62,
                RFC 3413, December 2002.

   [RFC3414]    Blumenthal, U. and B. Wijnen, "User-based Security Model
                (USM) for version 3 of the Simple Network Management
                Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.

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

   [RFC3418]    Presuhn, R., "Management Information Base (MIB) for the
                Simple Network Management Protocol (SNMP)", STD 62,
                RFC 3418, December 2002.

   [RFC3490]    Faltstrom, P., Hoffman, P., and A. Costello,
                "Internationalizing Domain Names in Applications
                (IDNA)", RFC 3490, March 2003.




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   [RFC3584]    Frye, R., Levi, D., Routhier, S., and B. Wijnen,
                "Coexistence between Version 1, Version 2, and Version 3
                of the Internet-standard Network Management Framework",
                BCP 74, RFC 3584, August 2003.

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

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

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

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

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

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

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

12.2.  Informative References

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

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

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





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   [HEARTBEAT]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
                Layer Security and Datagram Transport Layer Security
                Heartbeat Extension", Work in Progress, February 2010.
















































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Appendix A.  Target and Notification Configuration Example

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

A.1.  Configuring a Notification Originator

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

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

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

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

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

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

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







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       snmpTargetParamsName            = "toNR"     (must match above)
       snmpTargetParamsMPModel         = 3 (SNMPv3)
       snmpTargetParamsSecurityModel   = 4 (TransportSecurityModel)
       snmpTargetParamsSecurityName    = "Joe Cool"
       snmpTargetParamsSecurityLevel   = 3          (authPriv)
       snmpTargetParamsStorageType     = 3          (nonVolatile)
       snmpTargetParamsRowStatus       = 4          (createAndGo0

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

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

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

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

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

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

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









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Author's Address

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

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









































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