Network Working Group                                            E. Lear
Internet-Draft                                             Cisco Systems
Expires: September 7, 2006                                    K. Crozier
                                                           March 6, 2006

  Using the NETCONF Protocol over Blocks Extensible Exchange Protocol

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Copyright Notice

   Copyright (C) The Internet Society (2006).


   This document specifies an application protocol mapping for the
   NETCONF protocol over the Blocks Extensible Exchange Protocol (BEEP).

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Why BEEP?  . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  BEEP Transport Mapping . . . . . . . . . . . . . . . . . . . .  4
     2.1.  NETCONF Session Establishment  . . . . . . . . . . . . . .  4
     2.2.  Starting a Channel for NETCONF . . . . . . . . . . . . . .  5
     2.3.  NETCONF Session Usage  . . . . . . . . . . . . . . . . . .  6
     2.4.  NETCONF Session Teardown . . . . . . . . . . . . . . . . .  6
     2.5.  BEEP Profile for NETCONF . . . . . . . . . . . . . . . . .  7
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   5.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 15

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1.  Introduction

   The NETCONF protocol [1] defines a simple mechanism through which a
   network device can be managed.  NETCONF is designed to be usable over
   a variety of application protocols.  This document specifies an
   application protocol mapping for NETCONF over the Blocks Extensible
   Exchange Protocol (BEEP) [7] .

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [2].

1.1.  Why BEEP?

   Use of BEEP is natural as an application protocol for transport of
   XML.  As a peer to peer protocol, BEEP provides an easy way to
   implement NETCONF, no matter which side of the connection was the
   initiator.  This "bidirectionality" allows for either manager or
   agent to initiate a connection.  This is particularly important to
   support large number of intermittently connected devices, as well as
   those devices that must reverse the management connection in the face
   of firewalls and network address translators (NATs).

   BEEP makes use of the Simple Authentication and Security Layer (SASL)
   [3].  The SASL profile used by BEEP allows for a simple and direct
   mapping to the existing security model for CLI, while transport layer
   security (TLS) [4] provides a strong well tested encryption mechanism
   with either server or server and client-side authentication.

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2.  BEEP Transport Mapping

   All NETCONF over BEEP implementations MUST implement the profile and
   functional mapping between NETCONF and BEEP as described below.

   For purposes of this document a manager is a NETCONF client, and an
   agent is a NETCONF server.  Use of client/server language in BEEP is
   avoided because of the common notion that in networking clients
   connect to servers.

2.1.  NETCONF Session Establishment

   Managers may be either BEEP listeners or initiators.  Similarly,
   agents may be either listeners or initiators.  Thus the initial
   exchange takes place without regard to whether a manager or the agent
   is the initiator.  After the transport connection is established, as
   greetings are exchanged, they SHOULD each announce their support for
   TLS and optionally SASL.  Once BEEP greeting messages are exchanged,
   if TLS is to be used and available by both parties, the listener
   STARTs a channel with the TLS profile.

   Once TLS has been started, a new BEEP greeting message is sent by
   both initiator and listener, as required by the BEEP RFC.

   After all BEEP greeting messages are exchanged in order for roles to
   be clear, the agent MUST advertise the NETCONF profile.  The manager
   MUST NOT advertise the NETCONF profile.  If the agent side of the
   communication (either initiator or listener) receives a BEEP
   <greeting> element that contains the NETCONF profile, it MUST close
   the connection.  Similarly, if neither side issues a NETCONF profile
   it is equally an error, and the listener MUST close the connection.

   At this point, if SASL is desired, the initiator starts a BEEP
   channel to perform a SASL exchange to authenticate itself.  Upon
   completion of authentication the channel is closed.  That is, the
   channel is exclusively used to authenticate.

   Examples of both TLS and SASL profiles can be found in [7].

   It is anticipated that the SASL PLAIN mechanism will be heavily used
   in conjunction with TLS.[5] In such cases, in accordance with RFC
   2595 the PLAIN mechanism MUST NOT be advertised in the first BEEP
   <greeting>, but only in the one following a successful TLS
   negotiation.  This applies only if TLS and SASL PLAIN mechanisms are
   both to be used.  To avoid risk of eavesdropping, the SASL PLAIN
   mechanism MUST NOT be used over unencrypted channels.  More specifics
   about the use of SASL and TLS are mentioned in Security
   Considerations below.

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   Once authentication has occurred, there is no need to distinguish
   between initiator and listener.  We now distinguish between manager
   and agent, and it is assumed that each knows its role in the

2.2.  Starting a Channel for NETCONF

   The manager now establishes a new channel and specifies the single
   NETCONF profile.  For example:

         (M = Manager ; A = Agent )

         M: MSG 0 1 . 10 48 116
         M: Content-type: application/beep+xml
         M: <start number="1">
         M:   <profile uri="" />
         M: </start>
         M: END
         A: RPY 0 1 . 38 87
         A: Content-Type: application/beep+xml
         A: <profile uri="" />
         A: END

   At this point we are ready to proceed on BEEP channel 1 with NETCONF

   Next the manager and the agent exchange NETCONF <hello> elements on
   the new channel so that each side learns the other's capabilities.
   This occurs through a MSG.  Each side will then respond positively.
   The following example is adapted from [1] Section 8.1:

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       A: MSG 1 0 . 0 429
       A: Content-type: application/beep+xml
       A: <hello xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       A:   <capabilities>
       A:     <capability>
       A:       urn:ietf:params:netconf:base:1.0
       A:     </capability>
       A:     <capability>
       A:       urn:ietf:params:netconf:capability:startup:1.0
       A:     </capability>
       A:     <capability>
       A:     </capability>
       A:   </capabilities>
       A:   <session-id>4</session-id>
       A: </hello>
       A: END

       M: RPY 1 0 . 0 0
       M: END

   Future NETCONF capabilities may require additional BEEP channels.
   When such capabilities are defined, a BEEP mapping must be defined as

   At this point, the NETCONF session is established, and capabilities
   have been exchanged.

2.3.  NETCONF Session Usage

   Nearly all NETCONF operations are executed through the <rpc> element.
   To issue an RPC, the manager transmits on the operational channel a
   BEEP MSG containing the RPC and its arguments.  In accordance with
   the BEEP standard, RPC requests may be split across multiple BEEP

   Once received and processed, the agent responds with BEEP RPY
   messages on the same channel with the response to the RPC.  In
   accordance with the BEEP standard, responses may be split across
   multiple BEEP frames.

2.4.  NETCONF Session Teardown

   Upon receipt of <close-session> from the manager, once the agent has
   completed all RPCs, it will close BEEP channel 0.  When an agent
   needs to initiate a close it will do so by closing BEEP channel 0.

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   Although not required to do so, the agent should allow for a
   reasonable period for a manager to release an existing lock prior to
   initiating a close.  Once the agent has closed channel 0, all locks
   are released, and each side follows tear down procedures as specified
   in [8].  Having received a BEEP close or having sent <close-session>,
   a manager MUST NOT send further requests.  If there are additional
   activities due to expanded capabilities, these MUST cease in an
   orderly manner, and should be properly described in the capability

2.5.  BEEP Profile for NETCONF

   Profile Identification:

   messages exchanged during Channel Creation: not applicable

   Messages starting one-to-one exchanges: "hello", "rpc", "rpc-reply"

   Messages in positive replies: "rpc-reply"

   Messages in negative replies: "rpc-reply"

   Messages in one-to-many exchanges: none

   Message syntax: [1]

   message semantics: [1]

   Contact Information: c.f., the "Author's Address" section of this

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3.  Security Considerations

   Configuration information is by its very nature sensitive.  Its
   transmission in the clear and without integrity checking leaves
   devices open to classic so-called "person in the middle" attacks.
   Configuration information often times contains passwords, user names,
   service descriptions, and topological information, all of which are
   sensitive.  A NETCONF application protocol, therefore, must minimally
   support options for both confidentiality and authentication.

   The BEEP mapping described in this document addresses both
   confidentiality and authentication in a flexible manner through the
   use of TLS and SASL profiles.  Confidentiality is provided via the
   TLS profile, and is used as discussed above.  In addition, the server
   certificate shall serve as the server's authentication to the client.
   The client MUST be prepared to recognize and validate a server
   certificate, and SHOULD by default reject invalid certificates.

   In order to validate a certificate the client must be able to access
   a trust anchor.  While such validation methods are beyond the scope
   of this document, they will depend on the type of device and
   circumstance.  Both the implementor and the administrator are
   cautioned to be aware of any circular dependencies various methods
   may introduce.  For instance, OCSP servers may not be available in a
   network cold start scenario, and would be ill advised for core
   routers to depend on to receive configuration at boot.

   For client-side authentication there are several options.  The client
   MAY provide a certificate during the initiation phase of TLS, in
   which case the subject of that certificate shall be considered
   principle for authentication purposes.  Once again, server
   implementors should be aware of any interdependencies that could be
   created through protocols used to validate trust anchors.

   TLS endpoints may be authorized based on subject name or certificate
   authority (CA), depending on circumstances.  For instance, it would
   be unwise for a core internet router to allow a netconf agent
   connection simply based on a valid certificate signed by a common CA,
   but not unreasonable to allow a connection from an agent with a
   particular distinguished name.  On the other hand, it might be
   desirable for enterprises to trust certificates signed by CAs of
   their network operations team.

   In the case where the client has not authenticated through TLS, the
   server SHOULD advertise one or more SASL profiles, from which the
   client will choose.  In the singular case where TLS is established
   the minimum profile MAY be PLAIN.  Otherwise, implementations MUST
   support the DIGEST-MD5 profile as described in [6], and they MAY

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   support other profiles such as OTP.[10]

   Different environments may well allow different rights prior to and
   then after authentication.  An authorization model is not specified
   in this document.  When an operation is not properly authorized then
   a simple rpc-error containing "permission denied" is sufficient.
   Note that authorization information may be exchanged in the form of
   configuration information, which is all the more reason to ensure the
   security of the connection.

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4.  IANA Considerations

   The IANA is requested to assign a TCP port for NETCONF, and to
   register the BEEP profile contained here-in.

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5.  Acknowledgments

   This work is the product of the NETCONF IETF working group, and many
   people have contributed to the NETCONF discussion.  Most notably, Rob
   Ens, Phil Schafer, Andy Bierman, Wes Hardiger, Ted Goddard, and
   Margaret Wasserman all contributed in some fashion to this work,
   which was originally to be found in the NETCONF base protocol
   specification.  Thanks also to Weijing Chen, Keith Allen, Juergen
   Schoenwaelder, Marshall Rose, and Eamon O'Tuathail for their very
   constructive participation.  The authors would also like to thank
   Elwyn Davies for his constructive review.

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6.  References

6.1.  Normative References

   [1]  Enns, R., "NETCONF Configuration Protocol",
        draft-ietf-netconf-prot-08 (work in progress), September 2005.

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

   [3]  Myers, J., "Simple Authentication and Security Layer (SASL)",
        RFC 2222, October 1997.

   [4]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
        RFC 2246, January 1999.

   [5]  Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595,
        June 1999.

   [6]  Leach, P. and C. Newman, "Using Digest Authentication as a SASL
        Mechanism", RFC 2831, May 2000.

   [7]  Rose, M., "The Blocks Extensible Exchange Protocol Core",
        RFC 3080, March 2001.

   [8]  Rose, M., "Mapping the BEEP Core onto TCP", RFC 3081,
        March 2001.

6.2.  Informative References

   [9]   Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler,
         "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
         REC REC-xml-20001006, October 2000.

   [10]  Newman, C., "The One-Time-Password SASL Mechanism", RFC 2444,
         October 1998.

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Appendix A.  Change Log

   08: Editing errors found by Bruce Moon.  Changes to URNs.

   07: Match URN changes to core draft (one change).

   06: Changes (fix references, IANA section) from AD comments.

   05: improved advice on use of tls and SASL profiles.

   04: complete revamp of the profile.  Added <hello> as well as

   03: minor gnits relating to <close-session>

   02: added comments about locking

   01: Removed management channel, rpc-status, rpc-abort, and associated
   profile changes.

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Authors' Addresses

   Eliot Lear
   Cisco Systems
   Glattzentrum, Zurich  8301


   Ken Crozier


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