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Versions: 00 01 02 03 04 05 06 RFC 4742

Network Working Group                                       M. Wasserman
Internet-Draft                                                ThingMagic
Expires: August 24, 2005                                      T. Goddard
                                               ICEsoft Technologies, Inc.
                                                        February 20, 2005

     Using the NETCONF Configuration Protocol over Secure Shell (SSH)

Status of this Memo

    This document is an Internet-Draft and is subject to all provisions
    of Section 3 of RFC 3667.  By submitting this Internet-Draft, each
    author represents that any applicable patent or other IPR claims of
    which he or she is aware have been or will be disclosed, and any of
    which he or she become aware will be disclosed, in accordance with
    RFC 3668.

    Internet-Drafts are working documents of the Internet Engineering
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    This Internet-Draft will expire on August 24, 2005.

Copyright Notice

    Copyright (C) The Internet Society (2005).


    This document describes a method for invoking and running the NETCONF
    configuration protocol within a Secure Shell (SSH) session as an SSH

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Table of Contents

    1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
    2.  Starting NETCONF over SSH  . . . . . . . . . . . . . . . . . .  3
      2.1   Capabilities Exchange  . . . . . . . . . . . . . . . . . .  4
    3.  Using NETCONF over SSH . . . . . . . . . . . . . . . . . . . .  5
    4.  Exiting the NETCONF Subsystem  . . . . . . . . . . . . . . . .  6
    5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
    6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
    7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
    8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  7
      8.1   Normative References . . . . . . . . . . . . . . . . . . .  7
      8.2   Informative References . . . . . . . . . . . . . . . . . .  8
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  8
        Intellectual Property and Copyright Statements . . . . . . . . 10

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1.  Introduction

    The NETCONF protocol [I-D.ietf-netconf-prot] is an XML-based protocol
    used to manage the configuration of networking equipment.  NETCONF is
    defined to be session-layer and transport independent, allowing
    mappings to be defined for multiple session-layer or transport
    protocols.  This document defines how XMLCONF can be used within a
    Secure Shell (SSH) session, using the SSH connection protocol
    [I-D.ietf-secsh-connect] over the SSH transport protocol
    [I-D.ietf-secsh-transport].  This mapping will allow NETCONF to be
    executed from a secure shell session by a user or script.

    Throughout this document, the terms "client" and "server" are used to
    refer to the two ends of the SSH transport connection.  The client
    actively opens the SSH connection, and the server passively listens
    for the incoming SSH connection.  The terms "manager" and "agent" are
    used to refer to the two ends of the NETCONF protocol session.  The
    manager issues NETCONF RPC commands, and the agent replies to those
    commands.  When NETCONF is run over SSH using the mapping defined in
    this document, the client is always the manager, and the server is
    always the agent.

2.  Starting NETCONF over SSH

    To run NETCONF over SSH, the client will first establish an SSH
    transport connection using the SSH transport protocol, and the client
    and server will exchange keys for message integrity and encryption.
    The client will then invoke the "ssh-userauth" service to
    authenticate the user, as described in the SSH authentication
    protocol [I-D.ietf-secsh-userauth].  Once the user has been
    successfully authenticated, the client will invoke the
    "ssh-connection" service, also known as the SSH connection protocol.

    After the ssh-connection service is established, the client will open
    a channel of type "session", which will result in an SSH session.

    Once the SSH session has been established, the user (or script) will
    invoke NETCONF as an SSH subsystem called "netconf".  Running NETCONF
    as an SSH subsystem avoids the need for the script to recognize shell
    prompts or skip over extraneous information, such as a system message
    that is printed at shell start-up.

    In order to allow NETCONF traffic to be easily identified and
    filtered by firewalls and other network devices, NETCONF servers MUST
    default to providing access to the "netconf" SSH subsystem only when
    the SSH session is established using the IANA-assigned TCP port
    <TBD>.  Servers SHOULD be configurable to allow access to the netconf
    SSH subsystem over other ports.

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    A user (or script), could use the following command line to invoke
    NETCONF as an SSH subsystem on the IANA-assigned port:

    [user@client]$ ssh -s server.example.org -p <TBD> netconf

2.1  Capabilities Exchange

    The server MUST indicate its capabilities by sending an XML document
    containing a <hello> element as soon as the NETCONF session is
    established.  The user (or script) can parse this message to
    determine which NETCONF capabilities are supported by the server.

    The client must also send an XML document containing a <hello>
    element to indicate the client's capabilities to the server.  The
    document containing the <hello> element must be the first XML
    document that the client sends after the NETCONF session is

    The following example shows a capability exchange.  Messages sent by
    the client are marked with "C:" and message sent by the server are
    marked with "S:".

    S: <?xml version="1.0" encoding="UTF-8"?>
    S: <hello>
    S:   <capabilities>
    S:     <capability>
    S:       urn:ietf:params:xml:ns:netconf:base:1.0
    S:     </capability>
    S:     <capability>
    S:       urn:ietf:params:xml:ns:netconf:base:1.0#startup
    S:     </capability>
    S:   </capabilities>
    S:   <session-id>4<session-id>
    S: </hello>
    S: ]]>]]>

    C: <?xml version="1.0" encoding="UTF-8"?>
    C: <hello>
    C:   <capabilities>
    C:     <capability>
    C:       urn:ietf:params:xml:ns:netconf:base:1.0
    C:     </capability>
    C:   </capabilities>
    C: </hello>
    C: ]]>]]>

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    Although the example shows the server sending a <hello> message
    followed by the client's message, both sides will send the message as
    soon as the NETCONF subsystem is initialized, perhaps simultaneously.

3.  Using NETCONF over SSH

    A NETCONF over SSH session consists of the manager and agent
    exchanging complete XML documents.  Once the session has been
    established and capabilities have been exchanged, the manager will
    send complete XML documents to the server containing <rpc> elements,
    and the agent will respond with complete XML documents containing
    <rpc-reply> elements.

    As the previous example illustrates, a special character sequence,
    ]]>]]>, is sent after each XML document in the NETCONF exchange.
    This character sequence cannot legally appear in an XML document, so
    it can be unambigiously used to indentify the end of the current
    document in the event of an XML syntax or parsing error, allowing
    resynchronization of the NETCONF exchange.

    To continue the example given above, an XMLCONF over SSH session to
    retrieve a set of configuration information might look like this:

    S: <?xml version="1.0" encoding="UTF-8"?>
    S: <rpc message-id="105" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    S:   <get-config>
    S:     <source><running/></source>
    S:     <config xmlns="http://example.com/schema/1.2/config">
    S:      <users/>
    S:     </config>
    S:   </get-config>
    S: </rpc>
    S: ]]>]]>

    C: <?xml version="1.0" encoding="UTF-8"?>
    C: <rpc-reply message-id="105"
    C:   <config xmlns="http://example.com/schema/1.2/config">
    C:     <users>
    C:       <user><name>root</name><type>superuser</type></user>
    C:       <user><name>fred</name><type>admin</type></user>
    C:       <user><name>barney</name><type>admin</type></user>
    C:     </users>
    C:   </config>
    C: </rpc-reply>
    C: ]]>]]>

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4.  Exiting the NETCONF Subsystem

    Exiting NETCONF is accomplished using the <close-session> operation.
    An agent will processe RPC messages from the manager in the order in
    which the are received.  When the agent processes a <close-session>
    command, the agent shall respond, terminate the SSH session, and
    close the TCP connection.  The agent MUST NOT process any RPC
    commands received on the current session after the <close-session>

    To continue the example used in previous sections, an existing
    NETCONF subsystem session could be closed as follows:

    S: <?xml version="1.0" encoding="UTF-8"?>
    S: <rpc message-id="106" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    S:   <close-session/>
    S: </rpc>
    S: ]]>]]>

    C: <?xml version="1.0" encoding="UTF-8"?>
    C: <rpc-reply id="106" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    C:   <ok/>
    C: </rpc-reply>
    C: ]]>]]>

5.  Security Considerations

    NETCONF is used to access and modify configuration and state
    information, so the ability to access this protocol should be limited
    to users and systems that are authorized to view or modify the
    agent's configuration and state data.

    The identity of the server MUST be verified and authenticated by the
    client before password-based authentication data or any configuration
    data is sent to the server.  The identity of the client MUST also be
    verified and authenticated by the server to ensure that the incoming
    client request is legitimate before any configuration or state data
    is sent to the client.  Neither side should establish a NETCONF over
    SSH connection with an unknown, unexpected or incorrect identity on
    the opposite side.

    Configuration data may include sensitive information, such as
    usernames or security keys.  So, NETCONF should only be used over
    communications channels that provide strong encryption for data
    privacy.  This document defines a NETCONF over SSH mapping which
    provides for support of strong encryption and authentication.

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    If the NETCONF server provides remote shell access through insecure
    protocols, such as rsh or Telnet, care should be taken to prevent
    execution of the NETCONF program when strong user authentication or
    data privacy is not available.  Because it may be difficult or
    impossible in some operating environments to determine whether a
    shell command was accessed over a secure protocol such as SSH or an
    insecure protocol such as Telnet, it may be necessary to disable
    insecure shell access to the system to prevent insecure access to the
    NETCONF program.  Alternatively, it would be possible to disable
    NETCONF access from the command line, only allowing NETCONF to be
    accessed through invocation of the SSH "netconf" subsystem.

    This document requires that servers default to allowing access to the
    "netconf" SSH subsystem only when using a specific TCP port assigned
    by IANA for this purpose.  This will allow NETCONF over SSH traffic
    to be easily identified and filtered by firewalls and other network
    nodes.  However, it will also allow NETCONF over SSH traffic to be
    more easily identified by attackers.

    This document also recommends that servers be configurable to allow
    access to the "netconf" SSH subsystem over other ports.  Use of that
    configuration option without corresponding changes to firewall or
    network device configuration may unintentionally result in the
    ability for nodes outside of the firewall or other administrative
    boundary to gain access to "netconf" SSH subsystem.

6.  IANA Considerations

    IANA is requested to assign a TCP port number which will be the
    default port for NETCONF over SSH sessions as defined in this

7.  Acknowledgements

    This document was written using the xml2rfc tool described in RFC
    2629 [RFC2629].

    Extensive input was received from the members of the NETCONF design
    team, including: Andy Bierman, Weijing Chen, Rob Enns, Wes Hardaker,
    David Harrington, Eliot Lear, Simon Leinen, Phil Shafer, Juergen
    Schoenwaelder and Steve Waldbusser.  The following people have also
    reviewed this document and provided valuable input: Bill Sommerfeld.

8.  References

8.1  Normative References


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               Enns, R., "NETCONF Configuration Protocol",
               Internet-Draft draft-ietf-netconf-prot-04, October 2004.

               Lonvick, C., "SSH Connection Protocol",
               Internet-Draft draft-ietf-secsh-connect-24, February 2005.

               Lonvick, C., "SSH Transport Layer Protocol",
               Internet-Draft draft-ietf-secsh-transport-23, February

               Lonvick, C., "SSH Authentication Protocol",
               Internet-Draft draft-ietf-secsh-userauth-26, February

8.2  Informative References

    [RFC0854]  Postel, J. and J. Reynolds, "Telnet Protocol
               Specification", STD 8, RFC 854, May 1983.

    [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
               June 1999.

    [RFC3667]  Bradner, S., "IETF Rights in Contributions", BCP 78,
               RFC 3667, February 2004.

    [RFC3668]  Bradner, S., "Intellectual Property Rights in IETF
               Technology", BCP 79, RFC 3668, February 2004.

Authors' Addresses

    Margaret Wasserman
    One Broadway, 14th Floor
    Cambridge, MA  02142

    Phone: +1 617 758-4177
    Email: margaret@thingmagic.com
    URI:   http://www.thingmagic.com

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    Ted Goddard
    ICEsoft Technologies, Inc.
    Suite 300, 1717 10th St. NW
    Calgary, AB  T2M 4S2

    Phone: +1 403 663-3322
    Email: ted.goddard@icesoft.com
    URI:   http://www.icesoft.com

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Copyright Statement

    Copyright (C) The Internet Society (2005).  This document is subject
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