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Versions: 00 01 02 03 04 05 06 RFC 4742

Network Working Group                                       M. Wasserman
Internet-Draft                                                ThingMagic
Expires: November 29, 2004                                    T. Goddard
                                                                  IceSoft
                                                             May 31, 2004


     Using the NETCONF Configuration Protocol over Secure Shell (SSH)
                      draft-ietf-netconf-ssh-01.txt

Status of this Memo

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.

    Internet-Drafts are working documents of the Internet Engineering
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    This Internet-Draft will expire on November 29, 2004.

Copyright Notice

    Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

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










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Table of Contents

    1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

    2.  Starting NETCONF over SSH  . . . . . . . . . . . . . . . . . .  4
      2.1   Capabilities Exchange  . . . . . . . . . . . . . . . . . .  5

    3.  Using NETCONF over SSH . . . . . . . . . . . . . . . . . . . .  7

    4.  Exiting the NETCONF Subsystem  . . . . . . . . . . . . . . . .  8

    5.  Running NETCONF from an SSH Shell  . . . . . . . . . . . . . .  9
      5.1   Starting a NETCONF Shell Session . . . . . . . . . . . . .  9
      5.2   Exiting a NETCONF Shell Session  . . . . . . . . . . . . .  9

    6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11

    7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12

    8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13

    9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
    9.1   Normative References . . . . . . . . . . . . . . . . . . . . 14
    9.2   Informative References . . . . . . . . . . . . . . . . . . . 14

        Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14

        Intellectual Property and Copyright Statements . . . . . . . . 16























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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 a simple 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, the client is always the
    manager, and the server is always the agent.































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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.

    To the user (or script), running NETCONF as an SSH subsystem may look
    similar to the following example.  Although this example shows the
    text transmitted by both sides, the server MUST NOT echo the commands
    that it receives back to the client.




















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    <!-- The user (or script) invokes the SSH subsystem.  Depending upon
    the configuration of the client and server, the passphrase prompt
    may not be issued or may be replaced by a password prompt. -->

    [user@client]$ ssh -s server.example.org netconf
    Enter passphrase for key '/foo/.ssh/id_dsa':

    <!-- The NETCONF subsystem running on the server sends a complete
    XML document to the client/manager. -->

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

    <!-- The client/manager sends a complete XML document to the
    server/agent. -->

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

    While the NETCONF subsystem is active, the NETCONF manager can
    interact with the NETCONF agent by sending complete XML documents
    containing NETCONF RPC elements, and the NETCONF agent will respond
    by sending complete XML documents containing appropriate RPC replies.

2.1  Capabilities Exchange

    As indicated in the example above, 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 the
    user's expect 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
    established.



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
















































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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:


    <!-- The manager sends an XML document containing an <rpc>
    element. -->

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

    <!-- The agent responds with an XML document containing an
    <rpc-reply> element. -->

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



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4.  Exiting the NETCONF Subsystem

    Exiting NETCONF is accomplished using the <kill-session> operation.
    When a <kill-session> command is issued by the manager, the agent
    shall respond, terminate the SSH session, and close the TCP
    connection.

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


    <!-- The manager sends an XML document containing a <kill-session>
    operation. Question: Where do we get the session-id? Should it be
    sent in the <hello> message? Issue: The base specification forbids
    the use of kill-session to kill the current session.-->

    <?xml version="1.0" encoding="UTF-8"?>
    <rpc message-id="106" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
         <kill-session>
             <session-id>0</session-id>
         </kill-session>
    </rpc>
    ]]>]]>

    <!-- The agent returns an "OK" reply. -->

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

    <!-- The NETCONF subsystem exits, ending the SSH session and returning
    the user (or script) to the local shell prompt. -->

    [user@client]$
    ]]>]]>















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5.  Running NETCONF from an SSH Shell

    The techniques described in this document could be used to access the
    NETCONF protocol over the SSH shell session, or from other shell
    types such as a console session or a Telnet [RFC0854] connection.
    However, there are serious security implications associated with
    allowing NETCONF access via any method that does not provide strong
    support for user authentication, server authentication and data
    privacy.  See the Security Considerations section for more details.

    If the server supports NETCONF invocation from an SSH shell session,
    the user may choose to invoke a NETCONF program from the shell
    command line.  This would involve using SSH to establish a shell
    session, and entering the name of a NETCONF program (with the full
    path, if necessary) at the remote shell prompt.

5.1  Starting a NETCONF Shell Session

    To the user, the establishment of an SSH shell and the invocation of
    the NETCONF program may look similar to the following example:


    <!-- The user enters an SSH shell session. -->

    [user@client]$ ssh server.example.org
    user@server.example.org's password: ********

    <!-- At the shell prompt, the user invokes the NETCONF program, which
    in this example is called 'netconf', but which might have different
    names on different systems. -->

    [user@server]$ netconf

    <!-- The NETCONF program sends an XML document to the client. -->

    <?xml version="1.0" encoding="UTF-8"?>
    <hello>
        <capabilities>
            <capability>http://ietf.org/xmlconf/1.0/base</capability>
            <capability>http://ietf.org/xmlconf/1.0/base#lock</capability>
        </capabilities>
    </hello>
    ]]>]]>


5.2  Exiting a NETCONF Shell Session

    When the user has run NETCONF from a shell, he will need to exit the



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    NETCONF program using the <kill-session> operation, and then exit the
    remote shell to return to the local shell.  To continue the example
    used in previous sections, an existing NETCONF shell session could be
    closed as follows:


    <!-- The manager sends an XML document containing an <kill-session>
    operation Question: Where do we get the session-id?  Should it be
    sent in the <hello> message? -->

    <?xml version="1.0" encoding="UTF-8"?>
    <rpc message-id="102" xmlns="http://ietf.org/xmlconf/1.0/base">
         <kill-session>
             <session-id>0</session-id>
         </kill-session>
    </rpc>
    ]]>]]>

    <!-- The agent returns an "OK" reply. -->

    <?xml version="1.0" encoding="UTF-8"?>
    <rpc-reply id="102" xmlns="http://ietf.org/netconf/1.0/base">
        <ok/>
    </rpc-reply>
    ]]>]]>

    <!-- The NETCONF program exits, returning the user to the SSH prompt.
    The user then types 'exit' to exit the SSH shell and return to the
    local shell. -->

    [user@server]$ exit
    [user@client]$



















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6.  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.

    If the NETCONF server provides remote shell access through insecure
    protocols, such as 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.




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7.  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
    document.














































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8.  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
    Shoenwaelder and Steve Waldbusser.  The following people have also
    reviewed this document and provided valuable input: Bill Sommerfeld.









































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9.  References

9.1  Normative References

    [I-D.ietf-netconf-prot]
               Enns, R., "NETCONF Configuration Protocol",
               draft-ietf-netconf-prot-02 (work in progress), February
               2004.

    [I-D.ietf-secsh-connect]
               Ylonen, T., Kivinen, T., Rinne, T. and S. Lehtinen, "SSH
               Connection Protocol", draft-ietf-secsh-connect-18 (work in
               progress), October 2003.

    [I-D.ietf-secsh-transport]
               Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S.
               Lehtinen, "SSH Transport Layer Protocol",
               draft-ietf-secsh-transport-17 (work in progress), October
               2003.

    [I-D.ietf-secsh-userauth]
               Ylonen, T. and C. Lonvick, "SSH Authentication Protocol",
               draft-ietf-secsh-userauth-20 (work in progress), May 2004.

9.2  Informative References

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

    [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
               3", BCP 9, RFC 2026, October 1996.

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


Authors' Addresses

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

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




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    Ted Goddard
    IceSoft

    EMail: ted@icesoft.com















































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    HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgment

    Funding for the RFC Editor function is currently provided by the
    Internet Society.











































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