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Versions: (RFC 4742) 00 01 02 03 04 05 06 07 08 RFC 6242

Network Working Group                                       M. Wasserman
Internet-Draft                                    Painless Security, LLC
Expires: December 3, 2010                                     T. Goddard
                                              ICEsoft Technologies, Inc.
                                                            June 1, 2010


    Using the NETCONF Configuration Protocol over Secure Shell (SSH)
                  draft-ietf-netconf-rfc4742bis-01.txt

Abstract

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

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   material or to cite them other than as "work in progress."

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

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
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   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Terminology . . . . . . . . . . . . . . . . . . .  3
   3.  Starting NETCONF over SSH  . . . . . . . . . . . . . . . . . .  3
     3.1.  Capabilities Exchange  . . . . . . . . . . . . . . . . . .  4
   4.  Using NETCONF over SSH . . . . . . . . . . . . . . . . . . . .  5
   5.  Exiting the NETCONF Subsystem  . . . . . . . . . . . . . . . .  6
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   9.  Change Log . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     9.1.  Changes from RFC4742bis-00 to RFC4742-bis-01 . . . . . . .  9
     9.2.  Changes from RFC4742 to RFC4742bis-00  . . . . . . . . . .  9
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     10.1. Normative References . . . . . . . . . . . . . . . . . . .  9
     10.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

































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1.  Introduction

   The NETCONF protocol [RFC4741] 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 NETCONF can be used within a Secure Shell (SSH)
   session, using the SSH connection protocol [RFC4254] over the SSH
   transport protocol [RFC4253].  This mapping will allow NETCONF to be
   executed from a secure shell session by a user or application.

   Throughout this document, the two ends of the SSH connection are
   referred to as the SSH client and the SSH server, and the two ends of
   the NETCONF session are referred to as the NETCONF client and the
   NETCONF server.  The SSH client initiates the SSH connection and the
   SSH server accepts the connection.  The NETCONF client sends NETCONF
   operations, and the NETCONF server responds to those operations.
   There is no requirement that the NETCONF client reside on the SSH
   client or that the NETCONF server reside on the SSH server.

   Although this document gives specific examples of how NETCONF
   operations are sent over an SSH connection, use of this transport is
   not restricted to the operations shown in the examples below.  This
   transport can be used for any NETCONF operation.


2.  Requirements Terminology

   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 RFC 2119 [RFC2119].


3.  Starting NETCONF over SSH

   To run NETCONF over SSH, the SSH client will first establish an SSH
   transport connection using the SSH transport protocol, and the SSH
   client and SSH server will exchange keys for message integrity and
   encryption.  The SSH client will then invoke the "ssh-userauth"
   service to authenticate the user, as described in the SSH
   authentication protocol [RFC4252].  Once the user has been
   successfully authenticated, the SSH client will invoke the "ssh-
   connection" service, also known as the SSH connection protocol.

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




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   Once the SSH session has been established, the NETCONF client will
   invoke NETCONF as an SSH subsystem called "netconf".  Subsystem
   support is a feature of SSH version 2 (SSHv2) and is not included in
   SSHv1.  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 sent 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 830.
   Servers SHOULD be configurable to allow access to the netconf SSH
   subsystem over other ports.

   A user (or application) 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 830 netconf

   Note that the -s option causes the command ("netconf") to be invoked
   as an SSH subsystem.

3.1.  Capabilities Exchange

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

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

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











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

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

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

   As the previous example illustrates, a special character sequence,
   ]]>]]>, MUST be sent by both the NETCONF client and the NETCONF
   server after each XML document in the NETCONF exchange.  This
   character sequence cannot legally appear outside of a comment in an
   XML document, so it can be unambigiously used to identify the end of
   the current document, allowing resynchronization of the NETCONF
   exchange in the event of an XML syntax or parsing error.


4.  Using NETCONF over SSH

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

   To continue the example given above, a NETCONF over SSH session to



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   retrieve a set of configuration information might look like this:


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

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


5.  Exiting the NETCONF Subsystem

   Exiting NETCONF is accomplished using the <close-session> operation.
   A NETCONF server will process NETCONF operations from the NETCONF
   client in the order in which the are received.  When the NETCONF
   server processes a <close-session> operation, the NETCONF server
   shall respond and close the SSH session channel.  The NETCONF server
   MUST NOT process any NETCONF operations received after the <close-
   session> operation.

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










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

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


6.  Security Considerations

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

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

   Configuration or state 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.

   This document requires that SSH 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 SSH servers be configurable to



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   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.


7.  IANA Considerations

   Based on the previous version of this document, RFC 4742, IANA
   assigned port 830 as the default port for NETCONF over SSH sessions.

   IANA has also assigned "netconf" as an SSH Subsystem Name, as defined
   in [RFC4250], as follows:



              Subsystem Name                  Reference
              --------------                  ---------
              netconf                         RFC 4742


   IANA is requested to update these allocations to reference this
   document when it is published as an RFC.


8.  Acknowledgements

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

   Extensive input was received from the other 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: Olafur
   Gudmundsson, Sam Hartman, Scott Hollenbeck, Bill Sommerfeld, Bert
   Wijnen, Balazs Lengyel and Martin Bjorklund.


9.  Change Log

   [RFC Editor: Please remove this section before publication as an
   RFC.]







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9.1.  Changes from RFC4742bis-00 to RFC4742-bis-01

   o  Changed use of client/server, manager/agent to SSH client/server
      and NETCONF client/server.

   o  Consistently used term operation, instead of command or message.

   o  Clarified some sections based on review feedback.

   o  Fixed several typos.

9.2.  Changes from RFC4742 to RFC4742bis-00

   o  Integrated previously-approved errata from
      http://rfc-editor.org/errata_search.php?rfc=4742

   o  Removed text requiring implementations to skip to an XML start
      directive at the beginning of a session.

   o  Made it clear the ]]>]]> is illegal in XML documents only outside
      of comments.


10.  References

10.1.  Normative References

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

   [RFC4250]  Lehtinen, S. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Assigned Numbers", RFC 4250, January 2006.

   [RFC4252]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, January 2006.

   [RFC4253]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, January 2006.

   [RFC4254]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Connection Protocol", RFC 4254, January 2006.

   [RFC4741]  Enns, R., "NETCONF Configuration Protocol", RFC 4741,
              December 2006.







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10.2.  Informative References

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


Authors' Addresses

   Margaret Wasserman
   Painless Security, LLC
   356 Abbott Street
   North Andover, MA  01845
   USA

   Phone: +1 781 405-7464
   Email: mrw@painless-security.com
   URI:   http://www.painless-security.com


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

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























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