NETCONF over SSH: Using the NETCONF Configuration Protocol over Secure SHell (SSH)

Network Working Group                                       M. Wasserman
Request for Comments: 4742                                    ThingMagic
Category: Standards Track                                     T. Goddard
                                              ICEsoft Technologies, Inc.
                                                           December 2006


    Using the NETCONF Configuration Protocol over Secure SHell (SSH)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2006).

Abstract

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

Table of Contents

   1. Introduction ....................................................2
   2. Requirements Terminology ........................................2
   3. Starting NETCONF over SSH .......................................2
      3.1. Capabilities Exchange ......................................3
   4. Using NETCONF over SSH ..........................................5
   5. Exiting the NETCONF Subsystem ...................................6
   6. Security Considerations .........................................6
   7. IANA Considerations .............................................7
   8. Acknowledgements ................................................7
   9. References ......................................................8
      9.1. Normative References .......................................8
      9.2. Informative References .....................................8

1.  Introduction

   The NETCONF protocol [RFC4721] 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 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 remote procedure call (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.  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 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 [RFC4252].  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 application)
   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.
   However, even when a subsystem is used, some extraneous messages may
   be printed by the user's start-up scripts.  Implementations MUST skip
   over these messages by searching for an 'xml' start directive, which
   MUST be followed by a <hello> element in the 'NETCONF' namespace.

   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 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 application) 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.

   The following example shows a capability exchange.  Messages sent by
   the client are marked with "C:", and messages 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: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>
   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 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.

   As the previous example illustrates, a special character sequence,
   ]]>]]>, MUST be sent by both the client and the server after each XML
   document in the NETCONF exchange.  This character sequence cannot
   legally appear in an XML document, so it can be unambiguously 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 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 containing <rpc> elements to the server,
   and the agent will respond with complete XML documents containing
   <rpc-reply> elements.

   To continue the example given above, an NETCONF over SSH session to
   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.
   An agent will process RPC messages from the manager in the order in
   which they are received.  When the agent processes a <close-session>
   command, the agent shall respond and close the SSH session channel.
   The agent MUST NOT process any RPC commands received on the current
   session after the <close-session> command.

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

   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 agent's configuration and state or to modify the agent's
   configuration.

   The identity of the server MUST be verified and authenticated by the
   client according to local policy before password-based authentication
   data or any configuration or state data is sent to or received from
   the server.  The identity of the client MUST also be verified and
   authenticated by the server according to local policy to ensure that
   the incoming client request is legitimate before any configuration or
   state data is sent to or received from the 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 that
   provides for support of strong encryption and authentication.

   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 the firewall or other administrative
   boundary to gain access to "netconf" SSH subsystem.

7.  IANA Considerations

   IANA assigned a TCP port number that is the default port for NETCONF
   over SSH sessions as defined in this document.

   IANA assigned port <830> for this purpose.

   IANA is also requested to assign "netconf" as an SSH Service Name as
   defined in [RFC4250], as follows:

            Service Name                  Reference
            -------------                 ---------
            netconf                       RFC 4742

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, and Bert
   Wijnen.

9.  References

9.1.  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.

   [RFC4721]  Enns, R., Ed., "NETCONF Configuration Protocol", RFC 4721,
              December 2006.

9.2.  Informative References

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

Authors' Addresses

   Margaret Wasserman
   ThingMagic
   One Broadway, 5th Floor
   Cambridge, MA  02142
   USA

   Phone: +1 781 405-7464
   EMail: margaret@thingmagic.com
   URI:   http://www.thingmagic.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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