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Network Working Group                                       M. WassermanRequest for Comments: 4742                                    ThingMagicCategory: Standards Track                                     T. Goddard                                              ICEsoft Technologies, Inc.                                                           December 2006Using 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 Contents1. Introduction ....................................................22. Requirements Terminology ........................................23. Starting NETCONF over SSH .......................................23.1. Capabilities Exchange ......................................34. Using NETCONF over SSH ..........................................55. Exiting the NETCONF Subsystem ...................................66. Security Considerations .........................................67. IANA Considerations .............................................78. Acknowledgements ................................................79. References ......................................................89.1. Normative References .......................................89.2. Informative References .....................................8Wasserman & Goddard         Standards Track                     [Page 1]

RFC 4742                    NETCONF over SSH               December 20061.  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 inRFC 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 mayWasserman & Goddard         Standards Track                     [Page 2]

RFC 4742                    NETCONF over SSH               December 2006   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:".Wasserman & Goddard         Standards Track                     [Page 3]

RFC 4742                    NETCONF over SSH               December 2006   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.Wasserman & Goddard         Standards Track                     [Page 4]

RFC 4742                    NETCONF over SSH               December 20064.  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: ]]>]]>Wasserman & Goddard         Standards Track                     [Page 5]

RFC 4742                    NETCONF over SSH               December 20065.  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   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 dataWasserman & Goddard         Standards Track                     [Page 6]

RFC 4742                    NETCONF over SSH               December 2006   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            -------------                 ---------            netconfRFC 47428.  Acknowledgements   This document was written using the xml2rfc tool described inRFC2629 [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.Wasserman & Goddard         Standards Track                     [Page 7]

RFC 4742                    NETCONF over SSH               December 20069.  References9.1.  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.Wasserman & Goddard         Standards Track                     [Page 8]

RFC 4742                    NETCONF over SSH               December 2006Authors' 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.comWasserman & Goddard         Standards Track                     [Page 9]

RFC 4742                    NETCONF over SSH               December 2006Full Copyright Statement   Copyright (C) The IETF Trust (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST,   AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT   THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY   IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR   PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Wasserman & Goddard         Standards Track                    [Page 10]