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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
Obsoletes: 4742 (if approved)                                 T. Goddard
Intended status: Standards Track              ICEsoft Technologies, Inc.
Expires: September 16, 2011                               March 15, 2011


    Using the NETCONF Configuration Protocol over Secure Shell (SSH)
                  draft-ietf-netconf-rfc4742bis-08.txt

Abstract

   This document describes a method for invoking and running the NETCONF
   protocol within a Secure Shell (SSH) session as an SSH subsystem.
   This document obsoletes RFC 4742.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 16, 2011.

Copyright Notice

   Copyright (c) 2011 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   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
     4.1.  Framing protocol . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Chunked Framing Mechanism  . . . . . . . . . . . . . . . .  6
     4.3.  End-of-message Framing Mechanism . . . . . . . . . . . . .  7
   5.  Exiting the NETCONF Subsystem  . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     9.1.  Changes from RFC4742bis-07 to RFC4742-bis-08 . . . . . . . 11
     9.2.  Changes from RFC4742bis-06 to RFC4742-bis-07 . . . . . . . 11
     9.3.  Changes from RFC4742bis-05 to RFC4742-bis-06 . . . . . . . 11
     9.4.  Changes from RFC4742bis-04 to RFC4742-bis-05 . . . . . . . 11
     9.5.  Changes from RFC4742bis-03 to RFC4742-bis-04 . . . . . . . 11
     9.6.  Changes from RFC4742bis-02 to RFC4742-bis-03 . . . . . . . 11
     9.7.  Changes from RFC4742bis-01 to RFC4742-bis-02 . . . . . . . 12
     9.8.  Changes from RFC4742bis-00 to RFC4742-bis-01 . . . . . . . 12
     9.9.  Changes from RFC4742 to RFC4742bis-00  . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13























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1.  Introduction

   The NETCONF protocol [I-D.ietf-netconf-4741bis] 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.

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


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.

   The username provided by the SSH implementation will be made
   available to the NETCONF message layer as the NETCONF username
   without modification.  If the username does not comply to the NETCONF
   requirements on usernames [I-D.ietf-netconf-4741bis] , i.e., the
   username is not representable in XML, the SSH session MUST be
   dropped.  Any transformations applied to the authenticated identity
   of the SSH client made by the SSH server (e.g., via authentication
   services or mappings to system accounts) are outside the scope of
   this document.

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



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   session.

   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

   As specified in [I-D.ietf-netconf-4741bis] 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 message to determine which NETCONF
   capabilities are supported by the NETCONF server.

   As [I-D.ietf-netconf-4741bis] states the NETCONF client must also
   send an XML document containing a <hello> element to indicate the
   NETCONF client's capabilitiesto 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.  Data sent by the
   NETCONF client are marked with "C:" and data 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:netconf:base:1.1
   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:netconf:base:1.1
   C:     </capability>
   C:   </capabilities>
   C: </hello>
   C: ]]>]]>

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


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.

4.1.  Framing protocol

   The previous version of this document defined the character sequence
   "]]>]]>" as a message separator, under the assumption that it could
   not be found in well-formed XML documents.  However, this assumption
   is not correct.  It can legally appear in XML attributes, comments,
   and processing instructions.  In order to solve this problem, and at
   the same time be compatible with existing implementations, this
   document defines the following framing protocol.



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   The <hello> message MUST be followed by the character sequence
   ]]>]]>.  Upon reception of the <hello> message, the receiving peer's
   SSH Transport layer conceptually passes the <hello> message to the
   Messages layer.  If the :base:1.1 capability is advertised by both
   peers, the chunked transfer mechanism (see Section 4.2) is used for
   the remainder of the NETCONF session.  Otherwise, the old end-of-
   message based mechanism (see Section 4.3) is used.

4.2.  Chunked Framing Mechanism

   This mechanism encodes all NETCONF messages with a chunked framing.
   Specifically, the message follows the ABNF [RFC5234] rule Chunked-
   Message:


        Chunked-Message = 1*chunk
                          end-of-chunks

        chunk           = LF HASH chunk-size LF
                          chunk-data
        chunk-size      = 1*DIGIT1 0*DIGIT
        chunk-data      = 1*OCTET

        end-of-chunks   = LF HASH HASH LF

        DIGIT1          = %x31-39
        DIGIT           = %x30-39
        HASH            = %x23
        LF              = %x0A
        OCTET           = %x00-FF


   The chunk-size field is a string of decimal digits indicating the
   number of octets in chunk-data.  Leading zeros are prohibited, and
   the maximum allowed chunk-size value is 4294967295.

   As an example, the message:


       <rpc message-id="102"
            xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
         <close-session/>
       </rpc>


   could be encoded as (using '\n' as a visible representation of the
   LineFeed character):




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   C:  \n#4\n
   C:  <rpc
   C:  \n#18\n
   C:   message-id="102"\n
   C:  \n#79\n
   C:       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">\n
   C:    <close-session/>\n
   C:  </rpc>
   C:  \n##\n


   Conceptually, the SSH Transport layer encodes messages sent by the
   Messages layer, and decodes messages received on the SSH channel
   before passing them to the Messages layer.

   The examples for the Chunked Framing mechanism show all LineFeeds,
   even those which are not used as part of the framing mechanism.  Note
   that the SSH transport does not interpret the XML content thus it
   does not care of any optional XML-specific LineFeeds.

   In the second and third chunks quoted above, each line is terminated
   by a LineFeed.  For all the XML lines (except the last one), this
   example treats the LineFeed as part of the chunk-data and so
   contributing to the chunk-size.

   Note that there is no LineFeed character after the <rpc> end tag in
   this message.  The LineFeed required by the start of the end-of-
   chunks block immediately follows the last '>' character in the
   message.

   If the chunk-size and the chunk-size value respectively are invalid
   or an error occurs during the decoding process, the peer MUST
   terminate the NETCONF session by closing the corresponding SSH
   channel.  Implementations MUST ensure they are not vulnerable for a
   buffer overrun.

4.3.  End-of-message Framing Mechanism

   This mechanism exists for backwards compatibility with
   implementations of previous versions of this document.  It is only
   used when the remote peer does not advertise a base protocol version
   supporting chunked encoding, i.e. a NETCONF implementation only
   supporting :base:1.0.

   When this mechanism is used, the special character sequence ]]>]]>,
   MUST be sent by both the NETCONF client and the NETCONF server after
   each message (XML document) in the NETCONF exchange.  Conceptually,
   the SSH Transport layer passes any data found in between the ]]>]]>



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   characters to the Messages layer.

   A NETCONF over SSH session, using the backwards-compatible end-of-
   message framing, 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.
   A NETCONF server will process NETCONF messages from the NETCONF
   client in the order in which they 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 messages received after the <close-
   session> operation.

   To continue the example used in section 4.2, an existing NETCONF
   subsystem session could be closed as follows:






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   C: \n#140\n
   C: <?xml version="1.0" encoding="UTF-8"?>\n
   C: <rpc message-id="106"\n
   C:      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">\n
   C:   <close-session/>\n
   C: </rpc>
   C: \n##\n

   S: \n#139\n
   S: <?xml version="1.0" encoding="UTF-8"?>\n
   S: <rpc-reply id="106"\n
   S:            xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">\n
   S:   <ok/>\n
   S: </rpc-reply>
   S: \n##\n



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 requires 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



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   to be more easily identified by attackers.

   This document also recommends that SSH 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.

   RFC 4742 assumes that the EOM sequence, ]]>]]>, cannot appear in any
   well-formed XML document, which turned out to be mistaken.  The EOM
   sequence can cause operational problems and open space for attacks if
   sent deliberately in RPC messages.  It is however believed that the
   associated threat is not very high.  This document still uses the EOM
   sequence for the initial <hello> message to avoid incompatibility
   with existing implementations.  When both peers implement base:1.1
   capability, a proper framing protocol (Chunked Framing Mechanism, see
   Section 4.2) is used for the rest of the NETCONF session, to avoid
   injection attacks.


7.  IANA Considerations

   Based on the previous version of this document, RFC 4742, IANA
   assigned the TCP 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,



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   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, Balazs
   Lengyel, Bert Wijnen, Mehmet Ersue, Martin Bjorklund, Lada Lothka,
   Kent Watsen, and Tom Petch.


9.  Change Log

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

9.1.  Changes from RFC4742bis-07 to RFC4742-bis-08

   o  Additional clarifications and minor changes to address IESG review
      comments.

9.2.  Changes from RFC4742bis-06 to RFC4742-bis-07

   o  Minor changes to address IESG review comments.

9.3.  Changes from RFC4742bis-05 to RFC4742-bis-06

   o  Updated chunked encoding to include location of new lines.

   o  Updated examples to show new chunked encoding properly.

   o  Minor editorial fixes.

9.4.  Changes from RFC4742bis-04 to RFC4742-bis-05

   o  Added option for chunked encoding.

   o  Added 1.1 capability to enable chunked encoding.

9.5.  Changes from RFC4742bis-03 to RFC4742-bis-04

   o  Shortened text about EOM sequence.

   o  Added text to Security Considerations about EOM issues.

9.6.  Changes from RFC4742bis-02 to RFC4742-bis-03

   o  Added intended status and "obsoletes" to headers.

   o  Very minor editorial changes.





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9.7.  Changes from RFC4742bis-01 to RFC4742-bis-02

   o  Removed unneeded wording about client/server, made unnecessary by
      previous changes.

   o  Stated that how a server extracts the SSH user name is
      implementation-dependent.

   o  Further fixes to operation/message/data wording.

9.8.  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.

9.9.  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

   [I-D.ietf-netconf-4741bis]
              Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)",
              draft-ietf-netconf-4741bis-10 (work in progress),
              March 2011.

   [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.



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   [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.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

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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