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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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.
Wasserman & Goddard Expires November 29, 2004 [Page 1]
Internet-Draft NETCONF over SSH May 2004
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
Wasserman & Goddard Expires November 29, 2004 [Page 2]
Internet-Draft NETCONF over SSH May 2004
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.
Wasserman & Goddard Expires November 29, 2004 [Page 3]
Internet-Draft NETCONF over SSH May 2004
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.
Wasserman & Goddard Expires November 29, 2004 [Page 4]
Internet-Draft NETCONF over SSH May 2004
<!-- 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.
Wasserman & Goddard Expires November 29, 2004 [Page 5]
Internet-Draft NETCONF over SSH May 2004
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.
Wasserman & Goddard Expires November 29, 2004 [Page 6]
Internet-Draft NETCONF over SSH May 2004
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>
]]>]]>
Wasserman & Goddard Expires November 29, 2004 [Page 7]
Internet-Draft NETCONF over SSH May 2004
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]$
]]>]]>
Wasserman & Goddard Expires November 29, 2004 [Page 8]
Internet-Draft NETCONF over SSH May 2004
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
Wasserman & Goddard Expires November 29, 2004 [Page 9]
Internet-Draft NETCONF over SSH May 2004
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]$
Wasserman & Goddard Expires November 29, 2004 [Page 10]
Internet-Draft NETCONF over SSH May 2004
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.
Wasserman & Goddard Expires November 29, 2004 [Page 11]
Internet-Draft NETCONF over SSH May 2004
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.
Wasserman & Goddard Expires November 29, 2004 [Page 12]
Internet-Draft NETCONF over SSH May 2004
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.
Wasserman & Goddard Expires November 29, 2004 [Page 13]
Internet-Draft NETCONF over SSH May 2004
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
Wasserman & Goddard Expires November 29, 2004 [Page 14]
Internet-Draft NETCONF over SSH May 2004
Ted Goddard
IceSoft
EMail: ted@icesoft.com
Wasserman & Goddard Expires November 29, 2004 [Page 15]
Internet-Draft NETCONF over SSH May 2004
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property 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; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication 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 implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
Wasserman & Goddard Expires November 29, 2004 [Page 16]
Internet-Draft NETCONF over SSH May 2004
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Wasserman & Goddard Expires November 29, 2004 [Page 17]
