Network Working Group M. Wasserman
Internet-Draft ThingMagic
Expires: April 8, 2005 T. Goddard
ICEsoft Technologies, Inc.
October 8, 2004
Using the NETCONF Configuration Protocol over Secure Shell (SSH)
draft-ietf-netconf-ssh-02.txt
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Copyright Notice
Copyright (C) The Internet Society (2004).
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Starting NETCONF over SSH . . . . . . . . . . . . . . . . . . 3
2.1 Capabilities Exchange . . . . . . . . . . . . . . . . . . 4
3. Using NETCONF over SSH . . . . . . . . . . . . . . . . . . . . 5
4. Exiting the NETCONF Subsystem . . . . . . . . . . . . . . . . 6
5. Running NETCONF from an SSH Shell . . . . . . . . . . . . . . 7
5.1 Starting a NETCONF Shell Session . . . . . . . . . . . . . 7
5.2 Exiting a NETCONF Shell Session . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1 Normative References . . . . . . . . . . . . . . . . . . . . 10
9.2 Informative References . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . 13
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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 using the mapping defined in
this document, the client is always the manager, and the server is
always the agent.
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.
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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.
<!-- 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.
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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.
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.
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:
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<!-- 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>
]]>]]>
4. Exiting the NETCONF Subsystem
Exiting NETCONF is accomplished using the <close-session> operation.
An agend will processed RPC messages from the manager in the order in
which the are received. When the agent processes a <close-session>
command is, the agent shall respond, terminate the SSH session, and
close the TCP connection. 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:
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<!-- The manager sends an XML document containing a <close-session>
command. -->
<?xml version="1.0" encoding="UTF-8"?>
<rpc message-id="106" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<close-session>
</close-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]$
]]>]]>
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:
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<!-- 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
NETCONF program using the <close-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:
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<!-- The manager sends an XML document containing a <close-session>
command. -->
<?xml version="1.0" encoding="UTF-8"?>
<rpc message-id="102" xmlns="http://ietf.org/xmlconf/1.0/base">
<close-session>
</close-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]$
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.
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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.
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.
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
Schoenwaelder and Steve Waldbusser. The following people have also
reviewed this document and provided valuable input: Bill Sommerfeld.
9. References
9.1 Normative References
[I-D.ietf-netconf-prot]
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Enns, R., "NETCONF Configuration Protocol",
draft-ietf-netconf-prot-03 (work in progress), June 2004.
[I-D.ietf-secsh-connect]
Ylonen, T., Kivinen, T., Rinne, T. and S. Lehtinen, "SSH
Connection Protocol", draft-ietf-secsh-connect-19 (work in
progress), June 2004.
[I-D.ietf-secsh-transport]
Ylonen, T. and C. Lonvick, "SSH Transport Layer Protocol",
draft-ietf-secsh-transport-18 (work in progress), June
2004.
[I-D.ietf-secsh-userauth]
Ylonen, T. and C. Lonvick, "SSH Authentication Protocol",
draft-ietf-secsh-userauth-21 (work in progress), June
2004.
9.2 Informative References
[RFC0854] Postel, J. and J. Reynolds, "Telnet Protocol
Specification", STD 8, RFC 854, May 1983.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3667, February 2004.
[RFC3668] Bradner, S., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004.
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
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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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