Network Working Group M. Wasserman
Internet-Draft ThingMagic
Expires: April 16, 2006 T. Goddard
ICEsoft Technologies, Inc.
October 13, 2005
Using the NETCONF Configuration Protocol over Secure Shell (SSH)
draft-ietf-netconf-ssh-05.txt
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Copyright (C) The Internet Society (2005).
Abstract
This document describes a method for invoking and running the NETCONF
protocol within a Secure Shell (SSH) session as an SSH subsystem.
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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
5. Exiting the NETCONF Subsystem . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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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 NETCONF 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 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 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 [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 application)
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
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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.
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 <TBD> 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 message sent by the server are
marked with "S:".
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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:xml:ns:netconf:base:1.0#startup
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 unambigiously used to
indentify 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 to the server containing <rpc> elements,
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:
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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 processe RPC messages from the manager in the order in
which the are received. When the agent processes a <close-session>
command, 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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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 which
provides for support of strong encryption and authentication.
If the NETCONF server provides remote shell access through insecure
protocols, such as rsh or 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
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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.
IANA is also requested to assign "netconf" as an SSH Service Name as
defined in [I-D.ietf-secsh-assignednumbers], as follows:
Service Name Reference
------------- ---------
netconf [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,
Bert Wijnen.
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9. References
9.1. Normative References
[I-D.ietf-netconf-prot]
Enns, R., "NETCONF Configuration Protocol",
draft-ietf-netconf-prot-09 (work in progress),
October 2005.
[I-D.ietf-secsh-assignednumbers]
Lehtinen, S. and C. Lonvick, "SSH Protocol Assigned
Numbers", draft-ietf-secsh-assignednumbers-12 (work in
progress), March 2005.
[I-D.ietf-secsh-connect]
Lonvick, C. and T. Ylonen, "SSH Connection Protocol",
draft-ietf-secsh-connect-25 (work in progress),
March 2005.
[I-D.ietf-secsh-transport]
Lonvick, C., "SSH Transport Layer Protocol",
draft-ietf-secsh-transport-24 (work in progress),
March 2005.
[I-D.ietf-secsh-userauth]
Lonvick, C. and T. Ylonen, "SSH Authentication Protocol",
draft-ietf-secsh-userauth-27 (work in progress),
March 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
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Authors' Addresses
Margaret Wasserman
ThingMagic
One Broadway, 5th Floor
Cambridge, MA 02142
USA
Phone: +1 617 758-4177
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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