NETCONF Working Group Mohamad Badra
Internet Draft LIMOS Laboratory
Intended status: Standards Track September 2, 2008
Expires: March 2009
NETCONF over Transport Layer Security (TLS)
draft-ietf-netconf-tls-04.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
The Network Configuration Protocol (NETCONF) provides mechanisms to
install, manipulate, and delete the configuration of network devices.
This document describes how to use the Transport Layer Protocol (TLS)
to secure NETCONF exchanges.
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Table of Contents
1. Introduction...................................................3
1.1. Conventions used in this document.........................3
2. NETCONF over TLS...............................................3
2.1. Connection Initiation.....................................3
2.2. Connection Closure........................................4
3. Endpoint Authentication and Identification.....................4
3.1. Server Identity...........................................5
3.2. Client Identity...........................................6
3.3. Pre-shared key Authentication.............................6
4. Cipher Suite Requirements......................................7
5. Security Considerations........................................7
6. IANA Considerations............................................7
7. Acknowledgments................................................7
8. References.....................................................8
8.1. Normative References......................................8
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1. Introduction
The NETCONF protocol [RFC4741] defines a simple mechanism through
which a network device can be managed. NETCONF is connection-
oriented, requiring a persistent connection between peers. This
connection must provide reliable, sequenced data delivery, integrity
and confidentiality and peers authentication. This document
describes how to use TLS [RFC5246] to secure NETCONF connections.
Throughout this document, the terms "client" and "server" are used to
refer to the two ends of the TLS connection. The client actively
opens the TLS connection, and the server passively listens for the
incoming TLS 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 TLS using the
mapping defined in this document, the client is always the manager,
and the server is always the agent.
1.1. Conventions used in this document
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].
2. NETCONF over TLS
Since TLS is application protocol-independent, NETCONF can operate on
top of the TLS protocol transparently. This document defines how
NETCONF can be used within a Transport Layer Security (TLS) session.
2.1. Connection Initiation
The peer acting as the NETCONF manager MUST also act as the TLS
client. It MUST connect to the server that passively listens for the
incoming TLS connection on the IANA-to-be-assigned TCP port <TBA>.
It MUST therefore send the TLS ClientHello to begin the TLS
handshake. Once the TLS handshake has been finished, the client and
the server MAY then send their NETCONF exchanges. In particular, the
client will send complete XML documents to the server containing
<rpc> elements, and the server will respond with complete XML
documents containing <rpc-reply> elements. The client MAY indicate
interest in receiving event notifications from a NETCONF server by
creating a subscription to receive event notifications [RFC5277], in
which the NETCONF server replies to indicate whether the subscription
request was successful and, if it was successful, begins sending the
event notifications to the NETCONF client as the events occur within
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the system. All these elements are encapsulated into TLS records of
type "application data". These records are protected using the TLS
material keys.
Current NETCONF messages don't include a message's length. This
document uses consequently the same delimiter sequence defined in
[RFC4742] and therefore the special character sequence, ]]>]]>, to
delimit XML documents.
2.2. Connection Closure
Either NETCONF peer MAY stop the NETCONF connection at any time and
therefore notify the other NETCONF peer that no more data on this
channel will be sent and that any data received after a closure
request will be ignored. This MAY happen when no data is received
from a connection for a long time, where the application decides what
"long" means.
TLS has the ability for secure connection closure using the Alert
protocol. When the NETCONF peer closes the NETCONF connection, it
MUST send a TLS close_notify alert before closing the TCP connection.
Any data received after a closure alert is ignored.
Unless a fatal error has occurred, each party is required to send a
close_notify alert before closing the write side of the connection
[RFC5246]. The other party MUST respond with a close_notify alert of
its own and close down the connection immediately, discarding any
pending writes. It is not required for the initiator of the close to
wait for the responding close_notify alert before closing the read
side of the connection.
3. Endpoint Authentication and Identification
NETCONF requires that its transport provide mutual authentication of
client and server, so cipher suites that are anonymous or which only
authenticate the server to the client MUST NOT be used with NETCONF.
This document specifies how to use TLS with endpoint authentication,
which can be based on either preshared keys [RFC4279] or public key
certificates [RFC5246]. Some cipher suites (e.g.
TLS_RSA_PSK_WITH_AES_128_CBC_SHA) use both. Section 3.1 describes
how the client authenticates the server if public key certificates
are provided by the server, section 3.2 describes how the server
authenticates the client if public key certificates are provided by
the client, and section 3.3 describes how the client and server
mutually authenticate one another using a pre-shared key (PSK).
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3.1. Server Identity
During the TLS negotiation, the client MUST carefully examine the
certificate presented by the server to determine if it meets their
expectations. Particularly, the client MUST check its understanding
of the server hostname against the server's identity as presented in
the server Certificate message, in order to prevent man-in-the-middle
attacks.
Matching is performed according to these rules [RFC4642]:
- The client MUST use the server hostname it used to open the
connection (or the hostname specified in TLS "server_name"
extension [RFC4366]) as the value to compare against the server
name as expressed in the server certificate. The client MUST
NOT use any form of the server hostname derived from an
insecure remote source (e.g., insecure DNS lookup). CNAME
canonicalization is not done.
- If a subjectAltName extension of type dNSName is present in the
certificate, it MUST be used as the source of the server's
identity.
- Matching is case-insensitive.
- A "*" wildcard character MAY be used as the left-most name
component in the certificate. For example, *.example.com would
match a.example.com, foo.example.com, etc., but would not match
example.com.
- If the certificate contains multiple names (e.g., more than one
dNSName field), then a match with any one of the fields is
considered acceptable.
If the match fails, the client MUST either ask for explicit user
confirmation or terminate the connection and indicate the server's
identity is suspect.
Additionally, clients MUST verify the binding between the identity of
the servers to which they connect and the public keys presented by
those servers. Clients SHOULD implement the algorithm in Section 6
of [RFC5280] for general certificate validation, but MAY supplement
that algorithm with other validation methods that achieve equivalent
levels of verification (such as comparing the server certificate
against a local store of already-verified certificates and identity
bindings).
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If the client has external information as to the expected identity of
the server, the hostname check MAY be omitted.
3.2. Client Identity
Typically, the server has no external knowledge of what the client's
identity ought to be and so checks (other than that the client has a
certificate chain rooted in an appropriate CA) are not possible. If
a server has such knowledge (typically from some source external to
NETCONF or TLS) it MUST check the identity as described above.
3.3. Pre-shared key Authentication
[RFC4279] supports authentication based on pre-shared keys (PSKs).
These pre-shared keys are symmetric keys, shared in advance among the
communicating parties.
The PSK can be generated in many ways and its length is variable. It
is RECOMMENDED that implementations that allow the administrator to
manually configure the PSK also provide functionality for generating
a new random PSK, taking [RFC4086] into account.
If both the client and the server agree on using the pre-shared key
authentication, the server can provide a "PSK identity hint" in the
ServerKeyExchange message. If a hint is provided, the
psk_identity_hint is encoded in the same way as in [RFC4279] and
should be a string representation of the name of the server
recognizable to the administrator or his software. In the case where
the user types a server name to connect to, it should be that string.
If the string the user enters differs from the one returned as
psk_identity_hint, the software could display the server's name and
ask the user to confirm. For automated scripts, the names could be
expected to match. It is highly recommended that implementations set
the psk_identity_hint to the DNS name of the NETCONF server (i.e.,
the TLS server).
It is RECOMMENDED that users choose different PSKs for the different
servers they manage.
[RFC4279] defines some conformance requirements for the PSK, for the
PSK identity encoding and for the identity hint. Moreover, it
describes the management interface requirements for entering the PSK
and/or PSK identity (See Section 5 of [RFC4279] for a more detailed
description of these requirements). Those same requirements apply
here as well.
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4. Cipher Suite Requirements
A compliant implementation of the protocol specified in this document
MUST implement the cipher suite TLS_DHE_PSK_WITH_AES_128_CBC_SHA and
MAY implement any TLS cipher suite that provides mutual
authentication.
5. Security Considerations
The security considerations described throughout [RFC5246] and
[RFC4279] apply here as well.
This document in its current version doesn't support third party
authentication due to the fact that TLS doesn't specify this way of
authentication and that NETCONF depends on the transport protocol for
the authentication service. If third party authentication is needed,
BEEP or SSH transport can be used.
As with all schemes involving shared keys, special care should be
taken to protect the shared secret as well as to limit its exposure
over time. Alternatively, using certificates would provide better
protection.
6. IANA Considerations
IANA is requested to assign a TCP port number that will be the
default port for NETCONF over TLS sessions as defined in this
document.
IANA has assigned port <TBA> for this purpose.
7. Acknowledgments
A significant amount of the text in Section 3.1 was lifted from
[RFC4642].
The author would like to acknowledge David Harrington, Miao Fuyou,
Eric Rescorla, Juergen Schoenwaelder, Simon Josefsson, Olivier
Coupelon and the NETCONF mailing list members for their comments on
the document. The author appreciates also Bert Wijnen, Mehmet Ersue
and Dan Romascanu for their efforts on issues resolving discussion,
and Charlie Kaufman, Pasi Eronen and Tim Polk for the thorough review
of this document.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
June 2005.
[RFC4279] Eronen, P. and H. Tschofenig., "Pre-Shared Key Ciphersuites
for Transport Layer Security (TLS)", RFC 4279, December
2005.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS) Extensions",
RFC 4366, April 2006.
[RFC4642] Murchison, K., Vinocur, J., Newman, C., "Using Transport
Layer Security (TLS) with Network News Transfer Protocol
(NNTP)", RFC 4642, October 2006
[RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[RFC4742] Wasserman, M. and T. Goddard, "Using the NETCONF
Configuration Protocol over Secure Shell (SSH)", RFC 4742,
December 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol 1.2", RFC5246, August 2008.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event Notifications",
RFC 5277, July 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
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Author's Addresses
Mohamad Badra
LIMOS Laboratory - UMR6158, CNRS
France
Email: badra@isima.fr
Contributors
Ibrahim Hajjeh
INEOVATION
France
Email: hajjeh@ineovation.com
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