Internet Engineering Task Force M. Badra
INTERNET DRAFT LIMOS Laboratory
October 10, 2007 Expires: April 2008
NETCONF over TLS
<draft-badra-tls-netconf-04.txt>
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
The NETCONF configuration protocol provides mechanisms to install,
manipulate, and delete the configuration of network devices. This
document describes how to use TLS to secure NETCONF exchanges.
1 Introduction
The NETCONF protocol [NETCONF] defines a simple mechanism through
which a network device can be managed. NETCONF is connection-
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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 [TLS] to secure NETCONF connections.
1.2 Requirements language and Terminologies
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 [KEYWORDS].
1.3 Terminology
This document uses the following terms:
manager
It refers to the end initiating the NETCONF connection. It issues
the NETCONF RPC commands.
agent
It refers to the end replying to the manager's commands during the
NETCONF connection.
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 <TBC>.
It MUST therefore send the TLS ClientHello to begin the TLS
handshake. Once the TLS handshake has been finished, the manager and
the agent MAY then send their NETCONF exchanges. In particular, 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. The client MAY indicate
interest in receiving event notifications from a NETCONF server by
creating a subscription to receive event notifications [NETNOT], 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 the system. All these elements are encapsulated
into TLS records of type "application data". These records are
protected using the TLS material keys.
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Current NETCONF messages don't include a message's length. This
document uses consequently the same delimiter sequence defined in
[NETSSH] 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 processes a closure request of the
NETCONF connection, it MUST send a TLS close_notify alert before
closing the connection. Any data received after a closure alert is
ignored.
Unless some other fatal alert has been transmitted, each party is
required to send a close_notify alert before closing the write side
of the connection. 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
Usually, TLS uses public keys, Kerberos [TLSKERB], or preshared keys
[TLSPSK] for authentication.
When public key is used for authentication, TLS supports three
authentication modes: authentication of both parties, server
authentication with an unauthenticated client, and total anonymity.
User authentication in unauthenticated or authenticated client mode
is outside the scope of this document. User authentication should be
handled by either an extension of TLS (such as the TLS Inner
Application Extension [IATLS]) or an authentication extension of
NETCONF.
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
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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 [TLSEXT]) 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 [PKICERT] 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).
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
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a server has such knowledge (typically from some source external to
NETCONF or TLS) it MUST check the identity as described above.
4. Security Considerations
The security considerations described throughout [TLS] apply here as
well.
5. 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 <TBD> for this purpose.
6. Acknowledgment
The author would like to acknowledge Eric Rescorla and Juergen
Schoenwaelder for their detailed reviews of the content of the
document. The author appreciates also David Harrington, Miao Fuyou
and Dan Romascanu for their effort on issues resolving discussion.
7. References
7.1. Normative References
[NETCONF] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[TLS] Dierks, T. and E. Rescorla, "The TLS Protocol Version
1.1", RFC 4346, April 2005.
[TLSEXT] Blake-Wilson, S., et. al., "Transport Layer Security
(TLS) Extensions", RFC 4346, April 2006.
[TLSPSK] Eronen, P., et. al., "Pre-Shared Key Ciphersuites for
Transport Layer Security (TLS)", RFC 4279, December 2005.
[RFC4642] Murchison, K., Vinocur, J., Newman, C., "Using Transport
Layer Security (TLS) with Network News Transfer Protocol
(NNTP)", RFC 4642, October 2006
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[PKICERT] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
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April 2002.
[NETSSH] Wasserman, M. and T. Goddard, "Using the NETCONF
Configuration Protocol over Secure Shell (SSH)",
RFC 4742, December 2006.
[NETNOT] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", draft-ietf-netconf-notification-09.txt,
(work in progress), September 2007.
7.2. Informative References
[TLSKERB] Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher
Suites to Transport Layer Security (TLS)", RFC 2712,
October 1999.
[IATLS] Funk, P., et. al., "TLS Inner Application Extension
(TLS/IA)", draft-funk-tls-inner-application-extension-
03.txt (work in progress), June 2006.
Author's Addresses
Mohamad Badra
LIMOS Laboratory - UMR (6158), CNRS
France Email: badra@isima.fr
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