Network Working Group M. Badra
Request for Comments: 5539 CNRS/LIMOS Laboratory
Category: Standards Track May 2009
NETCONF over Transport Layer Security (TLS)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
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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 Security (TLS)
protocol to secure NETCONF exchanges.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . . 2
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 . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Client Identity . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
7. Contributor's Address . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
1. Introduction
The NETCONF protocol [RFC4741] defines a mechanism through which a
network device can be managed. NETCONF is connection-oriented,
requiring a persistent connection between peers. This connection
must provide integrity, confidentiality, peer authentication, and
reliable, sequenced data delivery.
This document defines "NETCONF over TLS", which includes support for
certificate-based mutual authentication and key derivation, utilizing
the protected ciphersuite negotiation, mutual authentication, and key
management capabilities of the TLS (Transport Layer Security)
protocol, described in [RFC5246].
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 [RFC2119].
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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 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 TCP port 6513. It MUST therefore send
the TLS ClientHello message to begin the TLS handshake. Once the TLS
handshake has finished, the client and the server MAY begin to
exchange NETCONF data. 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 server by creating a subscription to receive
event notifications [RFC5277]. In this case, the server replies to
indicate whether the subscription request was successful and, if it
was successful, the server begins sending the event notifications to
the client as the events occur within the system.
All NETCONF messages MUST be sent as TLS "application data". It is
possible that multiple NETCONF messages be contained in one TLS
record, or that a NETCONF message be transferred in multiple TLS
records.
This document uses the same delimiter sequence ("]]>]]>") defined in
[RFC4742], which MUST be sent by both the client and the server after
each XML document in the NETCONF exchange. Since this character
sequence can legally appear in plain XML in attribute values,
comments, and processing instructions, implementations of this
document MUST ensure that this character sequence is never part of a
NETCONF message.
Implementation of the protocol specified in this document MAY
implement any TLS cipher suite that provides certificate-based mutual
authentication [RFC5246]. The server MUST support certificate-based
client authentication.
Implementations MUST support TLS 1.2 [RFC5246] and are REQUIRED to
support the mandatory-to-implement cipher suite, which is
TLS_RSA_WITH_AES_128_CBC_SHA. This document is assumed to apply to
future versions of TLS; in which case, the mandatory-to-implement
cipher suite for the implemented version MUST be supported.
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2.2. Connection Closure
A TLS client (NETCONF manager) MUST close the associated TLS
connection if the connection is not expected to issue any NETCONF RPC
commands later. It MUST send a TLS close_notify alert before closing
the connection. The TLS client MAY choose to not wait for the TLS
server (NETCONF agent) close_notify alert and simply close the
connection, thus generating an incomplete close on the TLS server
side. Once the TLS server gets a close_notify from the TLS client,
it MUST reply with a close_notify unless it becomes aware that the
connection has already been closed by the TLS client (e.g., the
closure was indicated by TCP).
When no data is received from a connection for a long time (where the
application decides what "long" means), a NETCONF peer MAY close the
connection. The NETCONF peer MUST attempt to initiate an exchange of
close_notify alerts with the other NETCONF peer before closing the
connection. The close_notify's sender that is unprepared to receive
any more data MAY close the connection after sending the close_notify
alert, thus generating an incomplete close on the close_notify's
receiver side.
3. Endpoint Authentication and Identification
3.1. Server Identity
During the TLS negotiation, the client MUST carefully examine the
certificate presented by the server to determine if it meets the
client's 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 the rules below (following the
example of [RFC4642]):
o The client MUST use the server hostname it used to open the
connection (or the hostname specified in the TLS "server_name"
extension [RFC5246]) 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.
o If a subjectAltName extension of type dNSName is present in the
certificate, it MUST be used as the source of the server's
identity.
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o Matching is case-insensitive.
o A "*" wildcard character MAY be used as the leftmost name
component in the certificate. For example, *.example.com would
match a.example.com, foo.example.com, etc., but would not match
example.com.
o 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).
If the client has external information as to the expected identity of
the server, the hostname check MAY be omitted.
3.2. Client Identity
The server MUST verify the identity of the client with certificate-
based authentication 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.
4. Security Considerations
The security considerations described throughout [RFC5246] and
[RFC4741] apply here as well.
This document in its current version does not support third-party
authentication (e.g., backend Authentication, Authorization, and
Accounting (AAA) servers) due to the fact that TLS does not 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.
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An attacker might be able to inject arbitrary NETCONF messages via
some application that does not carefully check exchanged messages or
deliberately insert the delimiter sequence in a NETCONF message to
create a DoS attack. Hence, applications and NETCONF APIs MUST
ensure that the delimiter sequence defined in Section 2.1 never
appears in NETCONF messages; otherwise, those messages can be
dropped, garbled, or misinterpreted. If the delimiter sequence is
found in a NETCONF message by the sender side, a robust
implementation of this document should warn the user that illegal
characters have been discovered. If the delimiter sequence is found
in a NETCONF message by the receiver side (including any XML
attribute values, XML comments, or processing instructions), a robust
implementation of this document must silently discard the message
without further processing and then stop the NETCONF session.
Finally, this document does not introduce any new security
considerations compared to [RFC4742].
5. IANA Considerations
IANA has assigned a TCP port number (6513) in the "Registered Port
Numbers" range with the name "netconf-tls". This port will be the
default port for NETCONF over TLS, as defined in this document.
Registration Contact: Mohamad Badra, badra@isima.fr.
Transport Protocol: TCP.
Port Number: 6513
Broadcast, Multicast or Anycast: No.
Port Name: netconf-tls.
Service Name: netconf.
Reference: RFC 5539
6. Acknowledgements
A significant amount of the text in Section 3 was lifted from
[RFC4642].
The author would like to acknowledge David Harrington, Miao Fuyou,
Eric Rescorla, Juergen Schoenwaelder, Simon Josefsson, Olivier
Coupelon, Alfred Hoenes, and the NETCONF mailing list members for
their comments on the document. The author also appreciates 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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7. Contributor's Address
Ibrahim Hajjeh
Ineovation
France
EMail: ibrahim.hajjeh@ineovation.fr
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.
[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 Version 1.2", RFC 5246, August 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.
8.2. Informative References
[RFC4642] Murchison, K., Vinocur, J., and C. Newman, "Using
Transport Layer Security (TLS) with Network News Transfer
Protocol (NNTP)", RFC 4642, October 2006.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, July 2008.
Author's Address
Mohamad Badra
CNRS/LIMOS Laboratory
Campus de cezeaux, Bat. ISIMA
Aubiere 63170
France
EMail: badra@isima.fr
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