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rfc:rfc5539

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.

Copyright Notice

 Copyright (c) 2009 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents in effect on the date of
 publication of this document (http://trustee.ietf.org/license-info).
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

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.

Badra Standards Track [Page 1] RFC 5539 NETCONF over TLS May 2009

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].

Badra Standards Track [Page 2] RFC 5539 NETCONF over TLS May 2009

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.

Badra Standards Track [Page 3] RFC 5539 NETCONF over TLS May 2009

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.

Badra Standards Track [Page 4] RFC 5539 NETCONF over TLS May 2009

 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.

Badra Standards Track [Page 5] RFC 5539 NETCONF over TLS May 2009

 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.

Badra Standards Track [Page 6] RFC 5539 NETCONF over TLS May 2009

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

Badra Standards Track [Page 7]

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