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.

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].

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.

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.

   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.

   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.

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