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Versions: 00 01 02 03 04 draft-ietf-netconf-tls

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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   This Internet-Draft will expire on April 2008.

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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