TRAM                                                            P. Patil
Internet-Draft                                                  T. Reddy
Intended status: Standards Track                            G. Salgueiro
Expires: January 24, 2015                                          Cisco
                                                       M. Petit-Huguenin
                                                     Jive Communications
                                                           July 23, 2014

  Application Layer Protocol Negotiation (ALPN) for Session Traversal
                        Utilities for NAT (STUN)


   An Application Layer Protocol Negotiation (ALPN) label for the
   Session Traversal Utilities for NAT (STUN) protocol is defined in
   this document to allow the application layer to negotiate STUN within
   the Transport Layer Security (TLS) connection.  The STUN ALPN
   protocol identifier applies to both TLS and Datagram Transport Layer
   Security (DTLS).

Status of This Memo

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   This Internet-Draft will expire on January 24, 2015.

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   carefully, as they describe your rights and restrictions with respect
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   STUN can be securely transported using TLS-over-TCP (referred to as
   TLS [RFC5246]), as specified in [RFC5389], or TLS-over-UDP (referred
   to as DTLS [RFC6347]), as specified in

   ALPN [I-D.ietf-tls-applayerprotoneg] enables an endpoint to
   positively identify STUN protocol uses in TLS/DTLS and distinguish
   them from other TLS/DTLS protocols.  With ALPN, the client sends the
   list of supported application protocols as part of the TLS/DTLS
   ClientHello message.  The server chooses a protocol and sends the
   selected protocol as part of the TLS/DTLS ServerHello message.  The
   application protocol negotiation can thus be accomplished within the
   TLS/DTLS handshake, without adding network round-trips, and allows
   the server to associate a different certificate with each application
   protocol, if desired.

   For example, a firewall could block all outgoing traffic except for
   TCP traffic to specific ports (e.g., 443 for HTTPS).  A TURN server
   listening on its default ports (3478 for TCP/UDP, 5349 for TLS) would
   not be reachable in this case.  However, despite the restrictions
   imposed by the firewall, the TURN server can still be reached on the
   allowed HTTPS port if an ALPN STUN protocol identifier is used to
   establish the STUN application layer protocol as part of the TLS
   handshake.  In this case, the STUN ALPN identifier sent by the client
   will be used by the server to identify that the client intends to
   make a TURN request and it must act as a TURN server to relay the
   traffic to and from the remote peer.  Similarly, with Quick UDP
   Internet Connections (QUIC) [QUIC], a UDP-based transport protocol

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   that operates under SPDY [I-D.mbelshe-httpbis-spdy], a TURN server
   could be operated on the same ports as that of a SPDY server.

   This document defines an entry ("stun") in the "Application Layer
   Protocol Negotiation (ALPN) Protocol IDs" registry established by
   [I-D.ietf-tls-applayerprotoneg] to identify the STUN protocol.

   [[TODO: In various offline discussions some have expressed a desire
   to add an additional ALPN protocol identifier for TURN (see IANA
   Considerations below for example registration).  ALPN can be used
   more granularly to externally identify more of the protocol variants
   and their different properties (i.e., STUN and TURN over TLS/DTLS).
   The advantage in dividing it this way is that these different forms
   can be externally identified (obviously, there isn't any inherent
   value in the different identifiers from within the TLS
   handshake).There are two main disadvantages. the first is that this
   two application protocol approach may make implementations more
   complicated/confusing.  The second is that there may be difficulty in
   differentiating the two with ALPN when TURN was specifically designed
   to be able to run on the same port as STUN usage (in section 13 of
   RFC 5389).  Section of RFC 5245 explicitly says that "If the
   Allocate request is rejected because the server lacks resources to
   fulfill it, the agent SHOULD instead send a Binding request to obtain
   a server reflexive candidate."  Does that prove there is no need to
   differentiate TURN and STUN request on UDP/TCP or TLS and now DTLS?
   Are there sufficiently meaningful differences between the usages to
   warrant separate STUN and TURN ALPN identifiers?]]

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  IANA Considerations

   The following entry is to be added to the "Application Layer Protocol
   Negotiation (ALPN) Protocol IDs" registry established by

   The "stun" label identifies STUN over TLS/DTLS:

      Protocol: Session Traversal Utilities for NAT (STUN)

      Identification Sequence: 0x73 0x74 0x75 0x6E ("stun")

      Specification: This document (RFCXXXX)

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   [[TODO: Shown only as an example.  Remove the below registry entry if
   open issue above dictates a single STUN ALPN identifier is

   The "turn" label identifies TURN over TLS/DTLS:

      Protocol: Traversal Using Relays around NAT (TURN)

      Identification Sequence: 0x74 0x75 0x72 0x6E ("turn")

      Specification: This document (RFCXXXX)

4.  Security Considerations

   The ALPN STUN protocol identifier does not introduce any specific
   security considerations beyond those detailed in the TLS ALPN
   Extension specification [I-D.ietf-tls-applayerprotoneg].  It also
   does not impact the security of TLS/DTLS session establishment nor
   the application data exchange.

5.  Acknowledgements

   This work benefited from the discussions and invaluable input by the
   various members of the TRAM working group.  These include Simon
   Perrault, Paul Kyzivat, and Andrew Hutton.  Special thanks to Martin
   Thomson and Oleg Moskalenko for their constructive comments,
   suggestions, and early reviews that were critical to the formulation
   and refinement of this document.

6.  References

6.1.  Normative References

              Friedl, S., Popov, A., Langley, A., and S. Emile,
              "Transport Layer Security (TLS) Application Layer Protocol
              Negotiation Extension", draft-ietf-tls-applayerprotoneg-05
              (work in progress), March 2014.

              Belshe, M. and R. Peon, "SPDY Protocol", draft-mbelshe-
              httpbis-spdy-00 (work in progress), February 2012.

              Petit-Huguenin, M. and G. Salgueiro, "Datagram Transport
              Layer Security (DTLS) as Transport for Traversal Using
              Relays around NAT (TURN)", draft-petithuguenin-tram-turn-
              dtls-00 (work in progress), January 2014.

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              slides-88-tsvarea-10.pdf, "QUIC Slide Deck at IETF88,", .

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

6.2.  Informative References

   [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.

Authors' Addresses

   Prashanth Patil
   Cisco Systems, Inc.


   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103


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   Gonzalo Salgueiro
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709


   Marc Petit-Huguenin
   Jive Communications
   1275 West 1600 North, Suite 100
   Orem, UT  84057


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