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RFC 7443 - Application-Layer Protocol Negotiation (ALPN) Labels

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Internet Engineering Task Force (IETF)                          P. Patil
Request for Comments: 7443                                      T. Reddy
Category: Informational                                     G. Salgueiro
ISSN: 2070-1721                                                    Cisco
                                                       M. Petit-Huguenin
                                                      Impedance Mismatch
                                                            January 2015

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


   Application-Layer Protocol Negotiation (ALPN) labels for Session
   Traversal Utilities for NAT (STUN) usages, such as Traversal Using
   Relays around NAT (TURN) and NAT discovery, are defined in this
   document to allow an application layer to negotiate STUN usages
   within the Transport Layer Security (TLS) connection.  ALPN protocol
   identifiers defined in this document apply to both TLS and Datagram
   Transport Layer Security (DTLS).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   4
   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 [RFC7350].

   ALPN [RFC7301] enables an endpoint to positively identify an
   application protocol in TLS/DTLS and distinguish it 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.  Application protocol
   negotiation can thus be accomplished within the TLS/DTLS handshake,
   without adding network round-trips.

   STUN protocol usages, such as TURN [RFC5766], can be used to identify
   the purpose of a flow without initiating a session.

   This document proposes the following ALPN labels to identify STUN
   protocol [RFC5389] usages.

   'stun.turn':  Label to identify the specific use of STUN over (D)TLS
      for TURN (Section 4.6 of [RFC7350]).

   'stun.nat-discovery':  Label to identify the specific use of STUN
      over (D)TLS for NAT discovery (Section 4.1 of [RFC7350]).

2.  IANA Considerations

   The following entries have been added to the "Application-Layer
   Protocol Negotiation (ALPN) Protocol IDs" registry established by

   The "stun.turn" label identifies the use of TURN usage (D)TLS:

      Protocol: Traversal Using Relays around NAT (TURN)

      Identification Sequence: 0x73 0x74 0x75 0x6E 0x2E 0x74 0x75 0x72
      0x6E ("stun.turn")

      Specification: This document (RFC 7443)

   The "stun.nat-discovery" label identifies the use of STUN for the
   purposes of NAT discovery over (D)TLS:

      Protocol: NAT discovery using Session Traversal Utilities for NAT

      Identification Sequence: 0x73 0x74 0x75 0x6E 0x2E 0x6e 0x61 0x74
      0x2d 0x64 0x69 0x73 0x63 0x6f 0x76 0x65 0x72 0x79

      Specification: This document (RFC 7443)

3.  Security Considerations

   The ALPN STUN protocol identifier does not introduce any specific
   security considerations beyond those detailed in the TLS ALPN
   Extension specification [RFC7301].  It also does not impact the
   security of TLS/DTLS session establishment or application data

4.  References

4.1.  Normative References

   [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, <http://www.rfc-editor.org/info/rfc5389>.

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

   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,
              "Transport Layer Security (TLS) Application-Layer Protocol
              Negotiation Extension", RFC 7301, July 2014,

   [RFC7350]  Petit-Huguenin, M. and G. Salgueiro, "Datagram Transport
              Layer Security (DTLS) as Transport for Session Traversal
              Utilities for NAT (STUN)", RFC 7350, August 2014,

4.2.  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,


   This work benefited from the discussions and invaluable input by the
   various members of the TRAM working group.  These include Simon
   Perrault, Paul Kyzivat, Brandon Williams, 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.

   Barry Leiba, Stephen Farrell, Adrian Farrel, and Richard Barnes
   provided useful feedback during IESG review.  Thanks to Russ Housley
   for his Gen-ART review and Adam Langley for his IETF LC review
   comments as TLS expert.

   The authors would also like to express their gratitude to the TRAM WG
   chairs Gonzalo Camarillo and especially Simon Perrault, who also
   acted as document shepherd.  Lastly, we also want to thank the
   Transport Area Director Spencer Dawkins for his support and careful

Authors' Addresses

   Prashanth Patil
   Cisco Systems, Inc.

   EMail: praspati@cisco.com

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

   EMail: tireddy@cisco.com

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

   EMail: gsalguei@cisco.com

   Marc Petit-Huguenin
   Impedance Mismatch
   United States

   EMail: marc@petit-huguenin.org


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