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Internet Engineering Task Force (IETF)                          P. PatilRequest for Comments: 7443                                      T. ReddyCategory: Informational                                     G. SalgueiroISSN: 2070-1721                                                    Cisco                                                       M. Petit-Huguenin                                                      Impedance Mismatch                                                            January 2015Application-Layer Protocol Negotiation (ALPN) Labelsfor Session Traversal Utilities for NAT (STUN) UsagesAbstract   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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7443.Patil, et al.                 Informational                     [Page 1]

RFC 7443                   ALPN for STUN/TURN               January 2015Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .33.  Security Considerations . . . . . . . . . . . . . . . . . . .34.  References  . . . . . . . . . . . . . . . . . . . . . . . . .44.1.  Normative References  . . . . . . . . . . . . . . . . . .44.2.  Informative References  . . . . . . . . . . . . . . . . .4   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .4   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .51.  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.Patil, et al.                 Informational                     [Page 2]

RFC 7443                   ALPN for STUN/TURN               January 2015   '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   [RFC7301].   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      (STUN)      Identification Sequence: 0x73 0x74 0x75 0x6E 0x2E 0x6e 0x61 0x74      0x2d 0x64 0x69 0x73 0x63 0x6f 0x76 0x65 0x72 0x79      ("stun.nat-discovery")      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   exchange.Patil, et al.                 Informational                     [Page 3]

RFC 7443                   ALPN for STUN/TURN               January 20154.  References4.1.  Normative References   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security              (TLS) Protocol Version 1.2",RFC 5246, August 2008,              <http://www.rfc-editor.org/info/rfc5246>.   [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,              <http://www.rfc-editor.org/info/rfc6347>.   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,              "Transport Layer Security (TLS) Application-Layer Protocol              Negotiation Extension",RFC 7301, July 2014,              <http://www.rfc-editor.org/info/rfc7301>.   [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,              <http://www.rfc-editor.org/info/rfc7350>.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,              <http://www.rfc-editor.org/info/rfc5766>.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, 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.Patil, et al.                 Informational                     [Page 4]

RFC 7443                   ALPN for STUN/TURN               January 2015   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   reviews.Authors' Addresses   Prashanth Patil   Cisco Systems, Inc.   Bangalore   India   EMail: praspati@cisco.com   Tirumaleswar Reddy   Cisco Systems, Inc.   Cessna Business Park, Varthur Hobli   Sarjapur Marathalli Outer Ring Road   Bangalore, Karnataka  560103   India   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.orgPatil, et al.                 Informational                     [Page 5]