Application-Layer Protocol Negotiation (ALPN) Labels for Session Traversal Utilities for NAT (STUN) Usages
RFC 7443

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
Abstract
 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
 http://www.rfc-editor.org/info/rfc7443.
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RFC 7443 ALPN for STUN/TURN January 2015
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.
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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.
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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,
 <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.
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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.org
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