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.
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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]).
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.
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.
Prashanth Patil Cisco Systems, Inc. Bangalore India
Tirumaleswar Reddy Cisco Systems, Inc. Cessna Business Park, Varthur Hobli Sarjapur Marathalli Outer Ring Road Bangalore, Karnataka 560103 India
Gonzalo Salgueiro Cisco Systems, Inc. 7200-12 Kit Creek Road Research Triangle Park, NC 27709 United States
Marc Petit-Huguenin Impedance Mismatch United States