RFC 7443

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

📅 published January 2015, from ietf

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

Okay bestie, let's start with the title block! This is RFC 7443 from the IETF (Internet Engineering Task Force), published in January 2015. Its category is Informational, and its ISSN is 2070-1721. The authors are Prashanth Patil, Tirumaleswar Reddy, and Gonzalo Salgueiro (all from Cisco), plus Marc Petit-Huguenin from Impedance Mismatch. The title block doesn't list anything it obsoletes or updates, so it's a standalone doc 💅

Abstract ✨

So the abstract basically says this: ALPN labels for STUN usages, like TURN (Traversal Using Relays around NAT) and NAT discovery, get defined here so an application layer can negotiate STUN usages inside a TLS connection. The ALPN protocol identifiers in this doc work for both TLS and DTLS (Datagram Transport Layer Security) 🦋

Status of This Memo 📜

This document is not an Internet Standards Track specification. It's 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.

Info about this doc's current status, any errata, and how to give feedback is at http://www.rfc-editor.org/info/rfc7443.

Copyright Notice ©️

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 🌸

Here's the vibe: STUN can be transported securely over TLS-over-TCP (called TLS [RFC5246]), as specified in [RFC5389], or over TLS-over-UDP (called DTLS [RFC6347]), as specified in [RFC7350].

ALPN [RFC7301] lets an endpoint positively identify an application protocol in TLS/DTLS and tell it apart from other TLS/DTLS protocols. With ALPN, the client sends a list of the application protocols it supports as part of the TLS/DTLS ClientHello message. The server picks one and sends the selected protocol back in the TLS/DTLS ServerHello message. So application protocol negotiation can happen inside the TLS/DTLS handshake, without adding any network round-trips. Literally so efficient 🧚

STUN protocol usages, like TURN [RFC5766], can be used to identify the purpose of a flow without starting 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 [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.

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 🫶

Big shoutout time! This work benefited from the discussions and invaluable input of 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 forming and refining this document.

Barry Leiba, Stephen Farrell, Adrian Farrel, and Richard Barnes gave 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, they want to thank 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

That's the whole RFC, bestie! 🌈👑

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