RFC 7443 INFORMATIONAL TRANSPORT · SECURITY
ALPN for STUN: Application-Layer Protocol Negotiation (ALPN) Labels for Session Traversal Utilities for NAT (STUN) Usages
Defines labels for STUN protocols during TLS negotiation.
RFC EDITOR
Patil, P., Reddy, T., Salgueiro, G., and M. Petit-Huguenin, "Application-Layer Protocol Negotiation (ALPN) Labels for Session Traversal Utilities for NAT (STUN) Usages", RFC 7443, DOI 10.17487/RFC7443, January 2015, <https://www.rfc-editor.org/info/rfc7443>.
BIBTEX
@misc{rfc7443,
series = {Request for Comments},
number = 7443,
howpublished = {RFC 7443},
publisher = {RFC Editor},
doi = {10.17487/RFC7443},
url = {https://www.rfc-editor.org/info/rfc7443},
author = {P. Patil and T. Reddy and G. Salgueiro and M. Petit-Huguenin},
title = {{Application-Layer Protocol Negotiation (ALPN) Labels for Session Traversal Utilities for NAT (STUN) Usages}},
pagetotal = 5,
year = 2015,
month = jan,
} RFC text
Contents
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.
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
[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
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
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
AI ELI5
On this page
PROBLEMSTUN over TLS must identify which STUN usage (TURN, NAT discovery, etc.) will run on the connection, but no standard labels exist.
MECHANISMRFC 7443 registers two ALPN labels with IANA: 'stun.turn' for Traversal Using Relays around NAT (TURN) and 'stun.nat-discovery' for NAT detection.
WHY IT MATTERSApplications can now negotiate STUN usages during TLS handshake without adding extra round trips, simplifying protocol implementation.
§1ALPN for STUN Protocols
STUN (Session Traversal Utilities for NAT) is a protocol that helps applications discover whether they are behind a firewall and how to reach other hosts. STUN is now commonly run over TLS (for confidentiality) or DTLS (for datagrams). Applications using STUN have different purposes: TURN relays traffic, while other usages discover the local address. ALPN (Application-Layer Protocol Negotiation) is an extension to TLS that lets endpoints agree on which application protocol will run over a connection. The client sends a list of supported protocols, and the server chooses one. RFC 7443 registers ALPN labels for STUN usages so the negotiation can happen during the TLS handshake without extra messages.
When computers make a secure connection, they can tell each other what kind of traffic will flow through it. This document names the NAT-discovery services that use TLS.
§2The ALPN Labels
Two ALPN labels are registered. The label 'stun.turn' identifies STUN used for TURN: a relay service that forwards traffic when direct connections fail. The label 'stun.nat-discovery' identifies STUN used for discovering the address and port seen from outside a NAT box. Both labels work with TLS and DTLS. Endpoints include these labels in the ClientHello during the TLS handshake, and the server selects the one it supports.
'stun.turn' means the connection will relay traffic. 'stun.nat-discovery' means it will check what your address looks like from outside.
§3Security Implications
The ALPN extension for STUN introduces no new security considerations beyond what RFC 7301 (the ALPN specification) already defines. The labels themselves do not affect TLS/DTLS security, and they do not impact session establishment or application data exchange. Applications should follow the security guidance in the underlying STUN, TURN, and TLS/DTLS specifications.
These labels are just names and do not change how secure the connection is.
§4References
[RFC5389]RFC 5389Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, October 2008.October 2008[RFC7301]RFC 7301Friedl, S., Popov, A., Langley, A., and E. Stephan, "Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension", RFC 7301, July 2014.July 2014[RFC5766]RFC 5766Mahy, 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.April 2010