Internet Engineering Task Force (IETF) M. Petit-Huguenin Request for Comments: 7065 Impedance Mismatch Category: Standards Track S. Nandakumar ISSN: 2070-1721 G. Salgueiro P. Jones Cisco Systems November 2013
Traversal Using Relays around NAT (TURN) Uniform Resource Identifiers
This document specifies the syntax of Uniform Resource Identifier (URI) schemes for the Traversal Using Relays around NAT (TURN) protocol. It defines two URI schemes to provision the TURN Resolution Mechanism (RFC 5928).
Status of This Memo
This is an Internet Standards Track document.
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). Further information on Internet Standards is available in Section 2 of RFC 5741.
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This document specifies the syntax and semantics of the Uniform Resource Identifier (URI) scheme for the Traversal Using Relays around NAT (TURN) protocol.
The TURN protocol is a specification allowing hosts behind NAT to control the operation of a relay server. The relay server allows hosts to exchange packets with its peers. The peers themselves may also be behind NATs. RFC 5766 [RFC5766] defines the specifics of the TURN protocol.
The "turn" and "turns" URI schemes are used to designate a TURN server (also known as a relay) on Internet hosts accessible using the TURN protocol. With the advent of standards such as WebRTC [WEBRTC], we anticipate a plethora of endpoints and web applications to be able to identify and communicate with such a TURN server to carry out the TURN protocol. This implies that endpoints and/or applications must be provisioned with the appropriate configuration to identify the TURN server. Having an inconsistent syntax adds ambiguity and can result in non-interoperable solutions and implementation limitations. The "turn" and "turns" URI schemes help alleviate most of these issues by providing a consistent way to describe, configure, and exchange the information identifying a TURN server.
[RFC5928] defines a resolution mechanism to convert a secure flag, a host name or IP address, a potentially empty port, and a potentially empty transport to a list of IP address, port, and TURN transport tuples.
To simplify the provisioning of TURN clients, this document defines the "turn" and "turns" URI schemes that can carry the four components needed for the resolution mechanism.
The key words "MUST", "MUST NOT", "REQUIRED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] when they appear in ALL CAPS. When these words are not in ALL CAPS (such as "should" or "Should"), they have their usual English meanings, and are not to be interpreted as RFC 2119 key words.
The "turn" and "turns" URIs have the following formal ABNF syntax [RFC5234]:
turnURI = scheme ":" host [ ":" port ] [ "?transport=" transport ] scheme = "turn" / "turns" transport = "udp" / "tcp" / transport-ext transport-ext = 1*unreserved
<host> and <port> are specified in [RFC3986]. While these two ABNF productions are defined in [RFC3986] as components of the generic hierarchical URI, this does not imply that the "turn" and "turns" schemes are hierarchical URIs. Developers MUST NOT use a generic hierarchical URI parser to parse a "turn" or "turns" URI.
The <host>, <port>, and <transport> components are passed without modification to the [RFC5928] algorithm. <secure> is set to false if <scheme> is equal to "turn", and set to true if <scheme> is equal to "turns" and passed to the [RFC5928] algorithm with the other components.
The "turn" and "turns" URI schemes are used to designate a TURN server (also known as a relay) on Internet hosts accessible using the TURN protocol. The TURN protocol supports sending messages over UDP, TCP, or TLS-over-TCP. The "turns" URI scheme MUST be used when TURN is run over TLS-over-TCP (or, in the future, DTLS-over-UDP), and the "turn" scheme MUST be used otherwise.
The required <host> part of the "turn" URI denotes the TURN server host.
As specified in [RFC5766] and [RFC5928], the <port> part, if present, denotes the port on which the TURN server is awaiting connection requests. If it is absent, the default port is 3478 for both UDP and TCP. The default port for TURN over TLS is 5349.
Security considerations for the resolution mechanism are discussed in Section 5 of [RFC5928]. Note that this section contains normative text defining authentication procedures to be followed by turn clients when TLS is used.
The "turn" and "turns" URI schemes do not introduce any specific security issues beyond the security considerations discussed in [RFC3986].
Although a "turn" or "turns" URI does not itself include the username or password that will be used to authenticate the TURN client, in certain environments, such as WebRTC, the username and password will almost certainly be provisioned remotely by an external agent at the same time as a "turns" URI is sent to that client. Thus, in such situations, if the username and password were received in the clear, there would be little or no benefit to using a "turns" URI. For this reason, a TURN client MUST ensure that the username, password, "turns" URI, and any other security-relevant parameters are received with equivalent security before using the "turns" URI. Receiving those parameters over another TLS session can provide the appropriate level of security, if both TLS sessions are similarly parameterised, e.g., with commensurate strength ciphersuites.
Thanks to Margaret Wasserman, Magnus Westerlund, Juergen Schoenwaelder, Sean Turner, Ted Hardie, Dave Thaler, Alfred E. Heggestad, Eilon Yardeni, Dan Wing, Alfred Hoenes, and Jim Kleck for the comments, suggestions, and questions that helped improve "Traversal Using Relays around NAT (TURN) Uniform Resource Identifiers" by M. Petit-Huguenin (October 2011).
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RFC 7065 TURN URIs November 2013
Many thanks to Cullen Jennings for his detailed review and thoughtful comments on "URI Scheme for Traversal Using Relays around NAT (TURN) Protocol" by S. Nandakumar, et al. (October 2011).
Thanks to Bjoern Hoehrmann, Dan Wing, Russ Housley, S. Moonesamy, Graham Klyne, Harald Alvestrand, Hadriel Kaplan, Tina Tsou, Spencer Dawkins, Ted Lemon, Barry Leiba, Pete Resnick, and Stephen Farrell for the comments, suggestions, and questions that helped improve this document.
The authors would also like to express their gratitude to Dan Wing for his assistance in shepherding this document. We also want to thank Gonzalo Camarillo, the Real-time Applications and Infrastructure Area Director, for sponsoring this document as well as his careful reviews.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and Registration Procedures for New URI Schemes", BCP 35, RFC 4395, February 2006.
[WEBRTC] Bergkvist, A., Burnett, D., Jennings, C., and A. Narayanan, "WebRTC 1.0: Real-time Communication Between Browsers", World Wide Web Consortium WD WD-webrtc-20120821, August 2012, <http://www.w3.org/TR/2012/WD-webrtc-20120821>.
o One recurring comment was to stop using the suffix "s" on the URI scheme, and to move the secure option to a parameter (e.g. ";proto=tls"). We decided against this idea because the STUN URI does not have a ";proto=" parameter and we would have lost the symmetry between the TURN and STUN URIs.
o Following the advice of Section 2.2 of RFC 4395, and because the TURN URI does not describe a hierarchical structure, the TURN URIs are opaque URIs.
o <password> is not used in the URIs because it is deprecated [RFC3986]. <username> and <auth> are not used in the URIs because they do not guide the resolution mechanism.
o As discussed at IETF 72 in Dublin, there are no generic parameters in the URI to prevent compatibility issues.
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RFC 7065 TURN URIs November 2013
Marc Petit-Huguenin Impedance Mismatch
Suhas Nandakumar Cisco Systems 170 West Tasman Drive San Jose, CA 95134 US
Gonzalo Salgueiro Cisco Systems 7200-12 Kit Creek Road Research Triangle Park, NC 27709 US
Paul E. Jones Cisco Systems 7025 Kit Creek Road Research Triangle Park, NC 27709 US