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Internet Engineering Task Force (IETF)                 M. Petit-HugueninRequest for Comments: 7065                            Impedance MismatchCategory: Standards Track                                  S. NandakumarISSN: 2070-1721                                             G. Salgueiro                                                                P. Jones                                                           Cisco Systems                                                           November 2013Traversal Using Relays around NAT (TURN) Uniform Resource IdentifiersAbstract   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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7065.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Petit-Huguenin, et al.       Standards Track                    [Page 1]

RFC 7065                        TURN URIs                  November 2013Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .33.  Definitions of the "turn" and "turns" URI . . . . . . . . . .43.1.  URI Scheme Syntax . . . . . . . . . . . . . . . . . . . .43.2.  URI Scheme Semantics  . . . . . . . . . . . . . . . . . .44.  Security Considerations . . . . . . . . . . . . . . . . . . .55.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .55.1.  "turn" URI Registration . . . . . . . . . . . . . . . . .55.2.  "turns" URI Registration  . . . . . . . . . . . . . . . .66.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .67.  References  . . . . . . . . . . . . . . . . . . . . . . . . .77.1.  Normative References  . . . . . . . . . . . . . . . . . .77.2.  Informative References  . . . . . . . . . . . . . . . . .7Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .8Appendix B.  Design Notes . . . . . . . . . . . . . . . . . . . .8Petit-Huguenin, et al.       Standards Track                    [Page 2]

RFC 7065                        TURN URIs                  November 20131.  Introduction   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.2.  Terminology   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 asRFC 2119 key words.Petit-Huguenin, et al.       Standards Track                    [Page 3]

RFC 7065                        TURN URIs                  November 20133.  Definitions of the "turn" and "turns" URI3.1.  URI Scheme Syntax   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.3.2.  URI Scheme Semantics   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.Petit-Huguenin, et al.       Standards Track                    [Page 4]

RFC 7065                        TURN URIs                  November 20134.  Security Considerations   Security considerations for the resolution mechanism are discussed inSection 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.5.  IANA Considerations   This section contains the registration information for the "turn" and   "turns" URI Schemes (in accordance with [RFC4395]).5.1.  "turn" URI Registration   URI scheme name: turn   Status: permanent   URI scheme syntax: SeeSection 3.1.   URI scheme semantics: SeeSection 3.2.   Encoding considerations: There are no encoding considerations beyond   those in [RFC3986].   Applications/protocols that use this URI scheme name:      The "turn" URI scheme is intended to be used by applications with      a need to identify a TURN server to be used for NAT traversal.Petit-Huguenin, et al.       Standards Track                    [Page 5]

RFC 7065                        TURN URIs                  November 2013   Interoperability considerations: N/A   Security considerations: SeeSection 4.   Contact: Marc Petit-Huguenin <petithug@acm.org>   Author/Change controller: The IESG   References:RFC 70655.2.  "turns" URI Registration   URI scheme name: turns   Status: permanent   URI scheme syntax: SeeSection 3.1.   URI scheme semantics: SeeSection 3.2.   Encoding considerations: There are no encoding considerations beyond   those in [RFC3986].   Applications/protocols that use this URI scheme name:      The "turns" URI scheme is intended to be used by applications with      a need to identify a TURN server to be used for NAT traversal over      a secure connection.   Interoperability considerations: N/A   Security considerations: SeeSection 4.   Contact: Marc Petit-Huguenin <petithug@acm.org>   Author/Change controller: The IESG   References:RFC 70656.  Acknowledgements   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).Petit-Huguenin, et al.       Standards Track                    [Page 6]

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.7.  References7.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform              Resource Identifier (URI): Generic Syntax", STD 66,RFC3986, January 2005.   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF", STD 68,RFC 5234, January 2008.   [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.   [RFC5928]  Petit-Huguenin, M., "Traversal Using Relays around NAT              (TURN) Resolution Mechanism",RFC 5928, August 2010.7.2.  Informative References   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and              Registration Procedures for New URI Schemes",BCP 35,RFC4395, 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>.Petit-Huguenin, et al.       Standards Track                    [Page 7]

RFC 7065                        TURN URIs                  November 2013Appendix A.  Examples   Table 1 shows how the <secure>, <port>, and <transport> components   are populated from various URIs.  For all these examples, the <host>   component is populated with "example.org".   +---------------------------------+----------+--------+-------------+   | URI                             | <secure> | <port> | <transport> |   +---------------------------------+----------+--------+-------------+   | turn:example.org                | false    |        |             |   | turns:example.org               | true     |        |             |   | turn:example.org:8000           | false    | 8000   |             |   | turn:example.org?transport=udp  | false    |        | UDP         |   | turn:example.org?transport=tcp  | false    |        | TCP         |   | turns:example.org?transport=tcp | true     |        | TLS         |   +---------------------------------+----------+--------+-------------+                                  Table 1Appendix B.  Design Notes   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 ofSection 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.Petit-Huguenin, et al.       Standards Track                    [Page 8]

RFC 7065                        TURN URIs                  November 2013Authors' Addresses   Marc Petit-Huguenin   Impedance Mismatch   EMail: petithug@acm.org   Suhas Nandakumar   Cisco Systems   170 West Tasman Drive   San Jose, CA  95134   US   EMail: snandaku@cisco.com   Gonzalo Salgueiro   Cisco Systems   7200-12 Kit Creek Road   Research Triangle Park, NC  27709   US   EMail: gsalguei@cisco.com   Paul E. Jones   Cisco Systems   7025 Kit Creek Road   Research Triangle Park, NC  27709   US   EMail: paulej@packetizer.comPetit-Huguenin, et al.       Standards Track                    [Page 9]