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rfc:rfc7065

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

Abstract

 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.
 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/rfc7065.

Copyright Notice

 Copyright (c) 2013 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.

Petit-Huguenin, et al. Standards Track [Page 1] RFC 7065 TURN URIs November 2013

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
 3.  Definitions of the "turn" and "turns" URI . . . . . . . . . .   4
   3.1.  URI Scheme Syntax . . . . . . . . . . . . . . . . . . . .   4
   3.2.  URI Scheme Semantics  . . . . . . . . . . . . . . . . . .   4
 4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.1.  "turn" URI Registration . . . . . . . . . . . . . . . . .   5
   5.2.  "turns" URI Registration  . . . . . . . . . . . . . . . .   6
 6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
   7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
 Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .   8
 Appendix B.  Design Notes . . . . . . . . . . . . . . . . . . . .   8

Petit-Huguenin, et al. Standards Track [Page 2] RFC 7065 TURN URIs November 2013

1. 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 as RFC 2119 key words.

Petit-Huguenin, et al. Standards Track [Page 3] RFC 7065 TURN URIs November 2013

3. Definitions of the "turn" and "turns" URI

3.1. 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 2013

4. Security Considerations

 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.

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: See Section 3.1.
 URI scheme semantics: See Section 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: See Section 4.
 Contact: Marc Petit-Huguenin <petithug@acm.org>
 Author/Change controller: The IESG
 References: RFC 7065

5.2. "turns" URI Registration

 URI scheme name: turns
 Status: permanent
 URI scheme syntax: See Section 3.1.
 URI scheme semantics: See Section 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: See Section 4.
 Contact: Marc Petit-Huguenin <petithug@acm.org>
 Author/Change controller: The IESG
 References: RFC 7065

6. 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. References

7.1. 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, RFC
            3986, 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, 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>.

Petit-Huguenin, et al. Standards Track [Page 7] RFC 7065 TURN URIs November 2013

Appendix 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 1

Appendix 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 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.

Petit-Huguenin, et al. Standards Track [Page 8] RFC 7065 TURN URIs November 2013

Authors' 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.com

Petit-Huguenin, et al. Standards Track [Page 9]

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