Traversal Using Relays around NAT (TURN) Uniform Resource Identifiers
draft-petithuguenin-behave-turn-uris-03

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 that can be used to provision the configuration values needed by the resolution mechanism defined in [RFC5928].

Status of This Memo

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This Internet-Draft will expire on July 20, 2013.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Definitions of the TURN and TURNS URI
• 3.1. URI Scheme Syntax
• 3.2. URI Scheme Semantics
• 4. Security Considerations
• 5. IANA Considerations
• 5.1. TURN URI Registration
• 5.2. TURNS URI Registration
• 6. Acknowledgements
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Appendix A. Examples
• Appendix B. Release notes
• B.1. Design Notes
• B.2. Modifications between petithuguenin-behave-turn-uris-03 and petithuguenin-behave-turn-uris-02
• Authors' Addresses

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], 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 also implies those endpoints and/or applications to be provisioned with appropriate configuration required to identify the TURN server. Having an inconsistent syntax has its drawbacks and can result in non-interoperable solutions. It can result in solutions that are ambiguous and have implementation limitations on the different aspects of the syntax and alike. The "turn/turns" URI scheme helps alleviate most of these issues by providing a consistent way to describe, configure and exchange the information identifying a TURN server. This would also prevent the shortcomings inherent with encoding similar information in non-uniform syntaxes such as the ones proposed in [WEBRTC], for example.

[RFC5928] defines a resolution mechanism to convert a secure flag, a host name or IP address, an eventually empty port, and an eventually empty transport to a list of IP address, port, and TURN transport tuples.

To simplify the provisioning of TURN clients, this document defines a TURN and a TURNS URI scheme that can carry the four components needed for the resolution mechanism.

A reference implementation [REF-IMPL] is available.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Definitions of the TURN and TURNS URI

3.1. URI Scheme Syntax

The "turn" URI takes the following form (the syntax below is non-normative):

• turn:<host>:<port>
• turns:<host>:<port>

Note that the <port> part and the preceding ":" (colon) character, is OPTIONAL.

A TURN/TURNS URI has the following formal ABNF syntax [RFC5234]:

turnURI       = scheme ":" turn-host [ ":" turn-port ]
                [ "?transport=" transport ]
scheme        = "turn" / "turns"
transport     = "udp" / "tcp" / transport-ext
transport-ext = 1*unreserved
turn-host     = IP-literal / IPv4address / reg-name
turn-port     = *DIGIT
IP-literal    = "[" ( IPv6address / IPvFuture  ) "]"
IPvFuture     = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
IPv6address   =                              6( h16 ":" ) ls32
                /                       "::" 5( h16 ":" ) ls32
                / [               h16 ] "::" 4( h16 ":" ) ls32
                / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
                / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
                / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
                / [ *4( h16 ":" ) h16 ] "::"              ls32
                / [ *5( h16 ":" ) h16 ] "::"              h16
                / [ *6( h16 ":" ) h16 ] "::"
h16           = 1*4HEXDIG
ls32          = ( h16 ":" h16 ) / IPv4address
IPv4address   = dec-octet "." dec-octet "." dec-octet "." dec-octet
dec-octet     = DIGIT                 ; 0-9
                / %x31-39 DIGIT       ; 10-99
                / "1" 2DIGIT          ; 100-199
                / "2" %x30-34 DIGIT   ; 200-249
                / "25" %x30-35        ; 250-255
reg-name      = *( unreserved / pct-encoded / sub-delims )
					

<unreserved>, <sub-delims>, and <pct-encoded> are specified in [RFC3986]. The core rules <DIGIT> and <HEXDIGIT> are used as described in Appendix B of RFC 5234 [RFC5234].

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 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.

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.

4. Security Considerations

Security considerations for the resolution mechanism are discussed in [RFC5928].

The "turn" and "turns" URI schemes do not introduce any specific security issues beyond the security considerations discussed in [RFC3986].

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 that might need access to a TURN server.

Interoperability considerations: N/A

Security considerations: See Section 4.

Contact: Marc Petit-Huguenin <petithug@acm.org>

Author/Change controller: The IESG

References: RFCXXXX

[[NOTE TO RFC EDITOR: Please change XXXX to the number assigned to this specification, and remove this paragraph on publication.]]

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 that might need access to a TURN server 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: RFCXXXX

[[NOTE TO RFC EDITOR: Please change XXXX to the number assigned to this specification, and remove this paragraph on publication.]]

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 their comments, suggestions and questions that helped to improve the draft-petithuguenin-behave-turn-uri-bis document.

Many thanks to Cullen Jennings for his detailed review and thoughtful comments on the draft-nandakumar-rtcweb-turn-uri document.

Thanks to Bjoern Hoehrmann for his comments, suggestions and questions that helped to improve the this document.

The <turn-port> and <turn-host> ABNF productions have been copied from the <port> and <host> ABNF productions from [RFC3986].

7. References

7.1. Normative References

7.2. Informative References

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".