RTCWEB S. Nandakumar
Internet-Draft G. Salgueiro
Intended status: Standards Track P. Jones
Expires: April 27, 2012 Cisco Systems
October 25, 2011
URI Scheme for Traversal Using Relays around NAT (TURN) Protocol
draft-nandakumar-rtcweb-turn-uri-00
Abstract
This document is the specification of the syntax and semantics of the
Uniform Resource Identifier (URI) scheme for the Traversal Using
Relays around NAT (TURN) protocol.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. URI Scheme Definition . . . . . . . . . . . . . . . . . . . . . 3
3.1. URI Scheme Syntax . . . . . . . . . . . . . . . . . . . . . 3
3.2. URI Scheme Semantics . . . . . . . . . . . . . . . . . . . 4
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5.1. The 'turn' URI Scheme Registration . . . . . . . . . . . . 5
5.2. The 'turns' URI Scheme Registration . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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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/turns' URI scheme is 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 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 the WEBRTC Standards [WEBRTC], for example.
The 'turn/turns' URI scheme adheres to the generic syntax defined in
RFC 3986 [RFC3986].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. URI Scheme Definition
3.1. URI Scheme Syntax
The 'turn' URI takes the following form (the syntax below is non-
normative):
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turn:<userinfo>@<host>:<port>
turns:<userinfo>@<host>:<port>
Where <userinfo> with the "@" (at) sign character, as well as the
<port> part and the preceding ":" (colon) character, is OPTIONAL.
The normative syntax of the 'turn' URI is defined as shown in the
following Augmented Backus-Naur Form (ABNF) [RFC5234] rule:
turn-uri = turn-scheme ":" [ userinfo "@" ] host [ ":" port ]
turn-scheme = "turn"/"turns"
userinfo = user [ ":" password ]
user = 1*(%x21-24 / %x26-39 / %x3B-3F / %x41-7F
/ escaped)
; The symbols "%", ":", "@", and symbols
; with a character value below 0x21 may
; be represented as escaped sequences.
password = 1*(%x21-24 / %x26-3F / %x41-7F / escaped)
; The symbols "%", "@", and symbols with
; a character value below 0x21 may be
; represented as escaped sequences.
host = hostname / IPv4address / IPv6reference
hostname = *( domainlabel "." ) toplabel [ "." ]
domainlabel = alphanum / alphanum *( alphanum / "-" ) alphanum
toplabel = ALPHA / ALPHA *( alphanum / "-" ) alphanum
IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT
IPv6reference = "[" IPv6address "]"
IPv6address = hexpart [ ":" IPv4address ]
hexpart = hexseq / hexseq "::" [ hexseq ] / "::" [ hexseq ]
hexseq = hex4 *( ":" hex4 )
hex4 = 1*4HEXDIG
port = 1*DIGIT
alphanum = ALPHA / DIGIT
escaped = "%" HEXDIG HEXDIG
The current ABNF proposal doesn't specify a mechanism for handling
different transports. We have identified a possible solution and
will be included in the future version of the draft.
The <host>, <port> and <userinfo> rules are described in Appendix A
of RFC 3986 [RFC3986]. The core rules <ALPHA>, <DIGIT> and
<HEXDIGIT> are used as described in Appendix B of RFC 5234 [RFC5234].
3.2. URI Scheme Semantics
The TURN protocol supports sending messages over UDP, TCP or TLS-
over-TCP. The 'turns' URI scheme SHALL be used when TURN is run over
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TLS-over-TCP (or in the future DTLS-over-UDP) and the 'turn' scheme
SHALL be used otherwise. The <host> part of the 'turn' URI, which is
REQUIRED, denotes the TURN server host. The <userinfo> part,
identifies the credential required for the long-term credential
mechanism as described in the section 10.2 of RFC 5389 [RFC5389].
The <port> part, if present, denotes the port on which the TURN
server is awaiting connection requests. If it is absent, the default
port SHALL be 3478 for both UDP and TCP. The default port for TURN
over TLS SHALL be 5349.
4. Examples
URI to identify a long-term credential for the TLS-over-TCP
connection to TURN server, example.com, on default port 5349:
turns:username:password@example.com
URI to identify a long-term credential for the connection to TURN
server, example.com, on default port 3478:
turn:username:password@example.com
5. IANA Considerations
This document instructs IANA to register the 'turn' and 'turns' URI
schemes in the "Permanent URI Schemes" sub-registry in the "Uniform
Resource Identifier (URI) Schemes" IANA registry [URIREG]. These
registrations follows the URI Scheme Registration Template detailed
in Section 5.4 of RFC 4395 [RFC4395].
5.1. The 'turn' URI Scheme Registration
IANA registration of the the 'turn' URI scheme:
URI scheme name: turn
Status: Permanent
URI scheme syntax: see Section 3.1 of RFC XXXX [This document]
URI scheme semantics: see Section 3.2 of RFC XXXX [This document]
URI scheme encoding considerations: there are no other encoding
considerations for 'turn' URIs that are not described in RFC 5766
[RFC5766].
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Protocols that use the scheme: Traversal Using Relays around NAT
(TURN)
Security Considerations: see Section 6 of RFC XXXX [This document]
Contact: IESG <iesg@ietf.org>
Author/Change controller: IETF <ietf@ietf.org>
References: See Section 8 of RFC XXXX [This document]
5.2. The 'turns' URI Scheme Registration
IANA registration of the the 'turns' URI scheme:
URI scheme name: turns
Status: Permanent
URI scheme syntax: see Section 3.1 of RFC XXXX [This document]
URI scheme semantics: see Section 3.2 of RFC XXXX [This document]
URI scheme encoding considerations: there are no other encoding
considerations for 'turns' URIs that are not described in RFC 5766
[RFC5766].
Protocols that use the scheme: Traversal Using Relays around NAT
(TURN) when run over TLS-over-TCP.
Security Considerations: see Section 6 of RFC XXXX [This document]
Contact: IESG <iesg@ietf.org>
Author/Change controller: IETF <ietf@ietf.org>
References: See Section 8 of RFC XXXX [This document]
6. Security Considerations
The URI Scheme defined by this document for the Traversal Using
Relays around NAT (TURN) protocol needs to consider the security
considerations detailed in Section 17 of RFC 5766 [RFC5766].
As described in Section 3.2.1 of STD 66 [RFC3986], having
authentication information (specifically passwords) in a URI means
that the URI must be handled carefully:
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The passing of authentication information in clear text has proven
to be a security risk in almost every case where it has been used.
Section 3.2.1 contains advice on handling URI that contain passwords
in the userinfo portion. Implementations of this specification MUST
implement that advice.
Specifically if a URI that contains credentials leaks, then it would
allow an attacker to use the TURN server which is referenced by the
URI. Such an attack has two major impacts. First, it uses up the
operator's bandwidth. Second, if the operator bills the user for
TURN server usage, then it may expose the user to costs incurred by
the attacker. However, the attacker never obtains the user's private
information, nor does this attack allow for traffic amplification.
The expected use environment mitigates to some degree concerns about
TURN URIs compared to other URIs, such as HTTPS. First, users do not
dereference TURN URIs directly. Instead, they are passed to the TURN
stack. Thus, concerns about confusion or leakage due to the URI
being displayed to the user are significantly reduced; indeed the URI
need never be available to the user at all.
One of the primary use cases for a TURN URI with credentials is
WebRTC. In this case, a web server will be offering a calling
service and may have an associated TURN server it can use. In this
case, the browser will need to use the TURN server and the browser
has no long term or preexisting relationship with the TURN server.
The web server needs to provide some credential to the client which
it can use to access the TURN server. Since TURN authentication is
via username and password, this implies that the credential is a
username/password pair. While this must be transmitted securely
(i.e., over HTTPS), the security properties are the same whether the
password is carried separately or is part of the URL. Moreover,
because the web server and TURN servers can cooperate, a new password
can be issued for every call, making short-term credentials feasible
and thus significantly mitigating the risk.
If a TURN URI is transferred between hosts, it MUST be done over a
protocol that provides confidentiality such as HTTPS [RFC2818]. It
is RECOMMENDED that the credential only be valid for a single call
and preferably for no more than one day. that "preferably" is bad.
7. Acknowledgements
Many thanks to Cullen Jennings for his detailed review and thoughtful
comments on this document.
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We acknowledge the existence of
draft-petithuguenin-behave-turn-uri-bis-04 document as a parallel
effort in defining the URI scheme for TURN. Awareness of this draft
came late in the process and we have not had to time to reach out to
the author of that memo and discuss opportunities to collaborate on a
single document. It is our intentions to do so.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
8.2. Informative References
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", BCP 35,
RFC 4395, February 2006.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[URIREG] Internet Assigned Numbers Authority (IANA) Registry,
"Uniform Resource Identifier (URI) Schemes",
<http://www.iana.org/assignments/uri-schemes.html> .
[WEBRTC] W3C, "WebRTC 1.0: Real-time Communication Between
Browsers",
<http://dev.w3.org/2011/webrtc/editor/webrtc.html> .
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Authors' Addresses
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
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