Network Working Group M. Petit-Huguenin
Internet-Draft (Unaffiliated)
Intended status: Standards Track March 7, 2009
Expires: September 8, 2009
Traversal Using Relays around NAT (TURN) Uniform Resource Identifiers
draft-ietf-behave-turn-uri-01
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Abstract
This document defines two URI schemes and the resolution mechanism to
convert these URIs to a list of server transport addresses that can
be used between a Traversal Using Relays around NAT (TURN) client and
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server.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Syntax of a TURN or TURNS URI . . . . . . . . . . . . . . . . 3
4. TURN or TURNS URI Resolution . . . . . . . . . . . . . . . . . 4
5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.1. TURN URI Registration . . . . . . . . . . . . . . . . . . 7
7.2. TURNS URI Registration . . . . . . . . . . . . . . . . . . 7
7.3. RELAY Application Service Tag Registration . . . . . . . . 8
7.4. turn.udp Application Protocol Tag Registration . . . . . . 8
7.5. turn.tcp Application Protocol Tag Registration . . . . . . 9
7.6. turn.tls Application Protocol Tag Registration . . . . . . 9
8. Running Code Considerations . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Release notes . . . . . . . . . . . . . . . . . . . . 11
A.1. Modifications between -01 and -00 . . . . . . . . . . . . 11
A.2. Design Notes . . . . . . . . . . . . . . . . . . . . . . . 11
A.3. TODO List . . . . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
The TURN specification [I-D.ietf-behave-turn] defines a process for a
TURN client to find TURN servers by using DNS SRV resource records,
but this process does not let the TURN server administrators
provision the preferred TURN transport protocol between the client
and the server and for the TURN client to discover this preference.
This document defines a S-NAPTR application [RFC3958] for this
purpose. This application defines "RELAY" as application service tag
and "turn.udp", "turn.tcp", and "turn.tls" as application protocol
tags.
To simplify the provisioning of TURN clients, this document also
defines a TURN and a TURNS URI scheme and a resolution mechanism to
convert these URIs into a list of IP addresses, ports and TURN
transport protocols.
Another usage of the resolution mechanism described in this document
would be Remote Hosting as described in [RFC3958] section 4.4. For
example a VoIP provider who does not want to deploy TURN servers
could use the servers deployed by another company but could still
want to provide configuration parameters to its customers without
explicitly showing this relationship. The mechanism permits one to
implement this indirection, without preventing the company hosting
the TURN servers from managing them as it see fit.
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 [RFC2119].
3. Syntax of a TURN or TURNS URI
A TURN/TURNS URI has the following ABNF syntax [RFC5234]:
turnURI = scheme ":" host [ ":" port ] [ "?transport=" transport ]
scheme = "turn" / "turns"
transport = "udp" / "tcp" / transport-ext
transport-ext = 1*unreserved
<host>, <port> and <unreserved> are specified in [RFC3986].
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4. TURN or TURNS URI Resolution
The URI resolution algorithm uses <scheme>, <host>, <port> and
<transport> as input. It also uses a list ordered by preference of
TURN transports (UDP, TCP, TLS) supported by the application using
the TURN client. The output of the algorithm is a list of {IP
address, transport, port} tuples that a TURN client can try in order
to contact a TURN server.
The resolution stops when a TURN client gets a successful Allocate
response from a TURN server. After receiving a successful Allocate
response, the resolution context MUST be discarded and the URI
resolution algorithm MUST be restarted from the beginning for any
subsequent allocation.
In some steps <transport> and <scheme> have to be converted to a TURN
transport. If <scheme> is defined as "turn" and <transport> is
defined as "udp" then the TURN UDP transport is used. If <scheme> is
defined as "turn" and <transport> is defined as "tcp" then the TURN
TCP transport is used. If <scheme> is defined as "turns" and
<transport> is defined as "tcp" then the TURN TLS transport is used.
First the resolution algorithm checks that the URI can be resolved
with the list of TURN transports supported:
o If <scheme> is defined as "turn" and <transport> is defined as
"udp" but the list of TURN transports does not contain UDP then
the resolution MUST stop with an error.
o If <scheme> is defined as "turn" and <transport> is defined as
"tcp" but the list of TURN transports does not contain TCP or TLS
then the resolution MUST stop with an error.
o If <scheme> is defined as "turns" and <transport> is defined as
"udp" then the algorithm MUST stop with an error.
o If <scheme> is defined as "turns" and <transport> is defined as
"tcp" but the list of TURN transports does not contain TLS then
the resolution MUST stop with an error.
o If <scheme> is defined as "turns" and <transport> is not defined
but the list of TURN transports does not contain TLS then the
resolution MUST stop with an error.
o If <transport> is defined but unknown then the resolution MUST
stop with an error.
Then the algorithm applies the following steps.
1. If <host> is an IP address then it indicates the specific IP
address to be used. If <port> is not defined, the default port
declared in [I-D.ietf-behave-turn] for the SRV service name
defined in <scheme> is used. If <transport> is defined then
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<scheme> and <transport> are converted to a TURN transport as
specified above. If <transport> is not defined, the TURN
transports supported by the application are tried by preference
order. If the TURN client cannot contact a TURN server with this
IP address and port on any of the transports then the resolution
MUST stop with an error.
2. If <host> is a domain name and <port> is defined, then <host> is
resolved to a list of IP addresses via DNS A and AAAA queries.
If <transport> is defined then <scheme> and <transport> are
converted to a TURN transport as specified above. If <transport>
is not defined, the TURN transports supported by the application
are tried by preference order. If the TURN client cannot contact
a TURN server with this port and any combination of transports
and resolved IP addresses then the resolution MUST stop with an
error.
3. If <host> is a domain name and <port> is not defined but
<transport> is defined then <host> is converted to a list of IP
address and port tuples via a DNS SRV query as defined in
[I-D.ietf-behave-turn] section 6.1. <scheme> is used for the
service name and <transport> is used for the protocol name in the
SRV algorithm [RFC2782]. If the TURN client cannot contact a
TURN server at any of the IP address, port and transport tuples
returned by the SRV algorithm then the resolution MUST stop with
an error. The SRV algorithm recommends doing an A query if the
SRV query returns an error or no SRV RR. In this case the
default port declared in [I-D.ietf-behave-turn] for the SRV
service name defined in <scheme> must be used for contacting the
TURN server. Also in this case, this specification modifies the
SRV algorithm by recommending an A or AAAA query.
4. If <host> is a domain name and <port> and <transport> are not
defined, then <host> is converted to an ordered list of IP
address, port and transport tuples via the S-NAPTR algorithm
defined in [RFC3958] with a "RELAY" Application Service Tag. The
TURN transports supported by the application are converted in
Application Protocol Tags by using "turn.udp" if the TURN
transport is UDP, "turn.tcp" if the TURN transport is TCP and
"turn.tls" if the TURN transport is TLS. The order to try the
protocol tags is provided by the ranking of the first set of
NAPTR records. If multiple protocol tags have the same ranking,
the preferred order set by the application is used. If the TURN
client cannot contact a TURN server with any of the IP address,
port and transport tuples returned by the S-NAPTR algorithm then
the resolution MUST stop with an error. If the first NAPTR SRV
query does not return any result then <host> is converted to a
list of IP address and port tuples by using the algorithm
specified in step 3 for each of the TURN transports supported by
the application by order of preference.
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5. Example
With the DNS RRs in Figure 1 and a preferred protocol list of {TLS,
TCP, UDP}, the resolution algorithm will convert the "turn:
example.com" URI to the list of IP addresses, port and protocol
tuples in Table 1.
example.com.
IN NAPTR 100 10 "" "RELAY:turn.udp" "" datagram.example.com.
IN NAPTR 200 10 "" "RELAY:turn.tcp:turn.tls" "" stream.example.com.
datagram.example.com.
IN NAPTR 100 10 "S" "RELAY:turn.udp" "" _udp._turn.example.com.
stream.example.com.
IN NAPTR 100 10 "A" "RELAY:turn.tls" "" a.example.com.
IN NAPTR 200 10 "S" "RELAY:turn.tcp" "" _tcp._turn.example.com.
_udp._turn.example.com.
IN SRV 0 0 5000 a.example.com.
_tcp._turn.example.com.
IN SRV 0 0 5000 a.example.com.
a.example.com.
IN A 192.0.2.1
Figure 1
+-------+----------+------------+------+
| Order | Protocol | IP address | Port |
+-------+----------+------------+------+
| 1 | UDP | 192.0.2.1 | 5000 |
| 2 | TLS | 192.0.2.1 | 3478 |
| 3 | TCP | 192.0.2.1 | 5000 |
+-------+----------+------------+------+
Table 1
6. Security Considerations
Security considerations for TURN are discussed in
[I-D.ietf-behave-turn].
The Application Service Tag and Application Protocol Tags defined in
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this document do not introduce any specific security issues beyond
the security considerations discussed in [RFC3958].
The "turn" and "turns" URI schemes do not introduce any specific
security issues beyond the security considerations discussed in
[RFC3986].
7. IANA Considerations
This section contains the registration information for the "turn" and
"turns" URI Schemes (in accordance with [RFC4395]), one S-NAPTR
Application Service Tag, and three S-NAPTR Application Protocol Tags
(in accordance with [RFC3958]).
7.1. TURN URI Registration
URI scheme name: turn
Status: permanent
URI scheme syntax: See Section 3.
URI scheme semantics: See Section 4.
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 6.
Contact: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
References: This document.
7.2. TURNS URI Registration
URI scheme name: turns
Status: permanent
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URI scheme syntax: See Section 3.
URI scheme semantics: See Section 4.
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.
Interoperability considerations: N/A
Security considerations: See Section 6.
Contact: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
References: This document.
7.3. RELAY Application Service Tag Registration
Application Protocol Tag: RELAY
Intended usage: See Section 4.
Interoperability considerations: N/A
Security considerations: See Section 6.
Relevant publications: This document.
Contact information: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
7.4. turn.udp Application Protocol Tag Registration
Application Protocol Tag: turn.udp
Intended usage: See Section 4.
Interoperability considerations: N/A
Security considerations: See Section 6.
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Relevant publications: This document.
Contact information: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
7.5. turn.tcp Application Protocol Tag Registration
Application Protocol Tag: turn.tcp
Intended usage: See Section 4.
Interoperability considerations:
Security considerations: See Section 6.
Relevant publications: This document.
Contact information: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
7.6. turn.tls Application Protocol Tag Registration
Application Protocol Tag: turn.tls
Intended usage: See Section 4.
Interoperability considerations: N/A
Security considerations: See Section 6.
Relevant publications: This document.
Contact information: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
8. Running Code Considerations
o Zap [1]. Eilon Yardeni, 8x8 Inc. Implements version -00
9. Acknowledgements
Thanks to Eilon Yardeni, Dan Wing, Alfred Hoenes and Jim Kleck for
their comments, suggestions and questions that helped to improve this
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document.
This document was written with the xml2rfc tool described in
[RFC2629].
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
[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.
[I-D.ietf-behave-turn]
Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)",
draft-ietf-behave-turn-13 (work in progress),
February 2009.
10.2. Informative References
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", BCP 35,
RFC 4395, February 2006.
[I-D.wood-tae-specifying-uri-transports]
Wood, L., "Specifying transport mechanisms for retrieval
or delivery of URIs",
draft-wood-tae-specifying-uri-transports-04 (work in
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progress), February 2009.
URIs
[1] <http://www.croczilla.com/zap>
Appendix A. Release notes
This section must be removed before publication as an RFC.
A.1. Modifications between -01 and -00
o Fixed the contact email.
o Changed the IPR to trust200902.
o Added case for transport defined but unknown.
o Moved RFC 3958 to Normative References.
o Added study of [I-D.wood-tae-specifying-uri-transports] in TODO
list.
A.2. Design Notes
o The Application Service Tag is "RELAY" so other relaying
mechanisms than TURN (e.g., TWIST) can be registered as
Application Protocol Tags.
o S-NAPTR was preferred to U-NAPTR because there is no use case for
U-NAPTR.
o <password> is not used in the URIs because it is deprecated.
<username> is not used in the URIs because it is not used to guide
the resolution mechanism.
o As discussed in Dublin, there is no generic parameters in the URI
to prevent compatibity issues.
o Adding optional capabilities (IPv6 allocation, preserve bit,
etc...) in the resolution process was rejected at the Dublin
meeting.
A.3. TODO List
o Evaluate if [I-D.wood-tae-specifying-uri-transports] could be a
replacement for the ?transport= parameter.
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Author's Address
Marc Petit-Huguenin
(Unaffiliated)
Email: petithug@acm.org
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