Network Working Group M. Petit-Huguenin
Internet-Draft (Unaffiliated)
Intended status: Standards Track January 30, 2010
Expires: August 3, 2010
Traversal Using Relays around NAT (TURN) Resolution Mechanism
draft-ietf-behave-turn-uri-09
Abstract
This document defines a resolution mechanism to generate a list of
server transport addresses that can be tried to create a Traversal
Using Relays around NAT (TURN) allocation.
Status of this Memo
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Resolution Mechanism . . . . . . . . . . . . . . . . . . . . . 3
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Multiple Protocols . . . . . . . . . . . . . . . . . . . . 7
4.2. Remote Hosting . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Compatibility with TURN . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6.1. RELAY Application Service Tag Registration . . . . . . . . 9
6.2. turn.udp Application Protocol Tag Registration . . . . . . 9
6.3. turn.tcp Application Protocol Tag Registration . . . . . . 10
6.4. turn.tls Application Protocol Tag Registration . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Release notes . . . . . . . . . . . . . . . . . . . . 12
A.1. Modifications between ietf-09 and ietf-08 . . . . . . . . 12
A.2. Modifications between ietf-08 and ietf-07 . . . . . . . . 12
A.3. Modifications between ietf-07 and ietf-06 . . . . . . . . 12
A.4. Modifications between ietf-06 and ietf-05 . . . . . . . . 12
A.5. Modifications between ietf-05 and ietf-04 . . . . . . . . 12
A.6. Modifications between ietf-04 and ietf-03 . . . . . . . . 12
A.7. Modifications between ietf-03 and ietf-02 . . . . . . . . 13
A.8. Modifications between ietf-02 and ietf-01 . . . . . . . . 13
A.9. Modifications between ietf-01 and ietf-00 . . . . . . . . 13
A.10. Modifications between ietf-00 and petithuguenin-03 . . . . 13
A.11. Modifications between petithuguenin-03 and
petithuguenin-02 . . . . . . . . . . . . . . . . . . . . . 14
A.12. Modifications between petithuguenin-02 and
petithuguenin-01 . . . . . . . . . . . . . . . . . . . . . 14
A.13. Modifications between petithuguenin-01 and
petithuguenin-00 . . . . . . . . . . . . . . . . . . . . . 14
A.14. Design Notes . . . . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
The TURN specification [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 does
not allow the TURN client to discover this preference. This document
defines an S-NAPTR application [RFC3958] for this purpose. This
application defines "RELAY" as an application service tag and
"turn.udp", "turn.tcp", and "turn.tls" as application protocol tags.
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 sees fit.
[TURN-URI] can be used as a convenient way of carrying the four
components needed by the resolution mechanism described in this
document. A reference implementation is available [REF-IMPL].
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. Resolution Mechanism
The resolution mechanism is used only to create an allocation. All
other transactions use the IP address, transport and port used for a
successful allocation creation.
The resolution algorithm uses a boolean flag, <secure>; an IP address
or domain name, <host>; a port number that can be empty, <port>; and
a transport name that can be "udp", "tcp" or empty, <transport> as
input. This four parameters are part of the user configuration of
the TURN client. The resolution mechanism also uses as input a list
ordered by preference of TURN transports (UDP, TCP, TLS) supported
that is provided by the application using the TURN client. This list
reflects the capabilities and preferences of the application code
that is using the S-NAPTR resolver and TURN client, as opposed to the
configuration parameters that reflect the preferences of the user of
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the application. The output of the algorithm is a list of {IP
address, transport, port} tuples that a TURN client can try in order
to create an allocation on a TURN server.
An Allocate error response as specified in section 6.4 of [TURN] is
processed as a failure as specified by [RFC3958] section 2.2.4. The
resolution stops when a TURN client gets a successful Allocate
response from a TURN server. After an allocation succeeds or all the
allocations fail, the resolution context MUST be discarded and the
resolution algorithm MUST be restarted from the beginning for any
subsequent allocation. Servers blacklisted as described in section
6.4 of [TURN] MUST NOT be used for the specified duration even if
returned by a subsequent resolution.
First the resolution algorithm checks that the parameters can be
resolved with the list of TURN transports supported by the
application:
o If <secure> is false and <transport> is defined as "udp" but the
list of TURN transports supported by the application does not
contain UDP then the resolution MUST stop with an error.
o If <secure> is false and <transport> is defined as "tcp" but the
list of TURN transports supported by the application does not
contain TCP then the resolution MUST stop with an error.
o If <secure> is true and <transport> is defined as "udp" then the
algorithm MUST stop with an error.
o If <secure> is true and <transport> is defined as "tcp" but the
list of TURN transports supported by the application does not
contain TLS then the resolution MUST stop with an error.
o If <secure> is true and <transport> is not defined but the list of
TURN transports supported by the application 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.
After verifying the validity of the parameters, the algorithm filters
the list of TURN transports supported by the application by removing
the UDP and TCP TURN transport if <secure> is true. If the list of
TURN transports is empty after this filtering, the resolution MUST
stop with an error.
After filtering the list of TURN transports supported by the
application, the algorithm applies the steps described below. Note
that in some steps, <secure> and <transport> have to be converted to
a TURN transport. If <secure> is false and <transport> is defined as
"udp" then the TURN UDP transport is used. If <secure> is false and
<transport> is defined as "tcp" then the TURN TCP transport is used.
If <secure> is true and <transport> is defined as "tcp" then the TURN
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TLS transport is used. This is summarized in Table 1.
+----------+-------------+----------------+
| <secure> | <transport> | TURN Transport |
+----------+-------------+----------------+
| false | "udp" | UDP |
| false | "tcp" | TCP |
| true | "tcp" | TLS |
+----------+-------------+----------------+
Table 1
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 [TURN] for the "turn" SRV service name if <secure> is
false, or the "turns" SRV service name if <secure> is true MUST
be used for contacting the TURN server. If <transport> is
defined then <secure> and <transport> are converted to a TURN
transport as specified in Table 1. If <transport> is not
defined, the filtered 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 supported by the application 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 <secure> and <transport> are
converted to a TURN transport as specified in Table 1. If
<transport> is not defined, the filtered TURN transports
supported by the application are tried in preference order. The
TURN client can choose the order to contact the resolved IP
addresses in any implementation-specific way. If the TURN client
cannot contact a TURN server with this port, the transport or
list of transports, and the 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 the SRV algorithm defined in
[RFC2782] is used to generate a list of IP address and port
tuples. <host> is used as Name, a value of false for <secure> as
"turn" for Service, a value of true for <secure> as "turns" for
Service and <transport> as Protocol in the SRV algorithm.
<secure> and <transport> are converted to a TURN transport as
specified in Table 1 and this transport is used with each tuple
for contacting the TURN server. 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 [TURN] for the "turn"
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SRV service name if <secure> is false, or the "turns" SRV service
name if <secure> is true MUST be used for contacting the TURN
server. Also in this case, this specification modifies the SRV
algorithm by recommending an A and AAAA query. If the TURN
client cannot contact a TURN server at any of the IP address and
port tuples returned by the SRV algorithm with the transport
converted from <secure> and <transport> then the resolution MUST
stop with an error.
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] by using <host> as the initial target domain
name and "RELAY" as the Application Service Tag. The filtered
list of 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 Application Protocol Tags is provided by the ranking of the
first set of NAPTR records. If multiple Application Protocol
Tags have the same ranking, the preferred order set by the
application is used. If the first NAPTR query fails, the
processing continues in step 5. 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.
5. If the first NAPTR query in the previous step does not return any
result then the SRV algorithm defined in [RFC2782] is used to
generate a list of IP address and port tuples. The SRV algorithm
is applied by using each transport in the filtered list of TURN
transports supported by the application for the Protocol, <host>
for the Name, "turn" for the Service if <secure> is false or
"turns" for the Service if <secure> is true. The same transport
that was used to generate a list of tuples is used with each of
these tuples for contacting the TURN server. 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 [TURN] for
the "turn" SRV service name if <secure> is false, or the "turns"
SRV service name if <secure> is true MUST be used for contacting
the TURN server. Also in this case, this specification modifies
the SRV algorithm by recommending an A and AAAA query. If the
TURN client cannot contact a TURN server at any of the IP address
and port tuples returned by the SRV algorithm with the transports
from the filtered list then the resolution MUST stop with an
error.
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4. Examples
4.1. Multiple Protocols
With the DNS RRs in Figure 1 and an ordered TURN transport list of
{TLS, TCP, UDP}, the resolution algorithm will convert the parameters
<secure> with a value of false, <host> with a value of "example.net"
and <port> and <transport> been empty to the list of IP addresses,
port and protocol tuples in Table 2.
example.net.
IN NAPTR 100 10 "" RELAY:turn.udp "" datagram.example.net.
IN NAPTR 200 10 "" RELAY:turn.tcp:turn.tls "" stream.example.net.
datagram.example.net.
IN NAPTR 100 10 S RELAY:turn.udp "" _turn._udp.example.net.
stream.example.net.
IN NAPTR 100 10 S RELAY:turn.tcp "" _turn._tcp.example.net.
IN NAPTR 200 10 A RELAY:turn.tls "" a.example.net.
_turn._udp.example.net.
IN SRV 0 0 3478 a.example.net.
_turn._tcp.example.net.
IN SRV 0 0 5000 a.example.net.
a.example.net.
IN A 192.0.2.1
Figure 1
+-------+----------+------------+------+
| Order | Protocol | IP address | Port |
+-------+----------+------------+------+
| 1 | UDP | 192.0.2.1 | 3478 |
| 2 | TLS | 192.0.2.1 | 5349 |
| 3 | TCP | 192.0.2.1 | 5000 |
+-------+----------+------------+------+
Table 2
4.2. Remote Hosting
In the example in Figure 2, a VoIP provider (example.com) is using
the TURN servers managed by the administrators of the example.net
domain (defined in Figure 1). The resolution algorithm using the
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ordered TURN transport list of {TLS, TCP, UDP} would convert the same
parameters than in the previous example but with the <host> parameter
equal to "example.com" to the list of IP addresses, port and protocol
tuples in Table 2.
example.com.
IN NAPTR 100 10 "" RELAY:turn.udp:turn.tcp:turn.tls "" example.net.
Figure 2
4.3. Compatibility with TURN
In deployments where it is not possible to guarantee that all TURN
clients will support the resolution mechanism described in this
document, the DNS configuration should be done in a way that works
with both this resolution mechanism and the mechanism described in
[TURN]. The DNS RRs in Figure 3 can be used in conjunction with the
DNS RRs in Figure 1 and Figure 2 for this purpose.
_turn._udp.example.com.
IN SRV 0 0 3478 a.example.net.
_turn._tcp.example.com.
IN SRV 0 0 5000 a.example.net.
_turns._tcp.example.com.
IN SRV 0 0 5349 a.example.net.
Figure 3
5. Security Considerations
Security considerations for TURN are discussed in [TURN].
The Application Service Tag and Application Protocol Tags defined in
this document do not introduce any specific security issues beyond
the security considerations discussed in [RFC3958]. [RFC3958]
requests that an S-NAPTR application defines some form of end-to-end
authentication to ensure that the correct destination has been
reached. This is achieved by the Long-Term Credential Mechanism
defined in [RFC5389], which is mandatory for [TURN].
Additionally the usage of TLS [RFC5246] has the capability to address
the requirement. In this case the client MUST verify the identity of
the server by following the identification procedure in section 7.2.2
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of [RFC5389] and by using the value of the <host> parameter as the
identity of the server to be verified.
An implication of this is that the server's certificate could need to
be changed when SRV or NAPTR records are added. For example, a
client using just A/AAAA records, and configured with
"turnserver.example.net", expects to find the name
"turnserver.example.net" in the certificate. If a second client uses
SRV records and is configured with <host> parameter "example.com", it
expects to find "example.com" in the certificate, even if the SRV
record at _turns._tcp.example.com points to turnserver.example.net.
6. IANA Considerations
This section contains the registration information for one S-NAPTR
Application Service Tag and three S-NAPTR Application Protocol Tags
(in accordance with [RFC3958]).
6.1. RELAY Application Service Tag Registration
Application Protocol Tag: RELAY
Intended usage: See Section 3.
Interoperability considerations: N/A
Security considerations: See Section 5.
Relevant publications: This document.
[Note to RFC Editor: Replace "This document" with reference to this
document]
Contact information: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
6.2. turn.udp Application Protocol Tag Registration
Application Protocol Tag: turn.udp
Intended usage: See Section 3.
Interoperability considerations: N/A
Security considerations: See Section 5.
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Relevant publications: This document.
[Note to RFC Editor: Replace "This document" with reference to this
document]
Contact information: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
6.3. turn.tcp Application Protocol Tag Registration
Application Protocol Tag: turn.tcp
Intended usage: See Section 3.
Interoperability considerations:
Security considerations: See Section 5.
Relevant publications: This document.
[Note to RFC Editor: Replace "This document" with reference to this
document]
Contact information: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
6.4. turn.tls Application Protocol Tag Registration
Application Protocol Tag: turn.tls
Intended usage: See Section 3.
Interoperability considerations: N/A
Security considerations: See Section 5.
Relevant publications: This document.
[Note to RFC Editor: Replace "This document" with reference to this
document]
Contact information: Marc Petit-Huguenin <petithug@acm.org>
Author/Change controller: The IESG
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7. Acknowledgements
Thanks to Cullen Jennings, Alexey Melnikov, Scott Bradner, Spencer
Dawkins, Pasi Eronen, 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 this
document.
This document was written with the xml2rfc tool described in
[RFC2629].
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.
[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.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[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-16 (work in progress), July 2009.
8.2. Informative References
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[TURN-URI]
Petit-Huguenin, M., "Traversal Using Relays around NAT
(TURN) Uniform Resource Identifiers",
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draft-petithuguenin-behave-turn-uri-bis-01 (work in
progress), January 2010.
[REF-IMPL]
Petit-Huguenin, M., "Reference Implementation of TURN
resolver and TURN URI parser", January 2010, <http://
debian.implementers.org/stable/source/turnuri.tar.gz>.
Appendix A. Release notes
This section must be removed before publication as an RFC.
A.1. Modifications between ietf-09 and ietf-08
o Clarified that the identity to use for server certificate
verification is <host>
o Moved the reference implementation reference to the informative
references and changed the URL to something more stable.
A.2. Modifications between ietf-08 and ietf-07
o Added reference to TLS RFC.
o Removed usused references.
o Fixed reference to URI.
A.3. Modifications between ietf-07 and ietf-06
o Clarified "application code" meaning.
A.4. Modifications between ietf-06 and ietf-05
o Updated the short title to "TURN Resolution".
o Shorten I-D references.
o Nits
o Changed SHOULD NOT to MUST NOT for blacklist rule.
o Added notes to RFC editor.
A.5. Modifications between ietf-05 and ietf-04
o Moved the URI stuff to [TURN-URI].
A.6. Modifications between ietf-04 and ietf-03
o Improved the algorithm steps.
o It is possible to use a TLS transport event if the scheme is
turn:.
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o Clarified when to stop the resolution with an error in step 2.
o Added transport list filtering process.
o Improved security section following sec-dir review.
o Fixed nits reported by gen-art review.
o Added example for remote hosting.
o Removed URIs section.
o Editorial modification.
A.7. Modifications between ietf-03 and ietf-02
o A turn:<host>?transport=TCP URI fails if the list of supported
transports contains only TLS. Using a TLS transport in this case
was underspecified.
o Reordered paragraphes in section 4.
o Added table for conversion of <scheme> and <transport> to TURN
transport.
o Various editorial modifications.
o SRV algorithm changed to "...recommending an A and AAAA query."
o Put back the changelog for the versions before been accepted as WG
item.
A.8. Modifications between ietf-02 and ietf-01
o Shorten the abstract so it does not overflow on the second page.
o Added text to explicitly say that the resolution is only to create
an allocation.
o Added text about failures.
o Fixed the default port for TLS in the example.
o Changed some priority in the example for RFC3958 section 2.2.5.
o Fixed the service/protocol order for the SRV RR in the example.
o Removed reference to draft-wood-tae-specifying-uri-transports as
it has an experimental status.
A.9. Modifications between ietf-01 and ietf-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 draft-wood-tae-specifying-uri-transports in TODO
list.
A.10. Modifications between ietf-00 and petithuguenin-03
o Renamed the document to "draft-ietf-behave-turn-uri".
o Changed author affiliation.
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o Fixed the text in the IANA considerations.
A.11. Modifications between petithuguenin-03 and petithuguenin-02
o Added Running Code Consideration section.
o Added Remote Hosting example in introduction.
o Changed back to opaque URIs because of RFC4395 Section 2.2. Now
use "?" as separator.
o Added IANA considerations section.
o Added security considerations section.
A.12. Modifications between petithuguenin-02 and petithuguenin-01
o Receiving a successful Allocate response stops the resolution
mechanism and the resolution context must be discarded after this.
o Changed from opaque to hierarchical URIs because the ";" character
is used in <reg-name>.
o Various nits.
A.13. Modifications between petithuguenin-01 and petithuguenin-00
o Added <transport-ext> in the ABNF.
o Use the <rulename> and "literal" usages for free-form text defined
by RFC5234.
o Fixed various typos.
o Put the rule to convert <scheme> and <transport> to a TURN
transport in a separate paragraph.
o Modified the SRV usage to be in line with RFC 2782.
o Clarified that the NAPTR protocol ranking must be used before the
application ranking.
o Added an example.
o Added release notes.
A.14. 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 Adding optional capabilities (IPv6 allocation, preserve bit,
etc...) in the resolution process was rejected at the Dublin
meeting.
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Author's Address
Marc Petit-Huguenin
(Unaffiliated)
Email: petithug@acm.org
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