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Versions: (draft-petithuguenin-behave-turn-uri) 00 01 02 03 04 05 06 07 08 09 10 RFC 5928

Network Working Group                                  M. Petit-Huguenin
Internet-Draft                                            (Unaffiliated)
Intended status: Standards Track                       December 21, 2008
Expires: June 24, 2009


 Traversal Using Relays around NAT (TURN) Uniform Resource Identifiers
                     draft-ietf-behave-turn-uri-00

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on June 24, 2009.

Copyright Notice

   Copyright (c) 2008 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
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   to this document.

Abstract

   This document defines two URI schemes and the resolution mechanism to
   convert these URIs to a list of server transport addresses that can



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   be used between a Traversal Using Relays around NAT (TURN) client and
   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.  Design Notes . . . . . . . . . . . . . . . . . . . . . . . 11
     A.2.  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.

   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
       <scheme> and <transport> are converted to a TURN transport as
       specified above.  If <transport> is not defined, the TURN



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       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@8x8.com>

   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@8x8.com>

   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@8x8.com>

   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@8x8.com>

   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@8x8.com>

   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@8x8.com>

   Author/Change controller: The IESG


8.  Running Code Considerations

   The SIP client of the free and open source Zap project [1] uses the
   resolution mechanism and TURN URI described in this document.


9.  Acknowledgements

   Thanks to Eilon Yardeni, Dan Wing, Alfred Hoenes and Jim Kleck for



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   their comments, suggestions and questions that helped to improve this
   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.

   [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-12 (work in progress),
              November 2008.

10.2.  Informative References

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [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.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 115,
              RFC 4395, February 2006.

URIs

   [1]  <http://www.croczilla.com/zap>



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Appendix A.  Release notes

   This section must be removed before publication as an RFC.

A.1.  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.2.  TODO List

   (Empty)


Author's Address

   Marc Petit-Huguenin
   (Unaffiliated)

   Email: petithug@acm.org




















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