Network Working Group M. Petit-Huguenin Internet-Draft 8x8, Inc. Intended status: Standards Track July 14, 2008 Expires: January 15, 2009 Traversal Using Relays around NAT (TURN) Uniform Resource Identifiers draft-petithuguenin-behave-turn-uri-02 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 15, 2009. 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 server. Petit-Huguenin Expires January 15, 2009 [Page 1] Internet-Draft TURN URIs July 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Syntax of a TURN or TURNS URI . . . . . . . . . . . . . . . . . 3 4. TURN or TURNS URI Resolution . . . . . . . . . . . . . . . . . 3 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 9. Normative References . . . . . . . . . . . . . . . . . . . . . 7 Appendix A. Release notes . . . . . . . . . . . . . . . . . . . . 7 A.1. Modifications between -02 and -01 . . . . . . . . . . . . . 7 A.2. Modifications between -01 and -00 . . . . . . . . . . . . . 7 A.3. Design Notes . . . . . . . . . . . . . . . . . . . . . . . 8 A.4. TODO List . . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . . 9 Petit-Huguenin Expires January 15, 2009 [Page 2] Internet-Draft TURN URIs July 2008 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 this URIs into a list of IP addresses, ports and TURN transport protocols. 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 "://" authority [ "?" query ] scheme = "turn" / "turns" authority = host [ ":" port ] query = "transport=" transport transport = "udp" / "tcp" / transport-ext transport-ext = 1*unreserved , and are specified in [RFC3986]. 4. TURN or TURNS URI Resolution The URI resolution algorithm uses , , and 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 to contact a TURN server. Petit-Huguenin Expires January 15, 2009 [Page 3] Internet-Draft TURN URIs July 2008 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 and have to be converted to a TURN transport. If is defined as "turn" and is defined as "udp" then the TURN UDP transport is used. If is defined as "turn" and is defined as "tcp" then the TURN TCP transport is used. If is defined as "turns" and 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 is defined as "turn" and is defined as "udp" but the list of TURN transports does not contain UDP then the resolution MUST stop with an error. o If is defined as "turn" and 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 is defined as "turns" and is defined as "udp" then the algorithm MUST stop with an error. o If is defined as "turns" and is defined as "tcp" but the list of TURN transports does not contain TLS then the resolution MUST stop with an error. o If is defined as "turns" and 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 is an IP address then it indicates the specific IP address to be used. If is not defined, the default port declared in [I-D.ietf-behave-turn] for the SRV service name defined in is used. If is defined then and are converted to a TURN transport as specified above. If 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 is a domain name and is defined, then is resolved to a list of IP addresses via DNS A and AAAA queries. If is defined then and are converted to a TURN transport as specified above. If is not defined, the TURN transports supported by the application Petit-Huguenin Expires January 15, 2009 [Page 4] Internet-Draft TURN URIs July 2008 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 is a domain name and is not defined but is defined then 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. is used for the service name and is used for the protocol name in the SRV algorithm [RFC2782]. If the TURN client cannot contact a TURN server on 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 to do 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 must be used for contacting the TURN server. This specification also modifies this algorithm by recommending to do an A or AAAA query in this case. 4. If is a domain name and and are not defined, then 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 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. 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. Petit-Huguenin Expires January 15, 2009 [Page 5] Internet-Draft TURN URIs July 2008 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 TBD 7. IANA Considerations TBD 8. Acknowledgements Thanks to Eilon Yardeni, Dan Wing and Alfred Hoenes for their comments, suggestions and questions that helped to improve this Petit-Huguenin Expires January 15, 2009 [Page 6] Internet-Draft TURN URIs July 2008 document. 9. 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-09 (work in progress), July 2008. Appendix A. Release notes This section must be removed before publication as an RFC. A.1. Modifications between -02 and -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 . o Various nits. A.2. Modifications between -01 and -00 o Added in the ABNF. o Use the and "literal" usages for free-form text defined by [RFC5234]. Petit-Huguenin Expires January 15, 2009 [Page 7] Internet-Draft TURN URIs July 2008 o Fixed various typos. o Put the rule to convert and 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.3. Design Notes o The Application Service Tag is "RELAY" so other relaying mechanisms (e.g. TWIST) than TURN 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 is not used in the URIs because it is deprecated. is not used in the URIs because it is not used to guide the resolution mechanism. A.4. TODO List o Dan Wing: Add generic parameters on TURN URI. [Parameters can be optional or mandatory. Add text explaining that parameters to be defined in the future must be only for the purpose of guiding the resolution mechanism.] o Add security section. o Add IANA registration for the URI and Application Tags. Author's Address Marc Petit-Huguenin 8x8, Inc. 3151 Jay Street Santa Clara, CA 95054 US Phone: +1 408 654 0875 Email: marc@8x8.com Petit-Huguenin Expires January 15, 2009 [Page 8] Internet-Draft TURN URIs July 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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