Network Working Group C. Jennings Internet-Draft Cisco Systems Intended status: Standards Track July 5, 2008 Expires: January 6, 2009 DNS SRV Records for HTTP draft-jennings-http-srv-00 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 6, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document specifies a mechanism for an HTTP client to perform a DNS SRV lookup to find an HTTP server. The draft is being discussed on the apps-discuss@ietf.org list. Jennings Expires January 6, 2009 [Page 1] Internet-Draft HTTP SRV July 2008 1. Introduction The scarcity of IPv4 addresses makes it desirable to run HTTP servers on ports other than 80; but URLs like http://www.example.com:3142 are not particular good for humans to remember or use. DNS SRV records allow a DNS lookup of a name like www.example.com to provide both a port and the IP addresses of the HTTP server. This technique is also useful where users wish to run a web server behind a NAT but cannot control which port the NAT will allocate for this server. Analogous situations that arise include residential users who try to run HTTP servers on personal machines. A third use case for HTTP SRV is a situation in which all requests should be sent to a primary server, but if that server is down, then requests fall back to some alternative server. This specification does not update HTTP, and it is not expected that most browsers would support it for generic web use. It would be necessary, and supported, for particular applications using HTTP. For example, a portal such as Facebook often acts a web client and calls specific HTTP-based APIs on other web servers. These APIs may require the use of this specification. In this situation, the end user's web browser might not do the SRV lookup when it browsed to the portal web pages, but the HTTP calls that the portal made out to other sites to generate the content would use this mechanism. As such architectures become more common, DNS SRV would allow many servers that are just providing an API to run on ports other than 80, even though main portal sites may still be running on the well known ports. Eventually, web browsers may end up supporting these SRV lookups, as the implementation is trivial and has very little downside. 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. Recommendations HTTP[RFC2616] Clients compliant with this specification MUST perform an SRV lookup as specified in [RFC2782] when resolving the host portion of HTTP URI. As defined in the IANA port numbers registry, the service names used are _http and _https. As described in RFC 2782, if no SRV record is present, the resolution will fall back on Jennings Expires January 6, 2009 [Page 2] Internet-Draft HTTP SRV July 2008 using other DNS records. 4. Example In the following example, the client will do a lookup on the URI, which finds the SRV record that then points at the A record that points at the IP address. URI: http://example.com DNS SRV RR: _http._tcp.example.com. SRV 1 0 8080 host1.example.com. DNS A RR: host1.example.com. A 192.0.2.88 Figure 1 In this case the client would form a TCP connection to 192.0.2.88: 8080. 5. IANA Considerations This document makes no request of IANA. 6. Security Considerations This introduces no new security considerations beyond the common usage of HTTP. It is analogous to DNS CNAME records that redirect to other A records. 7. Acknowledgements This idea has been proposed by many people, including Mark Andrews and Thor Kottelin in an internet draft in 2000. 8. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, Jennings Expires January 6, 2009 [Page 3] Internet-Draft HTTP SRV July 2008 February 2000. Author's Address Cullen Jennings Cisco Systems 170 West Tasman Drive Mailstop SJC-21/2 San Jose, CA 95134 USA Phone: +1 408 902-3341 Email: fluffy@cisco.com Jennings Expires January 6, 2009 [Page 4] Internet-Draft HTTP SRV July 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Jennings Expires January 6, 2009 [Page 5]