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).
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.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
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]