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ID: Proxy autoconfig

From: Josh Cohen <josh@netscape.com>
Date: Thu, 27 Mar 1997 00:21:30 -0800 (PST)
To: http-wg@cuckoo.hpl.hp.com
Message-Id: <ML-3.1.859450890.113.josh@birdcage>
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/2924
Please have a look at this..

Josh Cohen				        Netscape Communications Corp.
Netscape Fire Department	               "My opinions, not Netscape's"
Server Engineering
josh@netscape.com                       http://home.netscape.com/people/josh/

Network Working Group                                         Josh Cohen
Internet-Draft                                   Netscape Communications
Expires in 6 Months                                        24 March 1997

                       Discovering proxy servers

Status of this Memo

   This document is an Internet-Draft.  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
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   To learn the current status of any Internet-Draft, please check the
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   ftp.isi.edu (US West Coast).


   This document describes a method for automating 'out of the box'
   configuration of WWW clients via the Server Location Protocol.

   Presently, the most popular method of automatic browser configuration
   is via a Proxy Autoconfig file, which is delivered upon request to
   the browser.  Unfortunately, the URL of this PAC file must still be
   specified by the user or administrator.


   The Server Location Protocol working group has defined a number of
   Internet Drafts on how to locate and advertise services on IP
   networks.  This draft suggests using the method described in [SRVURL]
   and [SVRADV] to advertise the URL of the autoconfig file.

   If has been suggested that a client should use DHCP in [KWAN] to
   determine this URL, but presently, there is no cross platform way to
   reference DHCP configuration options.  Because of this, the author
   suggests using the Server Location protocol.

J. Cohen                                                        [Page 1]

INTERNET-DRAFT         Discovering proxy servers           24 March 1997

   By following the recommendations in this draft, an administrator can
   expect that a user will procure a conforming web client, install it
   on their computer and have the product automagically configure itself
   for the appropriate proxy policies based on the clients domain.

Advertising the URL

   As specified in [SRVADV] and [SRVRR], service: URLs can be advertised
   via DNS.  The method for advertising these resources in DNS is based
   on TXT RRs and SRV RRs.  Presently, SRV records are not widely
   supported, so in the interim, [TXT] recommends using TXT records

   The service URL for a PAC file is a service URL defined in [SRVURL].
   The general format of a service: URL is:

   service: service-location

   The explicit format of the URL in DNS TXT records is defined in
   [FIND].  The general format is:

   <service> IN TXT "service:<srvtag>-<url>" [preference] [protocol

   According to [FIND], srvtag would be 'yp' short for yellow pages.
   This is the generic tag for services, as opposed to 'wp' or white
   pages for people.

   Service should be 'w3-ns-pac' to specify the type of configuration we
   are looking for.

   An example for a proxy called proxy1.foo.com on port 8080 whose PAC
   file is /proxy.pac is:

   w3-ns-pac IN TXT "service:yp-http://proxy1.foo.com:8080/proxy.pac"

Discovering the PAC URL

   A client should attempt to discover the PAC URL at least as often as
   upon each startup.  To do so it shall query DNS for TXT RRs with the
   identifier w3-ns-pac.

   It should start with the most specific domain, and the query, with a
   more general domain, until it finds an response.

   For example, for a client whose name is pc1.test.corp.foo.com, the
   client should query, in order:


J. Cohen                                                        [Page 2]

INTERNET-DRAFT         Discovering proxy servers           24 March 1997


   Note the final '.' to speed unsucessful queries.

The 'w3-ns-pac' specifier

   The specifier should is unique and it reflects:

   the functional area:      the world wide web

   the origination of:       ns (Netscape Communications)
   this resource format

   the type of resource:     PAC (Proxy Auto Config)

   By using unique identifiers, administrators can list other
   resources for other types of PAC files, should they use
   a browser which has its own format.

The PAC file format

   This format has generally become a defacto standard, but is
   not currently defined in any standards body.  Information can be
   found at: [PAC]

Security Considerations

   Since this discovery method depends on DNS, it is subject to the
   same concerns and restrictions as the Domain Name System with
   respect to security.

   It is presumed that this functionality will be of most use in an
   intranet deployment where the DNS servers, and proxy servers are
   maintained by the same organization.  Therefore, a certain degree
   of trust is assumed.


   [HTTP]     R. Fielding, J. Gettys, J.C. Mogul, H. Frystyk, T. Berners-Lee
              "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, Jan 1997

   [KWAN]     S. Kwan, "DHCP Option for Proxy Client Configuration File",
              draft-kwan-proxy-client-conf-00.txt,  March 1997

   [SRVRR]      A. Gulbrandsen, P. Vixie, "A DNS RR for specifying
              the location of services (DNS SRV)," RFC 2052, October 1996.

J. Cohen                                                        [Page 3]

INTERNET-DRAFT         Discovering proxy servers           24 March 1997

   [SRVURL]   E. Guttman, "The service: URL Scheme",
              <draft-ietf-svrloc-service-scheme-00.txt>, November 1996.

   [SVRLOC]   C. Perkins, S. Kaplan, J. Veizades, E. Guttman,
              "Service Location Protocol", draft-ietf-svrloc-protocol-15.txt,
              January 1997

   [SVRADV]   R. Moats, M. Hamilton, "Advertising Services",
              draft-ietf-svrloc-advertise-00.txt  February 1997

   [FIND]     R. Moats   M. Hamilton, "Finding Stuff (How to discover)",
               draft-ietf-svrloc-discovery-00.txt, February 1997

   [PAC]      A. Luotonen, "Netscape Proxy Autoconfiguration"
              March 1996

Author's Address

   Josh Cohen
   Netscape Communications Corporation
   501 E. Middlefield Rd
   Mountain View, CA 94043

   Phone (415) 937-4157
   EMail: josh@netscape.com

J. Cohen                                                        [Page 4]
Received on Thursday, 27 March 1997 00:51:46 UTC

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