Re: ID: Proxy autoconfig

A few observations.

1)  It is true that DHCP lease times can be "long-lived", i.e. on the
order of weeks in some practical cases.  However this is only important
if the URL that is delivered in the DHCP option changes, not the proxy
information.  The proxy information is buried in the file referenced by
the URL, and the client can reload the file at an arbitrary interval.
As long as the server that is distributing the URL doesn't change often,
you are ok.

2)  Using DNS will not work for mobile clients.  For example, consider a
laptop named SKWAN01.INTRA.MICROSOFT.COM.  While plugged into the
Microsoft corporate net, it queries for and receives the TXT RR:

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

I unplug my laptop and take it on a visit to Netscape.  When I plug into
the Netscape corporate network, I query for the TXT RR per above and the
query fails.  At this point, I have no way of finding the proxy servers
for that network, and automatic configuration fails.

3)  It is true that DHCP is not necessarily widely available today, but
if anything SRVLOC is less available.  The DHCP method at least gives
you something you can use now.

4)  The fact that there is no cross-platform API to retrieve DHCP
options is interesting, but does not block implementation.  While the
DHCP WG investigates this problem, use the platform-specific method for
retrieving options.  Please note that there is no cross-platform
standard API for retrieving TXT RRs from DNS.

I have attached my I-D info below for those interested.

Cheers,
- Stuart Kwan
Microsoft Corp.
______

 A New Internet-Draft is available from the on-line Internet-Drafts 
 directories.


       Title     : DHCP Option for Proxy Client Configuration File

       Author(s) : S. Kwan
       Filename  : draft-kwan-proxy-client-conf-00.txt
       Pages     : 3
       Date      : 02/26/1997

Application-level gateways are used on networks to provide controlled 
access to the Internet.  Clients in those networks must be configured 
with the name or address of available proxy servers, the list of local 
domain names, and other proxy client configuration information before 
they can access the Internet.  The defacto method of proxy client 
configuration is the download of a script or configuration file 
named by a URL.  This document describes a DHCP option in which to 
transmit this URL to a proxy client.


Internet-Drafts are available by anonymous FTP.  Login with the username
"anonymous" and a password of your e-mail address.  After logging in,
type "cd internet-drafts" and then
     "get draft-kwan-proxy-client-conf-00.txt".
A URL for the Internet-Draft is:
ftp://ds.internic.net/internet-drafts/draft-kwan-proxy-client-conf-00.tx
t

Received on Friday, 28 March 1997 14:11:55 UTC