Specify proxy web into dhcp ?

Niall O'Reilly Niall.oReilly at ucd.ie
Fri Feb 1 13:11:31 UTC 2008

On 31 Jan 2008, at 09:59, NOC Phibee wrote:

> it's possible to sent the proxy address and port in dhcp ?

	Yes, but you need the longer answer.

	You need to do the following.

	1. Provide a script (in JavaScript/ECMAScript) for the browser
	   to use to locate the appropriate proxy.  The browser will
	   expect the script to return a string containing one or more
	   proxy-location commands, like these:

     'PROXY proxy1.example.com:8432;'

	Multiple such commands can be used:

     'PROXY proxy1.example.com:8432;PROXY proxy2.example.com: 

	The script may contain clever logic to identify which proxy
	or chain of proxies is appropriate for a given client system.
	A number of suitable scripts are "out there".  Google is
	likely your friend.

	2. Make this script available on a convenient web server, ideally
	   on a suitably named, dedicated virtual host.  In order to
	   accommodate a variety of browser behaviour (some buggy!), you
	   should make the same script available via a number of URLs:


	The last of these is needed because some browsers systematically
	discard the final character of the value returned for DHCP
	option 252.

	Some browsers use a DNS-based method to construct the URL where
	they expect to find the script.  This is constructed by prefixing
	the name 'proxy' to the local domain, and then specifying port 80
	and the special file name 'proxy.pac'.

	Others refer first (or only?) to DHCP option 252 and use the
	value of this option, perhaps after truncating the final character.

	3. Advertise the preferred URL (host, port, file path) using DHCP
	   option 252:

     option option-252 code 252 = text;
     option option-252 "http://proxy.example.com:80/wpad.dat";

	4. Inform your customers of the browser settings they should use to
	   enable automatic proxy configuration.

	It may be worth searching any of 'proxy.pac', 'WPAD', or
	'Automatic Proxy Configuration' using your preferred search engine.

	I hope this helps.

	Best regards,

	Niall O'Reilly
	University College Dublin IT Services

	PGP key ID: AE995ED9 (see www.pgp.net)
	Fingerprint: 23DC C6DE 8874 2432 2BE0 3905 7987 E48D AE99 5ED9

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