Re: [squid-users] proxy.pac

From: Merton Campbell Crockett <>
Date: Mon, 1 Aug 2005 19:28:06 -0700 (PDT)

On Mon, 1 Aug 2005, Rodrigo A B Freire wrote:

> We use both WPAD and PAC... Inclusive, setting the WPAD in DHCP. No problem
> at all, no truncated requests in the access.log.

WPAD worked reasonably well for WindowsNT and Windows2000; however, there
was a problem with the file name in Windows2000 and the initial release of
WindowsXP. The Microsoft DHCP Service returned the wrong byte count for
the string returned for option 252. The DHCP Client compensated for this
by decrementing the string length. This resulted in the file name being
truncated when the ISC DHCP daemon was used. The solution was to define a
symlink --> proxy.pac.

Another issue was case of the file name. The complete URL needed to be
lowercase. I have a bad habit of using uppercase for host names. It's a
"cheap shot" way of identifying if a local name was used to resolve the
name. :-)

WindowsXP SP1 introduced another problem: the proxy.pac file does not
appear to be used except when it is passed as option 252 in response to a
DHCPINFORM request. It appears that WindowsXP systems with static IP
addresses will not use the proxy.pac file.

Another problem that appears to affect both Windows2000 and WindowsXP is
the cacheing of Web connections which is done by host name rather than
URL. I wrote a load-balancing proxy.pac file. If the first reference
causes proxy A to be selected, proxy A is used for all URLs involving that
host although the hashing algorithm would suggest that proxy B should have
been used for some of the requests. The Windows Registry needs to be
modified to overcome this cacheing behaviour.

Merton Campbell Crockett

> The proxy.pac?Type=WMT is when the Windows Media Player try to open a web
> URN.
> ----- Original Message ----- From: "Kevin" <>
> To: <>
> Cc: <>
> Sent: Monday, August 01, 2005 8:25 PM
> Subject: Re: [squid-users] proxy.pac
> On 8/1/05, <> wrote:
> > I'd reply to the question sent to the list, but I deleted it already.
> >
> > There's a bug in IE that truncates the last character of the
> > autoconfiguration file.
> If I'm reading this right, you're saying that this problem only happens
> when using Proxy Automatic Configuration (PAC) in combination with
> the automatic discovery feature (WPAD) of MSIE?
> > The problem is the packet which requests that file, sometimes get's
> > fragmented, not always.
> > This essentially causes IE to request two files: and c
> > A very simple work-around is to copy proxy.pac to
> > You should see somewhat more consistency here.
> Interesting. We support many thousands of Windows workstations,
> all using proxy.pac but none using WPAD.
> I do not see any requests for "" in the logs on the web server
> hosting the PAC file. I do see a ton of errors for some really humorous
> typos -- it's amazing how many different ways there are to creatively
> spell "proxy" :)
> Kevin Kadow
> (P.S. I do see a high number of requests for "proxy.pac?Type=WMT",
> is anybody else seeing these?)

BEGIN:				vcard
VERSION:			3.0
FN:				Merton Campbell Crockett
ORG:				General Dynamics Advanced Information Systems;
				Intelligence and Exploitation Systems
N:				Crockett;Merton;Campbell
TEL;TYPE=work,voice,msg,pref:	+1(805)497-5045
TEL;TYPE=work,fax:		+1(805)497-5050
TEL;TYPE=cell,voice,msg:	+1(805)377-6762
END:				vcard
Received on Mon Aug 01 2005 - 20:33:28 MDT

This archive was generated by hypermail pre-2.1.9 : Thu Sep 01 2005 - 12:00:01 MDT