WPAD – Web Proxy Autodiscovery Protocol

When using wpad there are some things that you should take note of;

• DHCP wpad will override DNS wpad
• DHCP 252 option can in some cases be slightly slower to resolve than DNS – there may be a patch for WinInet to resolve this.
  
• You should always use lower case – wpad.dat  (it is case sensitive)
• DHCP will allow either a URL or a file location for wpad.dat

Within IE on the LAN settings tab if you have WPAD “automatically detect settings” enabled and also configure a proxy server the WPAD should override the manual proxy configuration.

There is some good detail at the usual places http://en.wikipedia.org/wiki/Web_Proxy_Autodiscovery_Protocol

I’ve done a bit of work around WPAD, but have yet to write up a decent “how-to”. I’ll update this the next time i dabble in the area.

If you are using DNS you may have to remove the globalqueryblock for the wpad entry : http://support.microsoft.com/kb/968732/en-us

Here is a quick example of the syntax of a typical wpad.dat file…

   function FindProxyForURL(url, host) {
      // our local URLs from the domains below example.com don't need a proxy:
      if (shExpMatch(url,"*.example.com/*"))                  {return "DIRECT";}
      if (shExpMatch(url, "*.example.com:*/*"))               {return "DIRECT";}

      // URLs within this network are accessed through 
      // port 8080 on fastproxy.example.com:
      if (isInNet(host, "10.0.0.0",  "255.255.248.0"))    {
         return "PROXY fastproxy.example.com:8080";
      }

      // All other requests go through port 8080 of proxy.example.com.
      // should that fail to respond, go directly to the WWW:
      return "PROXY proxy.example.com:8080; DIRECT";
   }