Configuring WPAD (option 252)
The Web Proxy Auto-Discovery (WPAD) protocol is used by web browsers to locate a Proxy Auto-Config (PAC) file automatically.
The WPAD protocol can use a DNS or DHCP server to locate a PAC file. DHCP detection involves the URL being pushed to the user in the DHCP assignment, while DNS detection is based on an informed guess, using known information about the DNS. A web browser that supports both methods checks the DHCP assignment first, and then attempts the DNS method. If the browser is unable to load a PAC file through the DHCP or DNS methods, it will allow direct Internet access.
NOTE
The PAC file must have the file name wpad.dat for the DNS method to function.