I'll get questions from time to time from readers regarding their WPAD autodiscovery publishing not working correctly. They've created WPAD entries in DHCP and/or DNS but still the Firewall and Web Proxy clients aren't getting the autodiscovery information from the ISA Firewall. What's up with that?
What's usually up is that autodiscovery publishing wasn't enabled on the ISA Firewall Network on which you want it enabled. For example, go to the Networks node in the left pane of the ISA Firewall console and then click the Networks tab in the middle pane. Double click on the default Internal ISA Firewall Network.
In the Internal Properties dialog box, click on the Auto Discovery tab. Autodiscovery is disabled by default. You need to put a checkmark in the Publish automatic discovery information for this network checkbox. The default port is TCP 80. While you can change this to any port number you like, if you are using DNS WPAD, then you must leave it at TCP 80. If you're only using DHCP WPAD for autodiscovery, then you can use any port you like and configure your DHCP option to support this alternate port.