If you know every detail about your firewall, skip this section.
Still here? Great. There are really two major issues here. First, you have to figure out whether you’re using a proxy server or a packet-filtering firewall. Second, you need to figure out whether user authentication is in use.
Assuming that you have a working browser, finding your firewall type should be no problem. Fire up your browser and load a fairly complex page off the Internet (one that takes more than a second or two to load). While that’s happening, get into a DOS prompt and type the following:
netstat -a > before.txt
After that’s done, type this, but don’t press Enter yet:
netstat -a > after.txt
Now switch to the browser and refresh the page. ...