Windows 2000 comes with some rudimentary features to filter Internet traffic. Unfortunately, it can only filter incoming traffic, and you have to actually state which protocols and ports to let through, not which ones to block. However, in some situations, this filtering may prove helpful.

Click on the "Start" menu, choose "Settings", then "Network and Dial-Up Connections". Right-click on your main Internet connection's icon and choose "Properties". When the multi-tabbed "Properties" dialog box appears, select "General".

Click on "Internet Protocol (TCP/IP)" and click the "Properties" button. When the "Properties" dialog box appears, click "Advanced". When the "Advanced TCP/IP Settings" multi-tabbed dialog box appears, click the "Options" tab. Now, double-click "TCP/IP Filtering".

From here, you can choose to turn on filtering by checking the "Enable TCP/IP Filtering (All adapters)" checkbox. By default, Windows is set up to allow in traffic on all TCP and UDP ports, using all protocols. If you want to change any of these options, select the "Permit only" radio button next to the group that you wish to filter, then click "Add" to add in TCP ports, UDP ports, or IP protocols that you want to permit inbound access. When you are done, press "OK".

Note that if you are not careful and do not add in enough ports or protocols, you may temporarily lose access to most, or all, of the Internet. If this happens, go back and allow more ports or protocols, or clear the checkbox to disable filtering altogether.