But Internet connection that makes gaming so much fun also serves as a doorway through which nefarious hackers can send malicious code, causing havoc with your computer. Broadband users are especially fertile targets for bad seeds. That's why a firewall is so important. A good firewall, such as Internet Connection Firewall (ICF) that comes with Windows XP, protects your computer from attacks.

A firewall works by blocking communication ports that are used to transfer data to and from your PC. However, games (and all applications that work over Internet) use those ports to communicate. This raises some questions that we frequently encounter on message boards and in Usenet: how does a firewall affect performance of online gaming? What do you have to do to enjoy online gaming with a firewall in place? I'll answer these questions in this article.

How Ports Work To get most out of online gaming through a secure connection, you have to have some idea of how games communicate over Internet and how a firewall works. Don't worry; this discussion won't get inaccessibly technical. I'll stick to layman's terms. To start with, let's look at how programs talk to each other over Internet. All Internet-aware programs communicate with each other through ports. What, exactly, is a port?

Think of your Internet connection as a water conduit. But instead of thinking of it as one big pipe, picture it as a conglomeration of thousands of small pipes: 65,535 of them, to be exact. That is number of Internet ports through which communications can take place.

Different services use different ports—the assignment of which service uses which port is more or less arbitrary. For example, World Wide Web communi- cations use port 80. Why port 80? Because a few years ago, a bunch of Internet-related people got together and decided that that's how it would be. Similarly, SMTP e-mail traffic uses port 25. Those same people decided that that's how that would go, and so on. These and other services use protocols to transmit and receive their data through these ports. Two protocols that they use are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

The 65,535 ports are divided into three groups: Well Known Ports (ports 0 through 1023), Registered Ports (ports 1024 through 49151), and Dynamic or Private Ports (all rest). A list of port numbers and what services commonly use them is kept up by Internet Assigned Numbers Authority.

Like other services, Internet components of games use ports and protocols to communicate over Internet. When you play Halo online with a bunch of other people, it has to transmit your keyboard and mouse-click data to server so it can tell when you move around or fire your weapon. In turn it has to transmit world data back to your computer so you can see where other people move so you can aim at them and chase them around. Halo and other multiplayer games like Quake family, Half-Life and mods such as Team Fortress Classic and popular Counter-Strike, Medal of Honor: Allied Assault, Battlefield 1942 send their data down ports and listen for data from same or other ports. Game matchmaker services like GameSpy Arcade also use ports to communicate.