IN THIS CHAPTER
Learning firewall basics
Making the most of Mac OS X's built-in application firewall
Configuring IPFW, a Unixbased firewall included with Mac OS X
Setting up and using several major third-party firewalls
Firewalls serve as gatekeepers between your Mac's software and the Internet —monitoring the traffic that passes back and forth and selectively allowing or blocking information with particular sources, destinations, or characteristics. You can think of them as something like burglar bars on windows, which allow light and air in and don't hinder conversations with someone on the other side but prevent the bad guys from climbing in to harm you or steal your stuff. A firewall can't protect you against every possible outside threat, and its efficacy depends almost entirely on how prudently you've configured it. But it's a common-sense measure that can greatly reduce your risks of outside attacks without interfering with your everyday use of the Internet.
Mac OS X includes two different built-in firewalls (or three, depending on how you count), and this chapter explains how they work, how best to configure them, and which one(s) you should use. If you want even more power or more control, you can choose any of several third-party firewalls for Mac OS X, which I also cover here.
You can purchase stand-alone firewall devices or configure a server to function solely as a firewall that protects the rest of your network, but this chapter focuses ...