Although I touched on firewalls several times earlier in this book, in this chapter, I went into detail about how they work, the various forms in which they appear, and how to put them to best use on your Mac. After giving an introduction to basic firewall concepts, I described the application firewall included with Leopard and Snow Leopard, explained how to configure it optimally, and also outlined some of its shortcomings. I next moved on to IPFW, a powerful Unix-based firewall that's been part of Mac OS X for years but which is normally hidden in Leopard and Snow Leopard.
For situations too complex for even IPFW, a third-party firewall may be a better choice, and Mac users have numerous options. So, I rounded out the chapter with descriptions of some of the most popular firewall applications that can run on your Mac.