You should now have a machine that can communicate with other Internet-connected machines, using a very basic rule set that serves as a starting point for controlling your network traffic. As you progress through this book, you’ll learn how to add rules that do various useful things. In Chapter 3, we will extend the configuration to act as a gateway for a small network. Serving the needs of several computers has some consequences, and we will look at how to let at least some ICMP and UDP traffic through, for your own troubleshooting needs if nothing else.

In Chapter 3, we’ll also consider network services that have consequences for your security, like FTP. Using packet filtering intelligently to handle services that are demanding, security-wise, is a recurring theme in this book.