Maximum Linux Security

Chapter 18. Linux and Firewalls

Sadly, whenever you connect your network to the outside world, you enter hostile territory. And there's no more hostile or dangerous territory than the Internet. On the Net, thousands of nameless, faceless attackers can probe and prod your network 24 hours a day, seven days week. To prevent this, you need either a firewall or a reasonable facsimile. That's what this chapter is all about.

What Is a Firewall?

A firewall, at its most basic, is a device that prevents outsiders from accessing your network. This device is typically a router, a standalone computer running packet filtering or proxy software, or a firewall-in-a-box (a proprietary hardware device that filters and proxies).

A firewall can serve as a single entry ...