If you haven't heard of TCP Wrappers, or are interested in making it work a bit better, this is a good article to read. TCP wrappers are designed to filter incoming connections to network services. In this article Paul Dunne . . . The firewall, which has served as the sentry between the outside world of the Internet and the internal agency network, may be moving inside the network perimeter to World Wide Web servers, PCs, modems and silicon chips. Such internal firewalls .
Network managers tend to see distributed firewalls as added firepower against . . .
Here is an interesting FAQ that you may want to consider reading. This FAQ describes basic Linux Ethernet connection and home LAN configuration. Particular emphasis is placed on network security and firewall construction. The examples are based on Red Hat Linux . . . This LG article discusses configuring an old 486 machine as a secure Internet gateway with two ethernet interfaces.