Linux Firewalls and Security

http://www.linux-firewall-tools.com/linux/

This is a fairly comprehensive site focused on firewalls and security issues in Linux. The “Reference Papers” area contains a link I’ve been looking for for awhile - “Service Port Numbers & Log Info.” This section alone is worth the clickthrough, and includes a FAQ on “Firewalls - What Am I Seeing,” as well as a list and explanation of commonly-probed ports. The other information on the site is just as useful. If you’re interested in Linux security (as everyone should be) be prepared to spend some interesting and useful time on Linux Security and Firewalls.