I've been working at getting a better firewall on my Linode. My problem is not with understanding the individual options of iptables, it's getting a cohesive overview so I can understand what I am doing and why. I used to have a book called Linux Firewalls by Robert L. Ziegler, that did a good job of explaining things, but it was all based on ipchains, the precursor to the current iptables. I discovered that sometime in the past, I had bought the third edition of this book - Linux Firewalls Third Edition by Steve Suehring and Robert L. Ziegler - which is based on iptables and is exactly what I need. It explains from the bottom up how iptables works, and what I need to achieve. I am now building a better firewall that suits my needs, and I understand what it is doing and why I am doing it.