Not all of these links are directly about building a router or firewall using GNU/Linux, but they offer information that is helpful in doing so.
- Martin's Linux Router Guide
- The SYSLINUX Project
- Using the initial RAM disk (initrd)
- Linux From Scratch version
- Using the RAM disk block device with Linux
- Manpage for mkisofs
- Linux Quick-Ref
- - Gentoo Linux Wiki
- System Log Management and Monitoring
- Chapter 10 from [[or>bssrvrlnx|Building Secure Servers with Linux ]
- Chapter 12 from [[or>|Linux Server Security, Second Edition ]
- Linux Documentation Project
- die.net - Linux Documentation
- GNU/Linux man pages
- linux.org - List of documentation resources
- Gentoo Linux -- Gentoo Documentation Resources
- Linux Gazette
- LQ Wiki
- Highly recommended. I have read ALOT of material from this site that got me started.
The main problem with listing books you learned with is that unless the topic doesn't change often, or it has been a short time since you started learning the topic, the books you suggest will likely be quite dated.
That is the problem here. GNU/Linux is in a rapid state of development and it's been many years since I first started using it.
[[amazon>0596007604|Running Linux] is a book I first picked up from  and read along with lots of printed guides from . I would still recommend it (the link is to a 5th edition copy) even though I would imagine some of the material might be dated.
Aside from that I would recommend reading about everything you can get your hands on from the links listed above and then try distrobutions.Try as many as you can force yourself to download and install and then stick to one for a while.
I recommend any of these as good ones to try:
- Ubuntu, Kubuntu, ... (other variations of Ubuntu)
- Fedora (FC3 was the last I used)