A thorough guide to Linux TCP/IP network adminstration examines the major flavors of Linux; covers routing, file management, directory services, e-mail, security, and internetworking with Samba; and provides implementation examples, troubleshooting tips, and much more. Original. (Advanced).
Any technical reference of this nature will become dated over time, but this one is quite well written. It covers both ipchains and iptables, with an emphasis on migrating from the former to the later. I picked it up when first moving to Linux admin (also my first job with any significant networking component), and I've never had any reason to regret it.