An excellent & quick read on the basics of networking for sys admins and the rest of us mere mortals! I especially liked the chapter on using tcpdump for packet sniffing.

Michael W. Lucas (yes, it's important to put the "W." in there if you do a Google search; you'll know what I mean if you leave it out) has a humourous and engaging writing style that gets right to the heart of solving those technical woes that might await you.