Java Network Programming, 2nd ed., by Elliotte Rusty Harold, O'Reilly, 2000.

Early chapters are a good explanation of Internet concepts.

A Brief History of the Future: The Origins of the Internet, by John Naughton, Weidenfeld, 1999.

Contains some very powerful arguments about freedom.

Where wizards stay up late: The Origins of the Internet, by Katie Hafner & Matthew Lyon, Simon & Schuster, 1996.

Reads like a thriller. A– great read. Traces the origins of the Internet, TCP/IP, and e-mail.

Internetworking with TCP/IP, Volume I: Principles, Protocols, and Architecture, 2nd ed., by Douglas Comer, Prentice-Hall Int., 1991

Very clear. Explains how the DNS system works, among many other things.