TCP/IP Illustrated, Vol. 1: The Protocols by W. Richard Stevens [0]

[0] https://www.amazon.com/TCP-Illustrated-Vol-Addison-Wesley-Pr...

Off the top of my head, an understanding of internet architecture is probably a fundamental thing to have. IP, TCP, HTTP, DNS, etc.

http://www.amazon.com/TCP-Illustrated-Vol-Addison-Wesley-Pro...