Books
Here is a list of some of the books I've used over the years:
- To understand TCP/IP basics: TCP/IP Illustrated, Volume 1: The Protocols (Second Edition) (by Addison-Wesley Professional Computing Series)
- A comprehensive, illustrated internet protocol reference, free on the Internet: The TCP/IP Guide (http://www.tcpipguide.com/)
- Many books from Cisco press are worth reading, both the technology and certifications books: http://www.ciscopress.com/
- Cisco design guides: Just Google the subject you're looking for