[aidenn0]

Comer's book "Computer Networks And Internets" is a decent introduction. If you are on a budget get one edition out-of-date; it's a college textbook so the previous edition is usually about 90% cheaper than the current edition.

Once you feel comfortable with the basics, start going through RFCs for what you are interested in. In most cases the RFCs describe not just the protocol, but the reasoning behind it as well.

For me though, I need to do more than read; I need to be "hands on." One example:

When I was in college, I wanted to learn the IRC protocol better, and I noticed it was text based, so (after reading through a couple of RFCs) I connected to an IRC server with telnet in one window and the spec in another window. about 6 hours later I was finally able to connect and send messages. Those 6 hours were both less boring and more educational than 6 more hours of reading would be.

Net results on my grades was either slightly negative, or a wash; I probably missed 2 or 3 classes during those 6 hours, but I got nearly double the next highest score on my Networking midterm 3 semesters later.