I'm a fan of lecture notes. http://www.cc.gatech.edu/~traynor/cs3251/f13/slides/

One fun thing is to download Wireshark and look at the packets being sent in detail when you do common things like browse the internet or use FTP.

I think this is a really good idea, but I'd add one alternate possibility is well. Doing this on a typical user's computer today will present a mind blowing amount of data--so much that it is easy to give up trying to figure out what's going on if you've never done it before. Instead, perhaps spin up a Linux VM, maybe even no GUI to start. Then run Wireshark on its interface. Much less noise. Should be much easier to begin dissecting.

No need for a VM, just do some filtering in Wireshark. This will help you understand even better what is possible (filter by IP, port, and many other things).

Agreed. I took a networking course at University, and at community college, but didn't really understand networking until I started fooling around with Wireshark.

For a little softer experience, you can load up Fiddler and just look at the HTTP traffic. It's a little mind boggling to me to envision trying to debug web apps without Fiddler, Chome devtools/Firebug and server-side logging inspectable at the same time.

Also a little terrifying to realize just how much incoming and outgoing traffic all the things on your computer are generating all the time.

It's even more fun to do it on a network, where you can see what things other people are doing.

Computer Networks by Tanenbaum: http://www.amazon.com/Computer-Networks-Edition-Andrew-Tanen...

It's a classic.

The CISCO press books for the CCNA course are fairly good.

I actually did the proper 4 semester CISCO academy course at night school a while back which should give you real hands on experience - one of the tests is the instructor breaks a system and you have to fix it

TCP/IP Illustrated is what I cut my teeth on back in the day. You will need to be able to read C to follow the code, which is mostly from the BSD TCP/IP stack IIRC.

The Stevens series is a classic, and you should find a used copy to stick on a bookshelf for the nerd cred and because they are damn fine boos, but I think you will find the Kozierok's TCP/IP Guide from No Starch Press to be a more modern and up-to-date text.

I ended up doing the CCNA course just to figure out how networking works. I was designing a distributed trading system and I wanted to actually understand how things worked rather than just cargo culting a few commands and praying. There's just so many acronyms in the networking space it's hard to figure out without an overview.

Even with the CCNA course, you're still not going to know about stuff like security and firewalls on a deep level.

But get the textbooks and read through them.

This is probably complete overkill , but my favorite is still McDysan/Spohn "ATM Theory and Applications." The first few chapters before you dive into the details about ATM are a very good overview of all communications systems.