Recently I taught the Network+ class. It's one I teach rarely, and that's too bad because it's one of my favorites; molding new minds and all that. I was reminded of the basics of networking: TCP/IP and its standard behavior, the three-way handshake and all that jazz.
How does one learn the inner workings of protocols? You learn them by reading RFC's, the standard way of documenting all protocols in networking. This will help in your studies of the protocols for exams as well as give you a leg up when it comes to real-world implementation.
I can't stress enough how much better I got at troubleshooting networks once I read some of the RFC's for the protocols we all know and love (or don't love for that matter). For example, how are you going to troubleshoot E-Mail servers without understanding how the SMTP protocol works in the first place?
Don't get me wrong, it is just as important to learn the nuances of the mail servers that manage those protocols, like Exchange or Postfix. But understanding how the protocol works is yet another tool you can use to troubleshoot what's happening under the hood.
It's kind of like if you are a race car driver, knowing where the pedals are and how to steer is great, but knowing how the car and its underpinnings work will make you a far better driver than your competitors. No, I'm not a race fan, but I have seen Days of Thunder and I think that's good enough. ;)
Here's an idea: if you are currently studying for an exam, pick a protocol and start reading the RFC. You don't have to be studying the Network+ to read RFC's. They apply to pretty much every certification out there. My favorite site to look them up is http://www.rfc-editor.org. There is an RFC for every standard protocol in existence. For example, if you are currently studying Windows DNS for the MCSA/MCSA/MCITP Server exam(s), read RFC 1034 and work your way up the related DNS RFC's. If you are working as a Windows Admin, I'm sure you'll agree that knowing DNS is crucial to maintaining and configuring Active Directory, among other things.
A couple of warnings, however. First of all, RFC's can be quite lengthy, so utilize the time wisely. Don't bog yourself down in the techno speak of the RFC's and don't let it distract you from your goal of getting certified. There are enough RFC's to keep you busy throughout your career. Second of all, the RFC's are not always written for the layman, so if you're just starting out, have patience and have Google handy. The knowledge will build over time and soon enough you will have to look things up less and less.
Here are some additional good RFC's to start:
1. RFC 761 Transmission Control Protocol
2. RFC 791 Internet Protocol
3. RFC 792 Internet Control Message Protocol
4. RFC 2616 Hypertext Transfer Protocol 1.1
Good luck on your RFC adventures.