Every so often I stumble across a blog post (or receive an e-mail) complaining how hard it is to learn the material needed to pass a certification exam. That’s definitely true if you try the memorization approach to networking: trying to cram as many facts as possible into your grey matter. However, it’s impossible to make any reasonable progress that way; to move forward, you have to handle networking like you would math or physics: having a firm basic foundation, you slowly expand it, all the time trying to fit the new concepts into a coherent model (let’s call it “the big picture”).
Every single internetworking technology (or solution) was invented and introduced for a very good reason; it was trying to solve a particular set of problems within an environment that posed a unique set of restrictions. Trying to memorize how something works (or how you configure a particular device feature) is close to impossible if you don’t have the big picture; it’s like trying to learn history by memorizing the years of important events, without understanding their correlation (yes, that’s how I was taught history ... and I promptly managed to forget most of it).
To really progress in your networking studies, you have to focus on understanding how various technologies work and why they work that way ... and then, if you’re at least a little bit devious, you start to experiment: imagine a crazy scenario that your theory (your mental “big picture”) predicts will fail, try it out in the lab, observe whether the results match with your mental model predictions, and try to fix it.