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have available... ... and then I break out the OSI model chart. Chins slump. People sigh, or at least wish they hadnt ordered decaf that morning. Okay, its not that bad. But it does temper the excitement a little. I always get a sense of why cant we just hurry up and get on the routers and switches? Why do we have to learn this dry stuff? One reason is that Cisco demands you know the OSI model inside and out for both the Intro and ICND exams. You have to admit thats a pretty good reason, but still, students find the OSI model information to be very dry. I understand that, because Ive been there. My first exposure to the OSI model was actually in a Novell Networking Technologies class, and man, was that chart ever dry. They crammed every known protocol (and some unknown ones, I think) into the OSI model. It looked like a giant jigsaw puzzle, and the real problem is that I didnt know what the heck most of that stuff was. So I dutifully attempted to memorize this massive chart. I managed to pass the exam, but I wondered what all that effort had really been for. Its not like you sit around in a server room or wiring closet and discuss the OSI model. As a CCNA candidate, you dont have to worry about all the protocols I memorized way back when, but you do have to know what happens at each layer. Which leads to this question: If I work with routers and switches, why do I have to know about all the other layers? Dont routers and switches just work at layer 2 and 3? Yes, switches work at Layer 2 and routers at Layer 3. But to truly understand networking, youve got to understand what happens at the other layers. Why? Most network administrators and engineers are going to spend a lot more time troubleshooting than installing. Thats just the way it is. And to troubleshoot effectively, youve got to know whats going on at all layers of the OSI model, not just layers 2 and 3. As someone whos done a lot of hiring and conducted a great many job interviews, I can tell you that the ability to troubleshoot is the number one quality I look for. Thats why I tell CCNA and CCNP candidates that theyve got to get all the hands-on practice they can while I understand the importance of theory, the only way to develop troubleshooting ability is to work on the real deal. No simulator program is going to teach you how to troubleshoot. Additionally, the only way to truly develop your troubleshooting abilities is to know whats going on over the entire network, not just the routers and switches. Troubleshooting always starts at Layer 1 if you dont find a problem at the Physical layer, and everythings fine with your routers and switches, how are you going to continue troubleshooting if you dont know what the next steps are as data moves closer to the end user? So when it comes to the OSI model, dont just give it a quick once-over and move on to the fun stuff in your CCNA studies. The tangible benefit of passing your exams is great, but its the hidden benefit of developing your own troubleshooting methodology that makes mastering the OSI model worthwhile. |
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