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Cisco Certification: The OSI Model Isn't Just For Exams Anymore! |
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There's nothing I enjoy more than teaching Cisco technologies,
especially CCNA candidates. Whether it's in-person or online,
everyone's excited to be there. There's a sense of anticipation
in the air, and everyone is ready to work hard, get their
hands on the racks of Cisco routers and switches I have available...
... and then I break out the OSI model chart. Chins slump.
People sigh, or at least wish they hadn't ordered decaf that
morning.
Okay, it's not that bad. But it does temper the excitement
a little. I always get a sense of "why can't 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
that's a pretty good reason, but still, students find the
OSI model information to be very dry. I understand that, because
I've 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
didn't 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. It's not like you sit around in a server
room or wiring closet and discuss the OSI model.
As a CCNA candidate, you don't 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? Don't 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,
you've 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. That's just
the way it is. And to troubleshoot effectively, you've got
to know what's going on at all layers of the OSI model, not
just layers 2 and 3.
As someone who's 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. That's why I tell CCNA
and CCNP candidates that they've 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 what's going on over the entire network,
not just the routers and switches. Troubleshooting always
starts at Layer 1; if you don't find a problem at the Physical
layer, and everything's fine with your routers and switches,
how are you going to continue troubleshooting if you don't
know what the next steps are as data moves closer to the end
user?
So when it comes to the OSI model, don't 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 it's
the hidden benefit of developing your own troubleshooting
methodology that makes mastering the OSI model worthwhile.
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage,
home of free CCNP and CCNA tutorials, The Ultimate CCNA Study
Package, and Ultimate CCNP Study Packages. For a FREE copy
of his latest e-books, “How To Pass The CCNA” and
“How To Pass The CCNP”, just visit the website!
You can also get FREE CCNA and CCNP exam questions every day!
Pass the CCNP exam with The Bryant Advantage!
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