Your Cisco CCENT and CCNA exams will test your ability to troubleshoot a network, and so will your real-world job as a network admin. From experience, I can tell you that the #1 rule of thumb to remember when you begin troubleshooting is…
Troubleshooting Starts At The Physical Layer!
Excuse the exclamation point there, but this is a very important concept that can save you a great deal of time and wasted effort. When you begin troubleshooting, make sure everything's working at the Physical layer of the OSI model. That's a format way of saying...
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Is this thing on?
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Is the right cable in use?
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Has the cable come loose just enough to bring things down?
That first bullet point is self-explanatory, so I'll leave that one alone. When it comes to the right cable, remember the basics:
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Crossover cables are required to connect switches for trunking
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Rollover cables are required to connect a laptop to the Console port of a router, and you may need an adapter to use a rollover cable with your laptop
Regarding that second bullet point, make sure that you have the rollover cable connected to the router's Console port, not the Auxilary port. It's quite easy to connect the rollover cable to the Aux port mistakenly, because those two ports are right next to each other on many Cisco routers, and they both accept RJ-45 connectors.
If you sit down at the console after connecting to a router and you see some unexpected output, perhaps a password prompt where there shouldn't be one, I can practically guarantee you connected your rollover cable to the Aux port. It happens to all of us. :)
Once we’ve checked our cables, we can use Cisco Discovery Protocol to ensure that the network’s routers and switches are connected the way we think they’re connected! We’ll look at CDP in the next installment of my exclusive Cisco CCENT / CCNA certification exam tutorial series!
