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Cisco CCNA / CCNP Exam Tutorial: Five Debugs You Must Know |
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To pass the BSCI exam and move one step closer to CCNP certification
success, you've got to know how and when to use debug commands
to troubleshoot and verify network operations. While you should
never practice debug commands on a production network, it's
important to get some hands-on experience with them and not
rely on "router simulators" and books to learn about
them.
When it comes to RIP, "debug ip rip" is the primary
debug to use. This debug will show you the contents of the
routing update packets, and is vital in diagnosing RIP version
mismatches and routing update authentication issues.
You know how to use the variance command to configure unequal-cost
load-sharing with IGRP, but IGRP has no topology table that
will give you the feasible successor metrics you need. With
IGRP, you need to use the "debug ip igrp transactions"
command to get these vital metrics.
Several factors are considered by OSPF-enabled routers when
it comes to forming adjacencies, including hello and dead
timer settings. If an adjacency doesn't form when you think
it should, run "debug ip ospf adj". The reason the
adjacency isn't forming is usually seen quickly with this
command's output.
Let's not ignore Layer Two! If frame relay mappings are not
forming according to your configuration, run "debug frame
lmi". This debug will allow you to quickly diagnose and
correct any LMI mismatches.
When it comes to PPP, it can be very frustrating to try to
spot a problem with a password or username. Instead of staring
at the configuration for 10 minutes, run "debug ppp negotiation"
and send a ping over the link. This command will help you
spot the router with the misconfigured username or password,
not to mention saving you a lot of time!
Effectively using debugs during your CCNA and CCNP exam study
will help you truly understand what's going on "behind
the command" - and it will really come in handy on that
day when your production network just isn't doing what you
(think) you told it to do!
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage,
home of free CCNA and CCNP 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”, visit the website and download
your free copies. You can also get FREE CCNA and CCNP exam
questions every day! Pass the CCNA exam with The Bryant Advantage!
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