Spanning Tree Cert Question

I failed my CCNA by 10 points yesterday and am going to take it again next Monday (before this exam expires). There was one particular question on the test that is driving me nuts and I can't seem to find the answer, if anyone can help, I'd appreciate it. The question was a multi-question multiple choice scenario with simulated CLI. I had console access to 1 switch of about

6 on a switched network (with a couple of routers thrown in for good measure) So from this one switch, I needed to execute dubug or sho commands to provide the answers to the questions. The one that hung me up was "which switch is the root bridge?" To the best of my recollection, I only had host names for the switches to identify them. I know I can find the MAC of the root by doing a "show spanning-tree" - but how can I identify the host name by MAC or the root bridge by name? Anyone? Thanks!
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I'm not sure what information are given in this scenario, but I would try to do this task just like I described below.

There is a couple of things you have to do:

  1. show spanning-tree - gives you root bridge's mac
  2. show arp - gives you root bridge's ip
  3. show cdp neigh detail - gives you root bridge's port number
  4. finally you have to check the topology and find name of a switch which port number you found in step 3.

Of course for example in step 2 you have to use information from step 1, in step 3 from step 2 and so on.

Reply to
Slawomir Kawala

check it out.....

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using the above info and a little working out you'll find it.......

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you can see the host name using the-show cdp neighbors detail command-but first you gotta find its ip add or interface on which is connected

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You guys rock! Thanks for the input. The only snag I hit was using sho arp - the remote switches didn't have entries in the local arp table, but I got all of the ip addresses of adjacent switches from sho cdp neighbor detail, pinged those ip addresses, then read the MACs from the arp table. This seems like it's pretty convoluted for a ccna exam - but I guess that's what makes it so fun! Thanks again to all who posted.


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Hi, I failed the exam twice (809 and 821 scores) and I got the same question twice, but I couldn't figure out the answer either. I think it might have something to do with IP ARP, e.g. "show ip arp | (mac address)".

That's a dirty one...

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Maybe you should try "show mac-address-table" ...a lot faster imo.

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Damir Zagar

Or try, and use the archive section for information?

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