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Hunting down the root bridge

Need to find out which switch is the root bridge for my STP domain, I have the mac address of the root from the "show spanning tree" command, now what is the quickest way to find what device it belongs to without going through and doing the "show spanning-tree, show version, etc" on every layer 2 device in the network? Thanks in advanced.

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Gold

Re: Hunting down the root bridge

You are still going to have to go though a number of switches but if you are lucky not all of them. You should see the port that the root bridge is connected to your switch in the show spanning tree. Just a mater of show cdp nei on the port and continue your way back

New Member

Re: Hunting down the root bridge

This may save you some time. If your goal for finding the current root is to ultimately change it to another switch, you may be able to get away with lowering the default priority on the desired root, i.e. 4096 and also chose a second switch to be a "back-up" root by setting it's priority higher then the desired root but lower then the default, i.e. 8096. Assuming you are running PVST, that will have to be done for each VLAN. In the event of a root failure, you'll at least know which switch will take over as the root bridge during the election process. If the priority of the current root bridge is in the 32768 range (+/- 5 or so)then odds are the bridge priorities weren't changed from the default, so the election of the root was based off the MAC address, since all bridge priorities default to 32768.

If that isn't your situation, then you'll be stuck performing a show mac-address-table xxxx.xxxx.xxxx (where the x's are the root bridge mac address) over and over to trace it through your LAN. Best advice would be to document the base mac for each network device as you trace the root so you have it on file.

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