STP question

CCNAwannabe

Okay I cannot find any documentation in any of my books or the web so im going to ask you guys.. Say you have 5 switches all connected in a loop and you only have access to one of them through the console how could you tell which switch was the root switch? what command in particular. I assume it would start with a show spanning-tree but none of my sims support anything that has to do with stp.

Thanks,
Rob

Kaminsky

Each switch keeps a record of who it thinks is the the Root and it is forced to publish this as it sends it's own bpdu's around. So it will publish it's own mac and the root mac.

Can't remember the command off hand but think it's something to do with show spantree. Could be wrong. real rusty on stp. Seeing as I am still to sit my ccna thats not a good thing... revise, revise, revise.

EdTheLad

"show spanning-tree" will show you the mac address of the root bridge.There are two options you can either document your network well, so that you know the mac addresses of every switch,which is recommended.Or you can do "show spanning-tree" and follow the root port towards the root bridge.If you generally leave the default stp costs, then it might be possible by looking at the value of the designated root cost to work out which switch is
root by calculating the link costs.

GeorgeMcFly22

If you can make a TelNet connection to the other switches, you can also use "show cdp neighbors detail" (if all are Cisco)