Finding Root Bridge

12beatechie

Hi,
I have a scenario here:
4 switches connected in a loop and running STP as shown below (Assume all the switches are configured correctly).

A <

---

> B <

---

> C <

---

> D <

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> A

My question is how do we find out which switch is the root bridge if there is only one PC connected to Switch A?

I understand that we can run the command "show spanning-tree" and "show cdp neighbor details" on Switch A to troubleshoot. But is that enough to find the root bridge?


Thanks in advance!

networker050184

When you use the show spann command it will tell you the the mac of the root and what port it is recieving bpdus from the root on. If the bridge is the root it will say this bridge is the root.

12beatechie

You mean if I issue the show spanning-tree command on Switch A it will show me the mac for all the 4 switches?

networker050184

Do you have any switches?? If you lab this situation yourself you will see the output. Issue the show spann command and it will give you the proper output to find the root. It will specifically tell you the id of the root. If the switch you are in is the root it will say this bridge is the root.

Mikdilly

If you did a show mac-address-table after the show spanning-tree and looked to see if any of the mac addresses listed matched to the root bidge's mac address and then got the interface associated with that mac address you could then do a show cdp neighbor to find out the name of the switch that is the root bridge.

nice343

show spanning-tree root

the root bridge will be labeled. one per vlan

on the root bridge it will say

This is the root bridge