Chapter 7: Spanning Tree Protocol (STP) 127
Section 7-4
You might have to troubleshoot a network that is foreign to you, or one that is not com-
pletely documented. In this case, you need to get an idea of the current active STP topol-
ogy, especially the root bridge location.
1. Find the root bridge.
a. Choose a switch to use as a starting point.
Ideally, you want to start out on the root bridge at the “top” of the STP hierar-
chy. If you don’t know which switch is the root for a given VLAN, any switch
will do as a starting point.
b. Display the root ID, local BID, and root port:
(exec) show spanning-tree vlan vlan
An example of the Supervisor IOS command follows:
switch# show spanning-tree vlan 534
Spanning tree 534 is executing the IEEE compatible Spanning Tree protocol
Bridge Identifier has priority 49152, address 0005.32f5.45ef
Configured hello time 2, max age 20, forward delay 15
Current root has priority 8000, address 00d0.0457.3a15
Root port is 67, cost of root path is 3006
Topology change flag not set, detected flag not set, changes 132
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0
Fast uplink switchover is enabled
Stack port is GigabitEthernet0/2
Interface Fa0/1 (port 13) in Spanning tree 534 is FORWARDING
Port path cost 3019, Port priority 128
Designated root has priority 8000, address 00d0.0457.3a15
Designated bridge has priority 49152, address 0005.32f5.45ef
Designated port is 14, path cost 3006
Timers: message age 0, forward delay 0, hold 0
BPDU: sent 2967446, received 0
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