10-26
Bridging—Transmitting Non-IP Traffic or Merging Two Networks
Troubleshooting Spanning Tree
Caution The debug spanning-tree events and debug spanning-tree bpdu
commands are particularly draining on the processor.
You can also use the BPDU debug commands to determine whether interfaces
are actually participating in the spanning tree. If interfaces are not receiving
BPDUs at all, you should check the running-config for an inadvertently applied
BPDU guard or filter.
Addressing Common Spanning Tree Problems
Problems with spanning tree include slow convergence and routers selecting
the wrong primary connection.
Some problems may be caused by other switches on the local network.
You can view information that will help you troubleshoot with this enable
mode command:
Syntax: show spanning-tree [<bridge group number>] [realtime]
You enter the command without any options to view the following spanning
tree information for all bridge groups:
■ root ID
■ timers
■ bridge ID
■ interfaces:
•role
•status
For example, Figure 10-6 displays the spanning tree instance for bridge
group 1.
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