To analyze the STP topology, follow these steps:
Step 1. Discover the Layer 2 topology. Use network documentation if it exists or use the show cdp neighbors command to discover the Layer 2 topology.
Step 2. After discovering the Layer 2 topology, use STP knowledge to determine the expected Layer 2 path. It is necessary to know which switch is the root bridge.
Step 3. Use the show spanning-tree vlan command to determine which switch is the root bridge.
Step 4. Use the show spanning-tree vlan command on all switches to find out which ports are in blocking or forwarding state and confirm your expected Layer 2 path.