Observe spanning-tree redundancy

Three Cisco switches form a triangle with two paths between the hosts.

Give switch one a lower bridge priority so it becomes the root for VLAN one.

On switch three, the root port forwards and the alternate port blocks.

Ping from one host to the other to check the starting path.

Shut down the root port on switch three to simulate a link failure.

The alternate port becomes the new root port and starts forwarding.

Ping again to confirm the hosts can communicate over the backup path.

Bring the original link up and check that the original port roles return.

Enable root guard on switch one’s port toward switch two.

A better priority from switch two puts the guarded port in a root-inconsistent state.

Restore switch two’s priority and check that the guarded port forwards again.

Finish with a successful ping to confirm the restored path.