SPANNING TREE LOOP GUARD FEATURE

As its name implies, Loop Guard is a method for ensuring that STP
loops never occur in a particular topology. Even though STP guards
against such loops as best it can, they could still occur because of
things like unidirectional link failures or switch congestion issues.
Loop Guard prevents loops conservatively by preventing alternate or
root ports from becoming DPs in the topology. If BPDUs are not
received on a non-DP, and Loop Guard is enabled, that port is moved
into the STP loop-inconsistent Blocking state, instead of the Listening /
Learning / Forwarding state.

Loop Guard operates only on ports that are considered point-to-point
by the spanning tree, and it cannot be run in conjunction with Root
Guard on an interface.

To enable Loop Guard, you can use the following global configuration
mode command:
spanning-tree loopguard default

Best Regards,
Deepak Arora