STP Query (Reason for port unblock)

We used to receive alert related to STP Root when we go through the log we found STP Root was previously blocked but next log we can see it is unblocked.

What cause the reason the unblocking of a port?

Log Example:
Jan 1 04:55:21.754: %SPANTREE-2-LOOPGUARD_BLOCK: Loop guard blocking port Port-channel2 on VLAN0951.
Jan 1 04:55:21.763: %SPANTREE-2-LOOPGUARD_UNBLOCK: Loop guard unblocking port Port-channel2 on VLAN0951.

Port-channel2 is up, line protocol is up (connected)
Received 14988323 broadcasts (14651304 multicasts)

The reason for the unblocking of a port in this log example is Loop Guard. Loop Guard is a feature in Spanning Tree Protocol (STP) that helps to prevent network loops. When a loop is detected on a port, Loop Guard blocks the port to prevent the loop from causing network instability. Once the loop is resolved, Loop Guard unblocks the port, allowing traffic to flow through it again.

1 Like

@atulsharma Sir Thanks for the reply. I want to learn more to understand this with example. Please help with some scenario in class to understand the same.

yesterday we discussed about root guard and Bpdu guard in the class.
Loop guard and UDLD topics we cover in ENCOR module.

@atulsharma Thank you Sir.