Port stuck in STP blocking state with BLK*(Loop_Inc)

A port is stuck in STP blocking state with BLK*(Loop_Inc).

Possible Cause

This situation occurs when the loop guard is configured on the port and the port stops receiving BPDUs. This is supposed to prevent loops when unidirectional link failures occur. However, the port is put into a BLK* (Loop_Inc) state. Use the following commands to confirm the details of the STP port state for the port:

•show spanning-tree interface <id> detail

•show spanning-tree interface <id>

Solution

Check the native VLAN configured at both ends (ports) of the link. Ensure that they have the same native VLAN. Once the native VLANs are synchronized, the port moves out of the inconsistency state.