Check topology Layer 2 change real time in Cumulus (STP issue related)

In Layer 2 network topology, when there is changes within the topology or new device connected with Layer 2 feature, the spanning tree feature will calculated again which device is gonna be root switch, which port is gonna be designated port, alternate port, etc.

In Cumulus, we can check which port is triggered by that changes, and the status at all port in that switch regarding of topology changes.

Use command: watch -n 1 “mstpctl showall | grep -Ei ‘topology change'”

You can see at the above picture.

• Time since topology change : time duration since the last topology change
• topology change count : amount topology change recorded start when it happened first time after there is no topology change
• topology change : status Layer 2 topology in real time if there is topology change or not (yes/no)
• topology change port : which port in the cumulus switch that getting topology change message
• last topology change port : the last port in the cumulus switch that getting topology change message

This command is useful when we getting STP/Loop issue but we cannot found where is the device in the Layer 2 network that triggered this event. With this command we can trace the port that getting topology change message, check the responsible device on that port, and so on. After that we can verifying that there is no topology change again in the network which this cumulus switch is connected.