stp_tcn_errors - high rate of STP topology changes on all switches

[allywenzel]

Over the Thanksgiving break we suddenly started seeing a high rate of STP topology changes around 5pm on 11/30. We were not in session and no changes or updates were made to the network since before 11/25. Does anyone have any ideas on where else to look? How to troubleshoot if no changes were made on the network, what would cause this problem?

Thank you.

[RaphaelL]

Hi ,

Where is the root bridge of your topology ? I would look at logs on that device and start from there.

[IvanJukic]

Hi @allywenzel ,

I do see this type of situation often. Usally something changes to cause this.  That log "stp_tcn_error" 'Topology Change Notification". Meaning the Layer 2 path or Spanning Tree is changing where all traffic should go. Most of the time, someone plugged in something. Or in your case, most likley a cable or device is misbehaving.

As @RaphaelL reccomended, check you RSTP Root and make sure it is it is in fact the Root.

Use the following guides to assist in the investigating and mitigation. 

https://documentation.meraki.com/MS/Monitoring_and_Reporting/Loop_and_MAC_Flap_Detection_on_MS

https://documentation.meraki.com/Architectures_and_Best_Practices/Cisco_Meraki_Best_Practice_Design/...