High Rate of STP topology changes on Port 48, 47, 46 and 45

[Juanf574]

good morning, i suddendly started seeing this error on my MS42 on an aggregate configuration.

does anyone have any clue?

Greatly appreciated.

[alemabrahao]

What device is connected to the ports? How is STP priority configured?

This can occur due to several reasons:

Port flaps between 2 switches: This can happen if the cable is faulty.
Delay in sending or receiving BPDUs: This could be due to high CPU usage or packet loss.

Here are some suggestions to troubleshoot and resolve this issue:

Check your cables: Ensure that the cables connecting the switches are not faulty.
Check your network design: Make sure that the Meraki switches are not ‘between’ two Cisco Catalyst switches. You ideally want a loop-free design where the downstream switches only connect to the core switch.
Configure your Cisco network for MST: If you’re using rapid-pvst, include VLAN 1 in the trunk between the Catalyst upstream switch and MS. This will ensure that the STP formatted BPDU makes it to the RSTP process.

[K2_Josh]

In the release notes for the most recent MS firmware it states this:
"

Ms4xx known issues

• When an SFP module is inserted/removed, BPDUs can be delayed leading to STP transitions in the network (predates MS 12)

"

According to the datasheet, it only lists the 24 port models as using the SFP ports as combo ports with the last four RJ45 ports, but my guess is that the datasheet is wrong about the 48 port variations and this could apply here.
https://meraki.cisco.com/lib/pdf/meraki_datasheet_ms22_ms42.pdf

[cmr]

MS4XX does not include MS42, that is a switch that went end of support over two years ago so it will be running an old software version.

[K2_Josh]

Yeah, my thought was that the MS42 might be running MS 12+ software and might still be affected by the same known issue as a switch in the MS4xx series.

[GIdenJoe]

Run a longer packet capture on those ports with the filter ether host 01:80:c2:00:00:00 and look at the bpdu's.

If your entire network consists of Meraki MS switches then make sure all your endpoint ports are in actual access mode.  Else you will have a topology change each time an endpoint comes online.

[K2_Josh]

100% agree. I would also review the STP Guard settings on all the ports to make sure it is intended and in alignment with Meraki documentation and best practices. And as always, remember that MX firewalls do not participate in STP.

Configuration:

https://documentation.meraki.com/MS/Port_and_VLAN_Configuration/Configuring_Spanning_Tree_on_Meraki_...

https://documentation.meraki.com/MS/Port_and_VLAN_Configuration/Spanning_Tree_Protocol_(STP)_Overvie... <- this links to a basic eLearning module that might be helpful, esp. if there are other switches in your network

Design docs:

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

https://documentation.meraki.com/MS/Meraki_Campus_LAN%3B_Planning%2C_Design_Guidelines_and_Best_Prac...