If you're seeing a number of STP changes then something is occurring in the network that is causing STP to reconverge. If this is happening again and again, then this will cause the switches to be unable to contact their DNS servers (either due to high-CPU, or pure network traffic), so the DNS misconfiguration is likely a secondary symptom. I'd be checking your network for Layer 2 loops and ensuring that STP is appropriately blocking them (ideally you'd remove all the Layer 2 loops and use LACP for redundancy), and finding out where the changes in the network are occurring that are causing a STP reconvergence. You mention Blade Servers, and that would be one of my starting points, especially if they have an switch in the chassis which will be non-Meraki (I've seen plenty of issues here in the past - generally devices that don't running STP and thus create loops in the network if you're not careful). I'd take the time to review the network against the Meraki MS best practice guide, https://documentation.meraki.com/Architectures_and_Best_Practices/Cisco_Meraki_Best_Practice_Design/Best_Practice_Design_-_MS_Switching/General_MS_Best_Practices. And I'd pay special attention to the Spanning Tree elements of it: Keep the STP diameter under 7 hops, such that packets should not ever have to travel across more than 7 switches to travel from one point of the network to the other BPDU Guard should be enabled on all end-user/server access ports to avoid rogue switch introduction in network Loop Guard should be enabled on trunk ports that are connecting switches Root Guard should be enabled on ports connecting to switches outside of administrative control Tell us how you go.
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