Good day all, I had a similar issue and would just like to share what resolved it for me. After getting a radius error stating in the logs stating that "The RADIUS Request message that Network Policy Server received from the network access server was malformed." I did a verbose packet capture and found that the packet was indeed not well formed and seems to be missing some data. Turns out this was caused by a Bad MTU size, since my radius server sits in the cloud and is reached via VPN. So the upstream provider used a MTU size of 1400 and Meraki MX by default uses 1500. as you can imagine this caused some issues with the radius packets. After logging a request for Meraki to change my MTU size to 1338, everything started working with Radius again. Here is an article about changing the MTU size for Meraki. https://documentation.meraki.com/zGeneral_Administration/Tools_and_Troubleshooting/Troubleshooting_MTU_Issues I ran this ping to test and kept lowering the MTU until I found the correct combo that produced a successful ping response. ping "My Radius Server" -l 1472 -f Hope this helps someone.
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