Something basic...
1. From the controllers management GUI can you click on the Controller tab (up top) ---> (left side menu) select Network tab ---> Utilities
2. Target IP Address:
3. Check off "Use specific source interface"
4. In the drop down select the interface that is listed as "MGMT plane only"
5. Press the Ping button
See if the controllers management interface can reach the RADIUS server.
Doug Hyde
Director, Technical Support / Extreme Networks