This is being done because the UDM-PRO web interface to set the MSS value for the device was not working for me. It was inconsistent at best and wrong most of the time. So I set the value directly ...
The UDM Pro and UDM Base are both supported ... If your TV box is connected to a downstream Ubiquiti switch: Go to Unifi Devices -> Click the switch the box is connected to -> Settings -> Click the ...