i'd have to test to see what it does. however, wan 2 of the mx i assume would be the comcast/cradlepoint wan IP under normal conditions? then if comcast fails the wan IP of the cradlepoint would now be the cell carrier IP?
but it would seem you're going to need port forwarding also on that cp device?
and perhaps not possible due to install location. but, could you instead land comcast on wan2 and use a usb modem connected to the mx250? that would eliminate the dual nat issue that appears would be the case when the CP is in front of the mx.
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