Re: Whoa, hang on
What subnets? Or for that matter what Wifi or Bluetooth? In the context of the avionics there isn't any.
But there are data diodes and gateways and things like that to ensure total isolation of passenger crap from real systems.
It's not like it's exactly complicated to implement a hard one way link to feed speed/altitude/heading/location with zero possibility of anything going the other way.