Mixed CAN networks
"I think one of the biggest problems for car manufacturers is that they sometimes mix the networks used to send engine and braking info with the entertainment system."
Because the driver controls (steering wheel buttons, etc.) are part of both mobility and entertainment functions, and they don't want the added costs of either putting two CAN controllers/transceivers on the steering wheel system or having a gateway/filter (essentially a CAN firewall).
But firewall location #1 NEEDS to be that OBD II port.