VEHICLE NETWORK SYSTEM, ELECTRONIC CONTROL UNIT, RECEPTION METHOD, AND TRANSMISSION METHOD

A vehicle network system includes a plurality of electronic control units that communicate through a bus in accordance with a CAN (Controller Area Network) protocol. A first electronic control unit transmits, through the bus, one or a plurality of data frames including an identifier (a MAC calculation target field type, a start flag, or the like) relating to data used for calculation for obtaining a message authentication code (MAC) indicating authenticity of transmission content. A second electronic control unit receives the one or plurality of data frames transmitted through the bus and performs a process for verifying the message authentication code in accordance with the identifier included in the one or plurality of data frames received.