A method in which first routers have an extended router function for a connection to a superordinate communication network, wherein second routers include a restricted router function for a connection to a subordinate field level subnetwork, where when further first routers are present, the router configuration units of the first routers each use priority values to check which first router has the highest priority value associated with it, where the first router having the highest priority value is configured as a superordinate router for a connection to a superordinate communication network so as to configure a modular control device of an industrial automation system that includes a central unit and at least one communication module that includes a respective integrated router, where router configuration units of the first routers detect available router functions and associated priority values of other routers.