Modular industrial automation device having - a central unit for processing control programs and at least one communication module, - a backplane bus system which is set up as an IPv4 subnetwork, - the central unit and the at least one communication module being connected to one another via the backplane bus system and each having - a router module (110, 120, 130) for implementing a communication protocol stack comprising network layer functions, - a first communication network adapter (111, 121, 131) for connecting the router module to the backplane bus system, - at least one second communication network adapter (112, 122, 132) for connecting the router module to a superordinate communication network set up as an IPv4 subnetwork or to a subordinate field level subnet set up as an IPv4 subnetwork, - a routing table (113, 123, 133) assigned to the router module, and - a routing configuration unit (114, 124, 134) for updating the respective routing table, - the routing configuration units being configured and set up to transmit routing information stored in the respective routing table to routing configuration units of other router modules, - the routing configuration units also being configured and set up to update the respective routing table on the basis of routing information which is received from routing configuration units of other router modules with regard to routes to IPv4 subnetworks assigned to other router modules, a default gateway and the connection between the associated router module and the backplane bus system. - a central unit for processing control programs and at least one communication module, - a backplane bus system which is set up as an IPv4 subnetwork, - the central unit and the at least one communication module being connected to one another via the backplane bus system and each having - a router module (110, 120, 130) for implementing a communication protocol stack comprising network layer functions, - a first communication network adapter (111, 121, 131) for connecting the router module to the backplane bus system, - at least one second communication network adapter (112, 122, 132) for connecting the router module to a superordinate communication network set up as an IPv4 subnetwork or to a subordinate field level subnet set up as an IPv4 subnetwork, - a routing table (113, 123, 133) assigned to the router module, and - a routing configuration unit (114, 124, 134) for updating the respective routing table, - a router module (110, 120, 130) for implementing a communication protocol stack comprising network layer functions, - a first communication network adapter (111, 121, 131) for connecting the router module to the backplane bus system, - at least one second communication network adapter (112, 122, 132) for connecting the router module to a superordinate communication network set up as an IPv4 subnetwork or to a subordinate field level subnet set up as an IPv4 subnetwork, - a routing table (113, 123, 133) assigned to the router module, and - a routing configuration unit (114, 124, 134) for updating the respective routing table, - the routing configuration units being configured and set up to transmit routing information stored in the respective routing table to routing configuration units of other router modules, - the routing configuration units also being configured and set up to update the respective routing table on the basis of routing information which is received from routing configuration units of other router modules with regard to routes to IPv4 subnetworks assigned to other router modules, a default gateway and the connection between the associated router module and the backplane bus system.