Modular industrial automation appliance having - a backplane bus system, - a plurality of functional modules connected to the backplane bus system that each comprise - a communication network adapter (111, 121) and - a functional unit (113, 123) for implementing a communication protocol stack, - a router module that is connected to the backplane bus system and that comprises - a communication network adapter and - a functional unit for implementing a router communication protocol stack, which functional unit is linked to said communication network adapter, characterized in that - the functional modules each comprise - a bridge element (112, 122) that is linked to the communication network adapter (111, 121) which it comprises and that has a first service access point for the functional unit (113, 123) for implementing the communication protocol stack and a second service access point that is associated with the backplane bus system, - wherein the communication protocol stacks of the functional modules (101, 102) comprise transport functions and wherein the communication protocol stacks of the functional modules (101, 102) comprise no routing functions, - the router module comprises - for each functional module (101, 102) a respective link element (132, 133) that links the functional unit for implementing the router communication protocol stack to the second service access point of the respective functional module via the backplane bus system, - wherein only the communication protocol stack of the functional unit of the router module comprises routing functions. - a backplane bus system, - a plurality of functional modules connected to the backplane bus system that each comprise - a communication network adapter (111, 121) and - a functional unit (113, 123) for implementing a communication protocol stack, - a communication network adapter (111, 121) and - a functional unit (113, 123) for implementing a communication protocol stack, - a router module that is connected to the backplane bus system and that comprises - a communication network adapter and - a functional unit for implementing a router communication protocol stack, which functional unit is linked to said communication network adapter, - a communication network adapter and - a functional unit for implementing a router communication protocol stack, which functional unit is linked to said communication network adapter, - the functional modules each comprise - a bridge element (112, 122) that is linked to the communication network adapter (111, 121) which it comprises and that has a first service access point for the functional unit (113, 123) for implementing the communication protocol stack and a second service access point that is associated with the backplane bus system, - wherein the communication protocol stacks of the functional modules (101, 102) comprise transport functions and wherein the communication protocol stacks of the functional modules (101, 102) comprise no routing functions, - the router module comprises - for each functional module (101, 102) a respective link element (132, 133) that links the functional unit for implementing the router communication protocol stack to the second service access point of the respective functional module via the backplane bus system, - wherein only the communication protocol stack of the functional unit of the router module comprises routing functions. - for each functional module (101, 102) a respective link element (132, 133) that links the functional unit for implementing the router communication protocol stack to the second service access point of the respective functional module via the backplane bus system, - wherein only the communication protocol stack of the functional unit of the router module comprises routing functions.