Method for operating an automation system having a first control unit and at least one second control unit and at least one third control unit for carrying out at least one automation process and for controlling a plurality of field devices, and having an external data infrastructure having a message distribution module for conveying data communication between communication participants in a communication network (109, 115), comprising the following steps: defining a first communication network, detecting the control units (101, 103) of the automation system, assigning the first control unit and the second control unit to the first communication network and identifying the first control unit and the second control unit as first communication participants in the first communication network by means of the message distribution module in a first identification step, transmitting a first network message, during data communication between the first communication participants in the first communication network, from the first control unit to the message distribution module of the external data infrastructure in a first transmission step, identifying the second control unit as the first communication participant addressed by the first control unit in the first communication network by means of the message distribution module in a second identification step, forwarding the first network message transmitted by the first control unit to the second control unit by means of the message distribution module in a forwarding step, receiving the forwarded first network message by means of the second control unit in a receiving step, and defining a second communication network and identifying the third control unit and the first control unit and/or the second control unit as second communication participants in the second communication network by means of the message distribution module in a third identification step, wherein data communication takes place solely between first communication participants in the first communication network or between second communication participants in the second communication network. defining a first communication network, detecting the control units (101, 103) of the automation system, assigning the first control unit and the second control unit to the first communication network and identifying the first control unit and the second control unit as first communication participants in the first communication network by means of the message distribution module in a first identification step, transmitting a first network message, during data communication between the first communication participants in the first communication network, from the first control unit to the message distribution module of the external data infrastructure in a first transmission step, identifying the second control unit as the first communication participant addressed by the first control unit in the first communication network by means of the message distribution module in a second identification step, forwarding the first network message transmitted by the first control unit to the second control unit by means of the message distribution module in a forwarding step, receiving the forwarded first network message by means of the second control unit in a receiving step, and defining a second communication network and identifying the third control unit and the first control unit and/or the second control unit as second communication participants in the second communication network by means of the message distribution module in a third identification step, wherein data communication takes place solely between first communication participants in the first communication network or between second communication participants in the second communication network.