A method for establishing a secure communication between an industrial controller system and a communication partner unit (18; 18 1, 18 2, 18 3) over a communication link, wherein: in a commissioning phase, the industrial controller system accepts an incoming communication from at least one first communication partner unit (18; 18 1, 18 2, 18 3) over a communication link, and establishes a bidirectional communication channel (24 1, 24 2, 24 3) with the at least one first communication partner unit (18; 18 1, 18 2, 18 3); and in an operation phase subsequent to the commissioning phase, the industrial controller system communicates with the at least one first communication partner unit (18; 18 1, 18 2, 18 3) via the established bidirectional communication channel (24 1, 24 2, 24 3), characterized in that the industrial controller system, in the operation phase, blocks an incoming communication from a second communication partner unit (26 1, 26 2) different from the at least one first communication partner unit (18; 18 1, 18 2, 18 3); wherein, in the commissioning phase, the industrial controller system accepts an identified incoming communication request over the communication link from any first communication partner unit (18; 18 1, 18 2, 18 3), and establishes a collection of the first communication partner units (18; 18 1, 18 2, 18 3) based on the incoming communications received from the at least one first communication partner unit (18; 18 1, 18 2, 18 3) over the communication link; wherein, in the operation phase, the industrial controller system accepts an incoming communication over the communication link if the incoming communication pertains to one of the at least one first communication partner units (18; 18 1, 18 2, 18 3) according to the collection; wherein, in the operation phase, the industrial controller system blocks an incoming communication from every second communication partner unit (26 1, 26 2) that does not pertain to the collection, or for which no instruction is received from a user; wherein the industrial controller system switches to the commissioning phase automatically upon start-up of the industrial controller system; wherein the industrial controller system switches from the commissioning phase to the operation phase in response to an elapsed time window and/or in response to a user instruction; wherein the commissioning phase is shorter than the operation phase; and wherein the industrial controller system switches from the operation phase back to the commissioning phase in response to a pre-determined event, wherein the pre-determined event comprises a reboot of the industrial controller system. in a commissioning phase, the industrial controller system accepts an incoming communication from at least one first communication partner unit (18; 18 1, 18 2, 18 3) over a communication link, and establishes a bidirectional communication channel (24 1, 24 2, 24 3) with the at least one first communication partner unit (18; 18 1, 18 2, 18 3); and in an operation phase subsequent to the commissioning phase, the industrial controller system communicates with the at least one first communication partner unit (18; 18 1, 18 2, 18 3) via the established bidirectional communication channel (24 1, 24 2, 24 3), characterized in that the industrial controller system, in the operation phase, blocks an incoming communication from a second communication partner unit (26 1, 26 2) different from the at least one first communication partner unit (18; 18 1, 18 2, 18 3); wherein, in the commissioning phase, the industrial controller system accepts an identified incoming communication request over the communication link from any first communication partner unit (18; 18 1, 18 2, 18 3), and establishes a collection of the first communication partner units (18; 18 1, 18 2, 18 3) based on the incoming communications received from the at least one first communication partner unit (18; 18 1, 18 2, 18 3) over the communication link; wherein, in the operation phase, the industrial controller system accepts an incoming communication over the communication link if the incoming communication pertains to one of the at least one first communication partner units (18; 18 1, 18 2, 18 3) according to the collection; wherein, in the operation phase, the industrial controller system blocks an incoming communication from every second communication partner unit (26 1, 26 2) that does not pertain to the collection, or for which no instruction is received from a user; wherein the industrial controller system switches to the commissioning phase automatically upon start-up of the industrial controller system; wherein the industrial controller system switches from the commissioning phase to the operation phase in response to an elapsed time window and/or in response to a user instruction; wherein the commissioning phase is shorter than the operation phase; and wherein the industrial controller system switches from the operation phase back to the commissioning phase in response to a pre-determined event, wherein the pre-determined event comprises a reboot of the industrial controller system.