A control apparatus for controlling an object under control, comprising: a first network controller and a second network controller (110, 120) each configured for exchanging data according to a first communication protocol with another control apparatus (1B, 1C); a packet transferring part (170, 172, 174, 176), coupled to the first network controller and the second network controller (110, 120), for receiving a packet from one of the first network controller and the second network controller (110, 120) and outputting a duplicate of the received packet; and a packet processing part, coupled to the packet transferring part (170, 172, 174, 176), for executing a process; characterized in that the packet transferring part (170, 172, 174, 176) is configured to determine, based on a header information of the packet received by the one of the first network controller and second network controller (110, 120), whether to output the duplicate of the received packet, wherein the packet transferring part (170, 172, 174, 176) is further configured to output the duplicate of the received packet by the other of the first network controller and the second network controller (110, 120) to the other control apparatus (1B, 1C) when the header information indicates that the received packet is a transferable packet directed to the other control apparatus (1B, 1C), to output the duplicate of the received packet to the packet processing part when the header information indicates that the received packet is a transferable packet directed to the control apparatus, wherein the packet processing part is further configured to execute the process in correspondence with the duplicate of the received packet given from the packet transferring part (170, 172, 174, 176), and to discard the packet when the header information indicates that the received packet is not a transferable packet, wherein the packet transferring part (170, 172, 174, 176) is configured to determine, based on a physical address designated as a destination of a packet received, from another network controller of the other control apparatus, by the one of the first network controller and the second network controller (110, 120), whether to output the duplicate of the received packet. a first network controller and a second network controller (110, 120) each configured for exchanging data according to a first communication protocol with another control apparatus (1B, 1C); a packet transferring part (170, 172, 174, 176), coupled to the first network controller and the second network controller (110, 120), for receiving a packet from one of the first network controller and the second network controller (110, 120) and outputting a duplicate of the received packet; and a packet processing part, coupled to the packet transferring part (170, 172, 174, 176), for executing a process; characterized in that the packet transferring part (170, 172, 174, 176) is configured to determine, based on a header information of the packet received by the one of the first network controller and second network controller (110, 120), whether to output the duplicate of the received packet, wherein the packet transferring part (170, 172, 174, 176) is further configured to output the duplicate of the received packet by the other of the first network controller and the second network controller (110, 120) to the other control apparatus (1B, 1C) when the header information indicates that the received packet is a transferable packet directed to the other control apparatus (1B, 1C), to output the duplicate of the received packet to the packet processing part when the header information indicates that the received packet is a transferable packet directed to the control apparatus, wherein the packet processing part is further configured to execute the process in correspondence with the duplicate of the received packet given from the packet transferring part (170, 172, 174, 176), and to discard the packet when the header information indicates that the received packet is not a transferable packet, wherein the packet transferring part (170, 172, 174, 176) is configured to determine, based on a physical address designated as a destination of a packet received, from another network controller of the other control apparatus, by the one of the first network controller and the second network controller (110, 120), whether to output the duplicate of the received packet.