A network device for a computer network, wherein said network device comprises - one or more communication channels, - at least one Physical Layer, PHY, chip, wherein said at least one PHY chip is configured for transmitting data in a raw data stream on said one or more communication channels, and - and at least one Media Access Control, MAC, chip which is configured ∘ for encapsulating data to be transmitted, the so-called transmission data, into frames, ∘ calculating a checksum, the so-called MAC checksum, for each of said frames, wherein the MAC checksum of a frame is calculated from the transmission data of said frame, ∘ writing the checksum of each frame into the corresponding frame, ∘ sending said frames to said at least one PHY chip for being transmitted by said at least one PHY chip via at least one of said communication channels of the network device, and wherein said at least one PHY chip is configured for receiving frames of said at least one MAC chip and to transmit the transmission data contained in said frames via its communication channel or via at least one of its communication channels, wherein the at least one PHY chip is further configured - to calculate, after receiving a frame from a MAC chip and before sending the transmission data of said frame in a raw data stream out to a communication channel, a checksum, the so-called PHY checksum, of the transmission data contained in said frame, and - to compare the MAC checksum of a frame with the PHY checksum calculated for this frame, and wherein the PHY chip is configured to transmit the transmission data contained in said frame via the at least one communication channel, if the comparison of the MAC checksum of a frame with the PHY checksum delivers identical values, and wherein the PHY chip or the network device containing this PHY chip is configured to execute at least one specified or specifiable action, if the comparison of the MAC checksum of a frame with the PHY checksum delivers values, which are not identical. - one or more communication channels, - at least one Physical Layer, PHY, chip, wherein said at least one PHY chip is configured for transmitting data in a raw data stream on said one or more communication channels, and - and at least one Media Access Control, MAC, chip which is configured ∘ for encapsulating data to be transmitted, the so-called transmission data, into frames, ∘ calculating a checksum, the so-called MAC checksum, for each of said frames, wherein the MAC checksum of a frame is calculated from the transmission data of said frame, ∘ writing the checksum of each frame into the corresponding frame, ∘ sending said frames to said at least one PHY chip for being transmitted by said at least one PHY chip via at least one of said communication channels of the network device, and wherein said at least one PHY chip is configured for receiving frames of said at least one MAC chip and to transmit the transmission data contained in said frames via its communication channel or via at least one of its communication channels, wherein the at least one PHY chip is further configured ∘ for encapsulating data to be transmitted, the so-called transmission data, into frames, ∘ calculating a checksum, the so-called MAC checksum, for each of said frames, wherein the MAC checksum of a frame is calculated from the transmission data of said frame, ∘ writing the checksum of each frame into the corresponding frame, ∘ sending said frames to said at least one PHY chip for being transmitted by said at least one PHY chip via at least one of said communication channels of the network device, - to calculate, after receiving a frame from a MAC chip and before sending the transmission data of said frame in a raw data stream out to a communication channel, a checksum, the so-called PHY checksum, of the transmission data contained in said frame, and - to compare the MAC checksum of a frame with the PHY checksum calculated for this frame,