A communication circuit in a network interface adapter for performing a checksum. One embodiment of the invention includes a network interface adapter having a network interface operable to receive a data packet having a header and a processor coupled to the network interface and operable to perform a checksum operation on each received data packet and operable to change the received data packet in response to the checksum operation. More specifically, the header in each received data packet is changed to a specific pattern of bits to indicate, in an easily recognizable manner, whether the received data packet has passed or failed the checksum.