in an embodiment , a method for finding duplex mismatches in a copper based network , includes : detecting late collisions and cyclic redundancy check errors ; if a port is in auto - negotiation and up in half - duplex and over threshold late collisions have been detected , then informing the user of a duplex mismatch and suggesting to the user to set the port to full duplex ; and if the port is in forced full - duplex mode and over threshold crc errors have been detected , then informing the user of a duplex mismatch and suggesting to the user to set the port to auto - negotiations mode .