A method is provided for use with an Ethernet Media Access Controller (MAC) and a look-up memory external to the MAC, the method determines whether to accept or to reject an Ethernet packet which is decoded by the MAC into a serial data (SRD) signal stream and a serial data clock (SRDCLK) signal, the method comprises the steps of: converting the SRD signal stream into byte frames and loading the frames into a receive FIFO of the MAC; while the receive FIFO is being loaded, producing by the MAC, a boundary delimiter (BD) signal stream which delimits the frame boundary of each byte frame; while the receive FIFO is being loaded, providing the SRD signal stream, the SRDCLK signal and the BD signal stream from the MAC to the look-up memory; while the receive FIFO is being loaded, determining whether a prescribed field in the packet matches information stored in the look-up memory; while the receive FIFO is being loaded, informing the MAC by the look-up memory whether a match has been detected.