| Here we have an example frame of an L2TP packet and its format. Notice that the L2TP header in this example is inside an IP and UDP header. Notice that the fields specify unique tunnel IDs and call IDs, and the UDP checksum is enabled to provide a higher level of error detection. The registered port number remains the same as L2F, but L2TP is considered version number two since it was designed to replace L2F.