Group Mask. Create a MLT abstraction layer to distribute traffic basd on (source, group) information of the multicast packet. The algorithm to pick the actual port nedds to generate a fairly random number for different combinations but a lways generate the same number for a given (source, group) pair. By default, the number of active ports of the MLT is used to MOD the pseudo-random number generated by the XOR of each byte of the masked group address with the masked source address.