WHY? Here is the general ideea why this feauture request have come. http://forum.mikrotik.com//viewtopic.php?p=23554
FEAUTURE REQUEST(very simple I think): Can you do that the entries in ARP TABLE (/ip arp) can be modified, from D(dynamic) to fixed, or manual? So that when user with that MAC address changes his IP cannot access network, because his MAC address is already bind to another IP. And anther important thing is a feauture that will log when users tries to change his IP. I think you understand what I wanted to tell.
is this is posibile to do, if so, pls tell when this feauture will be available, in what version?