CRS125 - Blocking DHCP

basically I wan to block DHCP traffic on my CRS125 from Edge Ports to stop unwanted DHCP traffic within the network but i keep getting bogged down.. on a router it would be a simple firewall rule but on CRS125 switch is a little different I presume Port Isolation? if anyone could point me in the right way that would be great!

Thanks
Rhodri

Take a look on the new CRS protocol level isolation example: http://wiki.mikrotik.com/wiki/Manual:CRS_examples#Protocol_Level_Isolation