Specify the action to perform when the switch receives an unknown multicast frame. Unknown multicast frames are addressed to multicast groups for which the Switch has not recorded any group members. Select flooding(1) to send the frame(s) to all ports of the same domain. Select drop(2) to discard the frame(s). Select drop-vlan(3) to discard the frame(s) on the specific VLAN(s). Note: If the new action is NOT drop-vlan(3), the zyMulticastUnknownMulticastFrameDropVlan(1~4)k will be cleared. If the zyMulticastUnknownMulticastFrameDropVlan(1~4)k are all Zero, the action 'drop-vlan(3)' cannot be selected. Thus, to perform action drop-vlan(3) must setup zyMulticastUnknownMulticastFrameDropVlan(1~4)k first.