/ip firewall raw
add action=drop chain=prerouting comment="Preventing UDP Flood Attack" dst-port=53 in-interface=pppoe-out1 protocol=udp
add action=accept chain=prerouting dst-port=53 in-interface=!pppoe-out1 limit=100,5:packet protocol=udp
add action=drop chain=prerouting dst-port=53 in-interface=!pppoe-out1 protocol=udp


Go to IP > DNS and disable "Allow Remote Requests"