Have you ever felt that internet access suddenly feels slow? it could be that someone is naughty who uses our public router IP as a DNS server,
usually this is indicated by the high upload speed to the internet, to avoid this we simply use the script below.
/ip firewall filter
add chain=input dst-port=53 in-interface=WAN protocol=tcp action=drop
add chain=input dst-port=53 in-interface=WAN protocol=udp action=drop
Credit: www.o-om.com