Wouldn't work directly here, as "ip fou add" reserves a local port, while in OP's case it's a reserved remote port. And reserving local port 53 in case of 53<->

Wouldn't work directly here, as "ip fou add" reserves a local port, while in OP's case it's a reserved remote port. And reserving local port 53 in case of 53<->53 packets would kill dns resolution. With an extra iptables rule should work though: iptables -t nat -A PREROUTING -s my.server -p udp --sport 53 -d DNAT --to 127.0.0.1:5555 ip fou add port 5555 ipproto 4