To add port forwarding rules to forward port 3307 on 83.227.241.4 to port 3306 on 172.16.1.10, use the following iptables commands:
# /usr/sbin/iptables -t nat -A PREROUTING -p tcp -i eth1 -d 83.227.241.4 --dport 3307 -j DNAT --to 172.16.1.10:3306
# /usr/sbin/iptables -A FORWARD -p tcp -i eth1 -d 172.16.1.10 --dport 3306 -j ACCEPT