iptables -I FORWARD -p tcp -d 192.168.178.12 --dport 3306 -j ACCEPT
iptables -t nat -A PREROUTING -i lo -p tcp --dport 3306 -j DNAT --to-destination 192.168.78.12:3306
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE


iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             192.168.178.12       tcp dpt:mysql

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination