In this example all incoming traffic on port 80 redirect to port 8123
iptables -t nat -I PREROUTING --src 0/0 --dst 192.168.1.5 -p tcp --dport 80 -j REDIRECT --to-ports 8123
In case of forwarding
sudo iptables -t nat -I PREROUTING --src 0/0 --dst 10.0.3.10 -p tcp --dport 63001 -j REDIRECT --to-ports 3306 sudo iptables -t nat -I PREROUTING --src 0/0 --dst 10.0.3.20 -p tcp --dport 63101 -j REDIRECT --to-ports 3306