iptables: Duplicating/Forwarding ports

Question

I\'m trying to connect to MySQL (Port 3306) from a network which blocks this port. But there is another port 110 open which I can use for this case. I\'m using MySQL for other a

Answer 1

When forwarding ports on ubuntu using iptables, you must:

• make a backup of your firewall settings

sudo iptables-save > iptables.backup

• make sure the entry port is open

sudo ufw allow 110/tcp

• add a prerouting rule in your firewall

sudo iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 110 -j REDIRECT --to-port 3306

Notice the use of -i eth0. This routes port 110 to 3306 on network eth0. To check all connection of your machine, use ifconfig.
If your machine is connected to multiple networks, you must use -i or it will not work!

• if you mess something up you can clean the NAT routing table with

sudo iptables -F -t nat

or restore iptables

sudo iptables-restore < iptables.backup