Send message by modbus Tcp over internet.

I am using modbus Tcp to send message from PLC M241 to PLC M251 of Schneider.
In local Lan, I sent and received message successful.
Now i want to send and receive message over internet.
How should i setup?
I opend port 502 and 8080 for two PLC.
Thank you!
Sending Modbus TCP data via the Internet directly is not advisable. Modbus TCP is not encrypted or protected in any way any anybody could read the message and change the data. You also run the risk of exposing your PLCs to attacks via the Internet. A better way to do this would be via some form of VPN that connects the two PLCs. VPNs provide secure encryption and protection of the data.