If you would like to verify that port forwarding is working correctly you can use a tool called netcat which is great for debugging all kinds of network issues. It allows you to easily read and write data over a network socket. You will need two computers (or a second virtual machine) in order to run this test and have some basic experience using the command line.
In this guide we'll show you how to use netcat to send data between two computers where one is connected to the VPN. We will call the computer connected to the VPN 'computer A' and the one not connected 'computer B'. The test will send data from computer B over the Internet to the VPN server and then through the VPN tunnel to computer A. By doing this you can prove that port forwarding is working correctly.
You will need netcat installed on both computer A and computer B. Computer A and B do not need to be running the same operating system. Netcat should be preinstalled on OSX and is available via most Linux package managers e.g. 'sudo apt-get install netcat'. On Windows you will need to download Netcat for Windows.
nc -l 40197
nc -l -p 40197
nc 188.8.131.52 40197
Once you have concluded the test stop netcat by pressing 'control-c' on both computers.