I wrote a simple server application in C. I managed to establish a connection using telnet. The problem is that I cannot reach the server if I specify public instead of local ip in telnet. I mean this worked
telnet 192.168.1.2 20600
while this didn't
telnet 188.8.131.52 20600
I read around the web this is a NAT configuration problem, but port 20600 seems to be open (according to http://www.canyouseeme.org/ and http://www.yougetsignal.com/tools/open-ports/). Besides I disabled firewall, so it can't be the cause of the failure...