I coded a little client-server and tested on my own machine using my private IP. It works, it connects fine and successfully runs a ping command. I rented a VPS and put the server to run in there and tried to connect to it and it successfully connected, but when I try to ping, the messages are never delivered.

My best guess is that the problem is that I'm using the university's WiFi and that the "PING" package is being dropped by the X.

Assuming I'm correct, my question is, who is X? And how do I solve this problem?

And if I'm not correct, what's happening? How does a public wifi differs from a private wifi?

Thank you!

Most likely a firewall at the cloud provider that is blocking ICMP packets. Could be the university WiFi, try testing some random address, say google.com, and see if it works.

Most corporate firewalls block ICMP packets, many university firewalls do as well. I guess the theory is that it makes snooping around the network a little harder.

Well, now I'm extra confused. I though it was much simpler like "change the port you are listening to 9090 and it should work".

Take any 1v1 turn-based strategy multiplayer game on Steam for instance. How do they do it?

When you say 'ping', are you talking about the ping command you run from the command line (which sends ICMP packets), or a 'PING' message in your own custom network protocol?

ICMP packets are very often blocked, custom protocols are sometimes blocked. For a custom protocol, port 80 (HTTP default port) is almost never blocked, so consider running your server process on port 80 during testing.

You know what guys, nevermind... my server works fine and I can communicate with it, there were a logic error in my ping command.

Let this post die silently while I leave without being noticed...