This began when I made a server for the game Rust. I have 4 friends that were going to join, but only one person of the four is unable to join. I had port forwarded, to my knowledge (and I checked multiple times), correctly. He and I both tried opening the ports in windows firewall, disabling windows firewall, disabling our antivirus/antimalware apps, and some other minor tweaks, without success. When this didn't work we tried to narrow down the problem to see if it possibly had anything to do with Rust specifically. We both created Minecraft servers. Surprisingly, other friends were able to join both my server and his, while only he couldn't join mine. As well, I was able to join his server. Seeing as everyone else could join my server, and the 25565 port appeared open on every port checker website I tested, I definitely port forwarded correctly. It's almost as if something on my end is blocking him only, perhaps by blocking his IP, be it windows firewall, my router's firewall, Malwarebytes, or something else. Any ideas?