Friend having trouble connecting to any online servers

[cocoasprinkle]

I'm posting here on behalf of my friend who recently wanted to join me and some others in a Ring Racers server. However, he's been completely unable to join any servers, regardless of the host. It often displays the error message that mentions the host needing to open port 5029, despite everybody else being able to connect to the host just fine, whether from the same country or not.
For context, this friend is from North Macedonia and the rest of the group is from the US, UK and Germany. He's also had issues with Slippi Dolphin before, which leads me to believe that this isn't just a Ring Racers issue, but if anyone has any potential leads then that would be hugely appreciated. Thanks!

 

[Eidolon]

There are a number of possible issues:

1. Their ISP is using Carrier-Grade NAT (CGNAT), which prevents NAT holepunching from working correctly both as a joiner and as a host. In these scenarios, if the host is behind NAT, they have to forward UDP port 5029 even if holepunching otherwise works for other joiners.
2. Their ISP is blocking or filtering traffic on port 5029, which would prevent connection to any server at all.

Slippi Dolphin also uses P2P for multiplayer like we do, and also uses STUN and holepunching to break through NAT, so it would be affected by the same issue. But, if they can't connect to any dedicated server in Ring Racers, then the problem is possibly #2, which we can't really help with. Dedicated servers do not have to forward ports because they are typically not behind NAT, i.e. they have a direct public IP address.

It is important to note that the in-game server list communicates directly with each server returned from the MS. So that server list will be empty if port 5029 is being filtered. If it is not empty, then it is not being filtered by the ISP.

Ultimately, while NAT holepunching works for a lot of scenarios, it is still important for the host to try to forward port 5029 if they know how to.