NAT is a bane of any Demonware title. But in order to understand how to fix it you'll need some theory first.
Client A <> firewall <> NAT <> Internet <> NAT <> firewall <> YouDue to p2p nature of any Demonware title online you need to be able to connect to all clients in a session. Game itself will try to take care of NAT and firewall set up, but sometimes it fails, due to various reasons. Plus situation with NATs in general got worse in recent years, which negatively affects connectivity.
Nat traversal in game works according to the following table
| Open | Moderate | Strict | |
|---|---|---|---|
| Open |
✅ |
✅ |
✅ |
| Moderate |
✅ |
✅ |
❌ |
| Strict |
✅ |
❌ |
❌ |
So with a strict NAT you can only connect to other players with moderate or open NAT, but not to other players with strict NAT.
It should be noted that in 50% of cases situation with NAT can't be improved.
Mobile hotspots in 90% of cases will result in strict NAT that can't be fixed. In some other cases your ISP is to blame. If you understand what "forward UDP port to your PC/PS3" means - do exactly that.
If you need some help with that:
Again, google
Or use this guide -
https://www.howtogeek.com/112564/how-to-create-advanced-firewall-rules-in-the-windows-firewall/
Just remember that on Action step of creating a new rule you want to Allow the connection , not Block it.