ModYour friend sees "The host did not answer in time" or a similar error? Go through these checks in order. Most problems are solved by the first two.
1. Did the port really open?¶
Open the host's CS2MultiplayerMod.log and look for the line containing UPnP:. If it says
the router refused, or that no router answered, the port is closed. Allow UPnP on the router
or forward the port by hand - see Set up port forwarding.
2. Is it the right address?¶
- Over the internet, your friends need your public address from
api.ipify.org, not the local one that starts with
192.168.or10.. - Many providers change the public address from time to time. Look it up again before each session.
- The port your friends enter has to be exactly the port you host on.
3. Is the firewall letting it in?¶
Windows Firewall, and any antivirus with its own firewall, has to allow Cities: Skylines II.
Open Windows Security ▸ Firewall & network protection ▸ Allow an app through firewall,
click Change settings and make sure Cities2 is ticked for the network type your PC uses
(Private, Public, or both).
4. Are you testing from inside your own network?¶
Joining your own public address from a PC in the same network fails on many routers, even when the forward works. Test with a friend outside your network, or from a phone hotspot. Players in your own network use your local address instead.
5. Are you behind CGNAT?¶
Open your router settings and compare the public address shown there (WAN IP) with the one from api.ipify.org. If they differ, your provider shares one public address between many customers and port forwarding cannot work. Use one of the alternatives below, or let someone else host.
6. Is the port already in use?¶
If the game reports that the hosting port is already being used, close any other running host or game instance. You can instead choose another TCP port, but the host, every joining player, the firewall rule and the router forwarding rule must all use that same new port.
Alternatives to port forwarding¶
| Alternative | When it works |
|---|---|
| Steam Relay | Everyone has the Steam copy of the game. No port, no router setup. |
| IPv6 | Both sides have IPv6. Nothing to forward, but the router's IPv6 firewall has to let the port in. |
| Hamachi or another VPN | Works on every copy of the game, with no router setup. Every player installs the VPN program. |