ModThis guide shows how to open a TCP port on your router so friends can join over the internet.
You may not need this at all
Port forwarding is only for direct connections over the internet.
- Steam Relay needs no port and no router setup at all.
- On the same network nothing has to be forwarded either.
- Over IPv6 nothing is forwarded, but your router's IPv6 firewall has to let the port in.
- Over Hamachi or another VPN nothing is forwarded.
- When hosting starts, the mod asks your router to open the port itself. Check first whether that worked - see Let the mod open the port.
The default port is TCP 25001. The host, every joining player, the firewall rule and
the router rule all have to use the same port.
Let the mod open the port¶
When you host with Direct Connection and LAN Only off, the mod asks your router to open the
port automatically (UPnP). The router's answer is written to the mod's log,
CS2MultiplayerMod.log in
%USERPROFILE%\AppData\LocalLow\Colossal Order\Cities Skylines II\Logs\. Look for the line
containing UPnP::
| Log line | Meaning |
|---|---|
UPnP: TCP port <port> forwarded to <address> automatically. |
Done. The line also names the public address your friends connect to. |
UPnP: The router refused to open TCP port <port> (...) |
The router has UPnP, but does not let this PC open ports. Allow it (below) or forward the port by hand. |
UPnP: No router answered. |
UPnP is switched off on the router, or the router does not support it. Switch it on or forward the port by hand. |
UPnP: The router accepted the request ... but does not report the mapping back. |
The router cannot be trusted to forward. Forward the port by hand. |
UPnP: Automatic port forwarding failed (...) or UPnP: No local network address ... |
Something went wrong while asking. Forward the port by hand. |
On a FRITZ!Box, UPnP has to be allowed for each device: open Internet ▸ Permit Access ▸ Port Sharing (German: Internet ▸ Freigaben ▸ Portfreigaben), edit your PC's entry and tick Permit independent port sharing for this device (Selbstständige Portfreigaben für dieses Gerät erlauben). Other routers usually have a single UPnP switch in their network settings.
What is port forwarding?¶
https://www.youtube.com/watch?v=WOZQppVNGvA
Setting up port forwarding¶
Forward TCP on your port to your PC's local IP address. The mod lists that address in its
log when hosting starts: Players on your network join via: <address>:<port>.
Set up port forwarding on these popular routers (third-party sites):
Your router not among them? Search for your router model plus "port forwarding" and you will find a tutorial.
Which address to give your friends¶
Your public IPv4 address, from api.ipify.org or your router's
overview page, together with the port. Not the local address that starts with 192.168. or
10. - that one only works inside your own network.
Many internet providers change your public address from time to time, for example once a day. Look it up again before every session instead of reusing an old one.