This problem is caused by wrong firewall or router settings in 99% of all cases!
1. Configure your router (if you are using one)
Most routers have a web interface which can be accessed with your browser.
A common address for it is
http://192.168.0.1.

However there are many routers which use other addresses.
Please check the manual of your router for details.
Contact the person who setup your router/internet if you need login data (or check the manual for defaults).
What you have to setup is
port-forwarding. CS2D uses the
UDP protcol and
UDP Port 36963
Unfortunately we can't provide information here how it works because it depends on your router.
So please either read the manual of your router or try to get info from the internet.
For example at
www.portforward.com
As alternative you can activate the
DMZ Host option if you don't manage to setup port-forwarding properly.
However this is a security risk and not recommended unless you are using a good software firewall.
2. Configure your firewall(s)
Make sure your firewall allows CS2D to access the internet!
You have to grant full internet access (incoming and outgoing) for
CounterStrike2D.exe and - if possible - allow all traffic on
UDP Port 36963!
Also make sure that Windows Firewall doesn't block CS2D! Read the
Windows Firewall article at Wikipedia!
3. Further problems and information
- Make sure that "Offline/LAN" (sv_lan) is DISABLED (0) when you're running a server

- Make sure that you see the IP of your server in the CS2D serverlist
- Restart your server/pc (not just CS2D) completely if your server's IP does NOT appear in the serverlist (go to cs2d.com/servers to see if your server is listed
- Start your server with the commandline parameter -realport if nobody can join and if the wrong port is listed in the serverlist (only happens with routers)
- Port 36963 is default. You can also configure everything for another port and use this port for your server
- Do not try to play CS2D when using a proxy. It will probably not work or it will be too slow
- Read this guide/checklist if you still have problems!
ATTENTION: Testing from within the same network might fail!
It is possible that people from within the same network/internet connection (e.g. 2 PCs connected to the same router, one hosting, other one viewing the serverlist) can't see each other.
This does NOT mean, that nobody sees your server! It can be caused by wrong router settings and many other things. It might work perfectly well for everyone outside your network!
Please ask someone who is not using the same internect connection to check if he sees your server!
Still having trouble? Please read
"My server is not in the serverlist" as well!