One of the most common problems in setting up OpenVPN is that the two OpenVPN daemons on either side of the connection are unable to establish a TCP or UDP connection with each other.
This is almost a result of:
- A perimeter firewall on the server's network is filtering out incoming OpenVPN packets (by default OpenVPN uses UDP or TCP port number 1194).
- A software firewall running on the OpenVPN server machine itself is filtering incoming connections on port 1194. Be aware that many OSes will block incoming connections by default, unless configured otherwise.
- A NAT gateway on the server's network does not have a port forward rule for TCP/UDP 1194 to the internal address of the OpenVPN server machine.
- The OpenVPN client config does not have the correct server address in its config file. The remote directive in the client config file must point to either the server itself or the public IP address of the server network's gateway.
- Another possible cause is that the windows firewall is blocking access for the openvpn.exe binary. You may need to whitelist (add it to the "Exceptions" list) it for OpenVPN to work.