Server: SuSE Linux 9.3
Client: Ubuntu Linux 5.10

I am trying to open up port 1194 so that I can set up a VPN connection. I have a server thats behind a router that I want to be able to connect into via an encrypted tunnel.

I have set up the router to forward port 22 TCP/UDP to the IP of the server for SSH login. I have also installed SSH on my server, and opened up SSH port 22 in the firewall on my server. I can connect easily through a standard SSH connection, and everything works great. When I run a port scan on the IP of my router (from an outside computer) it shows port 22 as being open. I am very happy with this set up.

I have set up the router to forward port 1194 TCP/UDP to the IP of the server for a VPN connection. I have also installed openvpn on my server, and opened up openvpn port 1194 in the firewall on my server. I cannot connect through my openvpn connection. When I run a port scan on the IP of my router it shows only only port 22 as being open. Port 1194 does not appear. I am very confused by this set up.

Here is my question: In order for a port scan to detect an open port, does it need to recieve a response from a computer? In other words, does port scanning check to see if there is a hole in the router to get through, or does it check to see if there is a hole in the router by getting a response from a computer? I am trying to figure out if it is my router that is causing the problem or my computer.

Final Note: I have taken down the firewall running on SuSE completely to see if that was the problem. However, it makes no difference whether the firewall is up or not. Only port 22 is shown during a port scan!

Try running a port scan on the firewall computer (SuSE) targeting the inside host (Ubuntu). That will tell you if the vpn port is open on the Ubuntu client.

For your general question, on port scans, if you look in the man page for nmap, you will see quit a number of scans that you can try, and the answer to your question depends on the type of scan you perform. Your firewall or the Ubuntu host could be configured to either reject or to drop requests.