In the course of this book we have already invoked openvpn several times from a command line. As a first example, we built a tunnel with a pre-shared key and a rather simple configuration file. Even though there are some other parameters set in the standard configuration file we used, the easiest command to start a tunnel with a static key is:

debian01:/etc/openvpn# openvpn --remote <IP of System B> --dev tun1 --ifconfig 10.3.0.1 10
.3.0.2 --secret /etc/openvpn/key.txt 

You see, it's very easy to connect two systems with an openvpn tunnel, when we know their IPs. All we need is a pre-shared key, a tunnel IP, and a decision on which device type to use.

If the second tunnel endpoint is a Linux system already provided with the pre-shared key /etc/openvpn/key.txt, then all we need to do to start our tunnel is enter the aforementioned command on system A, and enter the following command on system B:

/etc/openvpn# openvpn --remote <IP of System A>...