OpenVPN supports on-the-fly compression of the traffic that is sent over the VPN tunnel. This can improve the performance over a slow network line, but it does add a little overhead. When transferring uncompressible data (such as ZIP files), the performance actually decreases slightly.
If the compression is enabled on the server but not on the client, then the VPN connection will fail.
Set up the client and server certificates using the Setting up public and private keys recipe from Chapter 2, Client-server IP-only Networks. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.11. The client was running Fedora 22 Linux and OpenVPN 2.3.11. Keep the configuration file,