One of the lesser-known possibilities when using configuration files is the ability to include other configuration files. This can be especially handy when setting up a complex OpenVPN server, where multiple OpenVPN instances are offered simultaneously. The common configuration directives can be stored in a single file, whereas the connection-specific parts can be stored in a file for each instance. In this recipe, we will set up two OpenVPN instances, one using UDP and the other using TCP as the transport protocol.
Note that this option does not allow for the sharing of VPN IP address ranges between instances.
Set up the client and server certificates using the first 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.