дарю, первая ссылка гугла, со второго запроса http://sourceforge.net/p/openvpn/openvpn/ci/master/tree/README.IPv6 On systems that allow IPv4 connections on IPv6 sockets (all systems supporting IPV6_V6ONLY setsockopt), an OpenVPN server can handle IPv4 connections on the IPv6 socket as well, making it a true dual-stacked server. Use bind ipv6only to disable this behaviour. On other systems, as of 2.3.0, you need to run separate server instances for IPv4 and IPv6.