Some settings are missing in openvpn.conf for IPv6.
The client receives no IPv6 address.
server-ipv6 [IPv6 net]
tun-ipv6
push tun-ipv6
ifconfig-ipv6 [IPv6 address] [IPv6 net]/64
ifconfig-ipv6-pool [IPv6 addresspool]/64
Is there an IPv6 support for OpenVPN planned ?