In my earlier post (OpenVPN in Ubuntu 14.04) I have gone through the steps to install OpenVPN in Ubuntu; that was only for IPv4. To enable IPv6 in OpenVPN do the followings:

OpenVPN Server IP : 2001:df2:ee00:ee00::10/64

2001:df2:ee00:abcd::/64 has been routed to the OpenVPN server host. That mean users connected via OpenVPN will get one prefix from 2001:df2:ee00:abcd::/64 block.

Step 1: We need to edit OpenVPN configuration file and enable IPv6 tunnel service

vi /etc/openvpn/server.conf

Add the following :

server-ipv6 2001:0df2:ee00:abcd::/64
push tun-ipv6
ifconfig-ipv6 2001:0df2:ee00:abcd::1 2001:0df2:ee00:abcd::2
push "route-ipv6 2001:0df2:ee00:ee00::2/64"
push "route-ipv6 2000::/3"

Step 2: Enable IPv6 forwarding:

echo 1 > /proc/sys/net/ipv6/conf/all/forwarding

Step 3: Reload OpenVPN Service

/etc/init.d/openvpn restart

Try connect your OpenVPN client. Test the IPv6 reachablity by accessing http://test-ipv6.com/

1. To make IPv6 forwarding persistent remember, in /etc/sysctl.conf uncomment:
net.ipv6.conf.all.forwarding = 1

2. Make sure that you route 2001:df2:ee00:abcd::/64 to you OpenVPN Server. I have done this from my cisco router

ipv6 route 2001:df2:ee00:abcd::/64 2001:df2:ee00:ee00::10