I see now that both your sites have ipv6, i missed that point :-). But why do you want to tunnel ipv4 over an ipv6 tunnel? Just use a normal ipv4-vpn using OpenVPN? If you want to add complexity to the whole thing (for fun that is, as it makes no sense) you can use the ipv6 addresses of your vpn-gw's. But the whole thing seems very strange if you have ipv6-subnets on both sites. Just add ipv6 on client-net, and they will have direct access to each other. If you need secure communication between who specific clients, it is a totally different matter. -Anders