That's what I thought too, I really tried a lot of configuration client side, on different OS (linux, bsd...), but none was working reliably, even the provider

That's what I thought too, I really tried a lot of configuration client side, on different OS (linux, bsd...), but none was working reliably, even the provider preconfigured linux image. It might be client that are all broken or something else, to be honest I didn't investigate it further, as I don't need IPv6, I just wanted to be "ready" for the future.