Access LXC container from PPtP tunnel?

I have two Omnias connected together with a PPtP tunnel.

On the PPtP server, I’m running an LXC container, but I can’t ping it from the PPtP client Omnia (nor from any hosts connected to that one). The PPtP server gives out addresses from the same subnet the server is in.

How do I configure that? Do I have to add some route or iptables rule? I can ping other “physical” clients connected to the server Omnia.