Thank you for the idea! This is what I was looking for. I'll be giving a try to: mrouted protocol to set up my OSPF. But I will also give a try to the bridge configuration over the gif tunnel.
You can not route broadcast traffic and multicast traffic is only routable if you are running a multicast routing daemon on the concentrator. Maybe it is easier to use gif(4) interfaces and bridge(4) the together. In that case they behave like a local LAN and multicast and broadcast will just work.
