Java multicast and linux routers

I'm trying to multicast using the demo in the java tutorial and a linux
router, but while the regular datagram work, the multicast doesn't!

Why is thing happening? I've tried with coyote linux, freesco and bsdrouter, but seems like they don't route the packets.

Am I missing something?

Also, I've read that different kinds of multicast protocols exist. Which one is the Java one?

Thanks!
Saverio J(ava) Miroddi