Comment Re:so what is ipv6 good for? (Score 1) 236
You have to have multicast routing set up between you and the networks you want multicast to go to...and the clients have to 'subscribe' to your multicast group. They won't hear anything from you until they tell their local multicast router they want to talk to you.
So, yeah, multicast doesn't generally work unless you're on the same subnet. That said, here's a fun one to run under Linux:
ping6 -c2 ff02::1%eth0
Any hosts configured to respond to ICMP6 echo requests will send a reply. I once counted several hundred hosts on my VPS provider's network that way.