Let me prefix this by saying I'm not entirely clear on how multicast works. I have the gist of it, but not the underlying functionality.
A customer has configured a RHEL6 cluster between two Jboss nodes. Multicast is configured and I can ping 224.0.0.1 getting a response from both servers in the group. What I cannot do is ping each individual multicast IP assigned to each server.
Example:
Server 1 is 225.5.5.5 and server 2 is 225.5.5.6. I can ping neither of those IPs from the other.
Is this what I should expect to see? Only being able to ping the 224.0.0.1 IP and not the others? Am I supposed to configure the route to be on the same subnet as the multicast IPs or does 224.0.0.0 cover all subnet ranges?
Best Answer
You can only ping, via multicast, hosts which are subscribed to the multicast group which you are pinging. You need to be careful about which multicast groups you use, and, in general, you should use multicast groups from the administratively scoped range of
239.0.0.0/24, otherwise you risk stepping on registered groups which other software may be using.Normally, servers will send traffic to, not join, a multicast group. The multicast group is the destination address, and the source address is the regular IP address of the server.
Each host which wants to join a multicast group needs software which joins the specific multicast group, and the point of multicast is that multiple hosts join the same group to receive the same traffic which is only sent once from the multicast source.
Multicast will not leave the layer-2 domain (cross a router) unless you have multicast routing properly configured on all the routers in the path, which is why you can't multicast on the Internet unless you have a tunnel through which the multicast can travel.