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Does any one have any suggestions on how the above can be done?

Here's what I have tried so far -

1. Set up DHCP server on <intnet>. Attach eth0 of both machines to <intnet>, DHCP clients. They get 2 ip addresses on the same subnet (192.168.56.100 and 192.168.56.101) .. they can ping each other, they can see each other just fine. No multicast between them.

2. Attach eth0 of both machines to "Host Only network". The host has a IP address of 192.168.9.1, the 2 guests get 192.168.9.100, 192.168.9.101 ... each can ping the other two just fine. No multicast between them.

I have tried doing everything I know. Setting net.ipv4.icmp_ignore_all=0, net.ipv4.icmp_ignore_broadcasts=0, adding route 224.0.0.0 netmask 240.0.0.0 to each interface. MCAST is on (kernel settings), netstat -g says they are part of the 224.0.0.0 network ...

For what it's worth, the guests and the host are all CentOS 6.5. iptables service turned off, selinux disabled.

When I try to ping 225.0.0.37 (a random address on the multicast network) ... on a real network, every machine subscribed to that group responds to the ping. However, none of the guests do

Also, netstat -g says the RefCnt for the group is 1, when in reality it should be equal to 2 ...

Any ideas? Has anyone done something like this before?

Try setting the promiscious mode to "Allow Alll" in the adapter configuration of the VM