If I had the problem you describe, shouldn't the cluster work at first and then collapse after a couple of minutes? If so, this is not the case here. In my case it seems more as if the nodes don't join the same party for some reason.
WRT low level problems, I have tried a pair of small C-programs (I can post here if required) that create a multicast group and print messages (server side) that clients posted after joining the mcast group. That seems to work so far.
Cheers
Mobi.
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