[jgroups-users] Multicast UDP without higher level protocols?

Greetings form Oregon!

I have a question about the higher level protocols when it comes to UDP multicast:

I was working on some existing code tracking down some instances of what appeared to be possibly a split brain.  Their configuration was only the lowest level multicast: (Sorry about the old style, just wanted to replicate exactly what they had)

UDP(mcast_addr=228.9.7.9;mcast_port=45599; ucast_recv_buf_size=128K;ucast_send_buf_size=128K;mcast_recv_buf_size=128K;mcast_send_buf_size=128K)

So I created a test where a JChannel was created connecting to "Docker-JGroups" cluster and periodically "ping" with channel.send(Message)  I'd then watch the channel view and the results of who replied for each hosts.

I'd then fire this up in a batch of docker containers (# ranging from 3 to 20)

I'd then tweak the host iptables to either drop or reject the multicast packets coming through the docker "network"  I'd see the individual programs cease to find each other and be running in their own instance.  That's good

Then I'd delete the iptables rule and I'd see them all join up again into a single network cluster? (By single cluster, I mean, all the hosts are responding to the JChannel.send() again)

I thought things like FD, MERGE and pbcast.GMS were required for all of that to work properly?  In fact the only thing I can tell is that when I have only UDP protocol setup, that each node thinks it's the cluster coordinator, and failure detection seems to be a little faster with all the other protocols combined, but I can't tell any difference otherwise?

Obviously I'm missing something basic - would you mind explaining why the behavior is so similar despite the fact that there's only one protocol configured with this particular configuration?

Thanks so much!

                                                                                                                                                                                    -Mike

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