Split Brain

  Multicast problems:
     Switch dropping node from multicast group
     IGMP querier runs once per minute
     Slave probes missing master from 2nd missed heartbeat to timeout: unicast “limp-along” mode
  Network split:
     Set cluster_master_min_adv > 1 on clusters expected to have more than two nodes
     Heartbeat serial indicates more changes seen
     Self-declared master receives no traffic
     Dies seeing heartbeat on network re-establishment
  Crash:
     Slave node receiving probe responds with master address