How do cluster nodes communicate with one another?
Cluster nodes can communicate via any of three different protocols: TCP/IP, SHM (shared memory), and SCI (Scalable Coherent Interface). Where available, SHM is used by default between nodes residing on the same cluster host. SCI is a high-speed (1 gigabit per second and higher), high-availability protocol used in building scalable multi-processor systems; it requires special hardware and drivers. See Section15.10, Using High-Speed Interconnects with MySQL Cluster, for more about using SCI as a transport mechanism in MySQL Cluster.