What is the multicast address used for?

start of changePowerHA® SystemMirrorend of change uses multicast addresses for node failure detection, which indicates to the cluster manager when a fallover operation might be needed. A multicast address is also known as a class D address.

PowerHA SystemMirror uses a cluster health management layer within the AIX® operating system. This layer is called Cluster Aware (CAA). CAA uses AIX kernel-level code to exchange heartbeats over a network. This heartbeat exchange uses Fibre Channel adapters and uses disk-based messaging through the central repository for the cluster. CAA uses a multicast IP-based network communication mechanism to communicate between different nodes in a cluster.

start of changeIf you configure a linked cluster with multiple sites, you must specify one multicast address per site. A linked cluster contains nodes from sites at different geographical locations. Linked clusters do not require sites to share a repository disk or to support multicast communication.end of change

start of changeFor all other cluster types (non-site and stretched), only a single multicast address is needed for the entire cluster. A stretched cluster contains nodes from sites at the same geographical locations. Stretched clusters share at least one repository disk between sites.end of change

start of changeIf you do not provide the required multicast address, CAA creates one for you.end of change

For more information about multicast addresses, see the Multicast addresses topic in the AIX Information Center.