Multicast is a network communication technique that sends information packets to a group of destinations over an IP network.
Releases earlier than vSAN version 6.6 support IP multicast and used IP multicast communication as a discovery protocol to identify the nodes trying to join a vSAN cluster. Releases earlier than vSAN version 6.6 depend on IP multicast communication while joining and leaving the cluster groups and during other intra-cluster communication operations. Ensure that you enable and configure the IP multicast in the IP network segments to carry the vSAN traffic service.
An IP multicast address is called a Multicast Group (MG). IP multicast sends source packets to multiple receivers as a group transmission. IP multicast relies on communication protocols that hosts, clients, and network devices use to participate in multicast-based communications. Communication protocols such as Internet Group Management Protocol (IGMP) and Protocol Independent Multicast (PIM) are the main components and dependencies for the use of IP multicast communications.
While creating a vSAN cluster, a default multicast address is assigned to each vSAN cluster. The vSAN traffic service automatically assigns the default multicast address settings to each host. This multicast address sends frames to a default multicast group and multicast group agent.
When multiple vSAN clusters reside on the same Layer 2 network, VMware recommends changing the default multicast address within the additional vSAN clusters. This prevents multiple clusters from receiving all multicast streams. See VMware KB 2075451 for more information about changing the default vSAN multicast address.