Red Hat High Availability Add-On nodes communicate among each other using multicast addresses. Therefore, each network switch and associated networking equipment in the Red Hat High Availability Add-On must be configured to enable multicast addresses and support IGMP (Internet Group Management Protocol). Ensure that each network switch and associated networking equipment in the Red Hat High Availability Add-On are capable of supporting multicast addresses and IGMP; if they are, ensure that multicast addressing and IGMP are enabled. Without multicast and IGMP, not all nodes can participate in a cluster, causing the cluster to fail.