For each cluster member node, the Oracle mDNS daemon uses multicasting on all interfaces to communicate with other nodes in the cluster.
Multicast Requirements for Networks Used by Oracle Grid Infrastructure
Multicasting is required on the private interconnect. For this reason, at a minimum, you must enable multicasting for the cluster:
Across the broadcast domain as defined for the private interconnect
On the IP address subnet ranges 188.8.131.52/24 and optionally 184.108.40.206/24
You do not need to enable multicast communications across routers.