Context
Configuring basic IGMP snooping functions in a VLAN enables the switch to create and maintain a Layer 2 multicast forwarding table, based on which multicast data packets can be forwarded accurately to receivers over the data link layer.
Unknown multicast flows are those that do not match any entry in the multicast forwarding table or match multicast forwarding entries with an empty outbound interface list. These flows are not requested by users. The default method that a switch uses to process unknown IPv4 multicast flows depends on whether Layer 2 multicast is enabled and which Layer 2 multicast forwarding mode is used:
If Layer 2 multicast is not enabled on the switch, the switch broadcasts unknown multicast flows in the corresponding VLAN.
If Layer 2 multicast is enabled, the switch broadcasts unknown multicast flows in the corresponding VLAN in MAC address-based forwarding mode and drops unknown multicast flows in IP address-based forwarding mode.
