Dell EMC SmartFabric OS10 User Guide Release 10.5.0

Unknown multicast flood control

The unknown multicast flood control feature enables the system to forward unknown multicast packets only to a multicast router (mrouter).

When you enable multicast snooping, OS10 forwards multicast frames, whose destination is already learned, to their intended recipients. When the system receives multicast frames whose destination is not known, it floods the frames for all ports on the specific VLAN. All hosts that receive these multicast frames must process them. With multicast flood control, the system forwards unknown multicast frames only to the interface that leads to the mrouter. The mrouter can then forward the traffic to the intended destinations.

For multicast flood control to work, you must enable both IGMP and MLD snooping on the system. By default, multicast flood control, IGMP snooping, and MLD snooping are enabled.

The following describes a scenario where a multicast frame is flooded on all ports of all switches. The switches and hosts in the network need not receive these frames because they are not the intended destinations.

With multicast flood control, multicast frames, whose destination is not known, are forwarded only to the designated mrouter port. OS10 learns of the mrouter interface dynamically based on the interface where an IGMP membership query is received. You can also statically configure the mrouter interface using the ip igmp snooping mrouter and ipv6 mld snooping mrouter commands.