32.1.2 IGMP snooping and MLD snooping synopsis

Layer 2 switches forward multicast traffic to all ports within a VLAN. Therefore, when multicast is used on a network to which a Layer 2 switch is connected, unnecessary multicast traffic might be sent to ports that have no multicast traffic recipients.

IGMP snooping and MLD snooping monitor IGMP or MLD messages and forward multicast traffic to ports to which recipients are connected. This functionality can be used to suppress the forwarding of unnecessary multicast traffic for more efficient use of networks. The following figure gives an overview of IGMP snooping and MLD snooping.

Figure 32-2 IGMP snooping/MLD snooping overview

To detect ports to which multicast traffic recipients are connected, the Switch monitors group management protocol packets. The group management protocol sends and receives group membership information between router hosts by using IGMP on IPv4 networks and MLD on IPv6 networks. The protocol detects packets sent from the host, indicating group participation and leave, to learn the connected ports to which multicast traffic should be forwarded.