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IGMP allows a host to register group memberships with the local querier router to receive any datagrams sent to this router and targeted to a group with a specific IP Multicast address. The protocol also allows a router to learn the existence of group members on its directly attached networks. The router periodically sends a general query message to each of its local networks. Any host that is a member of any multicasting group identifies itself by a sending a response.
IGMP Snooping uses IGMP messages to prune group membership per port within a VLAN. The switch listens to group reports for each port and builds a database of multicast group members per port. Only those ports that are specified in the database receive multicast traffic, instead of all the ports in the VLAN.
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