Addressing

IGMP

Also called membership report, leave, querier, MLD

How a device tells its network which multicast groups it wants: reports to join, leaves to go, queries to check.

A receiver joins a group by sending an IGMP membership report; when it stops, it sends a leave to 224.0.0.2. Memberships expire, so one device on each network, the querier (normally the router), sends a general query to 224.0.0.1 every so often and every member answers with a report. After a leave, the querier asks about that group alone (a group-specific query) in case another member remains. IGMPv3 adds sources: this group, only from that sender. IPv6 does the same with MLD, part of ICMPv6.

See it on real machines

Learn it on real machines.