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  1. An IGMP-enabled router sends out several General Membership Queries at startup.
  2. Hosts that are members of specific multicast groups send Membership Reports back to the router to report their membership.
  3. The router receives the Membership Reports and builds lists of multicast group memberships for each attached network.
  4. The router sets an interval for each group's updates and sends a Group-Specific Membership Query with this information in the Maximum Response Time field.
  5. If router 'A' hears a query from another router (router 'B') on the same attached network, and router 'B' has a lower IP address, router 'A' will become a Non-Querier for that network. If, after a certain interval, router 'A' does not hear from router 'B' (the current Querier), router 'A' assumes the Querier is down and becomes the Querier for that network.


  1. When a host joins a multicast group, it sends a 'Membership Report' to the router.
  2. The router makes an entry in it's table and forwards the memberhsip report message.


  1. When a host leaves a multicast group, it sends a Leave Message to the router.
  2. The Querier router may, or may not send out a Group Specific Membership Query, based on whether or not the leaving host was the last host in the group.

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