Group Membership Reports

When a host receives a group membership query, it identifies the groups associated with the query and determines to which groups the query belongs. The host then sets a timer, with a value less than the Max Response Time field in the query, for each group to which it belongs.

When the timer expires, the host sends a group membership report to the group address. When a multicast router receives a report, it adds the group to the membership list for the network and sets a timer to the group membership interval. The router calculates the group membership interval using the following formula of configurable IGMP values:

( query interval x robustness value ) + query maximum response time

If this timer interval expires before the router receives another group membership report, the router determines that the group has no members left on the network.

IGMPv3 supports an extended report format you can use to report multiple groups and source lists in a single report.

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