Can a device process the report messages delivered after the maximum response time expires

The maximum response time of IGMP Query messages is used to control a host to send a Report message within the certain period. As long as the host sends a Report message within the maximum response time, the multicast routing entries required by the host are not aged and data forwarding is not interrupted.

The maximum response time configured on a device requires a host to send a Report message within a certain period. This is because entries on the device will time out and be aged. The initial timeout period is calculated as: Interval for sending general Query messages x IGMP robustness variable + Maximum response time. Zero-Packet-Loss cannot be guaranteed on the network and thus the network allows (IGMP robustness variable -1) times of packet loss as long as the host receives the last Query message and sends a Report message within the maximum response time. Then, the multicast routing entries required by the host are not aged and data forwarding is not interrupted.

If the host receives the Query message but sends a Report message after the maximum response time expires, and if the host is the only receiver of the group, data forwarding is interrupted though the device receives the Report message. This is because the IGMP entries on the device are already aged and deleted before the device receives the Report message. Data forwarding interruption can be avoided if the host sends a Report message within the maximum response time. The device, however, can process the Report message to create a new entry for data forwarding.

IGMP Report messages can be processed as long as the responser interfaces are configured with IGMP. IGMP Report message processing is irrespective of the maximum response time.

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