How Does IGMP Snooping Packet Suppression Solve the Image Pause Problem When There Are Many Multicast Users?

Figure 1 Traffic forwarding before and after IGMP snooping packet suppression is configured on Layer 2 multicast devices

On a multicast network shown in Figure 1, a large number of multicast users connect to Layer 2 multicast devices. IGMP snooping packet suppression is not configured on the Layer 2 multicast devices. If many users request multicast data, many IGMP Join messages are sent to the IGMP querier from Layer 2 multicast devices. The IGMP querier is burdened with IGMP Join messages and even drops some IGMP Join messages when the rate of traffic exceeds its processing capability. As a result, some multicast forwarding entries fail to be generated, so matching multicast data cannot be forwarded to receivers. The multicast users then experience image pauses in the video programs they are watching.

This problem can be prevented by configuring IGMP snooping packet suppression on the Layer 2 multicast devices. After this function is configured, a Layer 2 multicast device forwards only one IGMP Report/Leave message for a group to the IGMP querier in the following scenarios: When the first member joins a multicast group or a host sends a Report message in response to an IGMP Query message, the Layer 2 device forwards a Report message to the IGMP querier. The IGMP querier then creates or maintains the matching forwarding entry based on the Report message. When the last member of a group leaves the group, the Layer 2 device forwards a Leave message to the IGMP querier. The IGMP querier then deletes the matching forwarding entry. This mechanism greatly reduces the number of packets sent to the IGMP querier, thereby reducing the load of the IGMP querier and ensuring quality of the video-on-demand service.