IGMP Prompt-Leave

IGMP Prompt-Leave accelerates multicast devices' response to IGMP Leave messages.

When a host quits the multicast group G, the host sends the IGMP Leave message of G to the multicast device. Because of the report depression mechanism in IGMPv2, the multicast device cannot determine whether another host joins G. Therefore, the multicast device triggers a query on G. If another host joins G, the host sends the IGMP Report message of G to the multicast device. If the multicast device sends the query on G for several times, but receives no IGMP Report message from any host, the multicast device does not record information about G, and stops forwarding the multicast data of G to the relevant network segment.

If the multicast device is only connected to an access device that is enabled with IGMP proxy, when the access device leaves a multicast group G and sends the IGMP Leave message of G to the multicast device, the multicast device can identify that G contains no receivers and does not need to trigger the IGMP Query message. Then the multicast device can delete all records about G, and stop forwarding data of G to the relevant network segment. This is called IGMP Prompt-Leave.

After the multicast device is enabled with IGMP Prompt-Leave, the multicast device triggers no IGMP Query messages destined for the multicast group when the multicast device receives the IGMP Leave message from the multicast group. Then the multicast device deletes all records about the multicast group, and stops forwarding the data of the multicast group to the relevant network segment. In this manner, the multicast device responses faster to the IGMP Leave message.

The implementation of IGMP Prompt-Leave of (S,G) is same as that of IGMP Prompt-Leave of group G.

The IGMP On-Demand feature already includes the IGMP Prompt-Leave feature.