IGMP multi-instance allows a multicast device's interface to send and receive protocol packets based on the IGMP instance to which the interface belongs. When the interface receives an IGMP message, the multicast device identifies the instance to which the interface belongs and processes the message based on this instance's rules. When IGMP exchanges information with other multicast protocols, IGMP only notifies these multicast protocols in the instance.
For detailed IGMP message processing, see Principles of IGMP.