IGMP Only-Link refers to the mechanism that the interface of the multicast device that is connected to the host is only enabled with IGMP (rather than other upper-layer protocols such as PIM), and IGMP guides data forwarding on the corresponding network segment.
Compared with PIM-guided data forwarding on a network segment, IGMP Only-Link reduces the maintenance jobs of the multicast device on information such as PIM neighbors and state machine of the PIM interface.
After IGMP Only-Link is used, the querier provides the following functions:
By sending IGMP Query messages to hosts and receiving IGMP Report messages and Leave messages from hosts, the querier can know which multicast group contains receivers on the relevant network segment.
The querier maintains the Join/Leave status of the IGMP multicast group, and guides data forwarding on the relevant network segment according to the Join/Leave status.
The non-querier only maintains the Join/Leave status of the IGMP multicast group.