Dell S6100 Configuration Manual page 356

Figure 48. IGMP Version 3–Capable Multicast Routers Address Structure
Joining and Filtering Groups and Sources
The following illustration shows how multicast routers maintain the group and source information from unsolicited reports.
1 The first unsolicited report from the host indicates that it wants to receive traffic for group 224.1.1.1.
2 The host's second report indicates that it is only interested in traffic from group 224.1.1.1, source 10.11.1.1. Include messages prevents
traffic from all other sources in the group from reaching the subnet. Before recording this request, the querier sends a group-and-
source query to verify that there are no hosts interested in any other sources. The multicast router must satisfy all hosts if they have
conflicting requests. For example, if another host on the subnet is interested in traffic from 10.11.1.3, the router cannot record the
include request. There are no other interested hosts, so the request is recorded. At this point, the multicast routing protocol prunes
the tree to all but the specified sources.
3 The host's third message indicates that it is only interested in traffic from sources 10.11.1.1 and 10.11.1.2. Because this request again
prevents all other sources from reaching the subnet, the router sends another group-and-source query so that it can satisfy all other
hosts. There are no other interested hosts so the request is recorded.
356 Internet Group Management Protocol (IGMP)