Administrator Guide

Figure 12. IGMP version 3 Membership Report Packet Format
Joining and Filtering Groups and Sources
The below illustration shows how multicast routers maintain the group and source information from unsolicited reports.
• The rst unsolicited report from the host indicates that it wants to receive trac for group 224.1.1.1.
• The host’s second report indicates that it is only interested in trac from group 224.1.1.1, source 10.11.1.1. Include messages
prevent trac from all other sources in the group from reaching the subnet, so 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 conicting requests. For example, if another host on the subnet is interested in trac 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 specied sources.
• The host’s third message indicates that it is only interested in trac 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.
Figure 13. IGMP Membership Reports: Joining and Filtering
Internet Group Management Protocol (IGMP)
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