Administrator Guide
Figure 46. 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 rst unsolicited report from the host indicates that it wants to receive trac for group 224.1.1.1.
2 The host’s second report indicates that it is only interested in trac from group 224.1.1.1, source 10.11.1.1. Include messages prevents
trac 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
conicting requests. For example, if another host on the subnet is interested in trac 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 specied sources.
3 The host’s third message indicates that it is only interested in trac 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.
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Internet Group Management Protocol (IGMP)