Deployment Guide
To accommodate these protocol enhancements, the IGMP version 3 packet structure is dierent from version 2. Queries (shown below in
query packet format) are still sent to the all-systems address 224.0.0.1, but reports (shown below in report packet format) are sent to all the
IGMP version 3 — capable multicast routers address 224.0.0.22.
Figure 46. IGMP version 3 Membership Query Packet Format
Figure 47. 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 trac for group 224.1.1.1.
• 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 prevent
trac 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
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.
• 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.
Internet Group Management Protocol (IGMP)
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