214 | Internet Group Management Protocol (IGMP)w w w . d e l l . c o m | s u p p o r t . d e l l . c o m Joining and Filtering Groups and SourcesFigure 12-4 shows how multicast routers maintain the group and source information from unsolicitedreports.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, source10.11.1.1. Include messages prevent traffic from all other sources in the group from reaching thesubnet, so before recording this request, the querier sends a group-and-source query to verify that thereare no hosts interested in any other sources. The multicast router must satisfy all hosts if they haveconflicting 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 isrecorded. 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 and10.11.1.2. Because this request again prevents all other sources from reaching the subnet, the routersends another group-and-source query so that it can satisfy all other hosts. There are no other interestedhosts, so the request is recorded.Figure 12-4. IGMP Membership Reports: Joining and Filtering1/1Type: 0x22Number of Group Records: 1Record Type: 4Number of Sources: 0Multicast Address: 224.1.1.1Interface Multicast Group Filter Source SourceAddress Timer Mode Timer1/1 224.1.1.1 GMI ExcludeNone1/1 224.1.1.1 Include10.11.1.1 GMI1/1 224.1.1.1 Include10.11.1.1 GMI10.11.1.2 GMIIGMP Join messageType: 0x22Number of Group Records: 1Record Type: 3Number of Sources: 1Multicast Address: 224.1.1.1Source Address: 10.11.1.1Change to IncludeType: 0x22Number of Group Records: 1Record Type: 5Number of Sources: 1Multicast Address: 224.1.1.1Source Address: 10.11.1.2Allow NewState-change reports retransmittedQuery Robustness Value-1 times atUnsolicited Report IntervalQuerier Non-QuerierMembership Reports: Joining and Filtering124Type: 0x11Group Address: 244.1.1.1Number of Sources: 1Source Address: 10.11.1.1IGMP Group-and-SourceSpecific Query3fnC0072mp
