Joining And Filtering Groups And Sources - Dell Force10 C150 Configuration Manual

Figure 19-3. IGMP version 3 Membership Report Packet Format
Version IHL TOS
(4) (0xc0)

Joining and Filtering Groups and Sources

Figure 19-4
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 prevent traffic 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
conflicting requests. For example, if another host on the subnet is interested in traffic from 10.11.1.3,
then 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. Since 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.
406 | Internet Group Management Protocol
Flags TTL
Total Length Frag Offset
(1)
0x12: IGMP version 1 Membership Report
0x16: IGMP version 2 Membership Report
0x17: IGMP Leave Group
0x22: IGMP version 3 Membership Report
shows how multicast routers maintain the group and source information from unsolicited
Src IP Addr Dest IP Addr
Protocol Header
(2) Checksum (224.0.0.22)
Type Reserved Checksum Reserved
Record Type
Range: 1-6
Code: 1: Current state is Include
2: Current state is Exclude
3: State change to Include
4: State change to Exclude
5: Allow new sources and no state change
6: Block old sources and no state change
IGMP Packet
Options Padding
(Router Alert)
Number of Group Group Record 1 Group Record 2 Group Record N
Records
Value used by IGMP to calculate
multicast reception state
Auxiliary Data
Multicast Address
Number of Source
Length
Sources Addresses
(0)
Length of Auxiliary
Group address to which
Data field the group record pertains
Number of source addresses Source addresses
to be filtered to be filtered
Auxiliary Data
None defined in RFC 3376
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