Dell Force10 E300, Configuration Manual, Page: 406 / 1262

406 | Internet Group Management Protocol
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Figure 19-3. IGMP version 3 Membership Report Packet Format
Joining and Filtering Groups and Sources
Figure 19-4 shows how multicast routers maintain the group and source information from unsolicited
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.
fnC0071mp
Type Reserved Reserved Checksum Number of Group
Records Group Record 1
Value used by IGMP to calculate
multicast reception state
Group Record 2 Group Record N
Record Type
Auxiliary Data
Length
(0)
Multicast Address Number of
Sources Source
Addresses
Length of Auxiliary
Data field
Number of source addresses
to be filtered
Group address to which
the group record pertains
Auxiliary Data
Source addresses
to be filtered
None defined in RFC 3376
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
Version
(4) IHL TOS
(0xc0)
Total Length
Flags
Frag Offset Header
Checksum
Src IP Addr TTL
(1)
Protocol
(2)
Dest IP Addr
(224.0.0.22)
Options
(Router Alert) Padding
IGMP Packet
0x12: IGMP version 1 Membership Report
0x16: IGMP version 2 Membership Report
0x17: IGMP Leave Group
0x22: IGMP version 3 Membership Report