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FTOS Configuration Guide for the C-Series - Force10 Networks

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Figure 411 IGMP version 3 Membership Report Packet Format<br />

Version<br />

(4)<br />

IHL TOS<br />

(0xc0)<br />

Total Length Flags Frag Offset TTL<br />

Protocol<br />

Header<br />

(1)<br />

(2)<br />

Checksum<br />

Type Reserved Checksum Reserved Number of Group<br />

Records<br />

0x12: IGMP version 1 Membership Report<br />

0x16: IGMP version 2 Membership Report<br />

0x17: IGMP Leave Group<br />

0x22: IGMP version 3 Membership Report<br />

Joining and Filtering Groups and Sources<br />

Figure 412 shows how multicast routers maintain <strong>the</strong> group and source in<strong>for</strong>mation from unsolicited<br />

reports.<br />

1. The first unsolicited report from <strong>the</strong> host indicates that it wants to receive traffic <strong>for</strong> group 224.1.1.1.<br />

2. The host’s second report indicates that it is only interested in traffic from group 224.1.1.1, source<br />

10.11.1.1. Include messages prevent traffic from all o<strong>the</strong>r sources in <strong>the</strong> group from reaching <strong>the</strong><br />

subnet, so be<strong>for</strong>e recording this request, <strong>the</strong> querier sends a group-and-source query to verify that <strong>the</strong>re<br />

are no hosts interested in any o<strong>the</strong>r sources. The multicast router must satisfy all hosts if <strong>the</strong>y have<br />

conflicting requests. For example, if ano<strong>the</strong>r host on <strong>the</strong> subnet is interested in traffic from 10.11.1.3,<br />

<strong>the</strong>n <strong>the</strong> router cannot record <strong>the</strong> include request. There are no o<strong>the</strong>r interested hosts, so <strong>the</strong> request is<br />

recorded. At this point, <strong>the</strong> multicast routing protocol prunes <strong>the</strong> tree to all but <strong>the</strong> specified sources.<br />

3. The host’s third message indicates that it is only interested in traffic from sources 10.11.1.1 and<br />

10.11.1.2. Since this request again prevents all o<strong>the</strong>r sources from reaching <strong>the</strong> subnet, <strong>the</strong> router sends<br />

ano<strong>the</strong>r group-and-source query so that it can satisfy all o<strong>the</strong>r hosts. There are no o<strong>the</strong>r interested hosts<br />

so <strong>the</strong> request is recorded.<br />

586 Internet Group Management Protocol<br />

Src IP Addr<br />

Dest IP Addr<br />

(224.0.0.22)<br />

Record Type<br />

Options<br />

(Router Alert)<br />

Auxiliary Data<br />

Length<br />

(0)<br />

Length of Auxiliary<br />

Data field<br />

Group Record 1<br />

Value used by IGMP to calculate<br />

multicast reception state<br />

Number of<br />

Sources<br />

Range: 1-6<br />

Number of source addresses<br />

Code: 1: Current state is Include to be filtered<br />

2: Current state is Exclude<br />

3: State change to Include<br />

4: State change to Exclude<br />

5: Allow new sources and no state change<br />

6: Block old sources and no state change<br />

Padding IGMP Packet<br />

Group Record 2 Group Record N<br />

Multicast Address<br />

Group address to which<br />

<strong>the</strong> group record pertains<br />

Source<br />

Addresses<br />

Source addresses<br />

to be filtered<br />

Auxiliary Data<br />

None defined in RFC 3376<br />

fnC0071mp

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