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Lectures notes for 2010 - KTH

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Joining a Multicast Group<br />

• a process joins a multicast group on a given interface<br />

• host keeps a table of all groups which have a reference count ≥ 1<br />

IGMP Reports and Queries<br />

• Hosts sends a report when first process joins a given group<br />

• Nothing is sent when processes leave (not even when the last leaves),<br />

but the host will no longer send a report <strong>for</strong> this group<br />

• IGMP router sends queries (to address 224.0.0.1) periodically (one out<br />

each interface), the group address in the query is 0.0.0.0<br />

In response to a query, a host sends a IGMP report <strong>for</strong> every group with at<br />

least one process<br />

Routers<br />

• Note that routers have to listen to all 2 23 link layer multicast addresses!<br />

• Hence they listen promiscuously to all LAN multicast traffic<br />

Maguire Joining a Multicast Group 8: 21 of 78<br />

maguire@kth.se <strong>2010</strong>.03.21 Internetworking/Internetteknik

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