Interlogix NS4702-24P-4S-4X User Manual page 167

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IGMP Querier –
A router, or multicast-enabled switch, can periodically ask their hosts if they want to receive multicast traffic. If there is more than
one router/switch on the LAN performing IP multicasting, one of these devices is elected "querier" and assumes the role of
querying the LAN for group members. It then propagates the service requests on to any upstream multicast switch/router to
ensure that it will continue to receive the multicast service.
Multicast routers use this information, along with a multicast routing protocol such as
DVMRP or PIM, to support IP multicasting across the Internet.
Figure 4-8-4: IGMP State Transitions
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