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The states a computer will go through to join or to leave a multicast group are shown below:
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 4-7-4: IGMP State Transitions
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User's Manual of WGSW-2620HP
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