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PLANET WGSW-2620HP User Manual

Page 98

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User’s Manual of WGSW-2620HP

The states a computer will go through to join or to leave a multicast group are shown below:

Figure 4-7-4:

IGMP State Transitions

„

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.

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