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User’s Manual of ISW-1022M
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Non-Member
Delaying Member
Idle Member
Leave Group
Leave Group
(Stop Timer)
Join Group
(Send Report,
Start Timer)
Query Received
(Start Timer)
Report Received
(Stop Timer)
Timer Expried
(Send report)
Figure 5-57
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.