User’s Manual of NS2503-24P/2C
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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.
