ZyXEL Communications Dimension ES-3124 Support Notes page 57

ES-3100 Series Switch Support Notes
IP Multicasting
How to setup IGMP snooping in your switch?
Figure 1: IGMP and IGMP snooping
IGMP snooping is designed for application with deployment of multicast traffic.
It operates on the underlying IGMP mechanism where a layer two switch
passively listens to the IGMP Query, Report and Leave (IGMP version 2)
packets transmitted between the IGMP router and clients and collects passing
IGMP messages. After that, the switch records the message's group
registration information, and configures multicasting information accordingly. If
the multicast group information is unknown (not recorded on the switch), the
switch discards that multicast traffic. Only the registered clients that join the
group will receive multicast stream from the IGMP router. Thus this
significantly reduces the multicast traffic forwarded down to the clients.
Another advantage of IGMP snooping is to allow the intermediate switch to
learn multicast group information without manually configuring switches.
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