ZyXEL Communications ES 3500 Series Troubleshooting Manual page 59

Did the Zyxel switch receive the IGMP Join/Leave from the
multicast client?
Access CLI to verify whether or not the Zyxel switch receives the IGMP Join/Leave.
Figure 29
*The multicast group address will appear in the table if the switch receives the
IGMP Join. Likewise, the multicast group address will disappear from the table
if the switch receives the IGMP Leave.
If the switch can receive the IGMP Join/Leave, proceed to step 6.
If the switch cannot receive the IGMP Join/Leave, go to step 8.
Does the Zyxel switch indicate the known multicast group?
The Zyxel switch using L3 IGMP Routing will only start sending multicast stream when
two conditions are met:
a. The L3 IGMP Router is receiving a multicast stream from any interface.
b. The L3 IGMP Router received the IGMP Join for the same multicast stream it
receives.
When the two conditions are met, this stream will now be called a "known multicast
traffic". You can access the CLI of the Zyxel switch to verify which multicast
addresses are currently known.
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