Multicast/IGMP switch operation

Hi All, I need some advice concerning the correct operation for multicast and IGMP groups. Basically, my problem is that I have 2 Level 3 switches that operate differently for the same multicast traffic and I'm trying to work out why. However, first I need to understand what the correct operation should be.

Here are 2 scenarios. Which is correct?. The setup is say 5 PCs connected to a Level 3 switch with IGMP and IGMP snooping enabled.

1). Scenario 1 . PC 1 transmits a stream of multicast messages. The switch broadcasts these messages to all PCs (ie. the multicast messages are treated like broadcast messages).

2). Scenario 2. PC 1 transmits a stream of multicast messages. The switch acknowledges the multicast message but currently has no record of any of the other 4 PC joining this multicast group and therefore does not broadcast the messages to the other PCs. At a later time one of the PC can join the multicast group (via IGMP 'join') and receive the messages.

Which of these is the correct operation?. Basically, I want to get behvaiour 2 but I am experiencing behaviour 1.

Any ideas?.

Thanks in advance, Dave

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Multicast traffic only arrives at workstations listening for that multicast traffic. It is not broadcast to everyone.


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