Issue
We have 2 Bluecoat servers connected to the same switch that exchange multicast traffic. By default the switch may send multicast traffic to all ports. What is the best practice to optimize this traffic?
Resolution
If IGMP snooping is enabled and no multicast router is connected to the VLAN the switch may block this multicast traffic in an attempt to optimize traffic forwarding.
If a multicast capable router is connected to the VLAN and regularly sends out IGMP queries then IGMP snooping will work well moving this multicast traffic only between really interested receivers.
If no multicast router is connected to the VLAN/subnet then we should verify if our switch supports a feature called IGMP Snooping Querier that will send out the regular IGMP queries in order to make IGMP snooping to work correctly.
Otherwise we need to disable IGMP snooping on that specific VLAN (if no multicast router is connected and no switch in use can act as IGMP Snooping Querier) this will cause multicast traffic to be flooded on the VLAN like broadcast.
If servers are connected to 2 different switches and there is a trunk between these 2 switches then each switch will intercept the IGMP report of the locally connected server and should propagate it on the trunk towards the multicast router/IGMP Snooping Querier.
Source:- https://supportforums.cisco.com/message/3041967
