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C3750X -- Span traffic from FlexLink backup interface

Good morning forum, 


I have a question about FlexLink and SPAN. 

On my topology is present a multicast source with 2 interfaces. Multicast stream is active on both interfaces. 

These interfaces are connected to one 3750X on the same vlan but a FlexLink configuration is active. So one interface is "active" and one is on "standby" state. 

On switch is active a SPAN session that use, as source, rx vlan used for multicast source's interfaces. 

So the problem is that on SPAN's destination port is present the traffic that comes from both interfaces, although one is on standby state. 

On SPAN's destination port multicast stream is present twice, but if I try an IGMP request on the same switch of the source I receive that only one time. 

So the problem is present only for SPAN. 

Thank you for your help.