I create a VLAN interface in Layer-3 Switch and configure multicast traffic over this VLAN. But the multicast traffic is always duplicated after passing the Layer-3 Switch. I checked the throughput among devices and found that the layer3 switch receives traffic from a upstream router, and sends a copy back to the router. Then it sends double traffic to downstream device. Does anyone know why the traffic is doubled? How to figure it out? Thank you!