A CB device receives a first packet sent from another device through a stacking port. In response to determining, based on source port information carried in the first packet, that the first packet entered the stacking system from a PE device and the first packet is a non-unicast packet, the switch module performs mirroring processing to the first packet to obtain a mirrored packet, and transmits the first packet and the mirrored packet to a packet buffering module of the CB device. In response to determining that a second packet from the packet buffering module entered the stacking system from the PE device and the second packet is the non-unicast packet, the second packet is forbidden from being forwarded through a first-level stacking port of the CB device.