A first Virtual Device (VD) of a first member device connects to a first VD of a second member device via a stacking link that is established between the first member device and the second member device. A VD number of the first VD in the first member device is the same as that of the first VD in the second member device. When a unicast packet is received via a service port, the first VD of the first member device searches in a forwarding table of the first VD in the first member device. When the unicast packet is to be forwarded to another member device the search of the forwarding table, the first VD of the first member device forwards the unicast packet via the stacking link.