The virtual private wire service (VPWS) is a point-to-point L2VPN technology. A VLANIF interface does not support VPWS, and therefore you have to access a virtual private network (VPN) through a main interface. Such a configuration is not flexible because multiple users cannot access through the same physical interface. To ensure the access of multiple users through the same physical interface, you can use the QinQ stacking function on different sub-interfaces. This requires that CE-VLANs on PE1 and PE2 be the same.
On the network shown in Figure 1, a QinQ stacking sub-interface on PE1 adds an outer VLAN tag of the ISP network to its received user packets that carry a VLAN tag ranging from 1 to 200 on sub-interfaces. Then, PE1 sends these packets to the VPWS network.