On the network shown in Figure 1, a UPE receives user packets that carry double packets from a DSLAM. The inner and outer tags represent the service and user, respectively. However, the UPE only supports packets whose outer tag represents the service and inner tag represents the user. In this situation, you can configure VLAN tag swapping on the UPE to swap the inner and outer tags.
After VLAN tag swapping is configured, once the UPE receives packets with double VLAN tags, it swaps the inner and outer VLAN tags. VLAN tag swapping does not take effect on packets carrying a single tag.