121WAN, the sending port must record and remove the VLAN information of the packets. VLAN interfacesor Layer 3 Ethernet subinterfaces can be used for LAN-WAN communication.As shown in Figure 46, the VLANs of the customer network are called customer VLANs (CVLANs), andthe VLANs of the service provider network are called service provider VLANs (SVLANs). When a packetcarrying a CVLAN tag enters the service provider network, it is tagged with a SVLAN tag, andforwarded based on the SVLAN tag. When the packet is to be forwarded to an external WAN, thegateway (Device) must perform VLAN termination for the packet and remove the two layers of VLAN tagsfrom the packet before sending the packet to the WAN.Figure 46 VLAN termination enables LAN-WAN communicationVLAN termination configuration task listComplete the following tasks to configure VLAN termination:Task RemarksConfiguring TPID for VLAN-tagged packets OptionalEnabling a QinQ termination-enabled interface/subinterface to transmitbroadcast and multicast packets OptionalConfiguring QinQ termination RequiredConfiguring TPID for VLAN-tagged packetsIEEE 802.1Q inserts a four-byte VLAN tag field between the DA&SA field and the type field to carryVLAN-related information in an Ethernet frame header. Figure 47 shows the subfields in the VLAN tagfield in Ethernet II encapsulation. Other Ethernet encapsulation formats include 802.2 LLC, 802.2 SNAP,and 802.3 raw. Figure 48 compares the structure of a Dot1q packet and that of a QinQ packet.Figure 47 Subfields in the VLAN Tag fieldWANAdd a CVLAN tagEnable QinQ, andadd a SVLAN tagCreate a Layer 3 Ethernetsubinterface or VLANinterface to perform QinQterminationPacketsLayer 2 networkL2 Switch A L2 Switch B Device
