VLAN mapping technology changes VLAN tags in packets to map different VLANs.
Two Layer 2 user networks in the same VLAN can be connected through a backbone network. To ensure Layer 2 connectivity between users, and to uniformly deploy Layer 2 protocols, the two user networks need to interwork seamlessly. However, the backbone network cannot directly transmit VLAN packets from the user networks, because the VLAN plans on the backbone and user networks are different.
To solve this problem, configure VLAN mapping. When VLAN packets from a user network enter the backbone network, an edge device on the backbone network changes the customer VLAN (C-VLAN) ID to the service VLAN (S-VLAN ID). After the packets are transmitted, the edge device reverts the VLAN ID change. This ensures seamless interworking between the two user networks. The other method is to configure a Layer 2 tunneling technology such as QinQ or VPLS to encapsulate VLAN packets into packets on the backbone network so that VLAN packets are transparently transmitted. However, this method increases extra cost because packets are encapsulated. In addition, Layer 2 tunneling technology may not support transparent transmission of packets of some protocol packets. The other method is to configure VLAN mapping. When VLAN packets from a user network enter the backbone network, an edge device on the backbone network changes the C-VLAN ID to the S-VLAN ID. After the packets are transmitted to the other side, the edge device changes the S-VLAN ID to the C-VLAN ID. This method implements seamless interworking between two user networks.
Configuring VLAN mapping on the switch connecting the two user networks allows a user to manage the two networks as a single Layer 2 network, despite the differing VLAN plans of the user networks.