QinQ frame structure
A QinQ frame is transmitted double-tagged over the service provider network. As shown in Figure 63, the inner VLAN tag is the CVLAN tag, and the outer one is the SVLAN tag that the service provider has allocated to the customer.
QinQ uses CVLAN tags to transmit frames over the private network, and uses SVLAN tags to transmit frames over the public network. When a QinQ frame is transmitted over the public network, its CVLAN tag is transmitted as the payload.
Figure 63: Single-tagged Ethernet frame header and double-tagged Ethernet frame header
The default maximum transmission unit (MTU) of an interface is 1500 bytes. The size of an outer VLAN tag is 4 bytes. HP recommends you to increase the MTU of each interface on the service provider network to at least 1504 bytes.