TPID
The Tag Protocol Identifier (TPID) specifies the protocol type of a VLAN tag. The TPID value defined in IEEE 802.1Q is 0x8100.
Figure 1 shows the Ethernet packet format defined in IEEE 802.1Q. An IEEE 802.1Q tag, containing the TPID, is located between the Source Address field and the Length/Type field. The device checks the TPID value in a received frame to determine whether the VLAN tag is a service VLAN (S-VLAN) tag or customer (C-VLAN) tag. The device compares the configured TPID value with the TPID value in the frame. For example, if a frame carries the VLAN tag with TPID 0x8100 but the TPID configured for a customer network on a device is 0x8200, the device considers the frame untagged.
Different carriers may use different TPID values
in outer VLAN tags. To ensure that QinQ frames sent from a Huawei
device can be transmitted across a carrier network, set the TPID value
to that used by the carrier. Table 1 provides some
of the common protocol types and their TPID values, which should not
be used in such cases.