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The switch determines whether a received frame carries a SVLAN or CVLAN tag by checking the TPID
value. For example, if a frame carries a SVLAN tag with TPID value 0x9100 and a CVLAN tag with TPID
value 0x8100, and the configured TPID value of the SVLAN tag is 0x9100 and that of the CVLAN tag is
0x8200, the switch considers that the frame carries only the SVLAN tag but not the CVLAN tag.
The systems of different vendors might set the TPID of the outer VLAN tag of QinQ frames to different
values. For compatibility with these systems, modify the TPID value so that the QinQ frames, when sent to
the public network, carry the TPID value identical to the value of a particular vendor, allowing
interoperability with the switches of that vendor.
The TPID in an Ethernet frame has the same position as the protocol type field in a frame without a VLAN
tag. To avoid problems in packet forwarding and handling in the network, do not set the TPID value to
any of the reserved values.
Table 20 Reserved protocol type values
Protocols and standards
IEEE 802.1Q: IEEE standard for local and metropolitan area networks: Virtual Bridged Local Area
Networks
QinQ configuration task list
Complete the follows tasks to configure QinQ:
Configuring VLAN transparent transmission
Configuring an outer VLAN tagging policy
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