1-4
Figure 1-3 VLAN tag structure of an Ethernet frame
The device determines whether a received frame carries a SVLAN tag or a CVLAN tag by checking the
corresponding TPID value. Upon receiving a frame, the device compares the configured TPID value
with the value of the TPID field in the frame. If the two match, the devices considers that the frame
carries the VLAN tag. For example, if a frame carries a VLAN tag with the TPID value 0x9100 while the
configured TPID value of the VLAN tag is 0x8100, the device considers that the frame carries no VLAN
tag.
In addition, the systems of different vendors may set the TPID of the outer VLAN tag of QinQ frames to
different values. For compatibility with these systems, you can 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 to allow interoperability with the devices of that vendor.
The TPID in an Ethernet frame has the same position with the protocol type field in a frame without a
VLAN tag. To avoid problems in packet forwarding and handling in the network, you cannot set the TPID
value to any of the values in the table below.
Table 1-1 Reserved protocol type values
Protocol type Value
ARP 0x0806
PUP 0x0200
RARP 0x8035
IP 0x0800
IPv6 0x86DD
PPPoE 0x8863/0x8864
MPLS 0x8847/0x8848
IPX/SPX 0x8137
IS-IS 0x8000
LACP 0x8809
802.1x 0x888E
Cluster 0x88A7
Reserved 0xFFFD/0xFFFE/0xFFFF
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