H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 102)

12-3
For a WX6103 access controller switch interface board with both basic QinQ function and selective
QinQ function enabled, packets received are processed according to the settings of selective QinQ first.
Those that do not match selective QinQ settings are tagged with outer VLAN tags according to the basic
QinQ settings.
Modification of TPID Value of QinQ Frames
A VLAN tag uses the tag protocol identifier (TPID) field to identify the protocol type of the tag. The value
of this field, as defined in IEEE 802.1Q, is 0x8100.
Figure 12-2 shows the 802.1Q-defined tag structure of an Ethernet frame.
Figure 12-2 VLAN Tag structure of an Ethernet frame
On devices of different vendors, the TPID field of the outer VLAN tag of QinQ frames may have different
default values. You can set and/or modify this TPID value.
Normally, a frame with the TPID field being 0x8100 is regarded carrying a VLAN tag with it and is
processed in the preset way when it reaches a switch. Those with their TPID not being 0x8100 are
regarded carrying no VLAN tag.
After you configure the TPID value to be adjustable, the switch replaces the TPID value in the outer
VLAN tag of a received frame with the customer-defined value before forwarding the frame, so that the
frame, when arriving at the public network, is of specific protocol type. This enables a switch to
communicate with devices of other vendors.
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 12-1 Reserved protocol type values
Protocol type Value
ARP 0x0806
PUP 0x0200
RARP 0x8035
IP 0x0800
IPv6 0x86DD
PPPoE 0x8863/0x8864