Configuring Tpid On Layer 3 Ethernet/Aggregate Subinterfaces - HP A6600 Configuration Manual

Figure 58 Compare the structure of a Dot1q packet and that of a QinQ packet
6 bytes
DA
6 bytes
DA
The VLAN tag field contains the following subfields: TPID, Priority, CFI, and VLAN ID. TPID indicates
whether an Ethernet packet carries a VLAN tag, or whether the packet is a VLAN-tagged packet. The TPID
subfield contains 16 bits and usually takes the value of 0x8100. However, each vendor can define their
own TPID value.
To enable the interfaces to recognize VLAN-tagged packets whose TPID is not 0x8100 and communicate
with other vendors' devices, the router provides the TPID configuration function. After TPID is configured,
When receiving a packet, the router processes the packet according to
•
Table 22 TPID-based packet processing
TPID in outer VLAN tag
0x8100 or the user-defined value
0x8100 or the user-defined value
Not 0x8100 or the user-defined
value
• When sending out a packet, the router sets the TPID value in the packet's outer VLAN tag to the
user-defined value. If the TPID value is not defined, the router sets it to 0x8100. If the packet also has
an inner VLAN tag, the TPID value in the inner VLAN tag is always 0x8100.
If the current interface is up, upon the configuration of the TPID value, the interface is shut down and then
brought up to have the configuration take effect.
Even if you have used the dot1q ethernet-type command to define a TPID value other than 0x8100, the
router always processes packets with TPID value 0x8100 as VLAN-tagged packets. However, when the
router sends out a packet, it sets the packet's TPID to the user-defined value.
The TPID values set on the local and peer devices must be consistent. Otherwise, packets may fail to be
transmitted properly.

Configuring TPID on Layer 3 Ethernet/aggregate subinterfaces

When an interface receives a Layer 2 packet, it judges whether the packet is a VLAN-tagged packet
based on the packet's TPID value. If yes, the interface further judges whether the packet is a Dot1q or
QinQ packet, and processes the packet accordingly based on the VLAN termination configuration on the
interface.
6 bytes 4 bytes 2 bytes
User
SA Type
VLAN Tag
6 bytes 4 bytes 4 bytes
Nested
SA
VLAN Tag VLAN Tag
Outer
VLAN tag VLAN tag
TPID in inner VLAN tag
0x8100
Not 0x8100
—
46-1500 bytes
DATA
Dot1q packet structure
2 bytes 46-1500 bytes
User
Type DATA
Inner
163
4 bytes
FCS
4 bytes
FCS
QinQ packet structure
Table 22:
Process the packet as...
A QinQ packet
A Dot1q packet
An untagged Ethernet packet