97
Implementations of QinQ
The router supports basic QinQ only.
Basic QinQ enables a port to tag any incoming frames with its port VLAN (PVID) tag, regardless of
whether they have been tagged or not. If an incoming frame has been tagged, it becomes a
double-tagged frame. If not, it becomes a frame tagged with the port’s PVID tag.
Modifying the TPID value in a VLAN tag
A VLAN tag uses the tag protocol identifier (TPID) field to identify the protocol type of the tag. The default
TPID value is 0x8100.
Figure 34
VLAN Tag structure of an Ethernet frame
The router determines whether a received frame carries a service provider VLAN tag or a customer VLAN
tag by checking the corresponding TPID value. Upon receiving a frame, the router compares the
compares the configured TPID value with the value of the TPID field in the frame. If the two match, the
frame carries the corresponding VLAN tag. For example, if a frame carries VLAN tags with the TPID
value of 0x9200 whereas the configured TPID value of the service provider VLAN tag is 0x9100, the
router considers that the frame does not carry the service provider 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 network 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
.
Table 14
Reserved protocol type values
Protocol type Value
ARP 0x0806
PUP 0x0200
RARP 0x8035
IP 0x0800
IPv6 0x86DD
PPPoE 0x8863/0x8864
MPLS 0x8847/0x8848
