Implementations Of Qinq; Modifying The Tpid In A Vlan Tag - HP A6600 Configuration Manual

Implementations of QinQ

HP provides the following QinQ implementations: basic QinQ and selective QinQ.
Basic QinQ
1.
Basic QinQ enables a port to tag any incoming frames with its default VLAN 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 default VLAN tag.
Selective QinQ
2.
Selective QinQ is more flexible than basic QinQ. In addition to all functions of basic QinQ, selective
QinQ enables a port to perform the following per-CVLAN actions for incoming frames:
Tagging frames from different CVLANs with different SVLAN tags.
•
Marking the outer VLAN 802.1p priority based on the existing inner VLAN 802.1p priority.
•
Modifying the inner VLAN ID, in addition to tagging the frame with an outer VLAN tag.
•
Besides being able to separate the service provider network from the customer networks, selective QinQ
provides abundant service features and allows more flexible networking.

Modifying the TPID in a VLAN tag

A VLAN tag uses the TPID field to identify the protocol type of the tag. The default value of this field, as
defined in IEEE 802.1Q, is 0x8100.
Figure 50 shows the 802.1Q-defined tag structure of an Ethernet frame.
Figure 50 VLAN tag structure of an Ethernet frame
The router determines whether a received frame carries an SVLAN or CVLAN tag by checking the TPID
value. For example, if a frame carries an 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 router considers that the frame carries only the SVLAN tag but not the CVLAN tag.
In addition, devices of different vendors may set the TPID of the outer VLAN tag of QinQ frames to
different values. For compatibility with these devices, 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 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 values in Table 21.
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