H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 100)

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QinQ Configuration
The term switch in this document refers to a switch in a generic sense or an access controller
configured with the switching function unless otherwise specified.
When configuring QinQ, go to these sections for information you are interested in:
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Introduction to QinQ
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Configuring Basic QinQ
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Configuring Selective QinQ
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Configuring the TPID Value to Be Carried in VLAN Tags
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QinQ Configuration Example
Introduction to QinQ
In the VLAN tag field defined in IEEE 802.1Q, only 12 bits are used for VLAN IDs, so a switch can
support a maximum of 4,094 VLANs. In actual applications, however, a large number of VLANs are
required to isolate users, especially in metropolitan area networks (MANs), and 4,094 VLANs are far
from satisfying such requirements.
Understanding QinQ
The port QinQ feature is a flexible, easy-to-implement Layer 2 VPN technique, which enables the
access point to encapsulate an outer VLAN tag in Ethernet frames from customer networks (private
networks), so that the Ethernet frames will travel across the service provider’s backbone network
(public network) with double VLAN tags. The inner VLAN tag is the customer network VLAN tag while
the outer one is the VLAN tag assigned by the service provider to the customer. In the public network,
frames are forwarded based on the outer VLAN tag only, with the source MAC address learned as a
MAC address table entry for the VLAN indicated by the outer tag, while the customer network VLAN tag
is transmitted as part of the data in the frames.
Figure 12-1 shows the structure of 802.1Q-tagged and double-tagged Ethernet frames. The QinQ
feature enables a device to support up to 4,094 x 4,094 VLANs to satisfy the requirement for the amount
of VLANs in the MAN.