3Com 4210G Series, Configuration Manual, Page: 171 / 1133

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QinQ Configuration
When configuring QinQ, go to these sections for information you are interested in:
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Introduction to QinQ
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QinQ Configuration Task List
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Configuring Basic QinQ
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Configuring Selective QinQ
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Configuring the TPID Value in VLAN Tags
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QinQ Configuration Examples
Throughout this document, customer network VLANs (CVLANs), also called inner VLANs, refer to the
VLANs that a customer uses on the private network; and service provider network VLANs (SVLANs),
also called outer VLANs, refer to the VLANs that a service provider uses to carry VLAN tagged traffic
for customers.
Introduction to QinQ
Background
In the VLAN tag field defined in IEEE 802.1Q, only 12 bits are used for VLAN IDs, so a device can
support a maximum of 4094 VLANs. In actual applications, however, a large number of VLANs are
required to isolate users, especially in metropolitan area networks (MANs), and 4094 VLANs are far
from satisfying such requirements.
QinQ Mechanism and Benefits
The QinQ feature is a flexible, easy-to-implement Layer 2 VPN technique. It enables the edge device
on the service provider network 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 network
(public network) with double VLAN tags. QinQ enables a service provider to use a single SVLAN to
serve customers who have multiple CVLANs.
The devices in the public network forward a frame only according to its outer VLAN tag and learn its
source MAC address into the MAC address table of the outer VLAN. The inner VLAN tag of the frame
is transmitted as the payload.