3com S7906E Manuel De Montage
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QinQ Configuration
When configuring QinQ, go to these sections for information you are interested in:
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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.
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QinQ requires configurations only on the service provider network, not on the customer network.
Introduction to QinQ
QinQ stands for 802.1Q in 802.1Q. The QinQ feature is a flexible, easy-to-implement Layer 2 VPN
technique based on IEEE 802.1Q. 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.
Background and Benefits
In the VLAN tag field defined in IEEE 802.1Q, only 12 bits are used for VLAN IDs. As a result, a device
can support a maximum of 4094 VLANs. This is far from enough for isolating users in actual networks,
especially in metropolitan area networks (MANs).
By tagging tagged frames, QinQ expands the available VLAN space from 4094 to 4094 × 4094 and thus
satisfies the requirement for VLAN space in MAN. It mainly addresses the following issues:
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Releases the stress on the SVLAN resource.
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Enables customers to plan their CVLANs without conflicting with SVLANs.
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Provides an easy-to-implement Layer 2 VPN solution for small-sized MANs or intranets.
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Allows the customers to keep their current network configurations when the service provider
upgrades the service provider network, thus making the customer networks more independent.