H3C Technologies H3C S12500-X Series Switches - Manual (Page 139)

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Configuring QinQ
This document uses the following terms:
• CVLAN—Customer network VLANs, also called "inner VLANs," refer to VLANs that a customer
uses on the private network.
• SVLAN—Service provider network VLANs, also called "outer VLANs," refer to VLANs that a service
provider uses to transmit VLAN tagged traffic for customers.
Overview
802.1Q-in-802.1Q (QinQ) is an easy-to-implement L2 VPN technology that enables service providers to
extend Layer 2 Ethernet connections across a MAN between two customer sites.
QinQ enables service providers to separate customer traffic by adding a layer of service provider VLAN
tag (SVLAN tag) to customer traffic.
QinQ delivers the following benefits:
• Enables a service provider to use a single SVLAN to convey multiple CVLANs for a customer.
• Enables customers to plan CVLANs without conflicting with SVLANs.
• Enables customers to keep their VLAN assignment schemes unchanged when the service provider
changes its VLAN assignment scheme.
• Allows customers to use overlapping CVLAN IDs, because devices in the service provider network
make forwarding decisions based on SVLAN IDs instead of CVLAN IDs.
How QinQ works
As shown in Figure 36 , a QinQ frame transmitted over the service provider network carries the following
tags:
• CVLAN tag—Customer VLAN tag. The inner VLAN tag identifies the VLAN to which the QinQ
frame belongs when it is transmitted in the customer network.
• SVLAN tag—Service VLAN tag. The outer VLAN tag that the service provider allocates to the
customer. The SVLAN tag identifies the VLAN to which the QinQ frame belongs when it is
transmitted in the service provider network.