1-11 QinQ ConfigurationWhen configuring QinQ, go to these sections for information you are interested in:z Introduction to QinQz QinQ Configuration Task Listz Configuring Basic QinQz Configuring Selective QinQz Configuring the TPID Value in VLAN Tagsz QinQ Configuration ExamplesThroughout this document, customer network VLANs (CVLANs), also called inner VLANs, refer to theVLANs 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 forcustomers.Introduction to QinQQinQ stands for 802.1Q in 802.1Q. The QinQ feature is a flexible, easy-to-implement Layer 2 VPNtechnique based on IEEE 802.1Q. It enables the edge device on the service provider network toencapsulate an outer VLAN tag in Ethernet frames from customer networks (private networks), so thatthe Ethernet frames will travel across the service provider network (public network) with double VLANtags. QinQ enables a service provider to use a single SVLAN to serve customers who have multipleCVLANs.Background and BenefitsIn the VLAN tag field defined in IEEE 802.1Q, only 12 bits are used for VLAN IDs. As a result, a devicecan 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 thussatisfies the requirement for VLAN space in MAN. It mainly addresses the following issues:z Releases the stress on the SVLAN resource.z Enables customers to plan their CVLANs without conflicting with SVLANs.z Provides an easy-to-implement Layer 2 VPN solution for small-sized MANs or intranets.z Allows the customers to keep their current network configurations when the service providerupgrades the service provider network, thus making the customer networks more independent.
