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 QinQBackgroundIn the VLAN tag field defined in IEEE 802.1Q, only 12 bits are used for VLAN IDs, so a device cansupport a maximum of 4094 VLANs. In actual applications, however, a large number of VLANs arerequired to isolate users, especially in metropolitan area networks (MANs), and 4094 VLANs are farfrom satisfying such requirements.QinQ Mechanism and BenefitsThe QinQ feature is a flexible, easy-to-implement Layer 2 VPN technique. It enables the edge device onthe service provider network to encapsulate an outer VLAN tag in Ethernet frames from customernetworks (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 toserve customers who have multiple CVLANs.The devices in the public network forward a frame only according to its outer VLAN tag and learn itssource MAC address into the MAC address table of the outer VLAN. The inner VLAN tag of the frame istransmitted as the payload.
