This chapter describes how to enable QinQ operations on the switch and how to configure provider bridge S-VLANs and port assignments.

The IEEE 802.1ad specification, commonly known as QinQ or provider bridging, extends the IEEE 802.1Q standard by providing for a second tier of VLANs in a bridged network. The general purpose of QinQ is to allow frames from multiple customers to be forwarded (or tunneled) through another topology (provider network) using service VLANs or S-VLANs. The provider bridge, which may comprise multiple devices in the service provider domain, looks like a simple bridge port to the customer's traffic and maintains the customer's VLANs.

QinQ network diagram shows a sample QinQ topology and use model. Customer A has LANs spread across multiple site locations and may want to link them together in a single logical LAN. To do this, the customer could have a cable laid out for the entire distance interconnecting the three sites. A more cost-effective and scalable alternative, however, would be to tunnel frames through the provider's network to interconnect all the sites subscribing to the service. This solution can be delivered using QinQ.