Introduction to QinQ

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.

The following figure 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.
QinQ network diagram

The Service Provider and customers may belong to the same business entity, as in the case where a single enterprise uses QinQ to help segregate local networks and increase the scalability of their backbone infrastructure.