Dot1Q Tunnel / q-in-q Tunneling

Dot1Q tunnel or q-in-q tunneling is a technique generally used by service providers to extend customer's VLANs to different locations. It is done by encapsulating the customer VLAN inside another 802.1q encapsulation and because of this we must increase the system mtu on the service provider switches to something greater than 1500. In this blogtorial, we will take a look at a very simple topology with easy to follow configurations.

Here is the topology. 

Our objective: 

VLAN 10 in a Customer Site in California (SW1) needs to be extended to a Customer Site in Illinois (SW4).