Under QinQ, the provider network operates on
a different VLAN space, independent of the VLANs that are used in
the customer network.VLANs in a QinQ configuration
Customer VLANs (referred to as C-VLANs by the
IEEE 802.1ad specification) are not used to make any forwarding decisions
inside the provider network where customer frames get assigned to
service VLANs (S-VLANs). Inside the provider cloud, frames are forwarded
based on the S-VLAN tag only, while the C-VLAN tag remains shielded
during data transmission. The S-VLAN tag is removed when the frame
exits the provider network, restoring the original customer frame.
