Introduction to QinQ

Definition

QinQ expands VLAN space by adding an additional 802.1Q tag to 802.1Q tagged packets. It allows services in a private VLAN to be transparently transmitted over a public network. A packet transmitted on the backbone network carries two 802.1Q tags: a public VLAN tag and a private VLAN tag.

Purpose

Ethernet is widely used on ISP networks, but 802.1Q VLANs are unable to identify and isolate large numbers of users on metro Ethernet networks because the 12-bit VLAN tag field defined in IEEE 802.1Q only identifies a maximum of 4096 VLANs. QinQ was developed to expand VLAN space beyond 4096 VLANs so that a larger number of users can be identified on a metro Ethernet network.

QinQ was originally developed to expand VLAN space by adding an additional 802.1Q tag to an 802.1Q-tagged packet. In this way, the number of VLANs can increase to 4094 x 4094.

In addition to expanding VLAN space, QinQ is applied in other scenarios with the development of metro Ethernet networks and carriers' requirements on refined service operation. The outer and inner VLAN tags can be used to differentiate packets based on users and services. For example, the inner tag represents a user, while the outer tag represents a service. Moreover, QinQ is used as a simple and practical VPN technology because inner tags of QinQ packets are transparently transmitted over a public network. It extends core MPLS VPN services to metro Ethernet networks to establish an end-to-end VPN.

Since QinQ technology is easy to use, it has been widely applied in Internet Service Provider (ISP) networks. For example, QinQ is combined with multiple services in metro Ethernet solutions. Selective QinQ (VLAN stacking) makes QinQ more popular among ISPs. As the metro Ethernet develops, equipment vendors have developed their own metro Ethernet solutions, in which the simple and flexible QinQ technology plays an important role.

Benefits