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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 12

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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Introduction to QinQ

Introduction to QinQ

This section describes definition and purpose.


802.1Q-in-802.1Q (QinQ) technology improves VLAN utilization by adding another 802.1Q tag to a frame with an 802.1Q tag. A frame has double 802.1Q tags (one for the public network and the other for the private network), that is, 802.1Q-in-802.1Q (QinQ).


As Ethernet is widely used on ISP networks, 802.1Q VLANs are not enough to identify and isolate a large number of users on a metro Ethernet network. The 12-bit VLAN tag field defined in IEEE 802.1Q identifies a maximum of 4096 VLANs, which are insufficient for a large number of users on the MAN. QinQ technology is developed to solve this problem.

QinQ was originally developed to expand the VLAN space. It adds another 802.1Q tag to an 802.1Q-tagged frame, expanding the VLAN space to 4094 x 4094 (The values 0 and 4095 are reserved). Packets are forwarded based on their outer VLAN tags on the public network, and devices on the public network add the outer VLAN IDs to MAC address tables of the matching VLANs. Inner VLAN tags of packets are transmitted as data on the public network.

As metro Ethernet develops and requirements for precise management emerging, QinQ has more applications. In a QinQ frame, the inner 802.1Q tag identifies a user, and the outer 802.1Q tag identifies a service. QinQ frames traverse an ISP network with double tags, and the inner tag is transparently transmitted. Therefore, QinQ is also a simple and practical VPN technology on metro Ethernet, which is an extension to MPLS VPN on the core network. QinQ can be used with MPLS VPN to form an end-to-end VPN solution.


QinQ technology improves VLAN utilization by adding another 802.1Q VLAN tag to a frame with an 802.1Q VLAN tag. It brings the following advantages:
  • QinQ expands the VLAN space so that user isolation and identification are not limited.
  • In a QinQ packet, the inner 802.1Q tag identifies a user, and the outer 802.1Q tag identifies a service. The inner and outer tags facilitate service deployment.
Updated: 2019-08-09

Document ID: EDOC1000041694

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