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This article mainly explains "what are the basic knowledge points of QinQ". Friends who are interested may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn what are the basic knowledge points of QinQ.

QinQ is the abbreviation of 802.1Q in 802.1Q. It is a relatively simple layer 2 VPN protocol based on IEEE 802.1Q technology.

Introduction to QinQ

The VLAN ID domain defined by IEEE 802.1Q has 12 bits and can provide up to 4094 VLAN. However, in practical applications, especially in the metropolitan area network, a large number of VLAN are needed to isolate users, and 4094 VLAN is far from meeting the demand. QinQ enables the whole network to provide a maximum of 4094 × 4094 VLAN, which meets the demand for the number of VLAN in the metropolitan area network.

QinQ is the abbreviation of 802.1Q in 802.1Q. It is a relatively simple layer 2 VPN protocol based on IEEE 802.1Q technology.

By encapsulating a layer of VLAN Tag into a private network message, it carries two layers of VLAN Tag through the operator's backbone network (also known as the public network), so that the operator can use one VLAN to provide services for the user network containing multiple VLAN.

QinQ has the following advantages

To alleviate the growing shortage of VLAN resources on the public network.

Users can plan their own private network VLAN without conflict with the public network VLAN.

It provides users with a simple and flexible two-tier VPN solution.

When operators carry out VLAN planning, the user network does not have to change the original configuration, so that the user network has a strong independence.

How QinQ works

QinQ messages are transmitted in the operator's network with a double-layer VLAN Tag:

Inner VLAN Tag: the private network VLAN Tag,Customer VLAN Tag (CVLAN for short) of the user. The device relies on the Tag to transmit messages in the private network.

Outer VLAN Tag: public network VLAN Tag, Service VLAN Tag (referred to as SVLAN) assigned to users by operators. The device relies on the Tag to transmit QinQ messages in the public network.

In the process of public network transmission, the device only forwards the message according to the outer VLAN Tag, while the inner VLAN Tag will be transmitted as the data part of the message.

QinQ network topology

The private VLAN of user network An and B is VLAN 1-10 and VLAN 1-20, respectively. The public network VLAN assigned by the operator to subscriber network An and B is VLAN 3 and VLAN 4, respectively.

When the message with private network VLAN Tag in subscriber network An and B enters the operator network, the public network VLAN Tag of VLAN 3 and VLAN 4 will be encapsulated on the outside of the message.

Messages from different user networks are isolated when transmitted in the operator network, even if the respective VLAN ranges of these user networks overlap, because the assigned public network VLAN is different, there will be no conflict when transmitted in the operator network.

When the message passes through the operator network and reaches the PE (Provider Edge, service provider network edge) device on the other side of the operator network, the message is stripped from the public network VLAN Tag and then transmitted to the CE (Customer Edge) device of the user network.

The implementation of QinQ

When the QinQ feature is configured on the port, the device adds the Tag of the default VLAN of this port to the message, regardless of whether the message received from the port has VLAN Tag or not:

If you receive a message with VLAN Tag, it becomes a message with two layers of Tag

If you receive a message without VLAN Tag, it becomes a message with the default VLAN Tag on this port.

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