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S9300, S9300E, and S9300X V200R012C00 Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, VLAN aggregation, MUX VLAN, VLAN termination, Voice VLAN, VLAN mapping, QinQ, GVRP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, HVRP, and Layer 2 protocol transparent transmission.
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Overview of QinQ

Overview of QinQ


802.1Q-in-802.1Q (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.


Ethernet is widely used on carrier networks. However, because the 12-bit VLAN tag field defined in IEEE 802.1Q identifies a maximum of 4096 VLANs, the number of users that 802.1Q VLANs can identify and isolate on metro Ethernet networks is insufficient. To address this issue, QinQ was developed to expand VLAN space beyond 4096 VLANs so that a larger number of users can be identified on metro Ethernet networks.

QinQ was originally developed to expand VLAN space by adding an additional 802.1Q tag to an 802.1Q-tagged packet. This increases the number of VLANs to 4094 x 4094.

As metro Ethernet networks develop and carriers need to refine their service operations, QinQ is applied in scenarios other than simply to expand VLAN space. For example, because the inner and outer VLAN tags can be used to differentiate packets based on users and services, the inner tag can represent a user and the outer tag can represent a service. In addition, QinQ can be used to provide simple VPNs because the inner tag of QinQ packets can be transparently transmitted over a public network. Therefore, it can extend core MPLS VPN services to metro Ethernet networks to establish an end-to-end VPN.

QinQ is easy to use and widely used on carrier networks. For example, it can be combined with multiple services in metro Ethernet solutions. Selective QinQ (VLAN stacking) makes QinQ services more popular among carriers. As metro Ethernet networks develop, QinQ plays an important role in enabling device vendors to develop custom metro Ethernet solutions.


QinQ offers the following benefits:
  • Extends VLAN space to isolate and identify more users.
  • Facilitates service deployment by allowing the inner and outer tags to represent different information. For example, the inner tag identifies a user and the outer tag identifies a service.
  • Allows carriers to implement refined service operation by providing diversified encapsulation and termination modes.
Updated: 2019-01-18

Document ID: EDOC1100038290

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