4.1 Introduction to QinQ
This section defines QinQ and describes its purpose and benefits.
Definition
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.
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 technology encapsulates an 802.1Q tag to an 802.1Q packet. With this extra tag, the
number of VLANs increases 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
functions as a simple and practical VPN technology by transparently transmitting private VLAN
services over a public network. It extends core MPLS VPN services to metro Ethernet networks
and implements an end-to-end VPN.
Benefits
QinQ offers the following benefits:
l
Extends the VLAN space to isolate and identify more users.
l
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.
l
Allows ISPs to implement refined service operation by providing diversified encapsulation
and termination modes.
4.2 QinQ Principles
This section describes the principles behind QinQ.
4.2.1 QinQ Fundamentals
QinQ expands VLAN space by adding an additional 802.1Q VLAN tag to an 802.1Q-tagged
packet. Devices forward packets over the public network according to outer VLAN tags of the
packets, and learn MAC addresses from the outer VLAN tags. The private VLAN tags in the
packets are forwarded as payload of the packets.
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
4 QinQ Configuration
Issue 01 (2014-11-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
122