3Com Switch 7750 Configuration Guide Guide

18
QINQ CONFIGURATION
QinQ Overview
Introduction to QinQ The QinQ function enables packets to be transmitted across the operators’
backbone networks with VLAN tags of private networks encapsulated in those of
public networks. In public networks, packets of this type are transmitted by their
outer VLAN tags (that is, the VLAN tags of public networks). And those of private
networks which are encapsulated in the VLAN tags of public networks are
shielded.
Figure 39 illustrates the structure of a packet with single VLAN tag.
Figure 39 Structure of the packets with single VLAN tag
Figure 40 illustrates the structure of a packet with nested VLAN tags.
Figure 40 Structure of packets with nested VLAN tags
Compared with MPLS-based Layer 2 VPN, QinQ has the following features:
■ It enables Layer 2 VPN tunnels that are simpler.
■ QinQ can be implemented through manual configuration, without the support
of signaling protocols.
The QinQ function provides you with the following benefits:
■ Saves public network VLAN ID resource.
■ You can have VLAN IDs of your own, which is independent of public network
VLAN IDs.
■ Provides simple Layer 2 VPN solutions for small-sized MANs or intranets.
Implementation of QinQ QinQ can be implemented by enabling the QinQ function on ports.
With the QinQ function enabled for a port, the switch will tag a received packet
with the default VLAN tag of the receiving port no matter whether or not the
packet already carries a VLAN tag, and the switch will learn the source MAC
address of the packet into the MAC address table of the default VLAN. If the
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