3Com Switch 7754, Configuration Manual

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19
Q
IN
Q C
ONFIGURATION
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 43 illustrates the structure of a packet with single VLAN tag.
Figure 43 Structure of the packets with single VLAN tag
Figure 44 illustrates the structure of a packet with nested VLAN tags.
Figure 44 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:
Destination MAC address
0 31
Data
Source MAC address
15
VLAN Tag
Destination MAC address
0 31
Data
Source MAC address
15
Inner VLAN Tag
Outer VLAN Tag