H3C H3C S7500E-X, Руководство по настройке

Страница: 202 / 290

189
Configuring QinQ
This document uses the following terms:
•
CVLAN
—Customer network VLANs, also called inner VLANs, refer to VLANs that a customer
uses on the private network.
•
SVLAN
—Service provider network VLANs, also called outer VLANs, refer to VLANs that a
service provider uses to transmit VLAN tagged traffic for customers.
Overview
802.1Q-in-802.1Q (QinQ) adds an 802.1Q tag to 802.1Q tagged customer traffic. It enables a
service provider to extend Layer 2 connections across an Ethernet network between customer sites.
QinQ provides the following benefits:
•
Enables a service provider to use a single SVLAN to convey multiple CVLANs for a customer.
•
Enables customers to plan CVLANs without conflicting with SVLANs.
•
Enables customers to keep their VLAN assignment schemes unchanged when the service
provider changes its VLAN assignment scheme.
•
Allows different customers to use overlapping CVLAN IDs. Devices in the service provider
network make forwarding decisions based on SVLAN IDs instead of CVLAN IDs.
How QinQ works
As shown in Figure 56 , a QinQ frame transmitted over the service provider network carries the
following tags:
•
CVLAN tag
—Identifies the VLAN to which the frame belongs when it is transmitted in the
customer network.
•
SVLAN tag
—Identifies the VLAN to which the QinQ frame belongs when it is transmitted in the
service provider network. The service provider allocates the SVLAN tag to the customer.
The devices in the service provider network forward a tagged frame based on its SVLAN tag. The
CVLAN tag is transmitted as part of the frame's payload.
Figure 56 Single-tagged Ethernet frame header and double-tagged Ethernet frame header
As shown in Figure 57 , customer A has remote sites CE 1 and CE 4. Customer B has remote sites
CE 2 and CE 3. The CVLANs of the two customers overlap. The service provider assigns SVLANs 3
and 4 to customers A and B, respectively.