Quidway S3500-EA Series Operation Manual - page 2
Operation Manual - QinQ-BPDU Tunnel
Quidway S3500-EA Series Ethernet Switches
Chapter 1 QinQ Configuration
Huawei Technologies Proprietary
1-1
Chapter 1 QinQ Configuration
1.1 Introduction to QinQ
1.1.1 Understanding QinQ
In the VLAN tag field defined in IEEE 802.1Q, only 12 bits are used for VLAN IDs, so a
device can support a maximum of 4,094 VLANs. In actual applications, however, a
large number of VLAN are required to isolate users, especially in metropolitan area
networks (MANs), and 4,094 VLANs are far from satisfying such requirements.
The port QinQ feature provided by the Quidway S3500-EA series Ethernet switches
enables the encapsulation of double VLAN tags within an Ethernet frame, with the inner
VLAN tag being the customer network VLAN tag while the outer one being the VLAN
tag assigned by the service provider to the customer. The devices of the service
provider forward frames based on the outer VLAN tag and add the source MAC
addresses to the MAC address table of the VLANs corresponding to the outer VLAN
tags. However, the customer network VLAN tag is shielded during data transmission.
Figure 1-1
shows the structure of 802.1Q-tagged and double-tagged Ethernet frames.
The QinQ feature enables a device to support up to 4,094 x 4,094 VLANs to satisfy the
requirement for the amount of VLANs in the MAN.
DA
(6B)
Etype
(2B)
SA
(6B)
User VLAN tag
(2B)
Data
FCS
(4B)
Len/Etype
DA
(6B)
ETYPE
(2B)
SA
(6B)
Nested VLAN TAG
(2B)
Data
FCS
(4B)
LEN/ ETYPE
(2B)
User VLAN TAG
(2B)
ETYPE
(2B)
Inner VLAN
TAG
Outer VLAN
TAG by Q-in-Q
Single-tagged
frame structure
(2B)
(0 to 1500B)
(0 to 1500B)
Double-tagged
frame structure
Figure 1-1
802.1Q-tagged frame structure vs. double-tagged Ethernet frame structure
Advantages of QinQ:
z
Addresses the shortage of public VLAN ID resource
z
Enables customers to plan their own VLAN IDs, with running into conflicts with
public network VLAN IDs.
z
Provides a simple Layer 2 VPN solution for small-sized MANs or intranets.