Chapter 1 Qinq Configuration; Introduction To Qinq; Understanding Qinq - H3C S5500-SI Series Operation Manual

Operation Manual – QinQ-BPDU TUNNEL
H3C S5500-SI Series Ethernet Switches

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 device 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 SA
(6B) (6B)
DA SA
(6B) (6B)
Figure 1-1 802.1Q-tagged frame structure vs. double-tagged Ethernet frame structure
Advantages of QinQ:
Addresses the shortage of public VLAN ID resource
Enables customers to plan their own VLAN IDs, with running into conflicts with
public network VLAN IDs.
Provides a simple Layer 2 VPN solution for small-sized MANs or intranets.
Etype User VLAN tag Len/Etype
(2B) (2B)
(2B)
ETYPE Nested VLAN TAG
ETYPE
(2B) (2B)
(2B)
Outer VLAN
TAG by Q-in-Q
Data FCS
(0 to 1500B)
(4B)
LEN/ ETYPE
User VLAN TAG
(2B)
(2B)
Inner VLAN
TAG
1-1
Chapter 1 QinQ Configuration
Single-tag ged
frame struc ture
Data FCS
Double-tagged
(0 to 1500B)
(4B)
frame structure