Operation Manual – QinQ-BPDU Tunneling
H3C S3610&S5510 Series Ethernet Switches
Chapter 1 QinQ Configuration
1-1
Chapter 1 QinQ Configuration
When configuring QinQ, go to these sections for information you are interested in:
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z
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Configuring MAC Address Synchronization
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Configuring the TPID to Be Used in the Outer Tag
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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
switch can support a maximum of 4,094 VLANs. In actual applications, however, a
large number of VLANs 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 is a flexible, easy-to-implement Layer 2 VPN technique, which
enables the access point to encapsulate an outer VLAN tag in Ethernet frames from
customer networks (private networks), so that the Ethernet frames will travel across the
service provider’s backbone network (public network) with double VLAN tags. The
inner VLAN tag is the customer network VLAN tag while the outer one is the VLAN tag
assigned by the service provider to the customer. In the public network, frames are
forwarded based on the outer VLAN tag only, with the source MAC address learned as
a MAC address table entry for the VLAN indicated by the outer tag, while the customer
network VLAN tag is transmitted as part of the data in the frames.
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.
Etype
DA
SA
User
VLAN Tag
Etype
DATA
FCS
DA
SA
Nested
VLAN Tag
DATA
FCS
User
VLAN Tag
6 bytes
6 bytes
Single-tagged frame
structure
Double-tagged frame structure
4 bytes
6 bytes
6 bytes
4 bytes
4 bytes
4 bytes
4 bytes
2 bytes
2 bytes
46 to 1500 bytes
46 to 1500 bytes
Outer
VLAN
tag
Inner
VLAN
tag
Figure 1-1
Single-tagged frame structure vs. double-tagged Ethernet frame structure
