What is QinQ
In this section, we will see about Switching concept QinQ. In service provider networks, This is very important. Service provider use this Switching function to pass customer data from one end to other end with two vlan id’s in own switching network.
Let’s see this concept in detail---
What is QinQ?
The QinQ technology is called VLAN dot1q tunnel, 802.1Q tunnel, VLAN Stacking technology. The standard comes from IEEE 802.1ad and it is the expansion of the 802.1Q protocol. QinQ adds one layer of 802.1Q tag (VLAN tag) based on the original 802.1Q packet head. With the double layers of tags, the VLAN quantity is increased to 802.1Q.
QinQ encapsulates the private network VLAN tag of the user in the public(service provider) network VLAN Tag to make the packet with double layers of VLAN Tags cross the backbone network (public network) of the operator. In the public network, the packet is passed according to the out layer of VLAN tag (that is the public network VLAN Tag) and the private network VLAN Tag of the user is shielded.
The formats of the common 802.1Q packet with one layer of VLAN TAG and the QinQ packet with two layers of VLAN TAGs are as follows:
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The formats of common VLAN packet and QinQ packet
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The formats of common VLAN packet and QinQ packet Two layers of VLAN tags can support 4K × 4K VLANs, meeting most of requirements ISP and overcoming limitation of VLANs.
QinQ features:
- Provide one simple L2 VPN tunnel for the user.
- Do not need the supporting of the protocol and signaling; be realized by the static configuration.
QinQ mainly solves the following problems:
- Shield the VLAN ID of the user, so as to save the public network VLAN ID resource of the service provider.
- The user can plan the private network VLAN ID, avoiding the confliction with the public network and other user VLAN IDs.
- Provide the simple L2 VLAN solution.
QinQ in Action
The upstream packet of the CE1 switch carries one layer of VLAN tag. The packet reaches the QinQ port of the PE1 switch. According to the configuration of the QinQ port, add one out layer of VLAN TAG to the packet. The packet with two layers of VLAN tags is forwarded to PE2 via the public network. On the QinQ port of PE2, the out layer of VLAN TAG is deleted, and the packet recovers to have one layer of VLAN Tag and is forwarded to CE2.
Realizing Modes of QinQ
QinQ is divided to two kinds, including basic QinQ and selective QinQ.
Basic QinQ:
When receiving the packet, the QinQ port adds the VLAN TAG of the default VLAN of the port to the packet no matter whether the packet has the VLAN TAG. Before the packet is forwarded out from the QinQ port, delete the out layer of TAG and then forward it. The disadvantage of the method is that the encapsulated out layer of VLAN cannot be selected according to the VLAN TAG of the packet
Selective QinQ:
The selective QinQ solves the disadvantage of the basic QinQ. When receiving the packet, the QinQ port adds the specified out layer of VLAN TAG to the packet according to the VLAN TAG of the packet. If the encapsulated out layer of VLAN TAG is not specified, add the VLAN TAG of the default VLAN of the port to the packet.
QinQ expansion: Configure the mapping entries on the QinQ port to replace the VLAN TAG of the packet with the specified VLAN TAG to realize the conversion of the VLAN TAG. The function is called VLAN Mapping.
TPID (Tag Protocol Identifier): It is one field in VLAN TAG, used to indicate the protocol type of VLAN TAG. IEEE 802.1Q protocol defines the value of the field as 0x8100 The default value of the out layer of TPID of QinQ is 0x8100. The TPID of the out VLAN TAG of the device QinQ packet of some manufacturer is 0x9100 or 0x9200. The user can modify the TPID of the port at the public network to realize the intercommunication of the devices of different manufacturers.
In next post we will see about configuration of Maipu Switches for QinQ, For Cisco QinQ configuration - Click here
Hope this post will help you for understanding concepts of QinQ.
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