Operation Manual – QinQ-BPDU TunnelingH3C S5500-EI Series Ethernet Switches Chapter 1 QinQ Configuration1-1Chapter 1 QinQ ConfigurationWhen configuring QinQ, go to these sections for information you are interested in:z Introduction to QinQz Configuring Basic QinQz Configuring Selective QinQz Configuring the TPID Value to Be Carried in VLAN Tagsz QinQ Configuration Example1.1 Introduction to QinQ1.1.1 Understanding QinQIn the VLAN tag field defined in IEEE 802.1Q, only 12 bits are used for VLAN IDs, so aswitch can support a maximum of 4,094 VLANs. In actual applications, however, alarge number of VLANs are required to isolate users, especially in metropolitan areanetworks (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, whichenables the access point to encapsulate an outer VLAN tag in Ethernet frames fromcustomer networks (private networks), so that the Ethernet frames will travel across theservice provider’s backbone network (public network) with double VLAN tags. Theinner VLAN tag is the customer network VLAN tag while the outer one is the VLAN tagassigned by the service provider to the customer. In the public network, frames areforwarded based on the outer VLAN tag only, with the source MAC address learned asa MAC address table entry for the VLAN indicated by the outer tag, while the customernetwork VLAN tag is transmitted as part of the data in the frames.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 therequirement for the amount of VLANs in the MAN.
