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S12700 V200R010C00 Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring link aggregation, VLANs, Voice VLAN, VLAN mapping, QinQ, GVRP, MAC table, STP/RSTP/MSTP, SEP, and so on.
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Introduction to VLAN Termination

Introduction to VLAN Termination


VLAN termination is a VLAN tag processing mechanism. After VLAN termination is enabled on a device, the device identifies VLAN tags in received packets, removes single or double tags from the packets, and then forwards packets at Layer 3 or takes other actions. These VLAN tags are only useful before termination, and are not used in Layer 3 forwarding or other processing.

A device with VLAN termination enabled processes incoming and outgoing packets as follows:
  • Removes VLAN tags from the packets received on interfaces, and then forwards the packets at Layer 3 or takes other actions.
  • Adds VLAN tags to the packets that will be sent out through interfaces.


Depending on the modes in which VLAN tagged packets are processed, VLAN termination has the following sub-functions:

  • Dot1q termination: removes the outer VLAN tag from the received single-tagged or double-tagged packets, and adds a VLAN tag to the packets to be sent by an interface.
  • QinQ termination: removes double VLAN tags from the received double-tagged packets, and adds double VLAN tags to the packets to be sent by an interface.

Generally, VLAN termination is configured on sub-interfaces. A sub-interface that terminates single tags in packets is called a Dot1q termination sub-interface, and a sub-interface that terminates double tags in packets is called a QinQ termination sub-interface.

Dot1q and QinQ VLAN tag termination sub-interfaces do not support transparent transmission of packets that do not contain a VLAN tag, and discard received packets that do not contain a VLAN tag.


After VLANs are assigned on a network, hosts in the same VLAN can communicate with each other at Layer 2, whereas hosts in different VLANs cannot. You can use VLANIF interfaces on a Layer 3 switch to implement inter-VLAN Layer 3 connectivity. As shown in Figure 8-1, when a Layer 3 switch uses only one Layer 3 Ethernet interface to connect to users or a network, this interface needs to transmit packets from multiple VLANs. A VLANIF interface cannot provide this function. You can virtualize a Layer 3 Ethernet interface into multiple logical sub-interfaces. The Layer 3 Ethernet interface is the main interface for the logical sub-interfaces.

Figure 8-1  Networking of configuring sub-interfaces to implement interworking

By default, a Layer 3 Ethernet sub-interface treats received VLAN packets as invalid packets and discards them; therefore, VLAN termination needs to be configured on the Layer 3 Ethernet sub-interface so that the sub-interface can remove VLAN tags from packets.

Updated: 2019-08-21

Document ID: EDOC1000142081

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