What is the role of VLAN in network engineering? What is VLAN?

August 8, 2022

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VLAN (Virtual Local Area Network) is a virtual local area network, which is a communication technology that logically divides a physical LAN into multiple broadcast domains.

At the time when the IEEE802.1Internetworking committee ended the revision of the initial VLAN standard. The newly introduced standard further improves the VLAN architecture, unifies the tag formats of different manufacturers in the Frame-Tagging method, and formulates the development direction of the VLAN standard in the future. The formed 802.1Q standard has been widely used in the industry. promotion. Later, in 1999, IEEE promulgated a draft 802.1Q protocol standard for standardizing VLAN implementations. The emergence of 802.1Q broke the deadlock that the virtual network depended on a single vendor, and promoted the rapid development of VLAN from one aspect.

What is the difference between VLAN data frames and traditional Ethernet data frames?


IEEE 802.1Q is the official standard of VLAN, adding 4-byte 802.1Q Tag to the traditional Ethernet data frame (between the source MAC address field and the protocol type field).

The VID (VLAN ID) field in the data frame is used to indicate the VLAN to which the data frame belongs, and the data frame can only be transmitted within the VLAN to which it belongs.

What is the role of VLAN?

A picture to understand the role of VLAN:


As can be seen from the above figure: by dividing different VLANs, hosts in a VLAN can communicate directly, but VLANs cannot communicate directly, thus limiting broadcast packets to one VLAN.

Here the editor summarizes the advantages of VLAN technology, let's take a look:

Restricting the broadcast domain: The broadcast domain is restricted to a VLAN, which saves bandwidth and improves network processing capability.

Enhanced LAN security: Packets in different VLANs are isolated from each other during transmission, that is, users in one VLAN cannot communicate directly with users in other VLANs.

Improve the robustness of the network: the fault is limited to one VLAN, and the fault in this VLAN will not affect the normal work of other VLANs.

Flexible construction of virtual work groups: VLANs can be used to divide different users into different work groups, and users in the same work group do not have to be limited to a fixed physical range, making network construction and maintenance more convenient and flexible.

How are VLAN data frames processed when passing through each interface?

What types of interfaces are there on the device? Let's take a look with me!


Access interface: the interface used to connect the user host on the switch, it can only be connected to the access link (Access Link).

Trunk interface: the interface on the switch used to connect with other switches, it can only be connected to the trunk link (Trunk Link).

In addition, there is another interface called Hybrid interface, which is an interface on the switch that can be connected to both user hosts and other switches. Hybrid interfaces can be connected to both access links and trunk links.

Note: When the Hybrid interface and the Trunk interface receive data, the processing method is the same. The only difference is that when sending data, a Hybrid interface can allow packets of multiple VLANs to be sent without tags, while a trunk interface can only allow packets of the default VLAN to be sent without tags.


Different interface types cause switches to process VLAN data frames differently. The specific processing method is as follows:

Access interface:

Trunk interface

Hybrid interface

In order to help friends better understand the processing of packets, you can also learn from the following table! ! !


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