What is Virtual LAN : Architecture, Types of Links & Differences

Transmission of digital data between various computers is known as data communication, and the exchange of data between two or more computers is known as a computer network or data network. The exchange of data can take place either wired or wirelessly. The LAN (Local Area Network) can broadcast the transmitter data to every receiver of the same LAN network using a switch or router device, but the main disadvantage of using a LAN is that it is a time-consuming process. Hence in order to overcome this disadvantage virtual local area network is used. This article explains the importance of Virtual LAN- virtual local area network and its protocol.

What is Virtual LAN?

Definition: A VLAN is a virtual area network that allows us to create multiple LAN networks, with the help of a single switch and also allows us to communicate between different VLAN- virtual local area network without using any physical intermediate device like a router. The main purpose of VLAN is that it can reduce congestion. For better understanding let us consider an example of a LAN and VLAN.

LAN Architecture

LAN architecture can be understood by the following example, in an organization let us assume there are 3groups, group1, group2, group3, if we don’t want anyone of the group to communicate with other groups then we use three separate switches and for intercommunication between three groups, we use an additional networking device router, which is known as the LAN. Where the maintenance cost and time consumption increases.


VLANs operate in the data link layer of the OSI model. Where we divide the devices in layer 2 of OSI and broadcast the data over layer3 of OSI. The communication between any two systems can take place using a medium like a router, similarly, if we consider the situation in LAN when a workstation transmits the data on to LAN bridge on receiving the data it tags both data and VLAN identifier. On tagging, this one can know from which VLAN the data has come from. This process of tagging is called explicit tagging.

The process of knowing which LAN, data is belonging to is known as implicit tagging, it can be identified based on delivered port information.  Tagging can be done either by MAC ( Medium Access Control), network address, or a combination of both. VLAN adds different ranges or classes of IP addresses to a group of  PC connected to the same switch. Where we create multiple networks with a single switch, it also allows communicating with other virtual LANs. The VLAN Standard that is currently being used is IEEE 802.1Q Draft Standard. VLANs are classified into three categories based on

Port Address

Where the membership is defined by the port of source VLAN. It operates in LAYER 1 of the OSI model. The disadvantage of this is that whenever the user switches to a new location that is a new bridge connection, then the user has to reconfigure the VLAN which is a time-consuming process. Example: Port 1, Port 2, Port 3, Port 4 are assigned to VLAN1, VLAN1, VLAN2, VLAN1.

MAC Address

VLAN uses the MAC address of the work station, the switch makes a note of all the LANs MAC address which are connected. The main disadvantage of this is that VLAN membership must be initialized to every user at the beginning of the communication. As the number of users increases, it will be difficult to assign each and every user.

Protocol Type

This type works in layer 2 of the OSI model, where the protocol can be assigned to different VLAN. For example, if we consider a protocol IP and IPX assigned to VLAN 1 and VLA 2.

Virtual LAN in Computer Network

VLAN in a computer network can be understood from the following example if we take a PC in department-1, we have a class A IP address, the PC in department-2 we have class B IP address, and the PC in department-3 we have class C IP address. Now if we want communication to take place between department-1 and department-2 and not with department-3, then we use VLAN as shown below.


Types of Links in Virtual LAN

There are three types of links available in VLAN they are,

  • Access Link
  • Trunk Link
  • Hybrid Link

Access Link

Access link connects the host directly to switch. The devices connected to the access link do not know that there are other VLANs connected to the network.

Trunk Link

The link which connects two or more VLAN- virtual local area network switches and carries the traffic between them. It is a point to point connection topology, which can be between two switches. Hence the router which routes the data packets can be minimized.

Hybrid Link

It is the combination of the access link and trunk link. It contains both known and unknown LANs and also tagged and untagged frames.

Virtual LAN(VLAN) Trunking

A network can have multiple VLAN- virtual local area network switches present on it. When a particular VLAN switch sends a broadcast message to another switch on the network, the receiving switch needs to identify the source of the message. This process of implementation is known as VLAN- virtual local area network Trunking.


Difference Between LAN and VLAN

The difference between LAN and VLAN are discussed below.



All the required configurations are done on PC Configurations are done on both the PC and the switch
Ports present in the switch cannot be configured Every port of the switch is configured
To communicate with another network a router is used. All the configuration is done using switch; hence no router is used.
Data travels in the same broadcast domain VLAN has its own broadcast domain
The network traffic is more The network traffic is less
Network cost is high The network cost is low.

VLAN Trunking Protocol

VTP or VLAN trunking protocol allows switches to synchronize there VLAN configuration. For instance, let us consider a scenario where we want to configure a new VLAN, then we should connect to an individual switch and type manually to configure. When there are more VLAN’s more switches are used, thus complexity increases.

Hence in order to overcome such difficulties, we configure the VLAN onto one switch, and other VLANs will synchronize and connect the VLAN simultaneously. This is how exactly the VLAN trunking protocol works. The individual switch which is used has its own VLAN database, with a revision number. The database changes whenever VLAN is connected or removed and the revision number is incremented by 1 VLAN 20. The code here is to have every single switch with the same VLAN database with the same revision number.


Summary Advertisements Messages

The messages are sent to let all the switches known the current revision number of VLAN- virtual local area network is by summary advertisements messages, which contains

  • VTP domain name: which relocate in a minute,
  • VTP password: which is received in a minute
  • the revision number: where each switch can compare with the own database, and
  • the follower’s field: which indicates other messages will follow.
  • These summary advertisements are transferred for every 5minutes.
  • This summary advertisement messages are used while updating a database.
  • Each switch communicates with each other by sending its own summary advertisements messages and makes sure their database matches with each-others by comparing it with revision numbers.

Subset Advertisements

Whenever there is an update in VLAN then the main switch will send the updated message to other switches that are in synchronization. This message is called Subset Advertisements. Which consists of the VTP domain name and all VLAN information. If there are several VLANs to be added more subset advertisements.

Advertisement Request

The advertisement request is used when the VTP domain name has changed or a switch receives a summary advertisement with a higher revision number than its earned. These messages allow the switch to request subset advertisements to synchronize its VLAN database.

Modes of Operation

VTP can operate in three modes

  • Server mode: Where it can create VLANs and sends updates and advertises the VTP database.
  • Client mode: They cannot create VLAN’s, they can only update from service switches and send updates and advertises VTP databases.
  • Transparent: VTP is disabled, they can create their own VLAN’s, does not update or advertise but forwards updates.

VTP Pruning

It is a feature of VTP that prevents unnecessary traffic from being sent to switches with no port on particular VLAN. The switches will prune VLAN from trunks in order to reduce any unnecessary bandwidth and resource usage. They do this by sending a join message.


The following are the requirements for VTP operation

  • Links must be trunks
  • Same VTP domain name
  • VTP password (optional).

Advantages of Virtual LAN

The advantages of VLAN are

  • Broadcast control: For any communication to take place over a network, the data must be broadcasted using various protocols. For instance, in a layer 2 network uses a single broadcast domain, which can broadcast up to long-distance, and consumes available bandwidth. Whereas a 3 -layer segments the broadcast domain. In order to overcome traffic problems, the large LAN is segmented into smaller VLANs, where the broadcast is sent to relevant VLAN only.
  • VLAN restricts sensitive data with high security
  • Larger VLANs are segmented into smaller VLANs which reduces cost compared to the router network.
  • Physical layer transparency.

Disadvantages of  Virtual LAN

The disadvantages of VLAN are

  • Complex to handle
  • More configurations are needed
  • Over headed.

Applications of Virtual LAN

The network technologies which uses VLAN are,

VLAN can be applicable in a local network like

  • Production
  • VoIP.


1). Why is VLAN used?

VLAN is used to overcome congestion in network communication when there are many networking sources. It is activated using the software.

2). Which domain VLAN works?

VLAN works in a broadcast domain.

3).  How many VLANs can switch support?

VTP version 1 and version 2 support VLAN IDs 1 to 1005.VTP version 3 supports the VLAN range of  (VLANs 1 to 4094).

4). What is the trunk port?

A trunk port carries traffic for all the VLAN that is accessible by a specific switch.

5). Can one port be a member of two VLANs?

A single port can not have access to two VLANs.

Thus, Communication between any two systems can take place using a medium, which can be wired or wireless. The computer networking uses the VLAN – Virtual Local Area Network concept which is, where we divide the physical network which is configured using software, it is used when there are a greater number of systems to be communicated over the computer network. It divides larger messages which are to be broadcasted into small blocks, also allows the network admin to have proper control over traffic using VLAN protocol.

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