What is VLAN?


What is VLAN?

I know that many of my students already know the answer to the question “What is VLAN”.  But here I am giving out a definition for those who want a deep dive into the theory of VLANs.  A VLAN is a logical grouping of switch ports and broadcast domains created by them.

 Why we need VLAN?

On a traditional/flat switching network, what if we have four nodes connected with one switch?Four PCs with One Switch

The above diagram is showing that, switch is connected to four computers. These systems are able to communicate with each other and are on same broadcast domain.  This means if one computer sends a broadcast, all other devices connected will receive it.  In small networks, broadcast might not be a big issue.  However, as the size of the network increases, broadcasts would become a big issue.  Another major concern is security. In the above network, all users are able to see all devices.

Example of VLAN

Now you can see in above scenario just with the logical grouping of the switch ports or creation of two VLANs, we have two broadcast domains. This means that if any device in each VLAN sends out a broadcast, it will propagate out only the ports in which belong to that same VLAN.  This has benefits for network management and network security.

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