What is a VLAN?

To answer this question, we first have to understand what a LAN is.

I know what you’re thinking, you already know what a LAN is right? Well only by returning to the basics, can we build on top of them.

LAN stands for Local Area Network, and that’s exactly what it is, a network which exists in the same local area as everything in it. The definition of local may mean within your house or within your company building, but generally refers to a single location.

Let us take the example of a LAN across a business site one step further.

Imagine we have a company which has its headquarters in a building consisting of 3 floors. Each floor has one switch managing the users there.

The layout is as below:

Floor 3: Sales and Finance
Floor 2: Marketing and Design
Floor 1: Design and Finance

As we can see, there are a mix of teams throughout the floors, some teams are on both floors – clearly this wasn’t well thought out!

Taking the Finance team as an example, they are both on Floors 1 and 3.

How can we make it that they can communicate with each other, while segregating them from the Design and Sales teams?

Here is where VLANs come in.

The ‘V’ in VLAN stands for ‘Virtual’, and it is exactly that, a virtual LAN that is not limited by physical boundaries.

We cannot cut the Switch port which the Finance Team members on the 3rd floor are plugged into and attach that to the Switch on the 1st floor, but we can add those ports to a specific VLAN – we can call it the ‘Finance VLAN’.

Once the relevant ports on both Switches are configured, they will now form a virtual LAN between them, can reach each other, and are segregated from the rest of the users, regardless of their physical location.

This allows Network Administrators to be flexible when grouping users together to share the same network resources.



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