What is a VLAN?

What is a VLAN?

Let's start with What is a LAN:

Okay, most of you already know what a LAN is but let’s give it a definition to make sure. We have to do this because, if you don’t know what a LAN is, you can’t understand what a VLAN is.

A LAN is a local area network and is defined as all devices in the same broadcast domain. If you remember, routers stop broadcasts, switches just forward them.

A VLAN is a Virtual LAN:

It allows you to have multiple broadcast domains on your network.

So what does that mean? It's a Logical (Software) way to break up your network at the switch level, without buying/using multiple physical switches. i.e. if you have only one switch, but need it to act as two independant switches - use a VLAN, don't buy a second physical switch.

Why use a VLAN:

Two good examples are:

1) If you have an iSCSI device on your network, such as a NAS storage device, if it's on its own VLAN you can seperate the traffic from the "regular" network for better performance and increased security.

2) If you have a Voice-over-IP Phone system (VoIP), its a great, and most likely mandatory, way to seperate Voice and Data on your single network.

On a switch, there is a "Default VLAN" by default that every physical port belongs to. So when you buy a new switch, take it out of the box, plug it in and start using it, you are already using the one default VLAN on it. Configure more VLAN's when you need to.