We have to introduce LAN because, if you don’t know what a LAN is, you can’t understand what a VLAN is.
What is a LAN?
A local area network (VLAN) is a computer network that connects computers and devices in a limited geographical area such as home, school, computer laboratory or office building.A LAN is a local area network and is defined as all devices in the same broadcast domain. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased telecommunication lines.
What is a VLAN?
Simply say, a VLAN is a virtual LAN. In technical terms, a VLAN is a broadcast domain created by switches. Normally, it is a router creating that broadcast domain. With VLAN’s, a switch can create the broadcast domain.
A virtual local area network, virtual LAN or VLAN, is a logical grouping of hosts or the network resources connected to a administratively definable switch port with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical local area network (LAN), but it allows for end stations to be grouped together even if they are not located on the same network switch. VLAN membership can be configured through software instead of physically relocating devices or connections.
This works by, you, the administrator, putting some switch ports in a VLAN other than 1, the default VLAN. All ports in a single VLAN are in a single broadcast domain.
Because switches can talk to each other, some ports on switch A can be in VLAN 10 and other ports on switch B can be in VLAN 10. Broadcasts between these devices will not be seen on any other port in any other VLAN, other than 10. However, these devices can all communicate because they are on the same VLAN. Without additional configuration, they would not be able to communicate with any other devices, not in their VLAN.
VLAN’s offer higher performance for medium and large LAN’s because they limit broadcasts. As the amount of traffic and the number of devices grow, so does the number of broadcast packets.
VLAN’s also provide security because you are essentially putting one group of devices, in one VLAN,
You need to consider using VLAN’s in any of the following situations:
You have more than 200 devices on your LAN
You have a lot of broadcast traffic on your LAN
Groups of users need more security or are being slowed down by too many broadcasts?
Groups of users need to be on the same broadcast domain because they are running the same applications. An example would be a company that has VoIP phones. The users using the phone could be on a different VLAN, not with the regular users.
Or, just to make a single switch into multiple virtual switches.