Technically, VLAN (virtual local area network) is also known as a virtual LAN. This technology can logically partition and isolate one or more physical LANs into multiple broadcast domains. And each broadcast domain is regarded as one VLAN. Generally, only devices under the same VLAN can communicate with each other. Why VLAN is used? Before VLAN, there was a single broadcast domain over the specified network, which is called as LAN (local area work). Just like the following LAN application topology showed, in order to communicate with host B, host A will broadcast its ARP (address resolution protocol) request to all the switches and other hosts over the same local area network.
However, when the network is bombarded with hosts and switches, it’s likely to lead to broadcast storms. Consequently, the hosts’ CPU and the bandwidth of the whole network will be greatly consumed. To solve that, VLAN arrives.
By configuring VLANs, you can divide a network into different broadcast domains. Packets sent from workstations on one network segment are transmitted by Bridges or switches that do not forward conflicts but broadcast to each network device. This simplifies many of the potential complications caused by Lans, including excessive network traffic and conflicts. In this way, network resources and bandwidth will be greatly saved, improving network flexibility and performance.