VLAN, or Virtual local area network, refers to a broadcast domain in which the devices are located on one or more LANs in a computer network. This grouping of devices are designed to communicate and transfer information, acting as though the grouping was all part of a single wire when in reality they’re found on independent segments using different switches. This allows network application separation, while still being a part of the same physical network allowing simpler cabling and streamlined deployment.
VLANs are able to be configured and divided on a more flexible level, in configurations that make the most logical sense for an organization. For example with VLANs, an organization has the power to choose network divisions by departments, teams, building floors or whatever configuration they feel is the best fit. VLANs have the ability to spread across multiple switches, on one or more broadcast domains and each VLAN is subsequently acting as it’s own broadcast domain.
In a LAN, every device in that LAN can communicate with every other device. If an individual wants to isolate one computer from another then they would have to build two physically separate LANs with two switches. With VLANs we can now have a single switch act as though it were multiple switches. Each virtual LAN is unaware of other VLANs on the same switch, just as if they were on different physical networks.
If an individual wants VLANs to go across two switches, the connection between those switches is called a "trunk". The VLAN tag tells a trunk port (the name of the switch port that is configured as an inter-switch trunk) which VLAN it belongs to. VLAN tags are used whenever more than one VLAN uses a single link. If only one VLAN is going to be used on a link then this is untagged. For example, a student's computer may always plug into the student VLAN. This port is "untagged" because I know any traffic on that port is in the Student VLAN.
While the benefits of VLANs pertain to individual organizations, many find that VLANs significantly increase adaptability and flexibility within their network. The adaptable grouping of VLANs also allows for streamlined network setups, avoiding complicated wiring and configurations. Other benefits include: