VLAN : A VLAN is a logically separate IP subnetwork. VLANs allow multiple IP networks and subnets to exist on the same switched network. For computers to communicate on the same VLAN, each must have an IP address and a subnet mask that is consistent for that VLAN.

The switch has to be configured with the VLAN and each port in the VLAN must be assigned to the VLAN. A switch port with a singular VLAN configured on it is called an access port. Remember, just because two computers are physically connected to the same switch does not mean that they can communicate.

Devices on two separate networks and subnets must communicate via a router (Layer 3), whether or not VLANs are used. We do not need VLANs to have multiple networks and subnets on a switched network, but there are definite advantages to using VLAN.