VLANs are broadcast domains defined within switches to allow control of broadcast, multicast, unicast, and unknown unicast within a Layer 2 device.
VLANs are defined on a switch in an internal database known as the VLAN Trunking Protocol (VTP) database. After a VLAN has been created, ports are assigned to the VLAN.
VLANs are assigned numbers for identification within and between switches. Cisco switches have two ranges of VLANs, the normal range and extended range.
VLANs have a variety of configurable parameters, including name, type, and state.
Several VLANs are reserved, and some can be used for internal purposes within the switch