VLANs allow segmentation of a single broadcast domain into multiple broadcast domains in a layer 2 switched network. A VLAN uses virtual boundaries to divide devices into different broadcast domains even if they are physically located on the same switch. Devices within a VLAN can communicate within the broadcast domain but a layer 3 device is required to allow inter-VLAN communication since each VLAN represents a separate IP subnet.

1. VLAN (Virtual Local Area Network)
www.netprotocolxpert.in

2.  In a layer 2 switched network, each network segment has its
own collision domain and all segments are in same broadcast
domain.
 Every broadcast is seen by every device on the network. A layer 3
device (typically a Router) is used to segment (divide)
a broadcast domain to multiple broadcast domains.

3. Layer 2 switched network where all network device are in a
single broadcast domain

4.  By default, all ports on a switch are in the same broadcast
domain.
 A Virtual Local Area Network, Virtual LAN, or VLAN, can be
used to segment (divide) a single broadcast domain to
multiple broadcast domains in a layer 2 switched network.

5. VLAN 1
VLAN 2
Layer 2 switched network with two VLAN, Each are in different
broadcast domain

6.  VLANs are not restricted to any physical boundary in the
switched network if the devices are interconnected using
switches.
 A VLAN can span across multiple switches, or it can be limited
within a switch.
 A VLAN must be configured as a separate Layer 3 IP subnet and
you need a Layer 3 device (typically a Router) to enable
communication between different VLANs.
 Therefore a VLAN = Broadcast Domain = A Separate IP subnet