What are VLANS ?

VLAN’s allow a network manager to logically segment a LAN into different broadcast domains. Since this is a logical segmentation and not a physical one, workstations do not have to be physically located together. Users on different floors of the same building, or even in different buildings can now belong to the same LAN. VLANs are created mainly for administrative purposes to ensure that network traffic is seen only by members of a specific group, rather than by all members of the LAN. This way confidentiality is maintained and additionally nodes are protected from unnecessary traffic. For example, in an enterprise, each department (like Engineering, HR, Accounts etc.) may be maintained as a separate VLAN. Similarly, in a campus or a university network, each department (e.g. maths, physics, computer science etc.) would typically be part of a separate VLAN.

Advantages of VLAN
1. It Reduces the size of broadcast domains

VLAN increase the numbers of broadcast domains while reducing their size. For example we have a network of 100 devices. Without any VLAN implementation we have single broadcast domain that contain 100 devices. We create 2 VLANs and assign 50 devices in each VLAN. Now we have two broadcast domains with fifty devices in each. Thus more VLAN means more broadcast domain with less devices.

2. Reduced Cost

VLAN’s can be used to create broadcast domains which eliminate the need for expensive routers.

3. Make device management easier

Device management is easier with VLANs. Since VLANs are a logical approach, a device can be located anywhere in the switched network and still belong to the same broadcast domain. We can move a user from one switch to another switch in same network while keeping his original VLAN. For example a company has a five story building and a single layer two network.So in this scenario, VLAN allows us to move the users from one floor to another floor while keeping his original VLAN ID. The only limitation we have is that device when moved, must still be connected to the same layer 2 network.

4. Solve broadcast problem

In practical environment we use VLAN to solve broadcast issue instead of router. Each VLAN has a separate broadcast domain. Logically VLANs are also subnets. Each VLAN requires a unique network number known as VLAN ID. Devices with same VLAN ID are the members of same broadcast domain and receive all broadcasts. These broadcasts are filtered from all ports on a switch that aren’t members of the same VLAN.