VLAN (Virtual Local Area Network)

Definition

A VLAN logically divides one physical switch into multiple separate networks. It keeps devices grouped even if they share the same switch.

Role: Network segmentation and traffic isolation.

What Problem It Solves

Without buying multiple switches, you can separate departments (HR, Sales, Servers), improving security and reducing unnecessary broadcast traffic.

What Happens If Not Used

All devices share one large network, causing more broadcasts, lower performance, and easier unauthorized access.

Easy Wording

A VLAN is like creating separate rooms inside one large office building.

Layman Example

One apartment building has one entrance, but each family has its own locked apartment. Everyone shares the building, not the living space.

Technical Example

Before VLAN:

PC → Switch → Every device receives broadcasts → Server.

After VLAN:

• Employee PC (VLAN 10) sends request.
• Switch forwards only within VLAN 10.
• Request reaches Web Server in VLAN 10.
• Devices in VLAN 20 never see it.

Limitation

Devices in different VLANs cannot communicate directly. To connect them securely, the next concept is Inter-VLAN Routing using a router or Layer 3 switch.