VLSM (Variable Length Subnet Masking)

Definition

• VLSM is subnetting where each subnet can have a different size based on the number of required hosts.
• It is the modern method used after planning departmental requirements and before assigning IPs.

What Problem It Solves

Eliminates unnecessary IP address waste by giving each department only the addresses it needs.

What Happens If Not Used

Small departments receive oversized subnets, leaving many IP addresses unused.

Easy Wording

VLSM gives every department a room that matches its size instead of giving everyone the same room.

Layman Example

A restaurant seats a couple at a 2-person table and a family at an 8-person table instead of giving everyone an 8-person table.

Technical Example

• Company receives 192.168.10.0/24.
• IT (100 hosts) gets /25.
• HR (50 hosts) gets /26.
• Finance (20 hosts) gets /27.
• Each subnet is assigned to its VLAN, and the Layer 3 switch routes between them.

Limitation: VLSM requires careful planning and calculations, though it provides much better IP utilization than FLSM.