Subnetting / FLSM

Definition

• Subnetting divides one IP network into multiple smaller networks (subnets). FLSM is a type of subnetting where every subnet is the same size.
• It sits in network design after you receive an IP network and before assigning IPs to devices or VLANs.

What Problem It Solves

• Separates departments or locations into independent networks.
• Reduces broadcast traffic and makes networks easier to manage.

What Happens If Not Used

Everyone stays in one large network, causing unnecessary broadcasts, poor organization, and weaker security.

Easy Wording

Subnetting divides one big neighborhood into smaller neighborhoods.

Layman Example

A school building is divided into equal-sized classrooms, even if some classes have fewer students.

Technical Example

• Company receives 192.168.10.0/24.
• Creates four equal /26 subnets.
• Assigns one subnet to each VLAN (HR, IT, Finance, Sales).
• Router performs inter-VLAN routing.

Limitation: Every subnet has the same size, so many IP addresses may be wasted.

Solution: VLSM, where each subnet is sized according to actual host requirements.