Subnet

Definition

A Subnet is a logical subdivision of a larger IP network. It separates networks into smaller isolated groups.

What Problem It Solves

Subnets solve network congestion and security fragmentation. By dividing a broad network into smaller isolated segments, it restricts network broadcasts to local hosts and enforces strict security boundaries (e.g., isolating production databases in private subnets).

What Happens If Not Used

Without subnets, broadcast traffic would overwhelm the network, and any compromised device on the network could directly sniff and access packets from other highly sensitive servers like the database.

Easy Wording

A subnet is a small network inside a bigger network.

Layman Example

Imagine:

Big Office

Floor 1 -> HR
Floor 2 -> Finance
Floor 3 -> IT

All belong to:

ABC Company

But each floor has:

• Separate rooms
• Separate permissions
• Separate employees

Each floor is like a Subnet.

Technical Example

Suppose AWS network:

VPC

10.0.0.0/16

Inside it:

Public Subnet

10.0.1.0/24

Contains:
Load Balancer
Backend API


Private Subnet

10.0.2.0/24

Contains:
PostgreSQL
Redis

Flow:

Internet
↓
Public Subnet
↓
Backend API
↓
Private Subnet
↓
Database

Database remains hidden from internet.