👈

• 🌐 What is Subnetting?
  • 🤔 Why do we need Subnetting?
    • 1️⃣ Better Network Management
    • 2️⃣ Security
    • 3️⃣ Reduced Network Traffic
    • 4️⃣ Required in AWS
  • 🧠 Basic IP Address Concept (Very Important)
  • 🧩 CIDR Notation (Foundation of Subnetting)
    • What does /24 mean?
  • 📊 Host Calculation Formula
  • 🧮 Example 1: /24 Network
    • Range:
  • ✂️ Subnetting Example (Very Important)
    • We have:
    • Step 1: Borrow bits
    • Step 2: New subnets
      • Subnet 1
      • Subnet 2
  • 🧠 Easy Trick to Remember
  • ☁️ Subnetting in AWS (Very Important)
    • Example AWS Setup
    • Public Subnet
    • Private Subnet
  • 🎯 Key Points for Exams (Cloud Practitioner)
  • 🧠 AWS Special Rule (Very Important)
  • 📌 Simple One-Line Definition (Exam Ready)

🌐 What is Subnetting?

Subnetting means:

Dividing one big network into smaller networks (sub-networks).

These smaller networks are called subnets.

🤔 Why do we need Subnetting?

There are 4 main reasons:

1️⃣ Better Network Management

• Easier to organize systems

• Example:

  • One subnet for servers
  • One subnet for databases
  • One subnet for users

2️⃣ Security

• You can restrict access between subnets

• Example:

  • Database subnet cannot be accessed directly from the internet

👉 Very important for AWS

3️⃣ Reduced Network Traffic

• Smaller networks = less broadcast traffic
• Faster communication

4️⃣ Required in AWS

In AWS:

• VPC = network
• Subnet = smaller network inside VPC

You cannot launch EC2 without a subnet.

🧠 Basic IP Address Concept (Very Important)

An IP address looks like this:

192.168.1.10

It has 32 bits (IPv4).

🧩 CIDR Notation (Foundation of Subnetting)

Subnetting uses CIDR.

Example:

192.168.1.0/24

What does /24 mean?

• 24 bits are for network
• Remaining bits are for hosts

📊 Host Calculation Formula

Number of hosts = 2^(host bits) - 2

Why -2?

• 1 for Network address
• 1 for Broadcast address

🧮 Example 1: /24 Network

192.168.1.0/24

• Total bits: 32
• Network bits: 24
• Host bits: 8

Hosts = 2^8 - 2 = 254

Range:

Network:   192.168.1.0
First IP:  192.168.1.1
Last IP:   192.168.1.254
Broadcast: 192.168.1.255

✂️ Subnetting Example (Very Important)

We have:

192.168.1.0/24

We want 2 subnets.

Step 1: Borrow bits

To create 2 subnets, borrow 1 bit.

/24 → /25

Step 2: New subnets

Subnet 1

192.168.1.0/25
Range: 192.168.1.0 – 192.168.1.127
Usable IPs: 126

Subnet 2

192.168.1.128/25
Range: 192.168.1.128 – 192.168.1.255
Usable IPs: 126

🧠 Easy Trick to Remember

☁️ Subnetting in AWS (Very Important)

Example AWS Setup

VPC: 10.0.0.0/16

You create subnets like:

Public Subnet:  10.0.1.0/24
Private Subnet: 10.0.2.0/24

Public Subnet

• Route to Internet Gateway
• EC2 can access internet

Private Subnet

• No direct internet
• Used for DB, backend

🎯 Key Points for Exams (Cloud Practitioner)

✔ Subnet = smaller network ✔ CIDR defines IP range ✔ AWS reserves 5 IPs per subnet ✔ Public subnet = route to IGW ✔ Private subnet = no IGW route

🧠 AWS Special Rule (Very Important)

In AWS, 5 IPs are always reserved:

Example for /24:

Total IPs: 256
Usable in AWS: 251

Reserved:

• Network address
• Router
• DNS
• Reserved future use
• Broadcast

📌 Simple One-Line Definition (Exam Ready)

Subnetting is the process of dividing a large IP network into smaller, manageable networks using CIDR notation.