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🔹 Introduction

Subnetting divides a large network into smaller subnetworks, improving security, performance, and efficient IP address usage.

CIDR (Classless Inter-Domain Routing) replaces classful addressing and allows flexible network prefix lengths.

1️⃣ What is Subnetting?

Subnetting breaks a network into multiple smaller networks by borrowing bits from the host portion.

✔ Benefits of Subnetting

• Efficient IP address usage
• Reduced broadcast traffic
• Improved security
• Better network management

✔ Subnetting Formula

Number of Subnets = 2^n  
Number of Hosts per Subnet = 2^(remaining bits) - 2

2️⃣ Subnetting Example (Detailed)

✔ Given:

Network: 192.168.10.0/24  
Required Subnets: 4

✔ Step 1: Borrow Bits

• 4 subnets needed → 2^n = 4 → n = 2 bits

✔ Step 2: New Subnet Mask

Original mask: /24 → 255.255.255.0  
Borrow 2 bits → new mask = /26 → 255.255.255.192

✔ Step 3: Subnet Calculation

3️⃣ CIDR (Classless Inter-Domain Routing)

CIDR replaces class A/B/C addressing and uses network prefixes like /16, /19, /23 instead of fixed class boundaries.

✔ CIDR Benefits

• Prevents IP address wastage
• Supports route aggregation (supernetting)
• Enables flexible subnet design
• Reduces routing table size

✔ CIDR Example

IP Block: 172.16.0.0/20  
Covers: 172.16.0.0 – 172.16.15.255  
Total Hosts: 4094

✔ Supernetting Example

Combining four /24 networks into one /22 block:

192.168.4.0  
192.168.5.0  
192.168.6.0  
192.168.7.0  
Combined → 192.168.4.0/22

4️⃣ Common CIDR Blocks and Host Capacity

📝 Conclusion

Subnetting and CIDR are essential for modern IP addressing, enabling efficient address utilization, improved routing, and scalable network design. CIDR’s flexibility has replaced traditional classful addressing and allows networks to grow or shrink as required.