Subnetting

🤔 What is Subnetting? (Basic Idea)

Subnetting means dividing one large network into multiple smaller networks, called subnets.

📌 In simple words:

Subnetting breaks a big network into smaller, manageable pieces.

🧠 Real-Life Analogy

🏢 Apartment Building Example

• One big building = One network

• Each floor = One subnet

• Each flat = One host

👉 Easier to manage, secure, and organize.

🧠 Simple Definition

📌 Subnetting is the process of dividing a single IP network into multiple smaller logical networks by borrowing bits from the host portion.

🎯 Why Do We Need Subnetting?

Subnetting is needed to:

• 💰 Reduce IP address wastage

• 🚀 Improve network performance

• 🔐 Increase security

• 📦 Control broadcast traffic

• 🧠 Make network management easier

🧭 Where Does Subnetting Work?

• Performed at the Network Layer

• Uses IP address + Subnet Mask

🧩 Key Concept: Subnet Mask

🔹 What is a Subnet Mask?

A Subnet Mask tells:

• Which part of IP is Network

• Which part is Host

📌 Example:

IP Address :192.168.1.10
Subnet Mask:255.255.255.0

🔢 Binary View (Very Important)

Subnet Mask: 255.255.255.0

Binary:

11111111.11111111.11111111.00000000

📌

• 1 → Network bit

• 0 → Host bit

🧠 Default Subnet Masks (Must Remember)

🔑 Golden Rule of Subnetting

👉 Subnetting borrows bits from the HOST portion to create more NETWORKS.

🪜 Subnetting Step-by-Step

We always answer subnetting questions using these steps:

✅ Step 1: Identify the Class

Example IP: 192.168.1.0

• First octet = 192

• 👉 Class C

✅ Step 2: Note Default Subnet Mask

Class C default mask:

255.255.255.0  →  /24

✅ Step 3: Determine Requirement

Question may ask:

• Number of subnets

• Number of hosts per subnet

📌 Example:

Create 4 subnets

✅ Step 4: Borrow Bits

Formula:

Numberofsubnets=2ⁿ

To create 4 subnets:

2² = 4

👉 Borrow 2 bits from host portion.

✅ Step 5: New Subnet Mask

Original mask: /24

Borrow 2 bits → New mask = /26

Subnet Mask:

255.255.255.192

Binary:

11111111.11111111.11111111.11000000

✅ Step 6: Calculate Hosts per Subnet

Formula:

Hostspersubnet=2ʰ −2

Remaining host bits = 6

2⁶ − 2 = 62 hosts

📦 Subnet Address Calculation

IP: 192.168.1.0/26

Block size:

256 − 192 = 64

📊 Subnet Table

🧠 Important Subnetting Formulas

🧠 Subnetting vs Supernetting (Preview)

📌 Supernetting is coming next 😉

🧠 Subnetting with Diagram (Conceptual View)

🧠 Memory Trick (Very Useful)

/24 → 256 hosts
/25 → 128
/26 → 64
/27 → 32
/28 → 16
/29 → 8
/30 → 4

⭐ One-Line Summary

🔹 Subnetting divides a large IP network into smaller, efficient, and manageable sub-networks by borrowing host bits.