Subnetting Basics

01Why Subnetting?

1. Efficiency - Better use of IP addresses
2. Security - Isolate networks from each other
3. Performance - Reduce broadcast traffic
4. Management - Organize the network

02IP Address Structure

IPv4 address consists of 32 bits:

192.168.1.100
↓
11000000.10101000.00000001.01100100

Network and Host Part:

[Network Part][Host Part]
192.168.1    .100
Network addr  Device addr

03Subnet Mask

Subnet mask separates network and host part:

04CIDR Notation

192.168.1.0/24
            ↓
         24 bits network
          8 bits host

/24 Example:

Mask: 255.255.255.0
Binary: 11111111.11111111.11111111.00000000
        ←── 24 bits ──→←── 8 bits ──→
        Network         Host

05Host Calculation

Formula: 2^n - 2 = Number of usable hosts

Why -2?

• 1 address: Network address (first)
• 1 address: Broadcast address (last)

06Special Addresses

Each subnet has 2 special addresses:

192.168.1.0/24

Network Address: 192.168.1.0    (unusable)
First Host:      192.168.1.1
Last Host:       192.168.1.254
Broadcast:       192.168.1.255  (unusable)

07Example: /26 Subnetting

Let's divide 192.168.1.0/24 into 4 subnets:

08Summary

• Subnetting = Dividing network
• Subnet mask separates network and host
• CIDR notation: /24, /25, /26...
• Host count: 2^n - 2