IP Addressing

Giving Every Device a Global Identity

1 The Problem We Must Solve

In the previous chapter, we learned:

• LAN communication uses MAC addresses
• But MAC addresses only work locally
• The internet connects millions of networks

So the Internet needs somethingn new:

A way to uniquely identify devices across the entire world.

A way to uniquely identify devices across the entire world.

Imagine sending a letter internatinally without addresses.

Impossible.

Networking needed a global addressing system.

This system is called:

IP Addressing

What Is an IP Address?

An IP address is:

A logical identifier assigned to a device so it can communicate across networks.

Example:

192.168.1.10

Unlike MAC addresses:

Why Logical Addresses?

Logical addresses allow structure.

Think of a postal address:

Country → City → Street → House

Similarly, IP addresses contain hierarchy.

This hierarchy allows routers to make intelligent decisions.

IPv4 Address Structure

IPv4 uses:

32 bits

Meaning:

32 binary digits

Example in binary:

11000000 10101000 00000001 00001010

Humans cannot easily read binary.

So we write it in decimal form.

Dotted Decimal Notation

Each 8 bits = 1 byte (octet).

192.168.1.10

Structure:

[8 bits].[8 bits].[8 bits].[8 bits]

Range of each section:

0 - 255

Two Parts of an IP Address

Every IP address has two logical components:

| Network Portion | Host Portion |

Network Portion

Identifies which network the device belongs to.

Like a city name.

Host Portion

Identifies which device inside that network.

Like a house number.

Example:

192.168.1.10

May mean:

• Network -> 192.168.1
• Host -> 10

Routers care about the network part.

Devices care about the host part.

How Does a Device Know the Split? (Subnet Mask)

A device needs instructions telling:

Which bits belong to network and which to host?

This instruction is called a:

Subnet Mask

Example:

IP Address : 192.168.1.10
Subnet Mask: 255.255.255.0

What the Mask Means

Binary form:

Subnet Mask:
11111111.11111111.11111111.00000000

Rule:

• 1s -> network bits
• 0s -> host bits

So:

• first 24 bits = network
• last 8 bits = host

CIDR Notation

Shortcut format:

192.168.1.10/24

"/24" means first 24 bits are network.

Why Subnetting Exists

Imagine one giant network with millions of devices.

Problems:

• huge broadcasts
• slow performance
• difficult management

Solution:

Divide networks into smaller parts

This is called:

Subnetting

Example

Instead of:

192.168.1.0 (one large network)

We create:

192.168.1.0/26
192.168.1.64/26
192.168.1.128/26
192.168.1.192/26

Now traffic stays localized.

Network scale efficiently.

Public vs Private IP Addresses

Not all IP addresses are global.

Private IP Addresses

Used inside local networks.

Ranges:

10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255

Your home Wi-Fi uses these.

Not directly reachable from Internet.

Public IP Addresses

Assigned globally by ISPs.

Unique worldwide.

Used for Internet communication.

Special IP Addresses

Network Address

Represents the network itself.

Example:

192.168.1.0

Broadcast Address

Sends message to all devices.

Example:

192.168.1.255

Loopback Address

127.0.0.1

Means:

“This computer itself.”

Used for testing networking software.

How Devices Decide Where to Send Data

When sending a packet, device asks:

Is destination inside my network?

Case 1: Same Network

Send directrly using MAC address

(No router needed.)

Case 2: Different Network

Send packet to:

Default Gateway (Router)

Router handles rest of journey.

Example – Visiting a Website

Your PC:

192.168.1.10

Website server:

8.8.8.8

Your PC realizes:

Not same network.

So it sends packet to router:

192.168.1.1

Router forward packet toward internet.

The IPv4 Address Exhaustion Problem

IPv4 provides:

2^32 ~ 4.3 billion addresses

Sounded huge in 1980s

Today:

• smartphones
• laptops
• IoT devices
• servers

Addresses ran out.

Solutions:

• NAT
• IPv6 (next-generation addressing)

Layer Interaction

When sending data:

Application Data
      ↓
TCP Segment
      ↓
IP Packet (IP Address added)
      ↓
Ethernet Frame (MAC added)
      ↓
Bits on wire

Each layer adds information.

This process is called encapsulation.