An IP (Internet Protocol) address is a unique numerical identifier assigned to a device on a network.

It operates at Layer 3 (Network Layer) of the OSI model and is used to identify where a device is on a network so data can be routed to it — even across the entire internet.

It serves two main purposes:

• Identifies a device on a network.
• Locates the device so data can be delivered to it.

Think of it like a postal address:

• Your home address tells the postal service where to deliver mail.
• An IP address tells the internet where to deliver data packets.

Suppose your laptop wants to open a website.

• You type www.example.com.
• The domain name is translated into an IP address using DNS.
• Your computer sends packets to that IP address.
• The web server sends the response back to your IP address.

Without IP addresses, devices wouldn't know where to send or receive information.

1. IPv4

IPv4 is the older and most widely used version.

• 32-bit address
• Four decimal numbers separated by dots
• Each number ranges from 0 to 255

Example:

192.168.1.10
 
172.16.0.5

Structure:

192 . 168 . 1 . 10
 ↑     ↑    ↑    ↑
8bit  8bit 8bit 8bit  = 32 bits total

Each section is called an octet.

Each address is split conceptually into two parts:

192.168.1.10
└─────┘ └──┘
Network   Host
 part     part

• Network part — identifies which network the device belongs to.
• Host part — identifies the specific device within that network.

Where this split happens is determined by the subnet mask.

Example in binary:

192 = 11000000
168 = 10101000
1   = 00000001
10  = 00001010

IP to Binary Converter

2. IPv6

IPv6 was introduced because IPv4 addresses were running out.

• 128-bit address
• Written in hexadecimal
• Eight groups separated by colons

Rules that make them shorter to write:

• Leading zeros in a group can be dropped: 0db8 → db8
• One run of consecutive all-zero groups can be collapsed to :: (only once per address):

Example:

2001:0db8:85a3:0000:0000:8a2e:0370:7334

Shortened form:

2001:db8:85a3::8a2e:370:7334

Older networking used five classes.

A subnet mask tells you how many bits belong to the network part vs. the host part.

It's often written in CIDR(Classless Inter-Domain Routing) notation (a slash followed by a number):

192.168.1.10/24

The /24 means the first 24 bits (3 full octets) are the network part, leaving the last 8 bits for hosts.

Example:

IP Address:
192.168.1.20
 
Subnet Mask:
255.255.255.0

This means:

Network:
192.168.1.0
 
Host:
20

A default gateway is the router that forwards traffic to other networks.

Example:

Computer:
192.168.1.20
 
Gateway:
192.168.1.1

When the computer wants to reach a website on the internet, it sends the data to the gateway first.

Used for testing the local machine.

IPv4: 127.0.0.1

Also called: localhost

It refers to your own computer.

When your device sends data:

1. It checks if the destination IP is on the same network or a different network.
2. If same network → uses ARP (Address Address Resolution Protocol) to find the destination's MAC address and sends directly.
3. If different network → sends the data to the default gateway (your router), which forwards it onward.

You (192.168.1.10) → Router (192.168.1.1) → Internet → Destination server

The IP address gets the data to the right network; the MAC address gets it to the right device once it arrives.

• IP address: Identifies and locates a device on a network.
• IPv4: 32-bit, e.g., 192.168.1.1.
• IPv6: 128-bit, e.g., 2001:db8::1.
• Public IP: Reachable on the internet.
• Private IP: Used within local networks.
• Static IP: Fixed address.
• Dynamic IP: Assigned automatically by DHCP.
• Subnet mask: Separates network and host portions.
• Gateway: Router used to reach other networks.
• Loopback: 127.0.
• MAC address: Physical device address; IP address Logical network address.