IP Addressing

Before learning subnet masks, CIDR, routers, NAT, or DHCP, first understand the core question:

How does a packet know where to go?

The answer starts with an IP address.

Why do we need an IP Address?

Imagine you want to send a parcel.

Can the delivery company deliver it if the parcel only says:

To:
John

No.

There could be thousands of people named John.

You need a proper address.

Computers are the same.

If your laptop wants to send data to Google, it needs to know which device on the internet should receive it.

That is why devices on a network use IP addresses.

What is an IP Address?

An IP address is a logical address assigned to a device on a network.

It helps identify:

Source IP: who is sending the data
Destination IP: who should receive the data

Example:

Your Laptop
IP: 192.168.1.20

↓

Google Server
IP: 142.250.xxx.xxx

When your laptop sends a packet, the packet contains:

Source IP      : 192.168.1.20
Destination IP : 142.250.xxx.xxx

Routers read the destination IP and forward the packet toward the correct network.

IPv4 Structure

The most common IP format you see is IPv4.

Example:

192.168.1.20

It has:

4 numbers
Dots between them
Each number ranges from 0 to 255

Each number is called an octet.

192 . 168 . 1 . 20

Each octet is 8 bits.

So IPv4 is:

4 octets × 8 bits = 32 bits

Why does each octet go from 0 to 255?

Because each octet is 8 bits.

An 8-bit binary number can represent:

00000000 = 0
11111111 = 255

So each part of an IPv4 address has a valid range of 0 to 255.

IP Address vs MAC Address

Do not confuse IP address and MAC address.

IP Address	MAC Address
Logical address	Hardware address
Used across networks	Used inside the local network
Can change	Usually fixed to the network interface

For now, remember:

IP tells us where the device is in the network. MAC helps with local delivery inside one network.

What comes under IP Addressing?

IP addressing becomes easier if you learn it as a tree:

IP Addressing
├── Network ID & Host ID
├── Subnet Mask
├── CIDR
├── Public vs Private IP
├── Router & Default Gateway
├── NAT
└── DHCP

Each child topic answers one specific question.

Start with Network ID & Host ID, because subnet masks and CIDR depend on that idea.

Interview Answer

If an interviewer asks:

What is an IP address?

You can answer:

An IP address is a logical address assigned to a device on a network. It identifies the source and destination of network packets. Routers use destination IP addresses to forward packets across networks. IPv4 addresses are 32-bit addresses written as four octets, such as 192.168.1.20.