IP Addressing – Complete Beginner-Friendly Guide (Easy to Understand)

🔍 What is an IP Address?

An IP Address (Internet Protocol Address) is a logical address used to identify every device connected to a network or the internet.

Just like your home has a unique address, computers and devices also get an address so they can send and receive data.

• IP address works at Network Layer (Layer 3) of the OSI Model.
• IPv4 uses 32 bits
• IPv6 uses 128 bits

An IP address has two parts:
1️⃣ Network Part → tells which network you belong to
2️⃣ Host Part → identifies the specific device inside that network

All devices in the same network share the same network prefix, but each device must have a unique host number.

IP Addresses are assigned by IANA (Internet Assigned Numbers Authority) — the global authority for IP allocation.

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🌐 Types of IP Addresses

1️⃣ IPv4 (32-bit)

Example: 192.168.1.10

2️⃣ IPv6 (128-bit)

Example: 2400:cb00:2048:1::c629:d7a2

“v” stands for version → IPv4 = version 4, IPv6 = version 6.

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🖥️ How to Check Your IP Address (Windows)

✔ Method 1 – Using CMD

1. Open Search → type cmd → press Enter
2. On the black window (Command Prompt), type: ipconfig
3. Press Enter → You will see your IP Address.

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✔ Method 2 – Using Network Settings

1. Press Windows Key + R
2. Type: ncpa.cpl
3. Press Enter → Network Connections will open
4. Right-click your connected network → Properties → Details
5. You can now see your IP address

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🧩 IPv4 Address Classes

IPv4 is divided into 5 classes, based on the first octet:

Class	First Octet Range	Binary Start	Prefix	Subnet Mask	Network Bits	Host Bits
A	1 – 126	0xxxxxxx	/8	255.0.0.0	8	24
B	128 – 191	10xxxxxx	/16	255.255.0.0	16	16
C	192 – 223	110xxxxx	/24	255.255.255.0	24	8
D	224 – 239	1110xxxx	Multicast	–	–
E	240 – 255	1111xxxx	Experimental	–	–

Class D & E are not used for device configuration.

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🎯 How to Identify IP Address Class Easily

Just look at the first octet:

✔ Class A

• Binary: 0xxxxxxx
• Decimal range: 1 to 126

✔ Class B

• Binary: 10xxxxxx
• Decimal range: 128 to 191

✔ Class C

• Binary: 110xxxxx
• Decimal range: 192 to 223

✔ Class D & E

• Reserved for special uses

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🔧 APIPA Address

APIPA = Automatic Private IP Addressing
Windows assigns APIPA when it cannot reach a DHCP Server.

APIPA Range:
➡ 169.254.0.0 – 169.254.255.255

This helps devices communicate inside the LAN, but not with the internet.

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🔐 Static IP vs Dynamic IP

✔ Static IP

• Manually assigned
• Never changes
• Used for servers, CCTV, routers, etc.

✔ Dynamic IP

• Assigned automatically by DHCP
• Changes every time you reconnect

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🌍 Private vs Public IP Address

🔸 Private IP

Used inside your LAN (home, office).
Not reachable from the internet.

Private IP ranges:

• Class A → 10.0.0.0 – 10.255.255.255
• Class B → 172.16.0.0 – 172.31.255.255
• Class C → 192.168.0.0 – 192.168.255.255

🔸 Public IP

• Provided by your ISP
• Globally unique
• Needed for internet access

Your router converts private → public using NAT (Network Address Translation).

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🧮 What is Subnet Mask?

A Subnet Mask identifies network bits and host bits.

• 255 = Network bit
• 0 = Host bit

Examples:

Class	Mask	Meaning
A	255.0.0.0	N.H.H.H
B	255.255.0.0	N.N.H.H
C	255.255.255.0	N.N.N.H

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✏ How to Calculate Subnet Mask from Prefix

Rule:
👉 Replace all network bits with 1 and host bits with 0

Example

IP = 192.168.1.0/24

• /24 → 24 network bits, 8 host bits

Binary of IP:

11000000.10100000.00000001.00000000

Now apply subnet mask:

11111111.11111111.11111111.00000000

Convert back to decimal:
➡ 255.255.255.0

This is the subnet mask.

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✅ Summary (Easy to Remember)

• IP = Logical Address (Layer 3)
• IPv4 = 32-bit, IPv6 = 128-bit
• Classes A, B, C used for networks
• Private IP stays inside LAN
• Public IP connects to internet
• APIPA = 169.254.x.x
• DHCP gives dynamic IP
• Subnet mask decides network & host parts

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