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• 🌐 IPv4 Address Structure, Private IPs, and Public IPs
  • 1️⃣ IPv4 Address Structure
    • What is an IPv4 Address?
    • Example:
  • 2️⃣ IPv4 Address Format
  • 3️⃣ Network Part vs Host Part
  • 4️⃣ Special IPv4 Addresses (Must Know)
  • 5️⃣ What Is a Private IP Address?
  • 6️⃣ Why Private IP Addresses Exist
  • 7️⃣ Private IP Ranges (VERY IMPORTANT – MEMORIZE)
  • 8️⃣ Characteristics of Private IPs
  • 9️⃣ What Is a Public IP Address?
  • 🔟 Characteristics of Public IPs
  • 1️⃣1️⃣ Public IPs in AWS (IMPORTANT)
  • 1️⃣2️⃣ Private vs Public IP (Clear Comparison)
  • 1️⃣3️⃣ How Private IP Accesses Internet
  • 1️⃣4️⃣ Public IP Access Flow
  • 1️⃣5️⃣ AWS Exam Traps (VERY IMPORTANT)
  • 1️⃣6️⃣ Elastic IP (Special Public IP)
  • 1️⃣7️⃣ Real-World Analogy
  • 1️⃣8️⃣ One-Line Exam Definitions
    • IPv4 Address:
    • Private IP:
    • Public IP:
  • 1️⃣9️⃣ Final Summary (Must Remember)

🌐 IPv4 Address Structure, Private IPs, and Public IPs

1️⃣ IPv4 Address Structure

What is an IPv4 Address?

An IPv4 address is a 32-bit number used to identify a device on a network.

It is written in dotted decimal format.

Example:

192.168.1.10

2️⃣ IPv4 Address Format

An IPv4 address has:

• 4 parts (octets)
• Each octet has 8 bits
• Each octet range: 0–255

Octet1.Octet2.Octet3.Octet4

Example:

11000000.10101000.00000001.00001010
   192       168        1        10

3️⃣ Network Part vs Host Part

An IPv4 address is divided into:

• Network portion → identifies the network
• Host portion → identifies the device

This division is defined using CIDR notation.

Example:

192.168.1.0/24

• Network part → first 24 bits
• Host part → last 8 bits

4️⃣ Special IPv4 Addresses (Must Know)

5️⃣ What Is a Private IP Address?

A Private IP address is an IP that:

• Is used inside internal networks
• Is not routable on the internet
• Must use NAT to access internet

6️⃣ Why Private IP Addresses Exist

Because:

• IPv4 addresses are limited
• Not every device needs public access
• Improves security
• Reduces cost

7️⃣ Private IP Ranges (VERY IMPORTANT – MEMORIZE)

These are defined by RFC 1918.

📌 These IPs cannot be used on the internet.

8️⃣ Characteristics of Private IPs

✔ Free to use ✔ Reusable across networks ✔ Hidden from internet ✔ Require NAT for internet access

Example:

10.0.1.15
192.168.1.10

9️⃣ What Is a Public IP Address?

A Public IP address is an IP that:

• Is globally unique
• Is routable on the internet
• Can be accessed from anywhere

Example:

3.110.45.21

🔟 Characteristics of Public IPs

✔ Globally unique ✔ Assigned by ISP / AWS ✔ Internet-routable ✔ Limited and valuable

1️⃣1️⃣ Public IPs in AWS (IMPORTANT)

In AWS:

• Public IPs are assigned to:

  • EC2 instances
  • Load Balancers
  • NAT Gateways

• Public IPs change when instance stops (unless Elastic IP)

1️⃣2️⃣ Private vs Public IP (Clear Comparison)

1️⃣3️⃣ How Private IP Accesses Internet

Private IP cannot talk to internet directly.

Flow:

Private IP
 ↓
NAT Gateway
 ↓
Internet Gateway
 ↓
Internet

1️⃣4️⃣ Public IP Access Flow

Public IP:

Internet
 ↓
Internet Gateway
 ↓
EC2 (Public IP)

1️⃣5️⃣ AWS Exam Traps (VERY IMPORTANT)

❓ Private IP can access internet directly ➡ ❌ False

❓ Public IP guarantees internet access ➡ ❌ False (route table + SG required)

❓ Same private IPs can exist in different VPCs ➡ ✅ True

1️⃣6️⃣ Elastic IP (Special Public IP)

Elastic IP:

• Static public IP
• Does not change
• Charged if unused

Used for:

• Fixed endpoints
• NAT Gateway
• Bastion hosts

1️⃣7️⃣ Real-World Analogy

1️⃣8️⃣ One-Line Exam Definitions

IPv4 Address:

A 32-bit numerical label used to identify a device on a network.

Private IP:

An IP address used inside private networks that is not routable on the internet.

Public IP:

A globally unique IP address that allows direct internet communication.

1️⃣9️⃣ Final Summary (Must Remember)

• IPv4 = 32-bit address
• Written as 4 octets
• Private IPs are internal
• Public IPs are internet-facing
• NAT connects private to public
• AWS uses both extensively