Private vs Public IP Addressing

Understand private and public IP addressing, address classes, and how NAT enables internal networks to access the internet.

Private vs Public IP Addressing

⭐ CCST GOLD LINE (Remember This!)

Private IP = Used inside a network (not reachable from internet)
Public IP = Used on the internet (globally reachable)

👉 If you remember this → many CCST questions become easy ✅

🔢 What is an IP Address? (Quick Recap)

An IP address is a unique number that identifies a device on a network.

🧠 Example: 192.168.1.10

🏠 What is a Private IP Address?

A private IP address is used inside a local network (LAN) and cannot be accessed directly from the internet.

📌 Assigned by:
  • Router (using DHCP)
📌 Used in:
  • Homes
  • Offices
  • Schools

Private vs Public IP Concept

Private vs Public IP Address

🔐 Private IP Address Ranges (VERY IMPORTANT)

Class Private IP Range
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

Classes of IP Addresses

IP Address Classes
🧠 Easy Example

Laptop IP: 192.168.1.10
Phone IP: 192.168.1.11

👉 Both are private IPs
✅ Advantages of Private IP
  • Free to use
  • Secure (not internet-reachable)
  • Reusable in different networks
❌ Disadvantages
  • Cannot access internet directly
  • Needs NAT to go online

🌍 What is a Public IP Address?

A public IP address is a globally unique address that is reachable on the internet.

📌 Assigned by:
  • ISP (Internet Service Provider)
📌 Used for:
  • Websites
  • Servers
  • Routers facing the internet
🧠 Easy Example

Google server IP: 142.250.182.14
Home router public IP: 103.21.244.0

👉 These are public IPs
✅ Advantages of Public IP
  • Internet reachable
  • Required for hosting websites
  • Globally unique
❌ Disadvantages
  • Limited availability
  • Less secure (exposed to internet)
  • Usually costs money

🧩 Private vs Public IP (Side-by-Side)

Feature Private IP Public IP
Scope Local network Internet
Reachable from internet ❌ No ✅ Yes
Reusable ✅ Yes ❌ No
Cost Free Paid
Example 192.168.1.10 142.250.182.14

🔁 What is NAT? (Network Address Translation)

NAT converts private IP addresses into a public IP address so devices can access the internet.

📌 NAT runs on:
  • Routers
  • Firewalls
🧠 Why NAT is Needed?

• Private IPs cannot go to internet directly
• Public IPs are limited

👉 NAT solves both problems ✅

NAT Working (Home Network)

Home Network NAT

Network Address Translation Diagram

NAT Diagram
🏠 Real-World NAT Example

Laptop: 192.168.1.10
Phone: 192.168.1.11

Router public IP: 103.21.244.0

👉 Many devices share one public IP

🧩 Types of NAT (Basic Awareness)

Type Meaning
Static NAT One private → one public
Dynamic NAT Private → public from pool
PAT (Most common) Many private → one public (using ports)
📌 PAT = Port Address Translation
📌 Used in almost all home routers

🛠️ CCST Troubleshooting Scenarios

Problem Likely Area
Device has IP but no internet NAT / Router issue
Website hosted but not reachable Public IP / NAT
Local devices work, internet fails NAT misconfiguration
🧠 Memory Tricks (Exam Gold 🥇)

Private IP = Inside
Public IP = Outside
NAT = Translator
Class C = Home networks