Networking - Public IP vs Private IP

1. What is an IP Address?

An IP address (Internet Protocol address) is a unique number assigned to every device connected to a network.
It’s like a home address for your device so data can reach the right place.

• Example: 192.168.1.10 or 203.122.45.67

• Two versions exist:

  • IPv4 → 32-bit address (e.g., 192.168.0.1)

  • IPv6 → 128-bit address (e.g., 2401:4900:30f0:1b2::2)

2. Public IP Address

A Public IP is an IP address that is assigned by your Internet Service Provider (ISP) and is accessible over the Internet.

Characteristics

• Globally unique → No two devices on the internet have the same public IP.

• Assigned by ISP or IANA (Internet Assigned Numbers Authority).

• Used for direct communication between devices over the internet.

• Needed for hosting websites, online gaming servers, VPN servers, etc.

Example Ranges

Public IPs exclude private ranges (we’ll discuss below).
For example:
8.8.8.8 → Google DNS
142.250.190.78 → google.com

Pros

• Accessible from anywhere.

• Suitable for servers and online services.

Cons

• Limited in number (especially IPv4).

• Less secure if exposed directly.

3. Private IP Address

A Private IP is an IP address used inside a local network (LAN) and not directly accessible from the internet.

Characteristics

• Used for communication within a private network.

• Assigned manually or automatically using DHCP.

• Cannot be routed on the internet.

• Multiple private networks can reuse the same IP range.

Private IP Ranges (IPv4)

Example:

• Router IP → 192.168.1.1

• Laptop → 192.168.1.5

• Mobile → 192.168.1.10

Pros

• Conserves public IP addresses.

• Increases security by isolating devices from direct internet exposure.

Cons

• Cannot access the internet directly without NAT.

4. NAT (Network Address Translation)

Since private IPs cannot access the internet directly, NAT converts a private IP into a public IP.

Example:

• Your laptop → 192.168.1.5 (private)

• Router converts it → 103.45.21.67 (public)

• Data goes to the internet → Response comes back → Router translates it back.

5. Key Differences Between Public and Private IP

6. Diagram

          INTERNET
             |
        Public IP: 103.45.21.67  ← Assigned by ISP
             |
        ┌───────────┐
        │   Router  │
        └───────────┘
          |       |       |
  192.168.1.2   192.168.1.5   192.168.1.10
   Laptop       Mobile        Printer
 (Private IPs used inside LAN)