Network Address Translation (NAT)

Definition

NAT (Network Address Translation) is a feature on a router that translates private IP addresses into a public IP address, and translates the replies back. It sits between your LAN and the Internet, allowing private devices to communicate with public servers. Key terms: Private IP, Public IP, Router, NAT Table, LAN, WAN.

What Problem It Solves

Private IPs (e.g., 192.168.1.10) cannot travel across the Internet. NAT lets many devices in one home or office share one public IP, conserving public IPv4 addresses.

What Happens If Not Used

Your devices with private IPs could not directly access websites, cloud services, or public servers. Every device would need its own public IP.

Easy Wording

NAT is a translator that lets your private home devices communicate with the public Internet.

Layman Example

Your apartment number (private IP) only makes sense inside your building. The building's street address (public IP) is what delivery companies use. The receptionist (router/NAT) forwards the package to the correct apartment.

Technical Example

Request Flow:

Browser → DNS → Web Server Public IP → PC (192.168.1.10) → Router (NAT: 192.168.1.10 → 103.x.x.x) → ISP → Internet → Web Server → Router (NAT: 103.x.x.x → 192.168.1.10) → PC

Limitation

NAT hides internal devices, so outside users cannot directly reach your PC.

Solution: Port Forwarding (or UPnP/IPv6) allows selected inbound connections.