What Is NAT?
Earlier, we learned that devices inside your network use private IP addresses while your router has a public IP address. But how does data from the internet reach the right device inside your network? That's where NAT comes in.
NAT (Network Address Translation) is the process your router uses to translate between private and public addresses, allowing multiple devices to share a single public IP.
How NAT Works
Think of NAT like an office receptionist managing phone calls. The office has one main phone number (public IP), but many employees with internal extensions (private IPs).
When someone inside calls out:
- The receptionist notes which extension made the call
- Places the call using the main number
- When the response comes back, routes it to the correct extension
Your router does the same thing with network traffic:
- Your laptop (192.168.1.5) requests a webpage
- The router records this request in its translation table
- It sends the request using your public IP address
- When the response arrives, the router checks its table
- It forwards the response to your laptop's private address
The Translation Table
The router maintains a table tracking active connections:
| Internal Address | Internal Port | External Port | Destination |
|---|---|---|---|
| 192.168.1.5 | 52847 | 52847 | 93.184.216.34:443 |
| 192.168.1.6 | 49152 | 49153 | 142.250.80.46:443 |
When responses arrive, the router uses this table to route packets to the correct internal device.
Why NAT Matters
NAT solves a critical problem: we have far more devices than available public IPv4 addresses. Without NAT, every phone, laptop, smart TV, and IoT device would need its own public address — impossible with IPv4's limited pool.
NAT also provides a basic layer of security. Devices inside your network aren't directly reachable from the internet unless the router is specifically configured to allow it.
Limitations
NAT can complicate certain applications that need incoming connections, like hosting a game server or running peer-to-peer software. These situations often require port forwarding — manually telling the router to send certain incoming traffic to a specific internal device.