What Is NAT? Network Address Translation Explained

NAT (Network Address Translation) is a method used by routers to translate private (internal) IP addresses to a public (external) IP address and vice versa. It allows multiple devices on a local network to share a single public IP address when accessing the internet.

NAT was invented as a practical solution to IPv4 address exhaustion. With only 4.3 billion IPv4 addresses available and billions of internet-connected devices, there simply aren't enough public IPs for every device. NAT allows your home or office to use a single public IP for dozens or even hundreds of devices.

When you check your IP on LookMyIP, you see your public IP — the one your router presents to the outside world. Your individual devices (phone, laptop, smart TV) each have their own private IPs that are invisible to the internet.

Here's what happens when a device on your home network visits a website:

1. Your laptop (private IP 192.168.1.100) sends a request to google.com.
2. The request reaches your router, which replaces the source IP (192.168.1.100) with the router's public IP (e.g., 203.0.113.50) and assigns a unique port number.
3. The router saves this mapping in its NAT translation table: "Port 54321 → 192.168.1.100".
4. Google's server receives the request from 203.0.113.50:54321 and sends its response back.
5. Your router receives the response, checks the NAT table for port 54321, and forwards the data to 192.168.1.100 (your laptop).

The external server never sees your private IP. It only communicates with your router's public IP. This translation happens transparently for every packet flowing through the router.

Static NAT (One-to-One): Maps one private IP to one public IP permanently. Used when a device (like a web server) needs a consistent public IP. Doesn't save addresses, so it's mainly used in business environments.

Dynamic NAT: Assigns public IPs from a pool on a first-come, first-served basis. When a device needs internet access, it gets a public IP from the pool. When it's done, the IP returns to the pool.

PAT (Port Address Translation) / NAT Overload: The most common type — what your home router uses. Multiple devices share one public IP, distinguished by unique port numbers. This is why it's also called "many-to-one" NAT.

CGNAT (Carrier-Grade NAT): Your ISP applies an additional layer of NAT, meaning your "public" IP is actually shared with other ISP customers. This is increasingly common as IPv4 addresses run out. You can detect CGNAT if your router's WAN IP differs from what LookMyIP shows.

Online gaming: NAT can cause issues with multiplayer gaming because incoming connections are blocked by default. Games may report your NAT type as "Strict" or "Moderate," limiting matchmaking. Port forwarding or UPnP can help.

VoIP and video calls: Services like Zoom and Skype use techniques like STUN and TURN servers to work around NAT. Occasionally, NAT causes call quality issues or connection failures.

Peer-to-peer (P2P): BitTorrent, file sharing, and P2P VPNs can struggle behind NAT since both peers may be behind routers that block incoming connections. NAT traversal techniques like hole punching help solve this.

Port forwarding: To run a server (game server, web server, security camera) behind NAT, you need to manually configure port forwarding on your router — telling it to send incoming traffic on a specific port to a specific internal device.

Double NAT: If you have two routers in series (e.g., ISP modem/router + your own router), you get double NAT, which can cause issues with gaming, VPN connections, and port forwarding. The fix is to put one device in bridge mode.

IPv6 was designed to eliminate the need for NAT entirely. With 340 undecillion available IPv6 addresses, every device can have its own globally unique public IP address.

In an IPv6 world, NAT is unnecessary — devices communicate directly with each other using their public IPs, with firewalls handling security instead of NAT providing an incidental security benefit by hiding internal addresses.

However, NAT is so deeply embedded in current networks that the transition away from it will take years. Many organizations use NAT even on IPv6 networks (NAT66) for policy reasons, despite it being technically unnecessary.