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What Is NAT (Network Address Translation)?

NAT (Network Address Translation) is a technique where a router rewrites the private source address of outgoing packets to its own public IP, and keeps a table to send the replies back to the right device. It lets a whole home, office or mobile network share one public IP address.

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how it works

How NAT works

Most NAT is really port address translation (often called NAPT or PAT, described in RFC 3022). When your laptop at 192.168.1.23 opens a connection from port 51000, the router replaces the source with its public IP and a free port, say 203.0.113.45:62001, and writes the pair into its translation table. Replies to port 62001 are rewritten back and delivered to the laptop.

Because the table is created by outgoing traffic, devices behind NAT can reach the internet but cannot be reached from it unless you set up port forwarding. That one-way door is why NAT also acts as a basic shield for home networks.

  • Inside (private)192.168.1.23:51000 (laptop)203.0.113.45:62001
  • Inside (private)192.168.1.40:49822 (phone)203.0.113.45:62002
  • Inside (private)192.168.1.51:50110 (TV)203.0.113.45:62003
why it matters

Why NAT matters for proxy users

NAT explains a lot about how websites treat IPs. When a site sees many users behind one address, it cannot block that address without blocking real customers, so shared consumer IPs get more patience than a single server IP.

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NAT: what it means for you
  • Mobile carriers run carrier-grade NAT, putting many subscribers behind each public IP. That is why mobile IPs are rarely blocked outright.
  • Office and school networks share one public IP across hundreds of people, so per-IP limits there are usually generous.
  • NAT does not hide you the way a proxy does. Your public IP is still your own network's, and it changes nothing about your location or ASN.
  • Behind NAT you cannot accept inbound connections, which is why proxies, not port forwarding, are used to send traffic out from other networks.
side by side

NAT vs proxy

Both make traffic leave from another IP, but they work at different layers and for different reasons.

  • NAT

    This term
    Works at
    Network layer: rewrites packet headers
    Configured on
    The router, invisible to apps
    Exit IP
    Your own network's public IP
    Authentication
    None

  • Proxy server

    Works at
    Application layer: opens its own connection to the site
    Configured on
    Each app or the OS, by address and port
    Exit IP
    The proxy provider's IP, in a location you choose
    Authentication
    Username and password or an IP allowlist

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Guides from the blog

Setup guides and best practices from the CleanProxies blog.

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Related terms

Terms that come up alongside NAT.

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NAT FAQs

Straight answers about NAT.

It is how your router lets every device in your home share one public IP address. The router swaps private addresses for its public one on the way out and keeps track of which reply belongs to which device.

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