What is pat?

PAT stands for Port Address Translation. It is a technique used in computer networking that lets many devices on a private home or office network share a single public IP address when they connect to the internet. PAT does this by assigning a different port number to each outgoing connection, so the router can keep track of which data belongs to which device.

Let's break it down

  • Every device on your local network has a private IP address (like 192.168.1.2).
  • Your internet service provider gives you one public IP address.
  • When a device wants to talk to the internet, the router changes the source address to the public IP and adds a unique port number (e.g., 50000).
  • The router stores a small table that maps “public IP + port” back to the original “private IP + original port”.
  • When a response comes back, the router looks up the table, swaps the address and port back, and sends the data to the right device.

Why does it matter?

PAT lets many devices use the internet without needing a separate public IP for each one, which saves address space (IPv4 addresses are limited) and reduces cost. It also adds a tiny layer of security because devices behind the router are not directly reachable from the outside world unless you set up special rules.

Where is it used?

  • Home Wi‑Fi routers that let phones, laptops, smart TVs, and IoT gadgets all go online.
  • Small office routers and firewalls.
  • Any network that has more devices than available public IP addresses, such as schools, cafés, and hotels.
  • Cloud services that provide NAT gateways for virtual machines.

Good things about it

  • Conserves public IP addresses, which are a scarce resource.
  • Simple to set up; most routers enable PAT by default.
  • Provides basic protection by hiding internal IP addresses from the internet.
  • Works with existing IPv4 infrastructure, so no need to upgrade to IPv6 immediately.

Not-so-good things

  • All devices share the same public IP, so if that IP gets blacklisted, every device is affected.
  • Some applications that need inbound connections (like online gaming, video conferencing, or remote desktop) may have trouble unless you configure port forwarding.
  • PAT adds a small amount of processing overhead on the router, which can become noticeable on very high‑traffic networks.
  • It does not replace a full firewall; additional security measures are still needed.