/ˌpiː-eɪ-ˈtiː/
n. “The magic that lets many devices share one public IP.”
PAT, short for Port Address Translation, is a type of network address translation (NAT) that allows multiple devices on a private network to share a single public IP address for outbound traffic. It achieves this by mapping each private device’s IP address and port to a unique port on the public IP, enabling the router to direct return traffic correctly.
Key characteristics of PAT include:
- IP Conservation: Allows many devices to use one public IP, reducing the need for multiple addresses.
- Port Mapping: Tracks which internal device is associated with each outgoing connection using source ports.
- Security Layer: Hides internal IP addresses from external networks, adding a basic layer of network protection.
- Common in Home & Enterprise Networks: Widely used in routers and firewalls for Internet connectivity.
Conceptually, PAT acts like a receptionist who directs incoming calls to the correct person in a building based on the extension (port) they dialed.
Here’s a simple conceptual example of PAT in a home network:
Private Network:
192.168.1.10 → Source Port 5000
192.168.1.11 → Source Port 5001
Public IP: 203.0.113.5
Outgoing packets are translated as:
192.168.1.10:5000 → 203.0.113.5:61000
192.168.1.11:5001 → 203.0.113.5:61001
Return traffic to 203.0.113.5:61000 goes to 192.168.1.10:5000
Return traffic to 203.0.113.5:61001 goes to 192.168.1.11:5001In essence, PAT efficiently multiplexes multiple private devices onto a single public IP using ports, enabling internet connectivity while conserving IP addresses and providing basic obfuscation of internal network structure.