PAT (Port Address Translation)

PAT (Port Address Translation) Explained

What Is PAT?

PAT stands for:

Port Address Translation

It allows multiple devices to share one public IP address using different port numbers.

Why PAT Is Important

IPv4 addresses are limited.

PAT allows:

👉 Thousands of devices 👉 One public IP

This makes the Internet scalable.

Visual Example

Real-World Example

Home Router

Devices:

Laptop → 192.168.1.10 Phone → 192.168.1.11 Tablet → 192.168.1.12

Router Public IP:

49.204.x.x

Router uses port numbers to identify each connection.

Example PAT Table

Private IPPrivate PortPublic IPPublic Port192.168.1.10500149.204.x.x10001192.168.1.11500249.204.x.x10002

Router maps connections using this table.

Real-World Troubleshooting

Problem:

Users cannot access external website.

Engineer checks:

PAT translation table.

Possible issue:

Port mapping conflict.

🎯 Interview Questions

Common questions:

• What is PAT?
• Difference between NAT and PAT?
• Why PAT is required?
• What is NAT overload?