Understanding the Difference Between NAT and PAT
As network administrators, we often encounter terms like NAT (Network Address Translation) and PAT (Port Address Translation). While they may seem similar, these two techniques serve distinct purposes in modern networking. In this article, we’ll delve into the world of IP addressing, explore the differences between NAT and PAT, and examine their applications.
What is NAT?
NAT is a technique used to allow multiple devices on a private network to share a single public IP address when accessing the internet or communicating with external networks. This is achieved by translating the private IP addresses of the devices into a single public IP address. When a device sends data to an outside host, the NAT router changes its source IP address and sends the data as if it originated from the NAT router’s own public IP address.
How does NAT work?
Here’s a step-by-step explanation:
- Private IP Address: A device on the private network has an IP address like
192.168.1.100. - NAT Router: The NAT router receives the request and translates the private IP address (
192.168.1.100) to a public IP address (8.8.8.8). - Request Sent: The NAT router sends the request on behalf of the device, using its own public IP address as the source.
- Response Received: The outside host responds to the request with data addressed to the NAT router’s public IP address (
8.8.8.8). - Translation Back: The NAT router translates the response back to the original private IP address (
192.168.1.100) and delivers it to the device.
What is PAT?
PAT, also known as Port Address Translation, is a variation of NAT that uses different ports on the same public IP address for multiple devices. This technique is useful when you need to allow multiple devices on a private network to access the internet or communicate with external networks without requiring additional public IP addresses.
How does PAT work?
Here’s how PAT works:
- Private IP Address: A device on the private network has an IP address like
192.168.1.100. - PAT Router: The PAT router receives a request from the device and translates its source port to a unique, available public port (e.g.,
12345). - Request Sent: The PAT router sends the request on behalf of the device, using the original private IP address and the translated public port as the source.
- Response Received: The outside host responds to the request with data addressed to the PAT router’s public IP address and the translated public port (
8.8.8.8:12345). - Translation Back: The PAT router translates the response back to the original private IP address and delivers it to the device.
Key Differences Between NAT and PAT
- Public IP Address: NAT uses a single public IP address for all devices, while PAT uses multiple ports on the same public IP address.
- Port Usage: NAT doesn’t use ports; instead, it translates entire IP addresses. PAT, on the other hand, uses different ports to differentiate between devices.
- Device Limitations: NAT is typically used with a limited number of devices (e.g., 253), while PAT can support thousands of devices.
Conclusion
In summary, both NAT and PAT are techniques for sharing public IP addresses, but they differ in their approach:
- NAT translates entire IP addresses to a single public IP address.
- PAT uses different ports on the same public IP address to differentiate between devices.
When deciding which technique to use, consider factors like the number of devices you need to support, your network architecture, and any specific requirements or restrictions imposed by ISPs or regulatory bodies. By understanding the differences between NAT and PAT, you’ll be better equipped to design and implement effective IP addressing solutions for your networks.
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