Introduction
Network address translation (NAT), port address translation (PAT), and port forwarding are all methods for managing IP addresses and ports between private and public networks. Understanding the differences between them is crucial for configuring networks and firewalls properly. In this article, I will explain in depth the differences between NAT, PAT, and port forwarding.
What is NAT?
NAT (network address translation) is a method of mapping multiple private IP addresses to a public IP address. Here is how it works:
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Devices on a private network are assigned private IP addresses like 192.168.1.5, 192.168.1.6, etc. These IP addresses are not routable on the public internet.
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The router connecting the private network to the internet has a public IP address, for example 12.34.56.78.
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When a device on the private network sends data to the internet, the router replaces the private source IP address with its own public IP address.
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The router maintains a NAT table to keep track of which private IP address maps to which connection.
The key points about NAT are:
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It allows multiple devices to share one public IP address. This conserves public IPv4 addresses.
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The internal private IP addresses are hidden from the public internet. This adds a layer of security.
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NAT operates at the IP layer (Layer 3). It translates IP addresses only.
What is PAT?
PAT (port address translation) is an extension of NAT that allows many devices to share a single public IP address. It maps both IP addresses and ports.
Here is how PAT works:
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Like NAT, private IP addresses are mapped to a public IP address.
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In addition, the source port of outgoing connections is mapped to a different port on the public IP address.
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The router maintains a PAT table to keep track of these IP and port mappings.
The key points about PAT are:
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Thousands of private IP addresses can share one public IP address.
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PAT provides additional security by obscuring the private ports.
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PAT operates at the transport layer (Layer 4). It translates both IP addresses and ports.
What is Port Forwarding?
Port forwarding is a way to open a specific port on your public IP address and forward data on that port to a private IP address on your network.
Here is how port forwarding works:
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You configure your router to accept incoming connections on a specific port or range of ports.
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You specify the private IP address to forward that incoming traffic to.
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The router forwards any data received on the public port to the specified private IP and port.
The key points about port forwarding are:
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It allows incoming connections from the internet to a device on your private network.
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It opens access to devices like security cameras or game servers to the public internet.
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It operates at the transport layer (Layer 4) and forwards both ports and IP addresses.
Key Differences Between NAT, PAT, and Port Forwarding
NAT
- Operates at Layer 3 (IP layer)
- Translates private IP addresses to public IP addresses
- Used to allow outbound internet connections
PAT
- Operates at Layer 4 (transport layer)
- Translates private IP addresses and ports to public IP address and ports
- Allows many private IPs to share one public IP address
Port Forwarding
- Operates at Layer 4 (transport layer)
- Forwards inbound traffic from a public port to a private IP address and port
- Opens access to services on your private network to the internet
Conclusion
In summary, NAT provides outbound internet access by translating private IP addresses to public. PAT extends NAT by also translating ports, allowing many private IP addresses to share one public IP. Port forwarding opens inbound access from the internet to a device on your private network. Understanding the difference between these technologies is key to configuring networking and security tools like routers, firewalls, and VPNs properly.
