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Last updated on 2024年8月9日

What are the differences and similarities between NAT and PAT (Port Address Translation)?

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NAT and PAT are two common techniques for translating IP addresses in a network. They both help to conserve public IP addresses and enhance security, but they also have some differences and similarities. In this article, you will learn what NAT and PAT are, how they work, and when to use them.

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Sajjid Salyani

Senior Consultant Engineer and Trainer at Siemens Digital Industries
Ajay Upadhyay

Information Security Expert / Cyber Security Enthusiast…
Bruno Jodas Assuino

Network Engineer | High-Frequency Trading | Cybersecurity Enthusiast

1 What is NAT?

NAT stands for Network Address Translation. It is a process that changes the source or destination IP address of a packet as it passes through a router or a firewall. NAT allows a network to use private IP addresses internally, while communicating with the public Internet using a limited number of public IP addresses. NAT can also hide the internal network topology and protect it from external attacks.

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Ajay Upadhyay

Information Security Expert / Cyber Security Enthusiast CISSP, CISM, CRISC, CCSP, CEH, CISA
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Among the most important techniques in networking are those handling IP address consumption and allowing communication: NAT and PAT. NAT changes private IPs to public IPs, increasing security by obscuring the internal network addresses. PAT, or overload, maps several devices to a single public IP address by using different port numbers, which allows several concurrent connections without additional public IP addresses. Both these methods are money-saving as they conserve public IP addresses and enhance security by masquerading the internal IP address from the external networks. Network administrators should know how both these differences can help in optimizing network configurations.

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Sajjid Salyani

Senior Consultant Engineer and Trainer at Siemens Digital Industries
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add a diagram and a use case and example with simple IP addresse NAT translations within a common network concept architecture

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2 What is PAT?

PAT stands for Port Address Translation. It is a type of NAT that also changes the source or destination port number of a packet. PAT enables multiple devices to share a single public IP address by assigning them different port numbers. PAT is also known as NAT overload or dynamic NAT, because it can handle more connections than the available public IP addresses.

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3 How does NAT work?

NAT works by creating a mapping table that records the relationship between the private IP address and port number of an internal device, and the public IP address and port number assigned by the router or firewall. When an internal device sends a packet to the Internet, NAT replaces the private IP address and port number with the public ones, and updates the mapping table. When a response packet arrives from the Internet, NAT looks up the mapping table and restores the original private IP address and port number, and forwards the packet to the internal device.

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Sajjid Salyani

Senior Consultant Engineer and Trainer at Siemens Digital Industries
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I would add the different names and variants of NAT and PAT. Also it has different names such as Masquerading that is used by Linux users. Also probably add what is supported in the majority of Stateful Networks Firewalls and what additional features are supported that can differentiate Firewalls

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4 How does PAT work?

PAT works similarly to NAT, but with an additional step of changing the port number. PAT assigns a unique port number to each connection from an internal device to the Internet, and adds it to the mapping table. PAT can use the same public IP address for multiple connections, as long as they have different port numbers. PAT can also use a pool of public IP addresses, and allocate them based on availability and load balancing.

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5 When to use NAT?

NAT is useful when you have a network that uses private IP addresses, and you want to connect it to the Internet without using too many public IP addresses. NAT can also help to improve security, by hiding the internal network structure and preventing direct access from the Internet. NAT can be static or dynamic, depending on whether the mapping between the private and public IP addresses is fixed or variable.

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Bruno Jodas Assuino

Network Engineer | High-Frequency Trading | Cybersecurity Enthusiast
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NAT can also be useful to avoid IP address conflict between private subnets from two different parties, that by coincidence lie within the same range. On this case, one of the parties must take initiative to NAT addresses to communicate to the other side - whoever is most convenient for both.

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6 When to use PAT?

PAT is useful when you have more devices than public IP addresses, and you want to enable them to access the Internet simultaneously. PAT can also help to improve security, by making it harder for attackers to identify and target specific devices based on their port numbers. PAT can be combined with static or dynamic NAT, depending on whether you want to assign specific public IP addresses to some devices or not.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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What are the differences and similarities between NAT and PAT (Port Address Translation)?

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1 What is NAT?

2 What is PAT?

3 How does NAT work?

4 How does PAT work?

5 When to use NAT?

6 When to use PAT?

7 Here’s what else to consider

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