NAT – Definition and meaning

NAT - Network Address Translation

NAT, or Network Address Translation, is a technology that makes it possible to change the IP addresses in a network while data packets are being sent over the Internet. This is done to optimise the use of IP addresses and increase the security and anonymity of the internal network structure. In this article, we look at what NAT is, how it works, the different types of NAT and its advantages and disadvantages.

What is NAT?

NAT is a technique used in routers to convert private IP addresses into public IP addresses and vice versa. This technique is particularly important as the IPv4 addressing scheme only provides a limited number of public IP addresses. By using NAT, several devices in a local area network (LAN) can use a single public IP address.

How does NAT work?

NAT works by redirecting data packets. Each time a device on the local network connects to the Internet, the source IP address sent in the data packets is replaced by the public IP address of the router. When the data packets return to the router, NAT indicates which internal client requested the packet and forwards it to the correct device accordingly. This is done using a NAT table that stores the mappings of internal to external addresses.

Types of NAT

• Static NAT: A fixed assignment is created between an internal IP address and an external IP address. This type of NAT is often used for servers that need to be accessible from the Internet.
• Dynamic NAT: In contrast to static NAT, dynamic NAT uses a group of public IP addresses that are assigned to the internal IP addresses, but not permanently. This enables more efficient utilisation of the address space.
• NAT overloading (PAT - Port Address Translation): This technique allows multiple devices on the internal network to use a single public IP address by using different ports to differentiate the connections. This method is the most common and is often used in home networks.

Advantages and disadvantages of NAT

Advantages

• Increased security: NAT hides the internal IP addresses from external attackers.
• Efficient utilisation of IP addresses: It allows multiple devices to access the Internet via a single IP address.
• Flexibility: Networks can change their internal IP addresses without affecting their external communication.

Disadvantages

• Complexity in setting up services: Setting up servers and services (such as VoIP or gaming) can be complicated as ports need to be manually forwarded.
• Performance losses: In busy networks, NAT can lead to a delay in data transmission.

Illustrative example on the topic: NAT

Imagine an office with 10 computers in a local area network (LAN), all connected via a single Internet connection. Each computer has a private IP address, e.g. 192.168.1.2, 192.168.1.3 etc. When the computer with the IP address 192.168.1.2 visits a website on the Internet, the router's NAT ensures that the request uses a public IP address, for example 203.0.113.5. When the website responds, the router knows which computer on the internal network the response belongs to and forwards the message to 192.168.1.2. In this way, all computers in the office can use the Internet without each of them needing their own public IP address.

Conclusion

NAT is a fundamental technology that enables modern Internet traffic and improves its security. By using NAT, organisations and home users can effectively manage their IP resources while protecting their networks. If you would like to learn more about related topics, please also visit our article on DNS or on firewalls.