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Address Translation: Definition, Types & Examples

Instructor: Lyna Griffin

Lyna has tutored undergraduate Information Management Systems and Database Development. She has a Bachelor's degree in Electrical Engineering and a Masters degree in Information Technology.

In this lesson we will understand the concept of Address Translations (AT) and why it is necessary in our Internet world today. We will examine the different types of Address Translations, their definitions, differences and their applications.

What is Address Translation?

Address Translation (AT) refers to the manipulation of IP addresses used to identify devices over the Internet. It serves to map private IP addresses within networks to public addresses which are routable over the Internet. The system is more often referred to as Network Address Translations (NAT). Why is this translation necessary? Why can't computers and devices interact on the internet with their private addresses? The answer is simple. Not enough addresses. The numbers of devices today are multiplying astronomically. The world today consists of billions of devices and if we were still using the IPv4 Internet Protocol we would have run out of addresses.

How Does This Translation Work?

This translation in layman's terms works by grouping. Devices within a common network are grouped accordingly and mapped to a single address or a pool of public addresses to represent their traffic on the Internet, through their Internet Service Provider (ISP). Every device which is on a network is uniquely identified by its IP address. As long as the device is within the private network, any range of IP addresses can be used. This means for example, Company A with 40 devices can use the 192.168.0.1-192.168.0.40 address range. Another independent Company B, in another location, can use the same range of addresses within their own private network and there will be no address conflicts. When these two companies need to communicate over the Internet they do so by the use of public IP addresses assigned through their ISPs. Company A is assigned public address 108.186.225.42 which is seen by everyone (public) and Company B assigned 108.186.225.05, completely unique. This is where the translation comes in. The ISP assigns a unique public address to any individual company or organization who wishes to access the Internet. Irrespective of the IP addresses used within the private network, all traffic emanating from and transmitted to company A has to use 108.186.225.42. The private addresses cannot be used.

We can see that address translation serves two purposes. It conserves the IP addresses in the public domain. Nodes in private networks do not need individual public IP addresses. Secondly, it serves as a layer of protection by hiding the real IP addresses within the private network. Let us examine the following illustration.

Company A's computer with private address 192.168.0.35 makes a request to a web server somewhere on the Internet. The NAT translates 192.168.0.35 to 108.186.225.42. 108.186.225.42 is used in the public domain of the Internet to contact the web server. The web server, in honoring the request, responds with a reply using 108.186.225.42 to return its response to the sender. The NAT then takes the web server's response and maps it to Computer A with private address 192.168.0.35.

Types of Address Translations

There are different types of address translations.

Network Address Translation (NAT)

Network Address Translation is defined as the mapping of an IP address within a private network to a public IP address in the public domain. There are two types of NATs. Static NAT and Dynamic NAT

Static NAT

With Static NAT address mapping, a private IP address say 192.168.0.35 is mapped permanently to a public IP address 108.186.225.42 as seen in Figure 1. A pool of addresses is made available to the NAT device to be statically assigned to various nodes on the network. Server A for example will always have the same Public IP assigned to it when accessing the Internet and other nodes on the network would use different public IPs. This is particularly useful when a server on a private network has to be remotely accessed via the Internet.


Static IP


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