Network Address Translation

Network Address Translation(NAT) is the process of converting one IP address to a different IP address. Simply it is the process of mapping one IP address to another. Why we need NAT and map one IP to another? The answer is a little bit big. Currently we adopts IPv4 to generate unique IP addresses for all the computers connected to the Internet. But we know that today's increased popularity of Internet make it difficult to assign unique IP address to all the computers connected to Internet. Growth of bigger companies shows thousands of computers in a company is nothing and with in many networks thousands of thousand computers are available. Is it possible to provide unique IP address to all the computers in these kinds of large companies ? No, so the idea of NAT invented.

Using the concept of Network Address Translation (NAT) we can easily assign IP address to all the computers present in the bigger companies by spending few actual addresses. Before explaining it we need to know the concept of private IP address and public IP address. Private IP address is a set of IP addresses which is not using for connecting to Internet. The ranges of private IP addresses are described below.

10.0.0.0 to 10.255.255.255

172.16.0.0 to 172.31.255.255

192.168.0.0 to 192.168.255.255

The computers in companies and a LAN are addressed by using private IP addresses. But by using private IP addresses they cannot access Internet. So the company should purchase a set of public IP addresses and using NAT they will convert the private IP address to the valid public IP address. So we can avoid the headache of assigning unique IP address to all computers present in the corporates. To implement it we are loosing the private IP addresses but we can use the same set of private IP addresses to the computers in a different corporate network. So NAT and the concept of private IP addresses helps us in better utilization of IP address.


Types of NAT


The NAT is divided in to the following categories.

1. Static NAT

2. Dynamic NAT

3. Port Address Translation (PAT)


In static NAT one unregistered (private) IP address is mapped to one registered (public) IP address. This kind of mapping is predefined one.
In dynamic NAT a pool of public IP addresses is shared by an entire private IP subnet. This mapping is not predefined but it is dynamic.In Port Address Translation (PAT)multiple unregistered IP addresses map to a single registered IP address by different TCP/UDP port numbers.

So in a nutshell:

1. That same company using NAT would only need 1 public IP address and would assign the computers on the local network internal IP addresses.

2. Hiding property of NAT

This “hiding” of the internal IP addresses works not onlyto allow for more Hosts to share the Internet, but also as a layer of security. By not allowing the outside world to know the precise IP addresses of your internal Hosts you take away a key piece of information that hackers could use to break into your network.