What is NAT in computer networks?

Before starting the explanation of Network Address Translation let’s recall some key points. That will help you to understand the explanation and working of NAT.

Key Points

We generally have two types of IP address, which are as follows −

Private IP address
Public IP address

Private IP address normally used in the LAN (Local area network) side of the Network.

Public IP address provided by the ISP is configured in the WAN side of the network.

Public IP addresses are always paid, while the private IP address is free.

Private IP addresses range as follows −

192.168.0.0 - 192.168.255.255 (65,536 IP addresses)
172.16.0.0 - 172.31.255.255 (1,048,576 IP addresses)
10.0.0.0 - 10.255.255.255 (16,777,216 IP addresses)

Now let us try to understand what Network Address Translation (NAT) is.

Step 1 − Consider you have internet provided by Internet Service Provider ABC.

Step 2 − So, they will give you connection to your Modem. That connection we used to call WAN.

Step 3 − This connection is always configured with a Public IP address.

Step 4 − Then, your LAN side of the MODEM is configured with a Private IP address.

Step 5 − That means your computer or laptop connected to the network receives a Private IP address.

Step 6 − As per the standard Private IP will not communicate with Public IP address at any Point of time.

Step 7 − To achieve this, Private IP addresses need to be translated to Public IP addresses with help of NAT.

Step 8 − In simple words, Network Address translation is used to translate Private IP address to Public IP address to communicate LAN side of the Device to Global Network. Network address translation can be processed in Router or Firewall.

Given below is the diagram of the NAT −

Working of NAT

Usually we used gateway router / Border devices used for NAT configuration. One of the interfaces for that device is connected to the local Area network (INSIDE) and one of the interfaces for this device connected to the outside network (OUTSIDE).

When we have received a request from our local machine it will hit the configuration pool then that Private IP will convert it into Public IP address and vice versa.

Inside worldwide location − IP address that speaks to at least one inside nearby IP delivers to the rest of the world. This is within have as observed from the external organization.

Outside residential area − This is the genuine IP address of the objective host in the nearby organization after interpretation.

Outside worldwide location − This is the external host as observed to structure the external organization. It is the IP address of the external objective host before interpretation.