How Network Address Translation (NAT) Works

The number of computers accessing the Internet is growing each day. Each computer must be assigned with a unique IP Address to prevent conflict with other computers. Increasing number of computers connected to the Internet resulted in some issues with regard to the availability of IP Addresses. How is it possible to connect two computers to the Internet with just a single modem? Most modems are assigned only a single IP Address. Network Address Translation solves these issues.

Network Address Translation is the software that modifies an IP Address from a private network to an IP Address available for public network. This allows you to connect multiple computers to the Internet using a single IP Address through the use of a router. Making it look like a single computer is accessing to the Internet by using a gateway.

Private networks can be considered as your personal network or the Local Area Connection (LAN). When a computer in your LAN accesses the Internet, it needs an IP Address that is for public network. The router then, through the use of NAT, modifies the IP Address of your computer into the IP Address of the modem connected to it. This happens to every request passing through the router. So the IP Address provided by the router to your computer will remain on your own computer and LAN. The request for Internet access will then be represented by your network gateway- the device that is connected to the network.

NAT are classified into three categories. These are the Static, Dynamic, Overlapping, and Overloading. Static NAT is done when a computer with a private address is assigned a dedicated public IP Address, also represented as one-on-one translation. Devices configured with static NAT can be accessed from outside the network.

Dynamic NAT on the other hand is the mapping of a private IP Address to a counter public IP Address randomly. The first computer on the network can take the first IP Address configured with the NAT and so on.

Overloading NAT is similar to dynamic NAT. However, each computer on a private network is assigned a unique IP Address. These computers then are mapped to a single Private IP Address through different port numbers, also referred as Port Address Translation (PAT).

Overlapping works when registered IP Addresses are also used by another network. This causes a conflict on the network. The router then analyzes every internal and external IP Address in order to reassign unique IP Addresses.

How does NAT help improve your network security? Dynamic NAT can serve as a preliminary firewall for your network. Only computers connected to your internal or local area connection can get access to the Internet passing through NAT. A foreign computer can only connect to the Internet once your computer initiates a connection to it allowing it to be mapped. Another advantage is the filtering and traffic logging capabilities for a NAT router. This allows an administrator to configure some restrictions to specific IP Address. Even block some websites or services a specific IP Address is limited to.

How will the router be able to track who made the request? Since the IP Address of an internal computer is replaced with an IP Address available for public network it can be confusing for humans to track it. However, routers automatically store it and once a response is received, routers then check the list and forward it back to the requesting computer.