What is NAT?
NAT, Network address translation is the process where a network device, usually a firewall, assigns a public address to a computer or group of computers inside a private network. The main use of NAT is to limit the number of public IP addresses an organization or company must use, for both economy and security purposes. 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.
How NAT works?
There are three categories relating to NAT. They 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. And 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 NAT improves 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 router tracks 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. You can consider a NAT router as a switchboard operator.
If network traffic comes into the NAT router that isn't the result of a machine making an outbound request, the NAT router doesn't know where to send that network traffic. So that traffic gets ignored. It doesn't get sent anywhere at all. The fact that an outside computer can¡¯t arbitrarily connect to computers behind the NAT router is a byproduct of how NAT works and is why the router companies call their products firewalls.
NAT is not the firewall
The protection offered by NAT is very limited. It will keep an attacker from sending Messenger popup spams to your computer. It will keep people from connecting to services and backdoors installed on your computer. But it won't keep trojans, viruses, and other malicious software from connecting to the Internet from your computer. It won't prevent unauthorized network traffic from leaving your computer and going onto the Internet. That's what modern firewalls do.
