What exactly is NAT (Network Address Translation)?

Local host needs public IP to access the internet but public IP is very limited in this world so private IP is used and with the help of NAT private IP is converted into public IP and internet access is provided to the local host. It translates the port numbers of the host with another port number that will be routed to the destination. NAT operates on a router or firewall. Generally, there are three types of NAT they are Static NAT, Dynamic NAT, and Port address translation (PAT). NAT is configured in the border of the router where one interface is in the local network and another in the global network. When the packet travels outside the local network, the local IP address is converted to the global IP address with the help of NAT, and when the packet travels outside the global network, the global IP address is converted into a local IP address. When there is no IP address left in the pool then the packet will drop out and the host unreachable packet is sent to the destination. 

Impact of NAT on Security

There is a shortage of public IP addresses so hosts use private IP addresses and NAT helps to convert the private IP address into a public IP address legally. It enables the private IP networks to access the internet. NAT conserves public addresses because it can be configured to advertise at a minimum only one public address for the entire network to the outside world.

Using NAT in our organization helps to keep internal IP addresses hidden that prevent direct attacks on the IP address. It allows access to more ports. The main problem organizations face is overlapping IP addresses and by the use of NAT, this problem can be reduced. The private IP address scheme can be changed with the help of NAT without affecting the public IP address.