NAT was strictly designed to preserve IP address space. NAT is a service that translates IP addresses, primarily the private IPs of devices on a network, into a public IP visible on the Internet. This allows devices on a private network to access the Internet without requiring each device to have its own public IP address.
However, with NAT, you can translate any IP address into another one, such as private into private, public into public, or public into a private IP address. NAT is usually implemented using hardware devices, such as routers or firewalls, or software running on a server or computer.
Take a look at the image above for a better understanding of NAT. PC1 uses a private IP address of 192.168.1.10 for internal communication within the enterprise network of 192.168.1.0/24.
However, when it needs to ping the public DNS server (8.8.8.8) on the internet, the router performs a NAT translation, which translates the private IP address used as a source IP in the packet into a public one, such as 203.0.113.1. Now the packet can be accepted by the service provider and eventually reach the destination IP on the internet.
Depending on whether only IP addresses are translated or IP addresses and port numbers, as well as the translation mechanism used, there are three types of NAT that you can implement:
- Static NAT,
- Dynamic NAT, and
- Port Address Translation (PAT).