Why NAT?
The current Internet uses IP addresses in the form xxx.xxx.xxx.xxx. A sample IP address might be 202.187.4.212. Because of the way these IP addresses are allocated, there started to be a shortage of available IP addresses. The current revision of IP (Internet Protocol) in use on the Internet is IPv4. IPv6 is largely a response to this potential IP address shortage. Unfortunately, IPv6 is going to take decades to implement. A much quicker fix was needed, and that fix was NAT.