NAT

Hi Dear,

One reason NAT exists is that, with IPv4, there are a severely limited number of addresses available (a theoretical maximum of about 4.3 billion). For this reason, in most residential circumstances, an Internet Service Provider provides at most one public IP address to a subscriber at a time. If you would like to send and receive packets on multiple machines, it is necessary to have some kind of a local-public conversion, in other words NAT.

IPv6 will change all that as there should be something like thousands or millions of IP addresses per square foot of the Earth's surface.

Hi friend!
Network Address Translation (NAT) firewalls are the process by which network devices (usually firewalls) assign public addresses to computers (or groups of computers) within a private network, running on routers to protect the private network. The primary purpose of NAT is to limit the number of public IP addresses that an organization or company must use for economic and security purposes.
NAT works by allowing Internet traffic to pass only when requested by devices on the private network. NAT firewalls protect the identity of the network and do not reveal internal IP addresses to the Internet.
This is because the router is assigned a public IP address when connected to the Internet. It is visible to the wider network and needs to communicate with the web server. Any device that is locally connected to the router has a private IP address, which does not allow them to "communicate" directly with the desired web server. That's where NAT comes in -- it directs traffic back and forth.
Hope to help you!