NAT stands for Network Address Translation, which is a technique employed for allow multiple devices on a private network to share a single public IP address when accessing the outside world, or communicating with external devices. This is necessary due to the limited number of IP addresses available, as most devices are assigned a private IP address by their router.

Private IP addresses are defined within, as per RFC 1918 and are not available on the public outside world; these include the ranges 192.168.0.0 to 192.168.255.255. When these devices try to communicate with the outside world, they employ this private IP address, but it's invisible to the external devices.

To address this issue, NAT is used to this problem. Here's how it operates: when a device on the private network initiates an internet request, the request is forwarded by the router to the internet service provider's router. The router then translates the private IP address of the device to a public IP address of the router, effectively hiding the device's IP address from the external world.

For incoming data requests, the procedure is reversed. The router receives the packet, determines the source based on a port number, and forwards it to the device on the private network.

There are two primary types of NAT used in modern networks: NAT-PAT and full-cone NAT.

• NAT-PAT stands for Network Address Translation-Port Address Translation. It's the most widely used type of NAT in use today. NAT-PAT maps the private IP address and a specific port number to a public IP address and a free port on the router.
  
  
• Full-cone NAT translates an entire private IP address range to one public IP address. This type of NAT is not as commonly used as NAT-PAT due to the limitations it imposes, but it is still used in some settings, including video games and streaming services that require multiple inbound connections.
  
  

In conclusion, 누누티비 Network Address Translation is an important technique used to overcome the limited availability of public IP addresses. It allows thousands of devices to be connected to the outside world without the need for unique public IP addresses.