Where is NAT usually implemented in a network setup?

Network Address Translation (NAT) is primarily implemented in a network setup at the boundary where a private network connects to a public network, typically the internet. The main function of NAT is to allow multiple devices on a private network to share a single public IP address when accessing external networks.

When devices on a private network (like a home or office network) make requests to the internet, their private IP addresses are not routable on the public internet. The NAT device, often a router, translates these private addresses to the public IP address assigned to the network. This process helps to conserve the number of public IP addresses used and provides an additional layer of security by keeping the internal IP addresses hidden from external entities.

Additionally, implementing NAT between private networks or solely on user devices does not fulfill its designed purpose of facilitating communication with external networks. Similarly, while NAT interacts with the public internet, it is not usually set up on the internet, but rather in the infrastructure that connects private networks to it.