NAT, or Network Address Translation, serves the primary purpose of allowing multiple devices on a local network to share a single public IP address when accessing the internet. Essentially, it acts as an intermediary between private networks and the wider internet. When a device on a private network sends a request to the internet, NAT translates its private IP address into the public IP address. When the response comes back, NAT translates it back to the appropriate private IP address, ensuring the correct device receives the data.
NAT has extended the life of IPv4 by alleviating the exhaustion of available IPv4 addresses. As IPv4 allows for roughly 4.3 billion unique addresses, the rapid growth of internet-connected devices raised concerns about a shortage of addresses. By enabling the same public IP address to serve multiple devices on a private local network (which can have a virtually unlimited number of private IP addresses), NAT has effectively stretched the availability of IPv4 addresses. This technological workaround has allowed more devices to connect to the internet without needing a unique public IP address for each one, thus delaying the transition to IPv6, which has a much larger address space.