What is the primary purpose of the Network Address Translation (NAT) function?

The primary purpose of Network Address Translation (NAT) is to allow private IP addresses to connect to the Internet. NAT operates on routers and modifies the IP address information in the headers of data packets as they pass between the local network and the Internet. This is essential because private IP addresses, which are used within local networks, are not routable on the Internet. By translating these private IP addresses into a public IP address, NAT enables multiple devices on a local network to share a single public IP address when accessing the Internet. This function is critical in conserving the public IP address space and allows for greater flexibility in managing IP address allocation within internal networks.

The other options, while relevant in various contexts, do not accurately describe the main purpose of NAT. For instance, caching data is related to performance optimization but falls outside of NAT's scope. Similarly, while NAT contributes to network security by obscuring internal IP addresses, its primary function is not to secure the network itself. Lastly, end-to-end connectivity is a concept more closely associated with IPv6's design, which was created to eliminate the need for NAT by allowing a vastly larger address space, rather than with the function of NAT itself in IPv4 networks.