What is the correct action to specify in the NAT rule for hiding a private network when connecting to the Internet?

The action that should be specified in the NAT rule for hiding a private network when connecting to the Internet is masquerade. This action is specifically designed to enable a network device, such as a router, to replace the private IP addresses of outgoing packets with its own public IP address.

When devices within a private network need to access the internet, they send their packets to the router, which uses the masquerade function to create a temporary mapping. Consequently, any responses from the internet are sent back to the public IP of the router, which then directs them to the appropriate private IP address based on the mapping it created. This process effectively "hides" the private network, ensuring that external entities only see the router's public IP address instead of the various private addresses behind it.

Masquerading is commonly used in situations where a router has multiple clients connecting to the internet, and it is especially useful when the router itself has a dynamically assigned public IP, as it can adapt to changes in that address seamlessly.