What is the correct action to be specified in the NAT rule to hide a private network when communicating to the outside world?

To hide a private network when communicating with the outside world, the action that should be specified in the NAT rule is masquerade. The masquerade action allows devices within a private network to access external networks (like the internet) by modifying the source IP addresses of outgoing packets to the public IP address of the router. This means that any responses from the external network are sent back to the router's public IP, which can then forward the traffic appropriately to the correct internal device.

This technique effectively hides the internal IP addresses from outside visibility, providing a level of privacy and security for the devices within the private network. Masquerading is generally used in scenarios where the router has a dynamically assigned public IP address, as it automatically adapts to the IP address changes without requiring additional configuration.

In contrast, the other options listed are not suitable for this purpose. Allow would permit traffic without address translation, passthrough does not modify the packet and implies that the packet should continue through the network without any alteration, and tarpit is used to intentionally slow down connections for security or research purposes rather than for hiding an internal network.