When a firewall takes an incoming request for a specific IP address and redirects it to an internal host, which of the following is being used?

NIS (Network Information Service) is a Unix/Linux directory service protocol used to share configuration files across hosts, and has no role in IP address translation or traffic redirection.

PAT (Port Address Translation) maps multiple internal private IPs to a single public IP by differentiating sessions with unique port numbers, and is primarily used for outbound traffic from many internal hosts sharing one public address.

NAT, specifically Destination NAT (DNAT), translates a public-facing IP address to an internal private IP when inbound traffic arrives at the firewall. This allows external requests targeting a public IP to be transparently forwarded to an internal host with a private address. Firewalls commonly implement this as inbound NAT rules or port forwarding entries.

NIC (Network Interface Card) is physical hardware that connects a device to a network, and performs no address translation or traffic redirection.