What is a practical test to confirm that a destination port forward is functioning?

• A. Ping the internal host from inside the network.
• B. View the router's SPI firewall status.
• C. Access the public IP on the forwarded port from outside the network and observe the internal host; check firewall NAT rules and logs.
• D. Check the DHCP server lease for the internal host.

Answer: (C)

Testing a destination port forward is about proving that an external client can reach the internal host through the router’s NAT mapping. The practical check is to access the router’s public IP on the forwarded port from a device outside your network and observe how the internal host responds. This directly validates the whole path: the external request arrives at the router, the NAT rule maps that port to the correct internal IP and port, the firewall allows the traffic, and the internal service answers. While doing this, review the router’s NAT/firewall configuration to confirm the exact internal target and port, and look at the logs to see the translation and the connection attempt reaching the host. This approach also helps confirm the internal service is listening on the expected port. If external access isn’t working, consider factors like ISP port blocking, double NAT, or hairpin NAT and test from a remote device or mobile data to rule them out.