220-1102 Question 552
Single answerPort forwarding/mappingA small business hosts an internal web application on a server with the private IP address 192.168.1.50. The office router receives a public IP address from the ISP, and remote employees need to access the web application from the internet. The technician confirms the web service is listening on TCP port 80 internally and that local users can reach the site by browsing to http://192.168.1.50. Which router configuration should the technician implement to allow internet users to reach the internal web server?
- A
Create a port forwarding rule that maps inbound TCP port 80 on the router's public interface to 192.168.1.50 on TCP port 80
- B
Enable DHCP reservation for 192.168.1.50 so the router automatically publishes the web server to the internet
- C
Configure DNS on the router to resolve the server name to 192.168.1.50 for external users
- D
Create a port triggering rule for TCP port 80 so the server opens port 80 only after an internal client starts a web session
Show answer and explanation
Correct answer: A
Explanation
The correct solution is to configure static port forwarding on the router so inbound TCP port 80 on the public interface is translated and sent to the internal server at 192.168.1.50:80. This is a common NAT/PAT use case in small offices when publishing an internal service to external users. Best practice is also to verify the internal server has a consistent IP address, often through a static address or DHCP reservation, but that step complements rather than replaces port forwarding. Documentation from major router vendors and networking references consistently describe port forwarding as the method used to allow unsolicited inbound traffic from a public network to reach a specific host on a private network behind NAT. In production environments, technicians should also consider security best practices, such as allowing only required ports, using HTTPS instead of HTTP when possible, and confirming host-based firewalls permit the service.
- A. Correct.
Correct. Port forwarding, also called port mapping, is the standard method for directing unsolicited inbound internet traffic received on a router's public IP and specific port to an internal host and port. In this scenario, forwarding TCP 80 to 192.168.1.50:80 allows external users to reach the internal web server through the NAT router.
- B. Incorrect.
Incorrect. A DHCP reservation helps ensure the server keeps the same internal IP address, which is useful for stable port forwarding rules, but it does not by itself expose the service to the internet. The misconception is confusing internal address management with NAT/firewall publishing.
- C. Incorrect.
Incorrect. External DNS can help users find the public IP address or a hostname, but DNS does not pass traffic through NAT to a private IP address like 192.168.1.50. Private RFC 1918 addresses are not routable on the public internet, so DNS alone cannot make the internal server reachable externally.
- D. Incorrect.
Incorrect. Port triggering is typically used for applications that initiate outbound traffic first and then temporarily open return ports. A public-facing web server must accept unsolicited inbound connections, so a static port forwarding rule is the appropriate solution. This option reflects a common confusion between port triggering and port forwarding.