220-1101 Question 145
Single answerPublic addressesA small business hosts a web application on a server inside its office. The server has the private IPv4 address 192.168.1.50, and the router connects to the internet using an address assigned by the ISP. Users on the local network can reach the site, but customers on the internet cannot. The technician confirms that the web service is running and that internal DNS is correct. Which change is required so internet users can access the server?
- A
Assign the server a public IP address that is routable on the internet
- B
Configure the router to forward incoming web traffic from the public IP address to 192.168.1.50
- C
Change the server IP address from 192.168.1.50 to 169.254.1.50
- D
Enable APIPA on the router so external clients can discover the server automatically
Show answer and explanation
Correct answer: B
Explanation
Public IPv4 addresses are globally routable, while private IPv4 addresses such as 192.168.1.0/24 are reserved for internal networks and are not routed across the internet. In a real-world small business environment, a server commonly keeps a private address and relies on the edge router's public IP address for internet-facing access. The required configuration is NAT/port forwarding on the router so traffic sent to the public address on the appropriate port is translated and forwarded to the internal host. This aligns with IETF RFC 1918 for private address space and standard SOHO/SMB network design practices used on A+ Core 1 topics covering public vs. private IP addressing and basic connectivity.
- A. Incorrect.
Incorrect. Although a public address is routable on the internet, in a typical small office network the server is intentionally kept on a private address behind a router or firewall. Reassigning the server directly to a public IP is usually unnecessary, may expose it without proper controls, and often is not possible unless the ISP provides additional public addresses and the network is designed for that use.
- B. Correct.
Correct. The office uses private addressing internally, so outside users cannot directly route to 192.168.1.50 because RFC 1918 private IPv4 ranges are not routable on the public internet. The router must use the public IP assigned by the ISP and perform port forwarding/NAT so inbound HTTP or HTTPS traffic arriving at the public address is sent to the internal server at 192.168.1.50.
- C. Incorrect.
Incorrect. 169.254.x.x is the APIPA/link-local range used for automatic self-assignment when a DHCP server is unavailable. These addresses are not publicly routable and would make the situation worse because they are intended only for local-link communication.
- D. Incorrect.
Incorrect. APIPA does not help internet clients discover or reach internal hosts. APIPA addresses are link-local, non-routable, and used as a fallback when DHCP fails. External access to an internal server requires a public address on the router and a mapping such as port forwarding, not APIPA.