N10-009 Question 14
Single answerLayer 7 - ApplicationA company hosts an internal web application for employee expense reporting. Users can reach the site by IP address, but when they browse to https://expenses.company.local, the page does not load and the browser reports that the server name cannot be resolved. Ping to the web server's IP succeeds, and HTTPS to the IP address works. The network administrator wants to restore access using the application's URL with the least disruptive fix. Which of the following should the administrator do FIRST?
- A
Create or correct the DNS A record for expenses.company.local so the hostname resolves to the web server's IP address
- B
Replace the web server's TLS certificate because HTTPS is failing for the application hostname
- C
Open TCP port 53 on the web server so clients can reach the application service
- D
Reconfigure the default gateway on client PCs so application traffic is routed correctly
Show answer and explanation
Correct answer: A
Explanation
This question tests practical troubleshooting of an Application layer dependency: DNS name resolution. At Layer 7, users typically access services by URL rather than IP address, and DNS is a core application service that maps hostnames to IP addresses. Because connectivity to the server by IP is successful, lower-layer issues such as routing and basic reachability are already ruled out. Because the browser specifically reports that the server name cannot be resolved, the most likely cause is a missing, incorrect, or stale DNS record for expenses.company.local. Best-practice troubleshooting follows the symptom chain: verify DNS resolution first, then validate HTTPS details such as certificates if resolution succeeds but secure access still fails. This aligns with standard enterprise troubleshooting methods and common DNS behavior documented by major vendors and operating system networking guides.
- A. Correct.
Correct. The key symptom is that users can access the application by IP address, but the hostname cannot be resolved. That indicates a name resolution problem at the Application layer, most likely a missing or incorrect DNS record. Creating or fixing the A record for expenses.company.local is the least disruptive and most direct first step to restore URL-based access.
- B. Incorrect.
Incorrect. A bad or mismatched TLS certificate can cause browser warnings or trust errors after the client reaches the server, but it does not typically cause a 'server name cannot be resolved' error. Name resolution must work before the browser can establish an HTTPS session using the hostname.
- C. Incorrect.
Incorrect. DNS typically uses port 53 on a DNS server, not on the web server unless that server is also providing DNS services. The scenario does not indicate that the web server is supposed to answer DNS queries. The problem is with hostname resolution, not with the application service port on the web server.
- D. Incorrect.
Incorrect. If the default gateway were misconfigured, broader connectivity issues would be expected. The scenario states that ping to the web server's IP succeeds and HTTPS by IP works, which shows that routing to the server is already functioning. The issue is specifically with resolving the application hostname.