N10-009 Question 288
Single answerUsers in one office report that they cannot access a newly deployed internal web application by URL from their workstations. The server team confirms the application is running and reachable from the server subnet. A technician verifies that affected users can still reach other internal resources and the internet. One user can successfully open the site by entering the web server's IP address directly, but not by using the application's hostname. Following best-practice troubleshooting to establish a theory of probable cause, which action should the technician take NEXT?
- A
Begin at the physical layer and replace patch cables at affected desks before checking any higher-layer services
- B
Use a divide-and-conquer approach by testing name resolution with tools such as nslookup or dig to determine whether the issue is DNS-related
- C
Escalate immediately to the application vendor because the web application is new and likely misconfigured
- D
Reboot the core switch to clear any stale forwarding entries that might prevent users from reaching the server
Show answer and explanation
Correct answer: B
Explanation
The best answer is to test DNS using a divide-and-conquer method. In Network+ troubleshooting, establishing a theory of probable cause means using the symptoms to narrow the fault domain instead of making random changes. Here, the ability to access the application by IP address but not by hostname is a classic indicator that Layer 7 naming or supporting DNS services should be investigated. This reflects both 'question the obvious' and 'consider multiple approaches' from the troubleshooting methodology. A top-to-bottom approach could also lead to DNS investigation because the issue appears at the application/name-resolution level, while a bottom-to-top approach would be less efficient given the evidence that lower layers are functioning. Common best practices from vendor documentation and operational runbooks recommend verifying DNS records, client DNS settings, suffix search behavior, and DNS server responses before escalating or making disruptive infrastructure changes.
- A. Incorrect.
This is not the best next step. Replacing patch cables is a bottom-to-top approach that starts at Layer 1, but the scenario already provides evidence that Layer 1 through Layer 3 connectivity is likely functioning: users can reach other internal resources and the internet, and at least one user can reach the site by IP address. Jumping to cable replacement ignores the obvious evidence and does not efficiently establish a probable cause.
- B. Correct.
This is correct. The symptom that the site works by IP address but not by hostname strongly suggests a name resolution problem rather than a physical, switching, or application availability issue. A divide-and-conquer approach is appropriate here because the technician already has evidence that network connectivity and the web service itself are likely working. Testing DNS with nslookup or dig helps confirm whether the hostname resolves correctly, whether the DNS server is reachable, and whether records are missing or incorrect.
- C. Incorrect.
This is incorrect. Although the application is newly deployed, the evidence does not yet point primarily to an application fault. The server team can reach it from the server subnet, and a user can access it by IP address, which suggests the application is up. Escalating immediately skips the required step of questioning the obvious and testing the most likely cause first.
- D. Incorrect.
This is incorrect. Rebooting the core switch is a disruptive action and is not justified by the symptoms. If stale forwarding entries or switching issues were the problem, users would be more likely to have broader connectivity failures, not a hostname-only access issue. Best practice is to gather evidence and test the most probable cause before making high-impact changes.