N10-009 Question 15
Single answerLayer 7 - ApplicationA company hosts an internal web application for inventory management. Users report that they can reach the server by IP address, but when they browse to https://inventory.corp.local, the page fails to load. A network technician verifies that the server is online, HTTPS on TCP port 443 is listening, and routing between the client and server is working. Which of the following application-layer services is the most likely cause of the problem?
- A
DNS
- B
DHCP
- C
NTP
- D
SNMP
Show answer and explanation
Correct answer: A
Explanation
The best answer is DNS. At the OSI Application layer, DNS provides hostname-to-IP resolution for client applications. When a user enters a URL such as https://inventory.corp.local, the client must first resolve the hostname before initiating the TCP and TLS/HTTPS connection. If the site is reachable by IP address but not by hostname, the problem is typically with DNS records, DNS server availability, or client DNS configuration. This aligns with common troubleshooting methodology used in enterprise environments: verify physical/network connectivity first, then test name resolution separately. Best practices from vendor and standards documentation for DNS troubleshooting include checking A/AAAA records, validating the configured DNS server on the client, and using tools such as nslookup or dig to confirm resolution results.
- A. Correct.
Correct. DNS is an Application layer service used to resolve hostnames such as inventory.corp.local into IP addresses. If users can access the web server by IP address but not by name, name resolution is the most likely failure point. This is a classic Layer 7 symptom because the application depends on DNS to translate the URL hostname before the HTTPS session can be established to the correct destination.
- B. Incorrect.
Incorrect. DHCP is also an Application layer protocol, but it is used to automatically assign IP addressing information such as IP address, subnet mask, default gateway, and DNS server settings. In this scenario, routing is working and users can already reach the server by IP, which indicates clients have functional IP connectivity. A DHCP issue could cause broader addressing problems, but it would not be the most likely reason that access by hostname fails while access by IP succeeds.
- C. Incorrect.
Incorrect. NTP is an Application layer protocol used for time synchronization. Incorrect time can affect certificate validation in some HTTPS scenarios, but the key detail here is that the application works when accessed by IP and fails only when using the hostname. That points much more directly to a name-resolution issue than to time synchronization.
- D. Incorrect.
Incorrect. SNMP is an Application layer protocol used for monitoring and managing network devices. It does not provide hostname resolution for client web access. Someone might choose SNMP because it is a common network service, but it is unrelated to resolving a URL into an IP address for a browser connection.