N10-009 Network Troubleshooting Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  The web server service is stopped

  Why it's wrong here

  If the web server service (e.g., Apache, Nginx, IIS) were stopped on the server, it would not be actively listening for incoming connections on TCP port 443. Consequently, a telnet attempt to the server's IP address on port 443 would fail, typically resulting in a "Connection refused" error or a timeout, as no application process would acknowledge the incoming SYN packet. Since the technician successfully established a telnet connection to port 443, it confirms that a service is indeed listening and responding on that port, indicating the web server application is running.

  When this WOULD be correct

  In a scenario where a user cannot access a web application and telnet to the server's IP on port 443 fails, the most likely cause would be that the web server service is stopped. For example, if the technician cannot telnet to the server on port 443, the service may not be running.

• ✗

  DNS resolution is failing for the FQDN

  Why it's wrong here

  DNS failure would prevent the browser from resolving the hostname, but the technician used the IP address successfully in ping and telnet. The browser could still fail if it relies on the hostname, but the symptom of 'Unable to connect' typically indicates a connection problem, not name resolution.

  When this WOULD be correct

  A user cannot access a website by its FQDN but can access it by IP address; pinging the FQDN fails while pinging the IP succeeds. This indicates DNS resolution failure.

• ✓

  The browser is configured to use an incorrect proxy server

  Why this is correct

  If the browser is set to use a proxy server that is unavailable or misconfigured, it will fail to connect to the web server even though network connectivity is fine. Telnet and ping bypass proxy settings, confirming the server is reachable.

• ✗

  A firewall is blocking TCP port 443

  Why it's wrong here

  A firewall, whether host-based or network-based, configured to block TCP port 443 would prevent the establishment of a TCP connection to that port. During a telnet attempt, the firewall would either drop the initial SYN packet, causing the connection to time out, or send an ICMP "Destination Unreachable - Communication Administratively Filtered" message, actively refusing the connection. The success of the telnet connection to port 443 explicitly demonstrates that no firewall is currently impeding the TCP handshake to that specific port on the target server.

  When this WOULD be correct

  A user cannot access an HTTPS website, and the technician finds that telnet to the server's IP on port 443 fails (connection refused or timeout), while ping to the server succeeds. This would indicate a firewall blocking TCP 443.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

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