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.

• ✓

  A) DNS configuration

  Why this is correct

  If a user can successfully ping the default gateway (an IP address) but cannot access external websites by their domain names, it strongly indicates a DNS resolution failure. DNS (Domain Name System) is responsible for translating human-readable domain names into numerical IP addresses that computers use for routing. Without correct DNS configuration, the client cannot resolve domain names to IP addresses, preventing access to external resources even if underlying network connectivity to the internet gateway exists.

• ✗

  B) DHCP server

  Why it's wrong here

  The user's report includes an IP address (192.168.1.100), which confirms that the client successfully obtained network configuration, including an IP address, subnet mask, and default gateway. DHCP's (Dynamic Host Configuration Protocol) primary role is to dynamically assign these network parameters to client devices. Since the client already has a valid IP address and can communicate locally, the DHCP server is functioning correctly and is not the source of this specific problem.

  When this WOULD be correct

  A technician should check the DHCP server when a user cannot obtain an IP address or receives an incorrect one (e.g., 169.254.x.x), or when multiple users report connectivity issues after a DHCP scope change.

• ✗

  C) Router's firewall ACLs

  Why it's wrong here

  While a router's firewall Access Control Lists (ACLs) could indeed block internet traffic, the user's ability to ping the default gateway demonstrates successful Layer 3 connectivity to the router itself. Firewall ACLs typically operate at Layer 3 and above, filtering traffic based on IP addresses and ports. If the router is reachable, the issue is more likely with name resolution or a higher-layer service rather than a blanket firewall block preventing *any* internet access.

  When this WOULD be correct

  A technician finds that a user cannot access any external resources, and pinging the default gateway fails. After verifying the IP configuration is correct, the technician should check the router's firewall ACLs to see if outbound traffic is being blocked.

• ✗

  D) Switch port VLAN assignment

  Why it's wrong here

  An incorrect VLAN assignment on the switch port would typically prevent the client from establishing any Layer 2 or Layer 3 connectivity within the local network, including reaching the default gateway. Since the user can successfully ping the gateway, their device is communicating on the correct local segment and can reach the router. Therefore, the switch port's VLAN assignment is functioning as expected for local network access.

  When this WOULD be correct

  If a user cannot access any network resources (local or internet) after a cable replacement, and other devices on the same switch port work, checking the switch port VLAN assignment would be appropriate to ensure the port is in the correct VLAN.

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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