N10-009 Networking Concepts Practice Question
A client obtains an IP address from a DHCP server but cannot resolve hostnames. The client can ping the default gateway and external IP addresses successfully. What is the most likely cause?
⚠ Common exam trap
The N10-009 exam often tests the distinction between IP connectivity and name resolution, trapping candidates who assume that successful pings to external IPs imply DNS is working, when in fact DNS is a separate service that must be explicitly configured.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DNS server misconfiguration
The client can ping external IP addresses and the default gateway, confirming that IP connectivity and routing are functional. However, the inability to resolve hostnames points directly to a DNS resolution failure, which occurs when the DNS server address is misconfigured or unreachable. Since DHCP provided the IP address, the DNS server setting is likely incorrect or missing in the DHCP scope.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Incorrect subnet mask
Why it's wrong here
An incorrect subnet mask would fundamentally alter the client's perception of its local network boundaries. If misconfigured, the client might incorrectly assume external IP addresses are on its local subnet, attempting to ARP for them instead of sending traffic to the default gateway. Conversely, it might incorrectly classify local IPs as external. Since the client can successfully ping external IP addresses, its subnet mask is correctly configured, allowing it to properly distinguish between local and remote destinations and route traffic accordingly.
When this WOULD be correct
In a scenario where a client obtains an IP address but cannot communicate with any devices outside its local subnet, including the default gateway, an incorrect subnet mask would be the likely cause.
- ✓
DNS server misconfiguration
Why this is correct
A DNS server misconfiguration means the client either has an incorrect DNS server IP address, or the assigned server is unreachable or non-functional. While the client can successfully obtain an IP address and establish basic IP connectivity (evidenced by pinging external IPs), it cannot translate human-readable hostnames (like www.example.com) into numerical IP addresses. This prevents web browsing or accessing resources by name, as the client doesn't know where to send the traffic for those hostnames.
- ✗
Default gateway not set
Why it's wrong here
The default gateway is essential for a client to communicate with any device outside its immediate local subnet. If the default gateway were not set or was misconfigured, the client would be unable to route traffic to external IP addresses, including those on the internet. The fact that the client can successfully ping external IP addresses definitively proves that a default gateway is correctly configured and operational, allowing traffic to leave the local network.
When this WOULD be correct
A client obtains an IP address but cannot ping the default gateway or any external IP addresses. The client can only communicate within its own subnet.
- ✗
Firewall blocking DNS
Why it's wrong here
While a firewall could specifically block DNS traffic (typically UDP/TCP port 53), the problem description indicates the client can successfully ping external IP addresses. This demonstrates that general outbound IP connectivity is functional. If a firewall were blocking DNS, it would prevent hostname resolution, but the ability to ping external IPs suggests that fundamental network access is not broadly obstructed, making a specific DNS server configuration issue more probable than a firewall rule.
When this WOULD be correct
A firewall blocking DNS would be correct if the client could not ping external IP addresses or the default gateway, but could obtain an IP address via DHCP. For example, if the firewall is configured to allow DHCP but block all other traffic except specific ports, and DNS (port 53) is explicitly blocked.
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.
✓DNS server misconfigurationCorrect answer▾
Why this is correct
A DNS server misconfiguration means the client either has an incorrect DNS server IP address, or the assigned server is unreachable or non-functional. While the client can successfully obtain an IP address and establish basic IP connectivity (evidenced by pinging external IPs), it cannot translate human-readable hostnames (like www.example.com) into numerical IP addresses. This prevents web browsing or accessing resources by name, as the client doesn't know where to send the traffic for those hostnames.
✗Incorrect subnet maskWrong answer — click to see why▾
Why this is wrong here
The client can ping external IP addresses successfully, which indicates that the subnet mask is correct; otherwise, routing to external IPs would fail.
★ When this WOULD be the correct answer
In a scenario where a client obtains an IP address but cannot communicate with any devices outside its local subnet, including the default gateway, an incorrect subnet mask would be the likely cause.
Why candidates choose this
Candidates may confuse symptoms of DNS failure with subnet mask issues, or incorrectly assume that an IP address obtained from DHCP implies a correct subnet mask.
✗Default gateway not setWrong answer — click to see why▾
Why this is wrong here
The client can ping the default gateway and external IP addresses, which indicates the default gateway is correctly configured. The issue is name resolution, not routing.
★ When this WOULD be the correct answer
A client obtains an IP address but cannot ping the default gateway or any external IP addresses. The client can only communicate within its own subnet.
Why candidates choose this
Candidates may confuse symptoms of DNS failure with gateway issues, or assume that hostname resolution requires a correctly set gateway.
✗Firewall blocking DNSWrong answer — click to see why▾
Why this is wrong here
The client can ping external IP addresses successfully, indicating that traffic to external networks is not blocked. A firewall blocking DNS would prevent DNS queries but not ICMP pings to external IPs; however, the ability to ping external IPs suggests no general firewall blocking of outbound traffic. The issue is specifically name resolution, not packet filtering.
★ When this WOULD be the correct answer
A firewall blocking DNS would be correct if the client could not ping external IP addresses or the default gateway, but could obtain an IP address via DHCP. For example, if the firewall is configured to allow DHCP but block all other traffic except specific ports, and DNS (port 53) is explicitly blocked.
Why candidates choose this
Candidates may think that if DNS is not working, a firewall must be blocking it, overlooking that successful pings to external IPs indicate general network connectivity is intact. They confuse name resolution failure with a firewall issue without considering the evidence of successful external pings.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.