DNS Resolution Failure from DHCP
A user reports that they cannot access the company intranet website at http://intranet. The technician opens a browser on the workstation and types the IP address 192.168.10.5, which successfully loads the intranet page. The workstation is configured to obtain IP settings automatically via DHCP. Which of the following is the MOST likely cause of the issue?
Quick Answer
The answer is that the DHCP server is not providing a DNS server address. This is correct because the user can reach the intranet by its IP address (192.168.10.5) but not by its hostname ("intranet"), which is a textbook symptom of a DNS resolution failure. Since the workstation obtains its IP settings automatically via DHCP, the missing piece is the DNS server address that DHCP should supply; without it, the browser cannot translate the hostname into an IP. On the CompTIA A+ Core 1 220-1101 exam, this scenario tests your understanding of how DHCP delivers more than just an IP—it also hands out critical options like the DNS server. A common trap is to blame the web server or the network connection, but the ability to load the page by IP proves connectivity is fine. Remember the mnemonic: “If the IP works but the name fails, check the DNS that DHCP mails.”
⚠ Common exam trap
The 220-1101 exam often tests the distinction between connectivity (IP works) and name resolution (hostname fails) to trap candidates into thinking the server is down or the hosts file is corrupted, when the real issue is a missing DNS server from DHCP.
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
✓
The DHCP server is not providing a DNS server address
The user can access the intranet by IP address but not by hostname, which indicates a name resolution failure. Since the workstation uses DHCP, the most likely cause is that the DHCP server is not providing a DNS server address, so the browser cannot resolve 'intranet' to an IP. This is a classic symptom of missing or misconfigured DNS settings from DHCP.
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 intranet server is down
Why it's wrong here
The page loads fine by IP, so the server is reachable and running; a downed server would fail on both. It is tempting because an unreachable intranet often means an outage, and that would be the answer if the IP address test had also failed.
- ✗
The workstation has a corrupted hosts file
Why it's wrong here
A corrupted or misconfigured hosts file could cause resolution failure for a specific hostname, but it is less common than a missing DNS server from DHCP. Additionally, the hosts file would affect all name resolution if severely corrupted, yet the IP address works fine.
- ✓
The DHCP server is not providing a DNS server address
Why this is correct
Name resolution fails because the DHCP scope supplies no DNS server address, so http://intranet cannot be resolved to 192.168.10.5. Direct IP access bypasses DNS entirely, confirming the resolver is the fault. The DHCP server must deliver a valid DNS option alongside the lease.
- ✗
The workstation's browser cache is full
Why it's wrong here
A full browser cache would slow browsing or serve stale content, but resolving by IP address while the hostname fails points to DNS. The DHCP scope likely omitted or misconfigured DNS servers; clearing the cache would be correct for stale or corrupted cached pages, not name resolution failure.
Visual reference
Quick reference
IPv4 Address Class Summary
| Class | First Octet Range | Default Mask | Networks | Hosts per Network |
|---|---|---|---|---|
| A | 1–126 | /8 (255.0.0.0) | 126 | 16,777,214 |
| B | 128–191 | /16 (255.255.0.0) | 16,384 | 65,534 |
| C | 192–223 | /24 (255.255.255.0) | 2,097,152 | 254 |
| D | 224–239 | N/A | Multicast groups | — |
| E | 240–255 | N/A | Reserved / experimental | — |
127.x.x.x is reserved for loopback. Modern networks use CIDR (classless) rather than classful addressing.
Go deeper
Related to this question
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Same concept, more angles
3 more ways this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A technician is troubleshooting a computer that cannot access any websites by their domain name (e.g., www.example.com) but can access websites by their IP address. The computer's IP configuration shows it received a valid IP address from the DHCP server. Which of the following is the MOST likely cause?
medium- A.The default gateway is incorrect
- ✓ B.The DNS server address is incorrect or unreachable
- C.The subnet mask is incorrect
- D.The DHCP lease has expired
Why B: The ability to access websites by IP address but not by domain name indicates that name resolution is failing. Since the computer has a valid IP address from DHCP, the most likely cause is that the DNS server address provided by DHCP is incorrect or unreachable, preventing the translation of domain names to IP addresses.
Variation 2. A user reports that they cannot access the internet, but they can access internal network resources by IP address. The technician runs ipconfig and sees IP address 192.168.1.12, subnet mask 255.255.255.0, default gateway 192.168.1.1, DNS server 192.168.1.1. The user can ping 192.168.1.1 and 8.8.8.8 successfully. However, they cannot ping www.google.com. Which of the following is the MOST likely cause?
medium- A.The default gateway is unreachable.
- ✓ B.The DNS server is not resolving hostnames.
- C.The subnet mask is incorrect.
- D.The NIC is faulty.
Why B: The user can ping the default gateway (192.168.1.1) and an external IP (8.8.8.8) successfully, which confirms that the network layer (IP routing) is working and the internet connection is functional. However, the inability to ping www.google.com by name while being able to ping by IP indicates that the DNS server (192.168.1.1) is failing to resolve the hostname to an IP address. Since the DNS server is the same as the default gateway, it is likely that the gateway device is not configured to perform DNS resolution or the DNS service is not running.
Variation 3. A user reports that they cannot access any websites using their web browser, but they can successfully ping external IP addresses such as 8.8.8.8. Other users on the same network are able to browse the internet normally. The technician checks the workstation's IP configuration and finds the following: IP 192.168.1.50, subnet mask 255.255.255.0, default gateway 192.168.1.1, DNS server 192.168.1.1. The technician can ping 192.168.1.1 successfully. Which of the following is the MOST likely cause?
medium- A.Incorrect subnet mask
- B.Incorrect default gateway
- ✓ C.DNS server not responding or misconfigured
- D.Firewall blocking web traffic (port 80/443)
Why C: The user can ping external IP addresses (e.g., 8.8.8.8) and the default gateway (192.168.1.1), confirming that IP routing and the gateway are functional. However, they cannot resolve domain names to IP addresses, which is a classic symptom of DNS failure. Since the DNS server is set to 192.168.1.1 (likely the gateway) and other users on the same network can browse normally, the issue is isolated to this workstation's DNS configuration or the DNS service on that server not responding to this specific client.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 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 220-1101 exam.