hardMultiple ChoiceObjective-mapped
DNS Server Unreachable — Troubleshooting Internet Access
Exhibit
Refer to the exhibit. C:\Users\Admin> ipconfig /all ... IPv4 Address. . . . . . . . . . . : 192.168.1.10 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.1.1 DNS Servers . . . . . . . . . . . : 8.8.8.8 ...
A user reports being unable to access the internet, but can reach other devices on the local network. Based on the exhibit, what is the most likely cause?
Quick Answer
The correct answer is that the DNS server is not reachable. When a user can communicate with other devices on the local network but cannot access the internet, the issue is typically with either the default gateway or DNS resolution; since local traffic works via IP addresses, a missing or unreachable DNS server prevents the system from translating domain names into IP addresses, blocking all internet access while leaving local connectivity intact. On the CompTIA ITF+ FC0-U61 exam, this scenario tests your understanding of the OSI model’s application and network layers, specifically how DNS operates separately from routing—a common trap is confusing a gateway failure (which would block all external traffic) with a DNS failure (which only blocks name resolution). To remember this, think of DNS as the phonebook: you can dial a local number (IP) directly, but without the phonebook, you cannot look up any new contacts (websites) to call.
⚠ Common exam trap
A common mix-up: candidates assume internet access failure is always a gateway problem, but the ability to reach local devices isolates the issue to DNS or gateway; the exhibit likely shows a valid gateway IP, making DNS the correct answer.
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 DNS server is not reachable.
Since the user can reach other devices on the local network but cannot access the internet, the issue is likely with the default gateway or DNS resolution. Option D is correct because if the DNS server is unreachable, the user can still communicate with local devices via IP addresses but cannot resolve domain names to access internet resources. The exhibit likely shows a valid IP address and subnet mask, but the DNS server address is missing or incorrect, preventing name resolution.
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 default gateway is missing.
Why it's wrong here
The default gateway is present and correct.
- ✗
The IP address is in the wrong subnet.
Why it's wrong here
The IP and subnet mask are consistent with the gateway.
- ✗
The subnet mask is incorrect.
Why it's wrong here
The subnet mask is standard for a /24 network.
- ✓
The DNS server is not reachable.
Why this is correct
The DNS server 8.8.8.8 might be blocked or unreachable.
Visual reference
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Same concept, more angles
2 more ways this is tested on FC0-U71
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. Refer to the exhibit. A user is unable to access the internet but can ping the default gateway. Based on the exhibit, what is the most likely cause?
hard- A.Firewall blocking traffic
- B.Duplicate IP address
- ✓ C.Incorrect DNS server
- D.Incorrect subnet mask
Why C: The user can ping the default gateway, which confirms that Layer 3 connectivity to the local network is working and that the firewall is not blocking ICMP traffic. However, the inability to access the internet (by name or IP) while local connectivity works points to a failure in name resolution. An incorrect DNS server address prevents the client from resolving domain names to IP addresses, which is the most likely cause given the symptoms.
Variation 2. A technician is troubleshooting a user's inability to access the internet. The user can ping the default gateway but cannot ping external websites. What is the most likely issue?
medium- A.Firewall is blocking all outbound traffic
- B.Default gateway is down
- C.IP address is misconfigured
- ✓ D.DNS server is not configured or is unreachable
Why D: The user can ping the default gateway, which confirms that the local network configuration (IP address, subnet mask, and gateway) is correct and that Layer 3 connectivity to the router is working. However, pinging external websites fails because the DNS server is not configured or unreachable, preventing the resolution of domain names to IP addresses. This is a classic symptom: internal connectivity works, but name resolution fails.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This FC0-U71 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 FC0-U71 exam.