hardMultiple Choice
XK0-006 Practice Question: A system administrator is troubleshooting a…
A system administrator is troubleshooting a network issue on a Linux server running CentOS 7. The server is unable to connect to the internet, but internal network connections work fine. The administrator checks the network configuration: the server has a static IP 192.168.1.100/24, default gateway 192.168.1.1, and DNS server 8.8.8.8. The administrator can ping the gateway but cannot ping 8.8.8.8. From the server, a traceroute to 8.8.8.8 stops at the gateway. The administrator also notices that the route table shows a default route via 192.168.1.1. What is the most likely cause?
⚠ Common exam trap
Watch out — candidates often think a reachable gateway and a default route guarantee internet connectivity, but they overlook the necessity of NAT for private-to-public IP translation in a typical SOHO or enterprise network.
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 router is not performing NAT correctly
The server can ping the gateway (192.168.1.1) but cannot reach 8.8.8.8, and traceroute stops at the gateway. This indicates that the server’s default route is correctly configured and the gateway is reachable, but the router is not forwarding traffic beyond the local subnet. Since internal connections work, the most likely cause is that the router is not performing Network Address Translation (NAT) correctly, which is required to translate private IP addresses (192.168.x.x) to a public IP for internet access.
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 router is not performing NAT correctly
Why this is correct
The gateway is reachable but external pings fail and traceroute halts there, meaning packets leave the host correctly but return traffic is not translated back. A faulty NAT configuration on the router prevents private 192.168.1.100 replies from reaching the internet.
- ✗
The DNS server is not responding
Why it's wrong here
Ping uses IP address, not DNS, so DNS is not the issue here.
- ✗
The default gateway is not reachable
Why it's wrong here
The administrator can already ping 192.168.1.1, so the gateway is reachable; the traceroute halting there indicates the gateway itself cannot forward traffic beyond the LAN, such as a missing NAT or upstream routing fault. This option is tempting because an unreachable gateway does break internet access, but the successful ping disproves it here.
- ✗
The subnet mask is incorrectly configured
Why it's wrong here
A wrong subnet mask would break local connectivity, yet the server pings its gateway and reaches internal hosts successfully, so 192.168.1.100/24 is correct. It is tempting because mask errors cause partial reachability, and would be correct if internal hosts on the same subnet were unreachable while the gateway responded.
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Linux Fundamentals and History
Key term
NAT
NAT (Network Address Translation) is a method that allows multiple devices on a private network to share a single public IP address when accessing the internet.
Key term
DNS
DNS is the system that translates human-friendly domain names like example.com into machine-readable IP addresses so computers can find each other on a network.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This XK0-006 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 XK0-006 exam.