The answer is a Layer 1 or Layer 2 issue, most likely a disconnected Ethernet cable or a switch port that is down. This is correct because being able to ping your own IP address confirms the network interface and TCP/IP stack are functioning properly on the local machine, but the failure to ping the default gateway indicates that traffic cannot leave the local subnet. On the CompTIA Linux+ XK0-005 exam, this scenario tests your ability to isolate physical versus logical connectivity problems; a common trap is assuming a misconfigured IP address or routing table when the real culprit is a loose cable or an administratively down switch port. Remember the mnemonic "Ping self works, ping gateway fails—check the cable and the switch rails."
XK0-005 Troubleshooting Practice Question
This XK0-005 practice question tests your understanding of troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A technician needs to troubleshoot a network connectivity issue on a Linux server. The server can ping its own IP address but cannot ping the default gateway. Which of the following is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Ethernet cable is disconnected or the switch port is down.
Option D is correct because the server can ping its own IP address (loopback or local interface), confirming that the network stack is functioning and the interface is up. However, the inability to ping the default gateway indicates a Layer 1 or Layer 2 issue, such as a disconnected Ethernet cable or a switch port that is administratively down, which prevents any traffic from leaving the local subnet.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 misconfigured in the routing table.
Why it's wrong here
A misconfigured gateway would cause 'Network is unreachable', not a timeout.
The iptables firewall is blocking outgoing ICMP traffic.
Why it's wrong here
A firewall would also block local pings if configured to block ICMP.
✓
The Ethernet cable is disconnected or the switch port is down.
Why this is correct
Local ping works (loopback or local IP) but external fails, indicating a layer 1/2 issue.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a routing or firewall issue (options A or C) because they focus on Layer 3, but the ability to ping the local IP proves the stack is healthy, pointing instead to a physical or data-link layer problem that prevents any off-subnet communication.
Detailed technical explanation
How to think about this question
When a server pings its own IP, the kernel loops the packet back internally without involving the physical network interface. To reach the default gateway, the server must send an ARP request to resolve the gateway's MAC address; if the Ethernet cable is disconnected or the switch port is down, the ARP request never reaches the gateway, and the ping fails with 'Destination Host Unreachable' or a timeout. In a real-world scenario, a technician would use `ip neigh` to check the ARP cache and `ethtool <interface>` to verify link status, confirming a Layer 1/2 fault.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Ethernet cable is disconnected or the switch port is down. — Option D is correct because the server can ping its own IP address (loopback or local interface), confirming that the network stack is functioning and the interface is up. However, the inability to ping the default gateway indicates a Layer 1 or Layer 2 issue, such as a disconnected Ethernet cable or a switch port that is administratively down, which prevents any traffic from leaving the local subnet.
What should I do if I get this XK0-005 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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