This CV0-004 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.
Network Topology
Refer to the exhibit. A cloud engineer is troubleshooting network connectivity to a server with IP 10.0.0.5. The server is on the same subnet. Based on the iptables rules shown, what is the most likely cause of the connectivity failure?
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 INPUT chain drops all traffic destined to the 10.0.0.0/8 network
Option D is correct because the INPUT chain has a rule that drops all traffic destined to the 10.0.0.0/8 network, which includes the target server at 10.0.0.5. Since the server is on the same subnet, traffic to it must traverse the INPUT chain on the local system, and this DROP rule will match and discard packets before any other rule can accept them. The rule's position and destination match make it the most direct cause of the connectivity failure.
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 FORWARD chain policy drops all traffic
Why it's wrong here
Incorrect; FORWARD chain policy is ACCEPT, and the rule drops all, but the issue is INPUT.
✗
The OUTPUT chain rejects all traffic to the server
Why it's wrong here
Incorrect; OUTPUT chain accepts all.
✗
The DROP rule in INPUT has zero packet count, so it is not effective
Why it's wrong here
Incorrect; zero count means no packets have matched yet, but the rule is still in effect.
✓
The INPUT chain drops all traffic destined to the 10.0.0.0/8 network
Why this is correct
Correct; the DROP rule in INPUT blocks traffic to 10.0.0.0/8.
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 overlook the INPUT chain's destination match and assume the FORWARD chain is responsible for same-subnet traffic, or they misinterpret a zero packet count as an inactive rule, when in fact the rule is simply waiting for matching traffic.
Trap categories for this question
Command / output trap
Incorrect; OUTPUT chain accepts all.
Detailed technical explanation
How to think about this question
In iptables, packet traversal for locally destined traffic follows the PREROUTING → INPUT chain path, where the INPUT chain filters packets before they reach local sockets. The 10.0.0.0/8 CIDR block is a Class A private range (RFC 1918), and a rule dropping all traffic to this entire subnet will block any host within it, including 10.0.0.5, regardless of the source. A common real-world scenario is misconfigured security policies that use overly broad subnet masks, inadvertently blocking legitimate traffic to specific hosts.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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 INPUT chain drops all traffic destined to the 10.0.0.0/8 network — Option D is correct because the INPUT chain has a rule that drops all traffic destined to the 10.0.0.0/8 network, which includes the target server at 10.0.0.5. Since the server is on the same subnet, traffic to it must traverse the INPUT chain on the local system, and this DROP rule will match and discard packets before any other rule can accept them. The rule's position and destination match make it the most direct cause of the connectivity failure.
What should I do if I get this CV0-004 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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