The answer is that the HTTP rule only allows traffic from the internal network. This is the most likely reason the web server is not accessible from the internet, because the iptables output shows an ACCEPT rule for port 80 that explicitly matches source IPs from the internal subnet, such as 192.168.1.0/24, while no corresponding rule permits traffic from external sources. Since iptables processes rules sequentially and the default policy typically drops or rejects unmatched packets, any HTTP request originating outside the internal network will be blocked before reaching the web server. On the CompTIA Linux+ XK0-005 exam, this scenario tests your ability to interpret iptables rule syntax and understand how source-based restrictions can inadvertently isolate services; a common trap is overlooking that a rule allowing internal traffic does not automatically permit external access. Remember the memory tip: “Internal allow does not external welcome”—always check the source address in the rule, not just the port.
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.
Network Topology
An administrator is troubleshooting a web server that is not accessible from the internet. The server is running on port 80. Based on the iptables output, which of the following is the MOST likely reason?
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 HTTP rule only allows traffic from the internal network.
The iptables output shows an HTTP rule that explicitly matches traffic from the internal network (e.g., 192.168.1.0/24) and does not include a rule allowing HTTP traffic from external (internet) sources. Since the web server is running on port 80 but the only HTTP rule restricts source IPs to the internal subnet, traffic from the internet is not matched by any ACCEPT rule and will be subject to the default policy. This is the most likely reason the server is inaccessible from the internet.
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 HTTP rule only allows traffic from the internal network.
Why this is correct
The rule for port 80 sources from 192.168.1.0/24, so internet traffic is blocked.
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.
Default policy is ACCEPT, but the DROP rule at the end drops unmatched packets.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that a default DROP policy is the primary cause of connectivity issues, when in fact a specific rule with an overly restrictive source or destination match is the actual problem.
Detailed technical explanation
How to think about this question
iptables processes rules in order within a chain; the first matching rule determines the packet's fate (ACCEPT, DROP, etc.). If no rule matches, the chain's default policy (e.g., ACCEPT or DROP) is applied. In this scenario, the HTTP rule likely uses `-s 192.168.1.0/24` to limit source addresses, so packets from the internet (not in that subnet) skip that rule and fall through to the default policy. If the default policy is ACCEPT, internet traffic would still be allowed, but if it is DROP, the traffic is dropped—but the core issue remains that the HTTP rule is too restrictive, not the default policy alone.
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 HTTP rule only allows traffic from the internal network. — The iptables output shows an HTTP rule that explicitly matches traffic from the internal network (e.g., 192.168.1.0/24) and does not include a rule allowing HTTP traffic from external (internet) sources. Since the web server is running on port 80 but the only HTTP rule restricts source IPs to the internal subnet, traffic from the internet is not matched by any ACCEPT rule and will be subject to the default policy. This is the most likely reason the server is inaccessible from the internet.
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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