The answer is the rule `-A INPUT -p tcp --dport 80 -j DROP` because in iptables, rule order determines precedence: the first matching rule is applied, so a DROP rule placed before any ACCEPT rule for the same port will block all traffic, including legitimate requests from the internal network 192.168.1.0/24. This tests your understanding of iptables rule order and DROP precedence, a common pitfall on the CompTIA Linux+ XK0-005 exam where candidates mistakenly assume that a later ACCEPT rule can override an earlier DROP. The trap is that iptables processes rules sequentially from top to bottom, so a DROP rule for port 80 will always take effect before any subsequent ACCEPT rule for that port, making the web server unreachable. Remember the memory tip: "First match wins—if DROP comes first, ACCEPT is cursed."
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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. After adding a firewall rule, the web server becomes unreachable from the internal network 192.168.1.0/24. Which line is the cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Line: -A INPUT -p tcp --dport 80 -j DROP
Option C is correct because the firewall rule `-A INPUT -p tcp --dport 80 -j DROP` explicitly drops all incoming TCP traffic destined for port 80, regardless of source. Since the web server listens on port 80, this rule blocks all HTTP requests, including those from the internal network 192.168.1.0/24. The rule is placed before any ACCEPT rule for the same port, so the DROP action takes precedence, making the server unreachable.
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.
✗
Default policy (INPUT ACCEPT)
Why it's wrong here
Default policy is ACCEPT; the DROP rule overrides.
✗
Missing rule for RELATED traffic
Why it's wrong here
Not relevant; the issue is rule order.
✓
Line: -A INPUT -p tcp --dport 80 -j DROP
Why this is correct
This rule drops all HTTP traffic, including from 192.168.1.0/24, before an ACCEPT rule.
Related concept
Read the scenario before looking for a memorised answer.
This rule is not reached because the DROP rule comes first.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may focus on the source IP restriction in option D and assume it is the cause, overlooking the fact that iptables processes rules in order and a preceding DROP rule for the same port will block all traffic, including from the allowed subnet.
Detailed technical explanation
How to think about this question
In iptables, rules are processed sequentially in the order they appear in the chain; the first matching rule determines the action. The `-A INPUT` appends rules to the end of the chain, so if a DROP rule for port 80 is added after an ACCEPT rule for the same port, the DROP rule would never be reached. However, in this scenario, the DROP rule is likely inserted before the ACCEPT rule (or the ACCEPT rule is missing), causing all port 80 traffic to be dropped. Real-world scenarios often involve misordered rules when administrators add restrictive rules without considering existing allow rules, leading to unintended service outages.
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 practitioner preparing for the XK0-005 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Line: -A INPUT -p tcp --dport 80 -j DROP — Option C is correct because the firewall rule `-A INPUT -p tcp --dport 80 -j DROP` explicitly drops all incoming TCP traffic destined for port 80, regardless of source. Since the web server listens on port 80, this rule blocks all HTTP requests, including those from the internal network 192.168.1.0/24. The rule is placed before any ACCEPT rule for the same port, so the DROP action takes precedence, making the server unreachable.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This XK0-005 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 XK0-005 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.