The answer is D because the rule order causes the deny to override the intended permit. Firewall rules are processed sequentially from top to bottom, and once a packet matches a rule, no further rules are evaluated. In this scenario, rule id=10 permits HTTP/HTTPS from internal to external, but rule id=20 blocks all traffic from the internal network, so any internet-bound traffic matches the deny rule first and is dropped before it ever reaches a later permit rule like id=30. This concept is critical for the ISC2 Certified in Cybersecurity CC exam, where a common trap is assuming that a later permit rule can override an earlier deny rule—it cannot, because the firewall stops processing after the first match. The search intent keyword “firewall rule order deny before allow” directly describes this pitfall: if a deny rule appears before an allow rule for the same traffic, the deny wins. Remember the memory tip: “First match wins, so order your denies before allows only if you intend to block—otherwise, place permits first.”
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of network security. 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.
Refer to the exhibit. A network administrator configured the following firewall rules. After implementation, users from the internal network cannot browse the internet. Which element is causing the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The rule order
The issue is that firewall rules are processed in sequential order from top to bottom, and the implicit deny-all rule at the end blocks any traffic that does not match an explicit permit rule. Since rule id=10 permits HTTP/HTTPS from internal to external, but rule id=20 blocks all traffic from the internal network, the deny rule (id=20) is evaluated before any later permit rule (id=30) and thus blocks all internet-bound traffic. The correct answer is D because the rule order causes the deny to override the intended permit.
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.
✗
Rule id=30
Why it's wrong here
Rule 30 is for DMZ traffic and does not affect internal internet browsing.
✗
Rule id=10
Why it's wrong here
The rule itself is not wrong; its placement is the issue.
✗
Rule id=20
Why it's wrong here
Rule 20 correctly allows internal traffic, but it is never reached.
✓
The rule order
Why this is correct
The deny rule should be after the allow rule to permit internal traffic first.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the concept that ACL rule order is critical — candidates mistakenly think that a permit rule later in the list can override an earlier deny, but the first-match principle means the deny is evaluated first and blocks the traffic permanently.
Detailed technical explanation
How to think about this question
Cisco ASA and IOS firewalls use first-match logic: once a packet matches a rule, no further rules are evaluated. This means a deny rule placed before a permit rule for the same traffic will block it, even if a later permit rule would have allowed it. In real-world scenarios, administrators often mistakenly place broad deny rules early in the ACL, forgetting that subsequent permit rules become unreachable. The implicit deny all at the end of every ACL is a standard security practice, but explicit denies earlier in the list can create unintended blocks.
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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The rule order — The issue is that firewall rules are processed in sequential order from top to bottom, and the implicit deny-all rule at the end blocks any traffic that does not match an explicit permit rule. Since rule id=10 permits HTTP/HTTPS from internal to external, but rule id=20 blocks all traffic from the internal network, the deny rule (id=20) is evaluated before any later permit rule (id=30) and thus blocks all internet-bound traffic. The correct answer is D because the rule order causes the deny to override the intended permit.
What should I do if I get this CC 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.
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Question Discussion
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