This CS0-003 practice question tests your understanding of security operations. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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. The JSON firewall rule is applied to a network segment. A security analyst needs to ensure that traffic from a new subnet 10.0.1.0/24 to the same destination is also allowed. Which of the following modifications should the analyst make?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change source_ip to "10.0.0.0/23"
Option C is correct because changing the source_ip to '10.0.0.0/23' expands the allowed source range to include both the original subnet (likely 10.0.0.0/24) and the new subnet 10.0.1.0/24, as a /23 prefix covers addresses from 10.0.0.0 to 10.0.1.255. This is the most efficient modification, requiring only a single rule change without adding complexity or reducing security posture.
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.
✗
Change destination_port to 80
Why it's wrong here
Changing the destination port would allow HTTP instead of HTTPS, altering the service.
✗
Add a second rule with source_ip "10.0.1.0/24"
Why it's wrong here
Adding a second rule works but is less efficient than modifying the existing rule.
✓
Change source_ip to "10.0.0.0/23"
Why this is correct
The /23 subnet encompasses both 10.0.0.0/24 and 10.0.1.0/24.
Related concept
Read the scenario before looking for a memorised answer.
✗
Change source_ip to "any"
Why it's wrong here
Allowing any source IP is overly permissive and increases risk.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the candidate's understanding of CIDR aggregation by presenting a scenario where adding a new subnet is required, and the trap is that candidates may incorrectly choose to add a second rule (Option B) instead of recognizing that a single prefix change (Option C) is the most efficient and secure modification.
Detailed technical explanation
How to think about this question
In firewall rule processing, CIDR notation defines the network prefix length; a /23 subnet mask (255.255.254.0) aggregates two /24 subnets (10.0.0.0/24 and 10.0.1.0/24) into a single contiguous block. This is a common technique in network segmentation to minimize rule count and simplify management, especially when subnets are adjacent. Real-world scenarios often involve merging VLANs or adding new subnets in a DMZ, where adjusting the prefix length is preferred over adding multiple rules to avoid performance degradation from excessive rule lookups.
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 CS0-003 question in full detail.
Security Operations — This question tests Security Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Change source_ip to "10.0.0.0/23" — Option C is correct because changing the source_ip to '10.0.0.0/23' expands the allowed source range to include both the original subnet (likely 10.0.0.0/24) and the new subnet 10.0.1.0/24, as a /23 prefix covers addresses from 10.0.0.0 to 10.0.1.255. This is the most efficient modification, requiring only a single rule change without adding complexity or reducing security posture.
What should I do if I get this CS0-003 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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