The correct answer is that the policy allows the DescribeInstances action only from IPs within the 10.0.0.0/16 range. This is because the IAM policy uses an explicit Allow effect combined with a condition key, aws:SourceIp, which restricts the source IP address to the specified CIDR block. Since all IAM policies have an implicit deny by default, only requests that match both the allowed action and the condition are permitted; any request from outside that IP range is automatically denied. On the ISC2 Certified in Cybersecurity CC exam, this tests your understanding of how AWS IAM policy conditions enforce network-level access control, a common scenario for securing management APIs. A frequent trap is assuming an Allow without a condition grants unrestricted access, but here the condition narrows the scope. Remember the memory tip: “Allow plus condition equals restricted permission; no condition, no restriction.”
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of network security. 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. Based on the exhibit, which statement best describes the effect of this policy?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Allows DescribeInstances action only from IPs within 10.0.0.0/16
The policy uses an 'Allow' effect with a condition that restricts the source IP to the 10.0.0.0/16 range. Since IAM policies default to implicit deny, only requests matching both the action (DescribeInstances) and the condition (source IP within 10.0.0.0/16) are allowed. This effectively permits DescribeInstances only from the specified CIDR block.
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.
✗
Allows all actions on EC2 instances from 10.0.0.0/16
Why it's wrong here
The policy only allows one specific action (DescribeInstances), not all actions.
✗
Allows DescribeInstances action from any IP but with a condition
Why it's wrong here
The condition restricts the source IP, so it does not allow from any IP; it only allows from the specified range.
✗
Denies DescribeInstances action from IPs outside 10.0.0.0/16
Why it's wrong here
The policy does not explicitly deny; it only allows for the specified condition. Implicit deny applies to other sources.
✓
Allows DescribeInstances action only from IPs within 10.0.0.0/16
Why this is correct
The Effect is Allow, the Action is ec2:DescribeInstances, and the Condition restricts the source IP to the 10.0.0.0/16 range.
Clue confirmation
The clue word "best" 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
ISC2 often tests the distinction between an explicit 'Allow' with a condition and an explicit 'Deny' — candidates mistakenly think a conditional allow is equivalent to a deny for non-matching sources, but the actual behavior is that non-matching requests are implicitly denied, not explicitly denied.
Detailed technical explanation
How to think about this question
In AWS IAM, an explicit 'Allow' with a condition key like 'aws:SourceIp' evaluates the request's source IP against the specified CIDR. If the condition is not met, the allow statement does not apply, and the implicit default deny takes effect, blocking the action. This is a common pattern for restricting API calls to trusted network ranges without using a separate deny statement.
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: Allows DescribeInstances action only from IPs within 10.0.0.0/16 — The policy uses an 'Allow' effect with a condition that restricts the source IP to the 10.0.0.0/16 range. Since IAM policies default to implicit deny, only requests matching both the action (DescribeInstances) and the condition (source IP within 10.0.0.0/16) are allowed. This effectively permits DescribeInstances only from the specified CIDR block.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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