The answer is that the VPC attribute 'enableDnsHostnames' is set to false, which directly prevents EC2 instances from receiving DNS hostnames and therefore blocks private DNS resolution between instances. This attribute must be true for instances to be assigned DNS names that can be resolved within the VPC, even when the DHCP option set correctly specifies AmazonProvidedDNS. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how VPC DNS attributes interact with DHCP options—a common trap is assuming that DNS resolution failures are caused by security groups or flow logs, when the root cause is often this simple boolean flag. Remember the memory tip: "Hostnames need Hostnames enabled"—if enableDnsHostnames is false, no private DNS names are generated, so no resolution is possible regardless of other settings.
ANS-C01 Network Management and Operations Practice Question
This ANS-C01 practice question tests your understanding of network management and operations. 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
A network engineer is troubleshooting an issue where an EC2 instance launched in VPC vpc-0abcd1234efgh5678 cannot resolve DNS names for other instances using their private DNS names. The VPC has DHCP options set with domain-name-servers=AmazonProvidedDNS. What is the most likely cause?
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 VPC attribute 'enableDnsHostnames' is set to false
Option B is correct because the command shows that EnableDnsHostnames is false, which means instances do not get DNS hostnames. Option A is incorrect because the DHCP option set is correct. Option C is incorrect because VPC Flow Logs are for network traffic, not DNS. Option D is incorrect because security groups do not affect DNS resolution.
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 VPC attribute 'enableDnsHostnames' is set to false
Why this is correct
Without hostnames, instances cannot resolve private DNS names.
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.
The security group on the instances blocks DNS traffic
Why it's wrong here
DNS traffic uses UDP/53, but the issue is with hostname assignment.
✗
The DHCP options set is not using AmazonProvidedDNS
Why it's wrong here
The DHCP options set is correct according to the scenario.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Scenario analysis trap
The DHCP options set is correct according to the scenario.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which ANS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Network Management and Operations — This question tests Network Management and Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VPC attribute 'enableDnsHostnames' is set to false — Option B is correct because the command shows that EnableDnsHostnames is false, which means instances do not get DNS hostnames. Option A is incorrect because the DHCP option set is correct. Option C is incorrect because VPC Flow Logs are for network traffic, not DNS. Option D is incorrect because security groups do not affect DNS resolution.
What should I do if I get this ANS-C01 question wrong?
Identify which ANS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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