The answer is that Private DNS is not enabled for the endpoint. This is the most likely reason because when Private DNS is disabled for a PrivateLink interface endpoint, the private DNS name for the service will not automatically resolve to the endpoint’s private IP addresses from on-premises clients; instead, it may resolve to the public IP of the service or fail entirely. For on-premises clients to connect using the private endpoint DNS name, the Private DNS option must be enabled, which creates a private hosted zone that maps the service’s DNS name to the endpoint’s private IPs within the associated VPC and its connected networks. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how PrivateLink DNS resolution works across hybrid environments, and it is a common trap to assume that an ‘available’ endpoint state guarantees connectivity. Remember: an available endpoint does not mean DNS is configured—always verify the Private DNS toggle. A useful memory tip is “DNS must be on for on-prem to be won.”
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 created a VPC interface endpoint for a third-party SaaS service using AWS PrivateLink. The endpoint shows 'available' state, but on-premises clients cannot connect to the service via the private endpoint DNS name. What is the MOST likely reason?
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
✓
Private DNS is not enabled for the endpoint.
Option B is correct because Private DNS for the endpoint must be enabled for the private DNS name to resolve correctly from on-premises. Option A is incorrect because the endpoint is in 'available' state. Option C is incorrect because the subnet IDs are present. Option D is incorrect because the endpoint type is Interface, not Gateway.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 endpoint is not in the 'available' state.
Why it's wrong here
The exhibit shows 'available' state.
✓
Private DNS is not enabled for the endpoint.
Why this is correct
Private DNS must be enabled for the private hosted zone to resolve the endpoint DNS name.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Command / output trap
The exhibit shows 'available' state.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Management and Operations — This question tests Network Management and Operations — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Private DNS is not enabled for the endpoint. — Option B is correct because Private DNS for the endpoint must be enabled for the private DNS name to resolve correctly from on-premises. Option A is incorrect because the endpoint is in 'available' state. Option C is incorrect because the subnet IDs are present. Option D is incorrect because the endpoint type is Interface, not Gateway.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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