The answer is that the on-premises network is not routing traffic to S3 through the Direct Connect public VIF, instead attempting to use the internet. This is because a public VIF provides direct, private access to AWS public services like S3 using public IP addresses, but the on-premises routers must have a specific route pointing S3 traffic toward the Direct Connect public VIF’s virtual interface; without that route, packets default to the internet path, which may be blocked or slower. On the ANS-C01 exam, this scenario tests your understanding of how Direct Connect public VIFs differ from private VIFs and VPC endpoints—a common trap is confusing the S3 VPC endpoint (which only works for instances inside the VPC) with on-premises access. Remember the memory tip: “Public VIF needs a public route; a VPC endpoint is VPC-only.”
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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.
A company wants to connect its on-premises data center to AWS using AWS Direct Connect with a public VIF to access Amazon S3. The on-premises network team reports that they can ping the Direct Connect public VIF IP but cannot access S3. The VPC has a private subnet with an S3 VPC endpoint. What is the most likely reason for the failure?
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 on-premises network is not routing traffic to S3 through the Direct Connect public VIF; instead, it is attempting to use the internet.
Option A is correct. To access S3 via public VIF, traffic must go through the internet route; the VPC endpoint is only for instances within the VPC. Option B is incorrect because public VIF uses public IPs, not private IPs. Option C is incorrect because Direct Connect can access public services. Option D is incorrect because security groups don't apply to on-premises traffic via Direct Connect.
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.
✗
Direct Connect does not support access to Amazon S3; you must use VPN.
Why it's wrong here
Direct Connect supports public VIF for S3 access.
✗
The S3 endpoint is configured in the VPC, but the on-premises traffic is not using the endpoint.
Why it's wrong here
Public VIF does not use VPC endpoints; it goes directly to S3 public endpoints.
✓
The on-premises network is not routing traffic to S3 through the Direct Connect public VIF; instead, it is attempting to use the internet.
Why this is correct
Public VIF requires proper routing; if not configured, traffic goes over internet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
A security group is blocking traffic from the on-premises network to S3.
Why it's wrong here
Security groups apply to EC2 instances, not to Direct Connect public VIF.
Common exam traps
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.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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 Design — This question tests Network Design — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The on-premises network is not routing traffic to S3 through the Direct Connect public VIF; instead, it is attempting to use the internet. — Option A is correct. To access S3 via public VIF, traffic must go through the internet route; the VPC endpoint is only for instances within the VPC. Option B is incorrect because public VIF uses public IPs, not private IPs. Option C is incorrect because Direct Connect can access public services. Option D is incorrect because security groups don't apply to on-premises traffic via Direct Connect.
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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Question Discussion
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