The correct answer is to add a route in route table rtb-12345678 that sends traffic to the S3 service via the VPC endpoint. A gateway VPC endpoint for S3 functions as a target in a route table, not as a resource that automatically routes traffic; without an explicit route pointing to the endpoint’s prefix list, packets destined for S3 will still traverse the internet or a NAT device, bypassing the endpoint and its associated policy. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding that gateway endpoints require a route table entry with the S3 service’s prefix list as the destination and the gateway endpoint ID as the target—a common trap is assuming endpoint association alone is sufficient. Remember the mnemonic “Gateway Needs a Gate” to recall that a gateway endpoint is useless without a route pointing traffic through it.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 has created a gateway VPC endpoint for S3 as shown in the exhibit. The endpoint is associated with route table rtb-12345678. An EC2 instance in a subnet that uses route table rtb-12345678 tries to download an object from my-bucket. The request fails with an access denied error. Which change should the engineer make to resolve the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a route in route table rtb-12345678 that sends traffic to the S3 service via the VPC endpoint.
Option D is correct because the endpoint policy requires the aws:SourceVpc condition to match the VPC ID, but the condition key is misspelled or the value is incorrect? Actually, the condition is correct. However, the error is likely because the route table does not have a route to the endpoint. Gateway endpoints require a route in the associated route table that points to the endpoint. Option A is wrong because the endpoint policy already allows s3:GetObject. Option B is wrong because the endpoint is already associated with the route table. Option C is wrong because the bucket policy is not shown; but the issue is likely the route. Option D is correct: add a route to the S3 service in route table rtb-12345678.
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.
✗
Associate the endpoint with a different route table.
Why it's wrong here
The endpoint is already associated with the correct route table; the route table needs a route.
✗
Add a bucket policy to my-bucket that allows access from the VPC endpoint.
Why it's wrong here
The endpoint policy already allows access; a bucket policy is not required, though it could be used.
✗
Modify the endpoint policy to allow all S3 actions.
Why it's wrong here
The policy already allows s3:GetObject; the issue is not the action.
✓
Add a route in route table rtb-12345678 that sends traffic to the S3 service via the VPC endpoint.
Why this is correct
Gateway endpoints require a route in the associated route table with destination the S3 prefix list and target the endpoint ID.
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 Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Add a route in route table rtb-12345678 that sends traffic to the S3 service via the VPC endpoint. — Option D is correct because the endpoint policy requires the aws:SourceVpc condition to match the VPC ID, but the condition key is misspelled or the value is incorrect? Actually, the condition is correct. However, the error is likely because the route table does not have a route to the endpoint. Gateway endpoints require a route in the associated route table that points to the endpoint. Option A is wrong because the endpoint policy already allows s3:GetObject. Option B is wrong because the endpoint is already associated with the route table. Option C is wrong because the bucket policy is not shown; but the issue is likely the route. Option D is correct: add a route to the S3 service in route table rtb-12345678.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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