← ANS-C01·Amazon Web Services

Question 1,043 of 1,705

Network Design →mediumMultiple ChoiceObjective-mapped

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 media company is designing a network for a new AWS environment. They have a VPC with public and private subnets in three Availability Zones. In the private subnets, they run a fleet of Amazon EC2 instances that process video files from an Amazon S3 bucket. The S3 bucket is in the same region. The company wants to ensure that all traffic to S3 stays within the AWS network and does not traverse the internet. They also need to allow the EC2 instances to access the internet for software updates, but only through a centralized NAT gateway. Currently, there is one NAT gateway in AZ1. The network engineer has created a VPC endpoint for S3 (Gateway type) and associated it with the route tables for the private subnets. However, the EC2 instances in AZ2 and AZ3 cannot reach the NAT gateway for internet access. 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.

A
The route table for private subnets now has a more specific route for S3 that overrides the default route to the NAT gateway
The endpoint adds a route for the S3 prefix list, but if the prefix list includes 0.0.0.0/0 erroneously, or if the endpoint route is not properly scoped, it can cause issues. More commonly, the endpoint adds a route for the S3 service (e.g., com.amazonaws.<region>.s3) which does not affect the default route. However, in some configurations, if the endpoint is added with a policy that allows all traffic, it might still work. The most likely issue is that the NAT gateway route is missing or the route table does not have a default route to the NAT gateway. But among the options, B is the closest because misconfiguration can lead to the endpoint route overriding the default route.
B
The VPC endpoint needs to be created in each Availability Zone
Why wrong: Gateway endpoints are not per-AZ; they are regional.
C
The NAT gateway is only available in the AZ where it is deployed
Why wrong: NAT gateway is deployed in a specific AZ but can be used by instances in other AZs if the route table directs traffic to it.
D
The S3 VPC endpoint is only accessible from the AZ where it was created
Why wrong: Gateway endpoints are regional and accessible from all AZs.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The route table for private subnets now has a more specific route for S3 that overrides the default route to the NAT gateway

The EC2 instances in AZ2 and AZ3 cannot reach the NAT gateway because the route tables for the private subnets in those AZs likely do not contain a default route (0.0.0.0/0) pointing to the NAT gateway. A NAT gateway is deployed in a specific AZ and its private IP is only accessible from other AZs if the route table explicitly directs traffic to it. Adding the S3 Gateway Endpoint does not affect internet routing; it only adds a more specific route for S3 traffic. Therefore, the underlying cause is that the NAT gateway is effectively only available within its own AZ due to missing routing. Option A is incorrect because the S3 endpoint route does not override the default route for internet traffic. Options B and D are false since Gateway Endpoints are regional and NAT gateways can be used cross-AZ with proper routing.

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 route table for private subnets now has a more specific route for S3 that overrides the default route to the NAT gateway
Why this is correct
The endpoint adds a route for the S3 prefix list, but if the prefix list includes 0.0.0.0/0 erroneously, or if the endpoint route is not properly scoped, it can cause issues. More commonly, the endpoint adds a route for the S3 service (e.g., com.amazonaws.<region>.s3) which does not affect the default route. However, in some configurations, if the endpoint is added with a policy that allows all traffic, it might still work. The most likely issue is that the NAT gateway route is missing or the route table does not have a default route to the NAT gateway. But among the options, B is the closest because misconfiguration can lead to the endpoint route overriding the default route.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The VPC endpoint needs to be created in each Availability Zone
Why it's wrong here
Gateway endpoints are not per-AZ; they are regional.
✗
The NAT gateway is only available in the AZ where it is deployed
Why it's wrong here
NAT gateway is deployed in a specific AZ but can be used by instances in other AZs if the route table directs traffic to it.
✗
The S3 VPC endpoint is only accessible from the AZ where it was created
Why it's wrong here
Gateway endpoints are regional and accessible from all AZs.

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.

Visual reference

Quick reference

AWS S3 Storage Class Comparison

Storage Class	Min Duration	Retrieval	Use Case
S3 Standard	None	Immediate	Frequently accessed data
S3 Standard-IA	30 days	Immediate	Infrequent access, rapid retrieval
S3 One Zone-IA	30 days	Immediate	Non-critical infrequent data
S3 Intelligent-Tiering	None	Immediate–hours	Unknown or changing access patterns
S3 Glacier Instant	90 days	Milliseconds	Archive with instant retrieval
S3 Glacier Flexible	90 days	Minutes–hours	Archive, flexible retrieval
S3 Glacier Deep Archive	180 days	Hours	Long-term compliance archive

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.

Related ANS-C01 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Network Management and Operations practice questions

Practise ANS-C01 questions linked to Network Management and Operations.

Network Security, Compliance and Governance practice questions

Practise ANS-C01 questions linked to Network Security, Compliance and Governance.

Network Design practice questions

Practise ANS-C01 questions linked to Network Design.

Network Implementation practice questions

Practise ANS-C01 questions linked to Network Implementation.

ANS-C01 fundamentals practice questions

Practise ANS-C01 questions linked to ANS-C01 fundamentals.

ANS-C01 scenario practice questions

Practise ANS-C01 questions linked to ANS-C01 scenario.

ANS-C01 troubleshooting practice questions

Practise ANS-C01 questions linked to ANS-C01 troubleshooting.

Practice this exam

Start a free ANS-C01 practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

ANS-C01 practice-test guide →Study guide →Browse all practice tests

FAQ

Questions learners often ask

What does this ANS-C01 question test?

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 route table for private subnets now has a more specific route for S3 that overrides the default route to the NAT gateway — The EC2 instances in AZ2 and AZ3 cannot reach the NAT gateway because the route tables for the private subnets in those AZs likely do not contain a default route (0.0.0.0/0) pointing to the NAT gateway. A NAT gateway is deployed in a specific AZ and its private IP is only accessible from other AZs if the route table explicitly directs traffic to it. Adding the S3 Gateway Endpoint does not affect internet routing; it only adds a more specific route for S3 traffic. Therefore, the underlying cause is that the NAT gateway is effectively only available within its own AZ due to missing routing. Option A is incorrect because the S3 endpoint route does not override the default route for internet traffic. Options B and D are false since Gateway Endpoints are regional and NAT gateways can be used cross-AZ with proper routing.

What should I do if I get this ANS-C01 question wrong?

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.

About these practice questions

Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

Keep practising

Question Discussion

Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.

Loading comments…

This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.