← ANS-C01·Amazon Web Services

Question 1,204 of 1,705

Network Design →hardMultiple ChoiceObjective-mapped

ANS-C01 Network Design Practice Question

This ANS-C01 practice question tests your understanding of network design. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 has a VPC with multiple subnets. They want to ensure that all outbound traffic from EC2 instances in the VPC goes through a centralized NAT device for inspection. They have deployed a NAT instance in a public subnet and configured the route tables for private subnets to point to the NAT instance. However, traffic is not being routed through the NAT instance. 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 source/destination check is enabled on the NAT instance.
By default, EC2 instances check that the source or destination of traffic matches their own IP. This must be disabled for NAT instances.
B
The NAT instance does not have a public IP address.
Why wrong: A NAT instance needs a public IP for internet access, but the question implies it is in a public subnet.
C
The route table for the private subnets does not have a default route (0.0.0.0/0) pointing to the NAT instance.
Why wrong: The description says the route tables are configured, so this is not the issue.
D
The security group of the NAT instance blocks outbound traffic.
Why wrong: While possible, the most common cause is source/destination check.

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 source/destination check is enabled on the NAT instance.

The source/destination check is a security feature on EC2 instances that prevents them from forwarding traffic unless the instance is the source or destination of the packet. Since a NAT instance must forward traffic that it did not originate (e.g., from private instances to the internet), this check must be disabled. When enabled, the NAT instance drops packets that are not addressed to itself, breaking the routing of outbound traffic through it.

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 source/destination check is enabled on the NAT instance.
Why this is correct
By default, EC2 instances check that the source or destination of traffic matches their own IP. This must be disabled for NAT instances.
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 NAT instance does not have a public IP address.
Why it's wrong here
A NAT instance needs a public IP for internet access, but the question implies it is in a public subnet.
✗
The route table for the private subnets does not have a default route (0.0.0.0/0) pointing to the NAT instance.
Why it's wrong here
The description says the route tables are configured, so this is not the issue.
✗
The security group of the NAT instance blocks outbound traffic.
Why it's wrong here
While possible, the most common cause is source/destination check.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume the issue is a missing route or security group rule, overlooking the fact that EC2 instances by default cannot act as routers unless the source/destination check is explicitly disabled.

Detailed technical explanation

How to think about this question

Under the hood, EC2 instances have a kernel-level iptables/netfilter rule that drops packets where the destination MAC address does not match the instance’s own MAC, unless source/destination check is disabled. This is implemented via the `ec2:SourceDestCheck` attribute on the network interface. In a real-world scenario, if you forget to disable this check, the NAT instance will silently drop forwarded packets, and you will see no traffic in VPC Flow Logs or tcpdump on the instance for forwarded flows.

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.

TExam Day Tips

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.

Visual reference

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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 — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The source/destination check is enabled on the NAT instance. — The source/destination check is a security feature on EC2 instances that prevents them from forwarding traffic unless the instance is the source or destination of the packet. Since a NAT instance must forward traffic that it did not originate (e.g., from private instances to the internet), this check must be disabled. When enabled, the NAT instance drops packets that are not addressed to itself, breaking the routing of outbound traffic through it.

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

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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.

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.