← ANS-C01·Amazon Web Services

Question 776 of 1,705

Network Management and Operations →mediumMultiple ChoiceObjective-mapped

Private Subnet Route Table Missing Route to NAT Gateway

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.

A company has a VPC with public and private subnets. The private subnets need to access the internet for software updates. The company has set up a NAT gateway in the public subnet. However, instances in the private subnet cannot reach the internet. 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 NAT gateway does not have a route to the internet gateway
Why wrong: NAT gateway in public subnet automatically uses the internet gateway; no explicit route needed.
B
The security group for the instances blocks outbound traffic
Why wrong: Security groups allow outbound traffic by default unless explicitly denied.
C
The NAT gateway is not associated with an Elastic IP
Why wrong: NAT gateway requires an Elastic IP, but the question implies it is set up, so this is likely not the issue.
D
The private subnet route table does not have a route to the NAT gateway
Without a default route to the NAT gateway, traffic from private subnet cannot reach the internet.

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 private subnet route table does not have a route to the NAT gateway

Option D is correct because instances in a private subnet require a route to the NAT gateway to reach the internet. The private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT gateway as its target. Without this route, traffic from private instances sent to the internet will not be directed to the NAT gateway, and will instead remain in the VPC or be dropped. Option A is incorrect because the NAT gateway itself resides in a public subnet and uses the internet gateway via that subnet's route table; it does not require its own route to the IGW. Option B is incorrect because security groups by default allow all outbound traffic, so this is unlikely to be the issue. Option C is incorrect because not having an Elastic IP would prevent the NAT gateway from having a public IP, but the question states a NAT gateway is set up, implying it has an Elastic IP; the more fundamental issue is the missing route.

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 NAT gateway does not have a route to the internet gateway
Why it's wrong here
NAT gateway in public subnet automatically uses the internet gateway; no explicit route needed.
✗
The security group for the instances blocks outbound traffic
Why it's wrong here
Security groups allow outbound traffic by default unless explicitly denied.
✗
The NAT gateway is not associated with an Elastic IP
Why it's wrong here
NAT gateway requires an Elastic IP, but the question implies it is set up, so this is likely not the issue.
✓
The private subnet route table does not have a route to the NAT gateway
Why this is correct
Without a default route to the NAT gateway, traffic from private subnet cannot reach the internet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.

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 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.

Visual reference

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 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: The private subnet route table does not have a route to the NAT gateway — Option D is correct because instances in a private subnet require a route to the NAT gateway to reach the internet. The private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT gateway as its target. Without this route, traffic from private instances sent to the internet will not be directed to the NAT gateway, and will instead remain in the VPC or be dropped. Option A is incorrect because the NAT gateway itself resides in a public subnet and uses the internet gateway via that subnet's route table; it does not require its own route to the IGW. Option B is incorrect because security groups by default allow all outbound traffic, so this is unlikely to be the issue. Option C is incorrect because not having an Elastic IP would prevent the NAT gateway from having a public IP, but the question states a NAT gateway is set up, implying it has an Elastic IP; the more fundamental issue is the missing route.

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.