- A
The security group of the EC2 instance blocks outbound HTTPS traffic.
Why wrong: Security groups are stateful and allow outbound by default.
- B
The NAT gateway does not have an Elastic IP address.
Why wrong: NAT gateway requires an Elastic IP for outbound traffic.
- C
The network ACL of the private subnet blocks inbound traffic from the NAT gateway.
Why wrong: NACLs are stateless; outbound rule is needed but route is primary issue.
- D
The route table in the private subnet does not have a default route to the NAT gateway.
Missing default route prevents internet access.
Question 797 of 1,705
Private Subnet Missing Route to NAT Gateway: Troubleshooting
This ANS-C01 practice question tests your understanding of network implementation. 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. An EC2 instance in a private subnet needs to download patches from the internet. The company has a NAT gateway in a public subnet. The EC2 instance can connect to other instances in the VPC but 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.
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 in the private subnet does not have a default route to the NAT gateway.
For an EC2 instance in a private subnet to reach the internet via a NAT gateway, the private subnet's route table must include a default route (0.0.0.0/0) pointing to the NAT gateway as the target. Without this route, traffic destined for the internet has no path to the NAT gateway, so the instance can communicate within the VPC but cannot reach external hosts. Option D correctly identifies this missing route as the most likely cause.
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 security group of the EC2 instance blocks outbound HTTPS traffic.
Why it's wrong here
Security groups are stateful and allow outbound by default.
- ✗
The NAT gateway does not have an Elastic IP address.
- ✗
The network ACL of the private subnet blocks inbound traffic from the NAT gateway.
Why it's wrong here
NACLs are stateless; outbound rule is needed but route is primary issue.
- ✓
The route table in the private subnet does not have a default route to the NAT gateway.
Why this is correct
Missing default route prevents internet access.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the distinction between security groups, network ACLs, and route tables, and the trap here is that candidates assume a connectivity issue must be a firewall or ACL block, overlooking the fundamental requirement of a correct default route in the subnet's route table.
Detailed technical explanation
How to think about this question
A NAT gateway operates at the network layer, translating private IP addresses to its Elastic IP for internet-bound traffic. The route table entry for 0.0.0.0/0 with the NAT gateway ID as the target is essential; without it, packets from the private subnet are dropped because the instance's default gateway is not set to the NAT gateway. In real-world scenarios, this misconfiguration is common when a VPC is created with default route tables that do not automatically include a route to the NAT gateway, leading to silent failures in internet access.
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.
- →
Network Implementation — study guide chapter
Learn the concepts, then practise the questions
- →
Network Implementation practice questions
Targeted practice on this topic area only
- →
All ANS-C01 questions
1,705 questions across all exam domains
- →
AWS Certified Advanced Networking Specialty ANS-C01 study guide
Full concept coverage aligned to exam objectives
- →
ANS-C01 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
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.
FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The route table in the private subnet does not have a default route to the NAT gateway. — For an EC2 instance in a private subnet to reach the internet via a NAT gateway, the private subnet's route table must include a default route (0.0.0.0/0) pointing to the NAT gateway as the target. Without this route, traffic destined for the internet has no path to the NAT gateway, so the instance can communicate within the VPC but cannot reach external hosts. Option D correctly identifies this missing route as the most likely cause.
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 →
Keep practising
More ANS-C01 practice questions
- A financial services company has a VPC with a public subnet and a private subnet. EC2 instances in the private subnet ne…
- A company is designing a network security architecture for a multi-account environment using AWS Transit Gateway. The se…
- A company is using AWS Direct Connect to connect its on-premises network to AWS. The company wants to encrypt all traffi…
- A company uses AWS Transit Gateway to connect multiple VPCs and on-premises networks via AWS Site-to-Site VPN. The secur…
- A company runs a web application on EC2 instances behind an Application Load Balancer (ALB). The application must be acc…
- A global e-commerce company uses a hub-and-spoke network topology with a transit VPC in us-east-1. Each spoke VPC has an…
Last reviewed: Jul 4, 2026
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.
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.
Sign in to join the discussion.