- A
The private subnet’s network ACL is blocking outbound traffic.
Why wrong: Network ACLs are stateless; default NACL allows all outbound.
- B
The NAT Gateway is not placed in a public subnet with a route to an internet gateway.
NAT Gateway must be in a public subnet with IGW route to translate and forward traffic.
- C
The security group for the private instances does not allow outbound HTTPS.
Why wrong: Security groups are stateful; outbound rules are not typically an issue for established connections.
- D
The NAT Gateway does not have an Elastic IP address assigned.
Why wrong: A NAT Gateway requires an Elastic IP to communicate with the internet.
Question 837 of 1,546
NAT Gateway in Public Subnet for Private Subnet Internet Access
This SOA-C02 practice question tests your understanding of networking and content delivery. 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. A NAT Gateway is deployed in the public subnet. Private EC2 instances need to download patches from the internet. The route table for the private subnet has a default route (0.0.0.0/0) pointing to the NAT Gateway. However, the instances 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 NAT Gateway is not placed in a public subnet with a route to an internet gateway.
The correct answer is B because a NAT Gateway must be deployed in a public subnet that has a route to an internet gateway. Although the private subnet's route table points to the NAT Gateway for default traffic, if the NAT Gateway's subnet lacks a route to an internet gateway, the NAT Gateway cannot forward traffic to the internet. Option A is incorrect because network ACLs could block traffic, but the stated issue—instances cannot reach the internet via a properly configured route—points to the NAT Gateway's subnet configuration as the most likely cause. Option C is incorrect because even if the private instances' security group allows outbound HTTPS, the NAT Gateway still needs internet connectivity. Option D is incorrect because while a NAT Gateway requires an Elastic IP address, the scenario assumes the NAT Gateway is deployed; typically, an Elastic IP is assigned during creation, so the missing route to the internet gateway is the more probable cause.
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 private subnet’s network ACL is blocking outbound traffic.
Why it's wrong here
Network ACLs are stateless; default NACL allows all outbound.
- ✓
The NAT Gateway is not placed in a public subnet with a route to an internet gateway.
- ✗
The security group for the private instances does not allow outbound HTTPS.
Why it's wrong here
Security groups are stateful; outbound rules are not typically an issue for established connections.
- ✗
The NAT Gateway does not have an Elastic IP address assigned.
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 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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
- →
Networking and Content Delivery — study guide chapter
Learn the concepts, then practise the questions
- →
Networking and Content Delivery practice questions
Targeted practice on this topic area only
- →
All SOA-C02 questions
1,546 questions across all exam domains
- →
AWS Certified SysOps Administrator Associate SOA-C02 study guide
Full concept coverage aligned to exam objectives
- →
SOA-C02 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related SOA-C02 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Monitoring, Logging, and Remediation practice questions
Practise SOA-C02 questions linked to Monitoring, Logging, and Remediation.
Reliability and Business Continuity practice questions
Practise SOA-C02 questions linked to Reliability and Business Continuity.
Deployment, Provisioning, and Automation practice questions
Practise SOA-C02 questions linked to Deployment, Provisioning, and Automation.
Security and Compliance practice questions
Practise SOA-C02 questions linked to Security and Compliance.
Networking and Content Delivery practice questions
Practise SOA-C02 questions linked to Networking and Content Delivery.
Cost and Performance Optimization practice questions
Practise SOA-C02 questions linked to Cost and Performance Optimization.
SOA-C02 fundamentals practice questions
Practise SOA-C02 questions linked to SOA-C02 fundamentals.
SOA-C02 scenario practice questions
Practise SOA-C02 questions linked to SOA-C02 scenario.
SOA-C02 troubleshooting practice questions
Practise SOA-C02 questions linked to SOA-C02 troubleshooting.
Practice this exam
Start a free SOA-C02 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 SOA-C02 question test?
Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The NAT Gateway is not placed in a public subnet with a route to an internet gateway. — The correct answer is B because a NAT Gateway must be deployed in a public subnet that has a route to an internet gateway. Although the private subnet's route table points to the NAT Gateway for default traffic, if the NAT Gateway's subnet lacks a route to an internet gateway, the NAT Gateway cannot forward traffic to the internet. Option A is incorrect because network ACLs could block traffic, but the stated issue—instances cannot reach the internet via a properly configured route—points to the NAT Gateway's subnet configuration as the most likely cause. Option C is incorrect because even if the private instances' security group allows outbound HTTPS, the NAT Gateway still needs internet connectivity. Option D is incorrect because while a NAT Gateway requires an Elastic IP address, the scenario assumes the NAT Gateway is deployed; typically, an Elastic IP is assigned during creation, so the missing route to the internet gateway is the more probable cause.
What should I do if I get this SOA-C02 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 SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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 →
Same concept, more angles
4 more ways this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company has a VPC with public and private subnets. A NAT Gateway is deployed in the public subnet to allow instances in the private subnet to access the internet. However, private instances cannot reach an external service at 203.0.113.50:443. What should be checked first?
hard- ✓ A.The route table for the private subnet has a route 0.0.0.0/0 pointing to the NAT Gateway.
- B.The NAT Gateway has an Elastic IP assigned.
- C.The security group for the NAT Gateway allows inbound traffic from the private subnet.
- D.The internet gateway is attached to the VPC.
Why A: The first thing to check when private instances cannot reach an external service is the route table for the private subnet. The private subnet must have a route 0.0.0.0/0 pointing to the NAT Gateway to route internet-bound traffic through it. Option B is incorrect because the NAT Gateway must have an Elastic IP to be reachable from the internet, but the issue described is outbound access from private instances; the NAT Gateway's Elastic IP is necessary but not the first check. Option C is incorrect because security groups for NAT Gateways are not used; NAT Gateways do not have security groups; instead, network ACLs on the subnets control traffic. Option D is incorrect because the internet gateway must be attached to the VPC for the NAT Gateway to work, but if private instances cannot reach the external service, the routing from the private subnet to the NAT Gateway is the primary suspect.
Variation 2. A company is designing a VPC with public and private subnets. The private subnets need internet access for patching, but must not be directly reachable from the internet. Which TWO components should be used together?
medium- A.VPC Peering connection
- B.Private subnet route table with a route to the Internet Gateway
- C.Internet Gateway attached to the VPC
- ✓ D.Private subnet route table with a route to the NAT Gateway
- ✓ E.NAT Gateway in a public subnet
Why D: The correct answers are D and E. A NAT Gateway placed in a public subnet (E) provides outbound internet access for instances in private subnets. The private subnet's route table must have a route pointing to the NAT Gateway (D) for internet-bound traffic. VPC Peering (A) connects VPCs but does not provide internet access. An Internet Gateway (C) attached to the VPC enables internet access for public subnets, but private subnets should not have a direct route to it. Option B (private route to IGW) would make the subnet public, violating the requirement. Therefore, D and E together provide the desired outbound-only internet access.
Variation 3. A company has a VPC with an Internet Gateway and a NAT Gateway. They launch an EC2 instance in a private subnet. The instance needs to download updates from the internet, but the security team wants to prevent any inbound traffic from the internet. Which route table configuration is correct for the private subnet?
medium- A.10.0.0.0/16 -> local; 0.0.0.0/0 -> VPC Peering
- B.0.0.0.0/0 -> Internet Gateway
- ✓ C.0.0.0.0/0 -> NAT Gateway
- D.No default route; only local routes.
Why C: Option C is correct because a private subnet requires a default route (0.0.0.0/0) to a NAT Gateway for outbound internet access while blocking inbound traffic. Option A is incorrect because a route to a VPC Peering connection does not provide internet access and is not relevant for internet updates. Option B is incorrect because a default route to an Internet Gateway would allow both inbound and outbound internet traffic, violating the security requirement. Option D is incorrect because without a default route, instances cannot reach the internet at all.
Variation 4. A company has a VPC with public and private subnets. A NAT Gateway is in the public subnet, and a private EC2 instance needs to download patches from the internet. The instance can reach the internet after a reboot. Which action should the SysOps administrator take to make the internet access persistent?
hard- ✓ A.Update the route table of the private subnet to point 0.0.0.0/0 to the NAT Gateway.
- B.Attach an internet gateway to the private subnet.
- C.Associate an Elastic IP with the NAT Gateway.
- D.Enable DNS resolution in the VPC.
Why A: Route tables must be manually updated after adding a NAT Gateway. The private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway.
Keep practising
More SOA-C02 practice questions
- A company uses an Amazon DynamoDB table with on-demand capacity mode. The table handles a workload with a steady baselin…
- A company uses Amazon CloudWatch Logs to store application logs. The SysOps administrator needs to count the occurrences…
- A SysOps administrator needs to monitor the CPU utilization of an Amazon EC2 instance and send an alert when it exceeds…
- A SysOps administrator needs to monitor the CPU utilization of an Amazon EC2 instance fleet and send an alert when the a…
- A company's security policy requires that all Amazon S3 buckets must have server-side encryption enabled. The SysOps adm…
- A SysOps administrator uses AWS CloudFormation to deploy a stack that includes an Amazon EC2 instance. The administrator…
Last reviewed: Jun 20, 2026
This SOA-C02 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 SOA-C02 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.