The answer is that the NAT Gateway lacks an Elastic IP address, which is a mandatory requirement for it to function. A NAT Gateway resides in a public subnet and must have an Elastic IP assigned to it so that the Internet Gateway can route return traffic back to the gateway; without this public IP, the NAT Gateway cannot translate private instance addresses for outbound internet access. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of the NAT Gateway Elastic IP requirement and how it differs from other connectivity components—a common trap is assuming a security group or route table misconfiguration is the culprit, but NAT Gateways do not use security groups. Remember the memory tip: “No EIP, no internet” for a NAT Gateway, and always verify that the Elastic IP is attached in the console before troubleshooting routes.
SOA-C02 Networking and Content Delivery Practice Question
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 SysOps Administrator manages a VPC with public and private subnets. The private subnets need to access the internet for software updates. The Administrator creates a NAT Gateway in a public subnet and updates the private subnet route table to point 0.0.0.0/0 to the NAT Gateway. However, instances in the private subnet still cannot reach the internet. What is the MOST likely reason?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The NAT Gateway does not have an Elastic IP address assigned.
Option B is correct because the NATGateway must have a public IP and the route table for the private subnet must point to the NAT Gateway ID. Option A is wrong because security group rules for private instances should allow outbound traffic (e.g., HTTPS), but by default outbound is allowed; the issue is likely the route. Option C is wrong because the NAT Gateway's security group is not used; NAT Gateways do not have security groups. Option D is wrong because the internet gateway must be attached to the VPC, not to the NAT Gateway.
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 security group on the private instances blocks outbound HTTPS traffic.
Why it's wrong here
By default, security groups allow all outbound traffic; unless explicitly removed, outbound is allowed.
✗
The internet gateway is not attached to the NAT Gateway.
Why it's wrong here
The internet gateway is attached to the VPC, not to individual resources like NAT Gateways.
✓
The NAT Gateway does not have an Elastic IP address assigned.
Why this is correct
A NATGateway requires an Elastic IP to communicate with the internet; without one, it cannot route traffic.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The NAT Gateway's security group is blocking inbound traffic from the private subnet.
Why it's wrong here
NAT Gateways do not have security groups; they use network ACLs and route tables.
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.
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 — 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 does not have an Elastic IP address assigned. — Option B is correct because the NAT Gateway must have a public IP and the route table for the private subnet must point to the NAT Gateway ID. Option A is wrong because security group rules for private instances should allow outbound traffic (e.g., HTTPS), but by default outbound is allowed; the issue is likely the route. Option C is wrong because the NAT Gateway's security group is not used; NAT Gateways do not have security groups. Option D is wrong because the internet gateway must be attached to the VPC, not to the NAT Gateway.
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
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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 an Application Load Balancer (ALB) that routes traffic to Amazon EC2 instances in private subnets of a VPC. The SysOps administrator needs to ensure that the EC2 instances can download software updates from the internet, but they must not be directly accessible from the internet. The solution should minimize operational overhead. Which solution should the administrator implement?
medium
A.Place the EC2 instances in a public subnet and configure security group inbound rules to block all traffic.
✓ B.Attach a NAT Gateway to a public subnet and configure the private subnet route table to send 0.0.0.0/0 traffic to the NAT Gateway.
C.Launch a NAT instance in a public subnet with an Elastic IP address and configure route tables accordingly.
D.Attach an Internet Gateway to the VPC and add a route to the private subnet route table pointing 0.0.0.0/0 to the Internet Gateway.
Why B: A NAT Gateway (option B) allows EC2 instances in private subnets to initiate outbound connections to the internet (e.g., for software updates) while preventing any unsolicited inbound connections from the internet. It is a fully managed AWS service that automatically scales and requires no patching, minimizing operational overhead compared to a NAT instance. The private subnet route table directs 0.0.0.0/0 traffic to the NAT Gateway, which is placed in a public subnet with an Elastic IP address to enable internet access.
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