The answer is that the NAT gateway’s subnet lacks a route to an internet gateway. For a NAT gateway to provide internet access to private subnets, it must be deployed in a public subnet whose route table includes a default route (0.0.0.0/0) pointing to an internet gateway; without this, the NAT gateway itself cannot reach the internet, breaking the connection for private instances. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of VPC routing dependencies and the distinction between managed NAT gateways and EC2-based NAT instances. A common trap is assuming the private subnet’s route is sufficient, but the critical missing piece is the NAT gateway’s own subnet route—not security groups, which don’t apply to NAT gateways, nor public IPs on private instances. Remember the memory tip: “NAT needs a path to the IGW first—check the gateway’s subnet route, not the private subnet’s.”
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.
An organization has a VPC with public and private subnets. The private subnets need to access the internet for software updates. A NAT gateway is deployed in a public subnet and the private subnet route table has a route for 0.0.0.0/0 pointing to the NAT gateway. However, instances in the private subnet cannot reach the internet. What could be the issue?
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's subnet does not have a route to an internet gateway
Option C is correct because the NAT gateway must be in a public subnet with an internet gateway route; if the route table for the NAT gateway's subnet does not have a default route to the IGW, the NAT gateway cannot reach the internet. Option A is wrong because security groups for the NAT gateway do not affect internet access; NAT gateways are managed services. Option B is wrong because the private instances need a route to the NAT gateway, not a public IP. Option D is wrong because the NAT gateway is in a public subnet, so the private subnet does not need a public IP.
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's subnet does not have a route to an internet gateway
Why this is correct
The NATgateway needs a route to the IGW to reach the internet.
The private subnet's network ACL blocks outbound HTTPS traffic
Why it's wrong here
That could be an issue, but the most likely cause is routing for the NATgateway itself.
✗
The security group attached to the NAT gateway does not allow outbound traffic
Why it's wrong here
NAT gateways do not use security groups; they are controlled by network ACLs.
✗
The private instances do not have a public IP address assigned
Why it's wrong here
Private instances route through the NATgateway, which provides internet access; they do not need public IPs.
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's subnet does not have a route to an internet gateway — Option C is correct because the NAT gateway must be in a public subnet with an internet gateway route; if the route table for the NAT gateway's subnet does not have a default route to the IGW, the NAT gateway cannot reach the internet. Option A is wrong because security groups for the NAT gateway do not affect internet access; NAT gateways are managed services. Option B is wrong because the private instances need a route to the NAT gateway, not a public IP. Option D is wrong because the NAT gateway is in a public subnet, so the private subnet does not need a public IP.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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