The answer is to check the route table and the security group. When troubleshooting private subnet internet access via NAT, the route table must contain a default route (0.0.0.0/0) pointing to the NAT gateway, and the security group attached to the EC2 instance must allow outbound traffic, such as HTTPS, to the internet. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how NAT gateways enable outbound-only connectivity from private subnets, a common trap being that engineers mistakenly check for a public IP on the instance or an internet gateway on the subnet, neither of which is required. Remember that the NAT gateway lives in a public subnet and handles translation, so the instance itself never needs a public IP. A useful memory tip is “Route to NAT, SG outbound—no public IP needed.”
DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. 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 DevOps engineer is troubleshooting an issue where an EC2 instance in a private subnet cannot reach the internet. The instance has a route to a NAT gateway. Which TWO of the following should the engineer check? (Choose TWO.)
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 of the private subnet has a route to the NAT gateway
Option A is correct because the route table must have a route to the NATgateway. Option B is correct because the security group must allow outbound traffic (e.g., HTTPS). Option C is wrong because the internet gateway is attached to the VPC, not the subnet. Option D is wrong because public IP is not needed for instances in private subnet using NAT. Option E is wrong because the NAT gateway is in a public subnet, but the instance is in private; the instance does not have 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 is in the same subnet as the instance
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.
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 DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Incident and Event Response — This question tests Incident and Event Response — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The route table of the private subnet has a route to the NAT gateway — Option A is correct because the route table must have a route to the NAT gateway. Option B is correct because the security group must allow outbound traffic (e.g., HTTPS). Option C is wrong because the internet gateway is attached to the VPC, not the subnet. Option D is wrong because public IP is not needed for instances in private subnet using NAT. Option E is wrong because the NAT gateway is in a public subnet, but the instance is in private; the instance does not have a public IP.
What should I do if I get this DOP-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 DOP-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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