ANS-C01 Network Security, Compliance and Governance Practice Question
A security engineer is troubleshooting connectivity issues. An EC2 instance cannot access the internet. The instance is in a private subnet with a route table that has a default route (0.0.0.0/0) pointing to a NAT gateway. The NAT gateway is in a public subnet with an Elastic IP. The security group allows all outbound traffic. What is the most likely cause?
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 network ACL in the public subnet is blocking inbound traffic to the NAT gateway
The network ACL in the public subnet must allow inbound traffic from the internet to the NAT gateway's Elastic IP. Option B is wrong because the route table in the private subnet is correct. Option C is wrong because the NAT gateway's security group is not a thing; it uses security groups for instances. Option D is wrong because the internet gateway is required and assumed attached.
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 network ACL in the public subnet is blocking inbound traffic to the NAT gateway
Why this is correct
NAT gateway needs inbound allowance for return traffic.
- ✗
The NAT gateway does not have a security group allowing outbound traffic
Why it's wrong here
NAT gateways do not use security groups.
- ✗
The internet gateway is not attached to the VPC
Why it's wrong here
Assumed attached.
- ✗
The route table in the private subnet has no route to the NAT gateway
Why it's wrong here
Stem says route exists.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.