ANS-C01 Network Management and Operations Practice Question
A company's VPC includes a public subnet with a NAT gateway and a private subnet with EC2 instances. The EC2 instances in the private subnet need to access the internet for software updates. The NAT gateway's Elastic IP is associated correctly, and the route tables are configured. However, the EC2 instances cannot reach the internet. 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 route table for the private subnet is missing a default route pointing to the NAT gateway.
The most common issue is that the route table for the private subnet does not have a default route (0.0.0.0/0) pointing to the NAT gateway. Without this route, traffic from the private subnet cannot be directed to the NAT gateway, and thus cannot reach the internet.
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 private subnet.
Why it's wrong here
NAT gateways must be in a public subnet to have internet access.
- ✓
The route table for the private subnet is missing a default route pointing to the NAT gateway.
Why this is correct
This is the most likely cause; without a default route to the NAT gateway, traffic cannot be routed out.
- ✗
The network ACL for the private subnet is blocking outbound traffic.
Why it's wrong here
Network ACLs are stateless and by default allow all outbound traffic; unless modified, this is not the issue.
- ✗
The security group for the EC2 instances does not allow outbound traffic.
Why it's wrong here
Security groups are stateful and allow outbound traffic by default unless explicitly denied.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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