ANS-C01 Network Design Practice Question
A company has a VPC with a public subnet and a private subnet. An EC2 instance in the private subnet needs to download patches from the internet. The instance is behind a NAT Gateway in the public subnet. The download is failing. Which configuration should the network engineer check FIRST?
⚠ Common exam trap
AWS often tests the misconception that a private instance needs a public IP or that NACLs are the primary cause of outbound internet failures, when in fact the missing default route to the NAT Gateway is the most common misconfiguration.
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 associated with the private subnet has a default route (0.0.0.0/0) pointing to the NAT Gateway.
For an EC2 instance in a private subnet to reach the internet via a NAT Gateway, the private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway. Without this route, traffic from the instance destined for the internet has no path to the NAT Gateway, causing the download to fail.
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 for the private subnet allows inbound HTTP/HTTPS traffic.
Why it's wrong here
Outbound traffic is needed, and NACL is secondary to routing.
- ✗
The EC2 instance has a public IP address assigned.
Why it's wrong here
Private instances do not need public IPs; they use NAT.
- ✗
The Internet Gateway is attached to the private subnet.
Why it's wrong here
IGW is attached to the VPC, not a subnet.
- ✓
The route table associated with the private subnet has a default route (0.0.0.0/0) pointing to the NAT Gateway.
Why this is correct
Correct: Without this route, traffic cannot reach the NAT Gateway.
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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.