ANS-C01 Network Implementation Practice Question
A company has a VPC with a CIDR of 10.0.0.0/16. The VPC has a public subnet 10.0.1.0/24 and a private subnet 10.0.2.0/24. An EC2 instance in the private subnet needs to download patches from the internet. Which configuration is required to provide outbound internet access to the private instance while preventing inbound internet traffic?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that an Internet Gateway can be used in a private subnet route table to provide outbound-only access, but the trap here is that an Internet Gateway is a symmetric gateway that allows inbound traffic unless explicitly blocked by a network ACL, which still does not prevent direct inbound connections to the instance's private IP.
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
✓
Deploy a NAT Gateway in the public subnet and add a default route in the private subnet route table pointing to the NAT Gateway
A NAT Gateway, deployed in a public subnet with an Internet Gateway, allows instances in a private subnet to initiate outbound traffic to the internet (e.g., to download patches) while preventing any unsolicited inbound traffic from the internet. The private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway ID. This design ensures the private instance's traffic is source-NATed to the NAT Gateway's Elastic IP, and the Internet Gateway only accepts responses to established outbound connections.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Attach an Internet Gateway to the private subnet and add a default route to the Internet Gateway in the private route table
Why it's wrong here
This would allow inbound internet traffic to the private subnet.
- ✗
Assign an Elastic IP to the private instance and update the security group to allow outbound traffic
Why it's wrong here
Assigning an EIP makes the instance publicly accessible.
- ✗
Add an Internet Gateway to the VPC and create a route in the private subnet to 0.0.0.0/0 via the Internet Gateway
Why it's wrong here
Internet Gateway requires the subnet to be public; private subnet route table cannot route directly to IGW.
- ✓
Deploy a NAT Gateway in the public subnet and add a default route in the private subnet route table pointing to the NAT Gateway
Why this is correct
NAT Gateway enables outbound-only internet access for private instances.
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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.