ANS-C01 Network Implementation Practice Question
A company has a VPC with public and private subnets in two Availability Zones. They have a NAT gateway in each AZ for outbound internet access. They recently added a third AZ and created a new private subnet. Instances in the new private subnet cannot reach the internet. The route table for the new subnet has a default route (0.0.0.0/0) pointing to a NAT gateway in the same AZ. What is the most likely cause?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that a NAT gateway only needs a route to the internet gateway, but the trap here is that candidates overlook the mandatory Elastic IP attachment, which is a prerequisite for the NAT gateway to function as an internet-facing device.
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 NAT gateway in the new AZ does not have an Elastic IP address attached
A NAT gateway requires an Elastic IP (EIP) address to function for outbound internet traffic. Without an EIP attached, the NAT gateway cannot translate private source IPs to a public IP, so instances in the new private subnet cannot reach the internet even though the route table correctly points to the NAT gateway in the same AZ.
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 security group attached to the NAT gateway blocks outbound traffic
Why it's wrong here
NAT gateways do not have security groups; they are controlled by route tables and network ACLs.
- ✗
The route table in the new private subnet does not have a route to the NAT gateway
Why it's wrong here
The route table has a default route pointing to the NAT gateway, so this is not the issue.
- ✓
The NAT gateway in the new AZ does not have an Elastic IP address attached
Why this is correct
A NAT gateway requires an Elastic IP to function; without it, outbound traffic fails.
- ✗
The NAT gateway is not in a public subnet in the new AZ
Why it's wrong here
NAT gateways must be in a public subnet, but the question does not indicate that it is not.
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JA
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.