ANS-C01 Network Implementation Practice Question
A financial services company has a VPC with a public subnet and a private subnet. EC2 instances in the private subnet need to download patches from the internet. The company has a NAT gateway in the public subnet. The route table for the private subnet has a default route (0.0.0.0/0) pointing to the NAT gateway. However, instances cannot reach the internet. The NAT gateway is in an 'available' state and has an Elastic IP attached. The security group for the NAT gateway allows all outbound traffic. What is the most likely cause of the issue?
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 public subnet does not have a default route (0.0.0.0/0) pointing to an internet gateway
The most likely cause is that the route table for the public subnet (where the NAT gateway resides) does not have a default route (0.0.0.0/0) pointing to an internet gateway. The NAT gateway needs this route to forward traffic from private instances to the internet. Option A is incorrect because security groups for NAT gateways do not block inbound traffic from private instances; they only control traffic to the NAT gateway itself. Option B is incorrect because bandwidth provisioning is not related to connectivity; the NAT gateway can handle traffic up to its bandwidth limit. Option C is incorrect because NAT gateways do not require IAM roles to access the internet; they use Elastic IPs.
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 for the NAT gateway is blocking inbound traffic from private instances
Why it's wrong here
Incorrect. Security groups for NAT gateways control traffic to the NAT gateway, not the traffic flowing through it. The security group is already allowing all outbound traffic, so this is not the issue.
- ✗
The NAT gateway is not provisioned with sufficient bandwidth
Why it's wrong here
Incorrect. Bandwidth provisioning would affect performance, not basic connectivity. The NAT gateway is in 'available' state and has an EIP, so it is capable of forwarding traffic.
- ✗
The NAT gateway does not have an IAM role to access the internet
Why it's wrong here
Incorrect. NAT gateways do not require IAM roles to access the internet. They use an Elastic IP for outbound traffic.
- ✓
The route table for the public subnet does not have a default route (0.0.0.0/0) pointing to an internet gateway
Why this is correct
Correct. The NAT gateway resides in a public subnet. For the NAT gateway to forward traffic to the internet, the route table associated with that public subnet must have a default route (0.0.0.0/0) pointing to an internet gateway. Without this route, traffic from the NAT gateway cannot reach the internet.
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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.