ANS-C01 Network Design Practice Question
A company's VPC has an internet gateway and a NAT Gateway in a public subnet. The private subnet route table has a default route pointing to the NAT Gateway. EC2 instances in the private subnet can access the internet, but cannot access an on-premises network connected via AWS Site-to-Site VPN. What is the most likely cause?
⚠ Common exam trap
AWS often tests the misconception that a NAT Gateway can forward traffic to a VPN or that the internet gateway is responsible for VPN routing, when in fact the route table's destination-based forwarding is the sole determinant of where traffic goes.
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 private subnet route table does not have a route to the on-premises network via the virtual private gateway.
The private subnet route table has a default route (0.0.0.0/0) pointing to the NAT Gateway, which allows outbound internet traffic. However, traffic destined for the on-premises network must be routed via the Virtual Private Gateway (VGW) attached to the VPC. Since the route table lacks a specific route (e.g., 10.0.0.0/8) pointing to the VGW, packets to the on-premises CIDR are instead sent to the NAT Gateway, which drops them because it has no route or interface for the on-premises network.
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 private subnet route table does not have a route to the on-premises network via the virtual private gateway.
Why this is correct
The default route to NAT Gateway takes precedence over VPN routes.
- ✗
The NAT Gateway is not configured to route traffic to the VPN.
Why it's wrong here
NAT Gateway only handles internet traffic.
- ✗
The internet gateway is not attached to the VPC.
Why it's wrong here
IGW is present and needed for NAT Gateway.
- ✗
The VPN connection is not advertising the on-premises CIDR via BGP.
Why it's wrong here
BGP would advertise the route, but the route table lacks a specific route.
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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.