ANS-C01 Network Design Practice Question
A company needs to provide internet access to instances in a private subnet while preventing inbound connections from the internet. Which AWS service should be used?
⚠ Common exam trap
AWS often tests the misconception that an Internet Gateway can be used in a private subnet with restrictive security groups or network ACLs, but the trap is that an Internet Gateway inherently allows bidirectional traffic and cannot prevent unsolicited inbound connections at the gateway level, whereas a NAT Gateway is specifically designed for outbound-only internet access.
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
✓
NAT Gateway
A NAT Gateway enables instances in a private subnet to initiate outbound IPv4 traffic to the internet (e.g., for software updates) while preventing any unsolicited inbound connections from the internet. It achieves this by translating the private source IP addresses of the instances to the NAT Gateway's Elastic IP address, and by default it does not allow inbound traffic unless an explicit inbound rule is added to the associated route table, which is not recommended for this use case.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
NAT Gateway
Why this is correct
Provides outbound only.
- ✗
Internet Gateway
Why it's wrong here
Allows inbound traffic.
- ✗
AWS Direct Connect
Why it's wrong here
Private connection to AWS.
- ✗
VPC Endpoint
Why it's wrong here
For private access to AWS services.
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Same concept, more angles
2 more ways this is tested on ANS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company needs to provide internet access to instances in a private subnet. The instances must not be directly accessible from the internet. Which AWS service should be used?
easy- A.VPC Peering
- B.AWS Direct Connect
- C.Internet Gateway
- ✓ D.NAT Gateway
Why D: A NAT Gateway enables instances in a private subnet to initiate outbound IPv4 traffic to the internet (e.g., for software updates) while preventing unsolicited inbound connections from the internet. It resides in a public subnet with an Elastic IP and uses source network address translation (SNAT) to translate the private IPs of the instances to the gateway's public IP, ensuring the instances remain inaccessible from the outside.
Variation 2. A company wants to provide internet access to instances in a private subnet using a NAT gateway. The NAT gateway is deployed in a public subnet with an Elastic IP. The private subnet route table has a default route pointing to the NAT gateway. However, instances in the private subnet cannot access the internet. What is the most likely cause?
easy- ✓ A.The public subnet route table does not have a route to the internet gateway.
- B.The security group assigned to the NAT gateway blocks outbound traffic.
- C.The private subnet route table has a route to the internet gateway instead of the NAT gateway.
- D.The NAT gateway does not have an Elastic IP associated.
Why A: The NAT gateway is deployed in a public subnet, but for it to route traffic to the internet, the public subnet's route table must have a default route (0.0.0.0/0) pointing to an internet gateway (IGW). Without this route, the NAT gateway cannot forward traffic from the private subnet to the internet, even though the private subnet's route table correctly points to the NAT gateway. This is the most likely cause because the NAT gateway itself needs internet access via the IGW to translate and forward traffic.
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.