ANS-C01 Network Design Practice Question
A company wants to provide internet access to instances in a private subnet without using a NAT Gateway, due to cost constraints. They have a public subnet with a bastion host that has a public IP. They also have a VPC with an Internet Gateway. What is the most cost-effective way to allow outbound internet access for instances in the private subnet?
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
✓
Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance.
Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance. A NAT instance is a cost-effective alternative to NAT Gateway, as it uses an EC2 instance with IP forwarding enabled and can be run on a low-cost instance type. It requires management but avoids NAT Gateway hourly charges. Option B is incorrect because a VPN connection to a third-party proxy introduces unnecessary complexity and cost. Option C is incorrect because VPC endpoints only provide access to specific AWS services (e.g., S3), not general internet access. Option D is incorrect because the bastion host is typically used for SSH access, and while it could be configured for NAT, it is not recommended for security reasons; a dedicated NAT instance in a public subnet is the proper approach.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance.
Why this is correct
NAT instance is a cost-effective alternative to NAT Gateway.
- ✗
Use a VPN connection to a third-party internet proxy.
Why it's wrong here
VPN is costly and adds complexity.
- ✗
Create a VPC endpoint for Amazon S3 and configure the private subnet to use it.
Why it's wrong here
VPC endpoint only provides access to specific AWS services, not the internet.
- ✗
Configure the bastion host as a NAT instance by enabling IP forwarding.
Why it's wrong here
Bastion host is for management, not for NAT; but could be used if configured, but usually not recommended.
Visual reference
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
Related to this question
About these practice questions
This ANS-C01 question is part of Courseiva's 1,621-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
Same concept, more angles
3 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 while preventing inbound connections from the internet. Which AWS service should be used?
easy- ✓ A.NAT Gateway
- B.Internet Gateway
- C.AWS Direct Connect
- D.VPC Endpoint
Why A: 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.
Variation 2. 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 3. 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.