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Network DesigneasyMultiple ChoiceObjective-mapped

ANS-C01 Network Design Practice Question

A company has a VPC with a CIDR block of 172.16.0.0/16. They have a public subnet (172.16.1.0/24) and a private subnet (172.16.2.0/24). They have an internet gateway attached to the public subnet. They launch an EC2 instance in the public subnet with a public IP address. The instance is running a web server on port 80. They also launch an EC2 instance in the private subnet that needs to download updates from the internet. The private subnet does not have a route to the internet. The company wants to provide internet access to the private instance in a secure and cost-effective manner. Which solution should they implement?

⚠ Common exam trap

Many exam-takers confuse a NAT Gateway with a NAT instance or assume a VPC Gateway Endpoint can provide general internet access, but the key distinction is that a NAT Gateway is a managed service for outbound-only internet access, while Gateway Endpoints are specific to AWS services like S3 and DynamoDB.

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

Create a NAT Gateway in the public subnet and add a route in the private subnet's route table pointing to the NAT Gateway

A NAT Gateway in the public subnet allows instances in the private subnet to initiate outbound connections to the internet (e.g., for downloading updates) while preventing inbound connections from the internet. The private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway. This is secure because the NAT Gateway uses Elastic IPs and does not accept unsolicited inbound traffic, and it is cost-effective as it is a managed service with no maintenance overhead.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • Create a NAT Gateway in the public subnet and add a route in the private subnet's route table pointing to the NAT Gateway

    Why this is correct

    NAT Gateway provides outbound internet access for private instances.

  • Create a VPC Gateway Endpoint for S3 and configure the private instance to use it

    Why it's wrong here

    Gateway Endpoint only provides access to S3, not general internet.

  • Create a forward proxy server in the public subnet and configure the private instance to use it

    Why it's wrong here

    Proxy server adds complexity and cost.

  • Create a NAT instance in the public subnet and configure the private instance to use it

    Why it's wrong here

    NAT instance is less reliable and requires management.

Visual reference

Inside (Private) PC-A 10.0.0.1 PC-B 10.0.0.2 NAT Router Outside (Public) 203.0.113.1 Inside Global Server PAT: many private IPs share one public IP via unique port numbers

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Last reviewed: Jun 24, 2026

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