ANS-C01 Network Implementation Practice Question
A company is deploying a VPC with public and private subnets. They want to allow instances in a private subnet to access the internet for software updates while preventing inbound internet traffic. Which configuration should be used?
⚠ Common exam trap
Many candidates confuse a NAT gateway's outbound-only behavior with an Internet Gateway's bidirectional routing, leading them to incorrectly select Option C, which would allow inbound traffic and violate the security requirement.
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
✓
Attach an internet gateway to the VPC, and create a NAT gateway in a public subnet. Add a route in the private subnet route table to the NAT gateway for 0.0.0.0/0
A NAT gateway, deployed in a public subnet with an Internet Gateway (IGW) attached, allows instances in private subnets to initiate outbound IPv4 traffic to the internet (e.g., for software updates) while the IGW's one-way translation prevents unsolicited inbound traffic from reaching the private instances. The private subnet's route table must include a default route (0.0.0.0/0) pointing to the NAT gateway's elastic network interface.
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 VPC endpoint for internet access
Why it's wrong here
VPC endpoints are for AWS services only.
- ✗
Use a transit gateway with a NAT instance
Why it's wrong here
A transit gateway interconnects VPCs and on-premises networks, but it does not provide outbound-only internet access or perform NAT. The scenario requires instances in a private subnet to initiate outbound traffic while blocking inbound connections, which demands a NAT gateway or NAT instance in a public subnet with a route table entry pointing 0.0.0.0/0 to that device. This option is tempting because a transit gateway is often used for centralised routing across multiple VPCs, and pairing it with a NAT instance could appear to combine connectivity with address translation; however, the transit gateway itself cannot replace the public subnet placement and default route needed for NAT to function correctly.
- ✗
Attach an internet gateway to the VPC and add a route in the private subnet to the internet gateway for 0.0.0.0/0
Why it's wrong here
Internet gateway allows inbound traffic.
- ✓
Attach an internet gateway to the VPC, and create a NAT gateway in a public subnet. Add a route in the private subnet route table to the NAT gateway for 0.0.0.0/0
Why this is correct
NAT gateway enables outbound internet from private subnets.
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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.