ANS-C01 Network Implementation Practice Question
A company is deploying a VPC with public and private subnets across two Availability Zones. They need to ensure that instances in the private subnets can access the internet for software updates without being directly reachable from the internet. Which AWS service should they use?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that an Internet Gateway can be used for private subnets by simply not assigning public IPs, but the trap here is that an Internet Gateway requires instances to have public IP addresses or Elastic IPs for outbound traffic, which still makes them potentially reachable from the internet if routes are misconfigured.
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 private subnets to initiate outbound traffic to the internet (e.g., for software updates) while preventing unsolicited inbound connections from the internet. It translates the private IP addresses of the instances to the NAT Gateway's Elastic IP address using source network address translation (SNAT). This satisfies the requirement of internet access without direct reachability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Virtual Private Gateway
Why it's wrong here
A Virtual Private Gateway is used for VPN connections to on-premises networks.
- ✗
VPC Peering Connection
Why it's wrong here
VPC Peering connects VPCs but does not provide internet access.
- ✗
Internet Gateway
Why it's wrong here
An Internet Gateway allows both inbound and outbound internet access, making instances reachable from the internet.
- ✓
NAT Gateway
Why this is correct
A NAT Gateway allows outbound internet traffic from private subnets while blocking inbound traffic.
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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 has a VPC with public and private subnets across two Availability Zones. The private subnets require outbound internet access for updates, but must not be directly reachable from the internet. The company has a NAT gateway in each public subnet. Security team reports that instances in private subnets cannot reach the internet. Which configuration should be verified first?
hard- ✓ A.Verify that the route table for the public subnets has a default route pointing to an internet gateway, and the private subnets' route table has a default route pointing to the NAT gateway
- B.Verify that the VPC has a VPC endpoint for S3 configured
- C.Verify that the network ACLs for the private subnets allow outbound traffic to 0.0.0.0/0
- D.Verify that the security groups attached to the instances allow outbound HTTPS traffic
Why A: For instances in private subnets to reach the internet via a NAT gateway, the private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT gateway, and the NAT gateway must be placed in a public subnet whose route table has a default route pointing to an internet gateway. If either route is missing, outbound internet access will fail. Option B is incorrect because VPC endpoints are for accessing specific AWS services (e.g., S3), not general internet access. Option C is incorrect because NACLs are stateless and by default allow all outbound traffic; although custom NACLs could block traffic, routing misconfiguration is a more common first issue. Option D is incorrect because security groups are stateful and outbound traffic is allowed by default; blocking outbound HTTPS would be an intentional change, not the first thing to verify.
Variation 2. Which THREE actions are required to enable an EC2 instance in a private subnet to download software updates from the internet? (Select THREE.)
medium- A.Allocate an Elastic IP and associate it with the NAT Gateway
- B.Configure the security group to allow outbound traffic to 0.0.0.0/0
- ✓ C.Create a NAT Gateway in a public subnet
- ✓ D.Add a route in the private subnet route table pointing to the NAT Gateway for 0.0.0.0/0
- ✓ E.Attach an Internet Gateway to the VPC
Why C: To enable an EC2 instance in a private subnet to download software updates from the internet, you need a NAT Gateway in a public subnet (Option C) which requires an Internet Gateway attached to the VPC (Option E) to route traffic to the internet. Additionally, the private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway (Option D). While a NAT Gateway does require an Elastic IP, this is automatically allocated and associated during creation, so it is not a separate action.
Variation 3. A company is migrating a legacy application that requires static IP addresses for its clients' firewall whitelisting. The application will be hosted on EC2 instances behind a Network Load Balancer (NLB) in a private subnet. Which approach should the company use to provide static IP addresses for outbound traffic?
medium- A.Assign Elastic IPs to the EC2 instances
- B.Use an internet-facing NLB with Elastic IPs
- C.Use a VPC endpoint for the application
- ✓ D.Deploy a NAT Gateway in a public subnet with an Elastic IP
Why D: A NAT Gateway in a public subnet with an Elastic IP provides a static source IP address for outbound traffic from private subnets. Since the EC2 instances are in a private subnet behind an NLB, they cannot directly reach the internet; the NAT Gateway translates their private IPs to the Elastic IP, which clients can whitelist. This ensures consistent outbound IPs without exposing the instances to inbound 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.