ANS-C01 Network Implementation Practice Question
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?
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
✓
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
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.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
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
Why this is correct
NAT gateway must be in a public subnet with a route to an internet gateway, and private subnets must route 0.0.0.0/0 to the NAT gateway.
- ✗
Verify that the VPC has a VPC endpoint for S3 configured
Why it's wrong here
VPC endpoints are for private access to AWS services, not general internet access.
- ✗
Verify that the network ACLs for the private subnets allow outbound traffic to 0.0.0.0/0
Why it's wrong here
NACLs are stateless and typically allow outbound traffic; default NACLs already allow all traffic.
- ✗
Verify that the security groups attached to the instances allow outbound HTTPS traffic
Why it's wrong here
Security groups are stateful and allow outbound traffic by default, so this is unlikely the issue.
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 |
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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.