The answer is adding a route to the public subnet’s route table pointing 0.0.0.0/0 to the Internet Gateway. This default route is the critical missing piece because the Internet Gateway itself is only a horizontally-scaled, redundant VPC component that provides a target for internet-bound traffic; without a route directing that traffic to the IGW, the gateway is effectively useless for the subnet. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of the three-layer internet access model: the IGW as the gateway object, the route table entry as the logical path, and the public IP assignment as the endpoint identifier. A common trap is confusing this with a NAT Gateway, which serves private subnets for outbound-only access, or assuming the IGW alone enables inbound reachability. Remember the memory tip: “IGW needs a signpost” — the route table entry is the signpost pointing 0.0.0.0/0 to the IGW, and without it, traffic has no path to or from the internet.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company needs to provide internet access to a VPC that has both public and private subnets. They have already created an Internet Gateway and attached it to the VPC. What else must be configured for instances in the public subnet to be reachable from the internet?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a route to the public subnet's route table pointing 0.0.0.0/0 to the Internet Gateway.
For internet access, the public subnet's route table must have a default route to the Internet Gateway. Additionally, the instances must have public IP addresses (auto-assign public IP or Elastic IP) and security groups/NACLs allowing inbound traffic. Option B (NAT Gateway) is for private subnets; Option C (VPN) is not needed; Option D (Transit Gateway) is not required.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 Gateway in the public subnet.
Why it's wrong here
NATGateway is for private subnets to access the internet outbound.
✓
Add a route to the public subnet's route table pointing 0.0.0.0/0 to the Internet Gateway.
Why this is correct
This enables traffic to flow between the subnet and the internet.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Add a route to the public subnet's route table pointing 0.0.0.0/0 to the Internet Gateway. — For internet access, the public subnet's route table must have a default route to the Internet Gateway. Additionally, the instances must have public IP addresses (auto-assign public IP or Elastic IP) and security groups/NACLs allowing inbound traffic. Option B (NAT Gateway) is for private subnets; Option C (VPN) is not needed; Option D (Transit Gateway) is not required.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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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 wants to provide internet access to instances in a public subnet. Which component must be attached to the VPC and have a route to it in the subnet's route table?
easy
A.Transit Gateway
B.Virtual Private Gateway
C.NAT Gateway
✓ D.Internet Gateway
Why D: Internet Gateway must be attached to the VPC and a default route pointing to it is needed for internet access.
Last reviewed: Jun 20, 2026
Question Discussion
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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.
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