- A
Configure security groups to allow outbound traffic from the instances
Security groups must allow outbound traffic for instances to communicate.
- B
Launch a NAT gateway in a public subnet and associate it with an Elastic IP
NAT gateway enables outbound internet for private subnets.
- C
Attach an Internet Gateway to the VPC and route all traffic to it
Why wrong: IGW is for both inbound and outbound, but routing all traffic to IGW would bypass inspection.
- D
Create VPC endpoints for all required AWS services
Why wrong: VPC endpoints are for private access to AWS services, not for general internet traffic.
- E
Configure route tables in each private subnet to send 0.0.0.0/0 traffic to a NAT gateway in a public subnet
Routes all outbound traffic to NAT gateway for inspection.
Quick Answer
The answer is to configure route tables in each private subnet to send 0.0.0.0/0 traffic to a NAT gateway in a public subnet. This works because a NAT gateway, placed in a public subnet with an associated Elastic IP, translates private IPv4 addresses to the gateway’s public IP, enabling outbound internet traffic while preventing inbound connections from the internet. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of centralized outbound traffic inspection—a common trap is confusing NAT gateways with egress-only internet gateways (which only handle IPv6) or VPC endpoints (which are for AWS services, not general internet access). The key is remembering that for IPv4 outbound traffic from private subnets, the default route must point to a NAT gateway, not an internet gateway, which is used for inbound traffic. Memory tip: “NAT for out, IGW for in, egress-only for IPv6.”
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 ensure that all outbound internet traffic from a VPC goes through a centralized inspection appliance. The VPC has multiple subnets. Which THREE steps are required to implement this?
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
Configure security groups to allow outbound traffic from the instances
Options A, C, and D are correct. An egress-only Internet Gateway is used for IPv6, but for IPv4, the default route points to a NAT gateway or appliance. However, the question implies IPv4; using a NAT gateway is common. Option A (route table) is essential. Option C (security groups) allows traffic. Option D (NAT gateway in public subnet) provides outbound connectivity. Option B is wrong because VPC endpoints are for AWS services, not internet. Option E is wrong because IGW is for inbound, not outbound inspection.
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.
- ✓
Configure security groups to allow outbound traffic from the instances
Why this is correct
Security groups must allow outbound traffic for instances to communicate.
Related concept
CIDR notation defines the prefix length.
- ✓
Launch a NAT gateway in a public subnet and associate it with an Elastic IP
- ✗
Attach an Internet Gateway to the VPC and route all traffic to it
Why it's wrong here
IGW is for both inbound and outbound, but routing all traffic to IGW would bypass inspection.
- ✗
Create VPC endpoints for all required AWS services
Why it's wrong here
VPC endpoints are for private access to AWS services, not for general internet traffic.
- ✓
Configure route tables in each private subnet to send 0.0.0.0/0 traffic to a NAT gateway in a public subnet
Common exam traps
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Configure security groups to allow outbound traffic from the instances — Options A, C, and D are correct. An egress-only Internet Gateway is used for IPv6, but for IPv4, the default route points to a NAT gateway or appliance. However, the question implies IPv4; using a NAT gateway is common. Option A (route table) is essential. Option C (security groups) allows traffic. Option D (NAT gateway in public subnet) provides outbound connectivity. Option B is wrong because VPC endpoints are for AWS services, not internet. Option E is wrong because IGW is for inbound, not outbound inspection.
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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Same concept, more angles
2 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. They have an EC2 instance in a private subnet that needs to access the internet for software updates. Which solution provides internet access while keeping the instance private?
medium- A.Attach an internet gateway to the VPC and assign a public IP to the EC2 instance.
- ✓ B.Create a NAT gateway in a public subnet, and update the private subnet's route table to point 0.0.0.0/0 to the NAT gateway.
- C.Use an AWS PrivateLink VPC endpoint for the software update service.
- D.Set up a VPC peering connection with another VPC that has internet access.
Why B: A NAT gateway in a public subnet allows instances in private subnets to initiate outbound internet traffic while preventing inbound traffic from the internet. Option B is correct. Option A (internet gateway) would expose the instance to inbound traffic if assigned a public IP. Option C (VPC peering) does not provide internet access. Option D (VPC endpoint) only provides access to specific AWS services, not general internet.
Variation 2. A company has a VPC with public and private subnets. The public subnet hosts a NAT gateway. The private subnet hosts EC2 instances that need to download patches from the internet. The EC2 instances have a security group that allows outbound HTTPS to 0.0.0.0/0. What additional configuration is required?
medium- A.Attach an internet gateway to the private subnet.
- B.Move the NAT gateway to the private subnet.
- ✓ C.Add a route in the private subnet's route table pointing 0.0.0.0/0 to the NAT gateway.
- D.Create a VPC endpoint for S3.
Why C: Option B is correct because private subnet instances need a route to the NAT gateway for internet access. Option A is wrong because an internet gateway is attached to the VPC, not the private subnet. Option C is wrong because the NAT gateway is already in the public subnet. Option D is wrong because a VPC endpoint is for private connectivity to AWS services, not for internet access.
Last reviewed: Jun 20, 2026
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