- A
Enable VPC Flow Logs on the internet gateway.
Why wrong: Internet gateway does not have network interfaces for flow logs.
- B
Create a VPC Flow Log for the VPC and filter by the NAT gateway's network interface.
Flow logs on the NAT gateway ENI capture outbound traffic from private subnets.
- C
Enable VPC Flow Logs on the NAT gateway's elastic network interface.
The NAT gateway's ENI sees all traffic from private subnets to the internet.
- D
Set up an AWS Site-to-Site VPN to route traffic through a third-party logging appliance.
Why wrong: This is overkill and not necessary for auditing.
- E
Enable AWS CloudTrail for the NAT gateway.
Why wrong: CloudTrail records API calls, not network traffic.
Question 177 of 1,705
Capturing NAT Gateway Traffic with VPC Flow Logs
This ANS-C01 practice question tests your understanding of network management and operations. 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 has a VPC with public and private subnets. The private subnets have a route to a NAT gateway for outbound internet access. The security team wants to audit all traffic from the private subnets to the internet. Which TWO steps should be taken to capture this traffic?
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
✓
Create a VPC Flow Log for the VPC and filter by the NAT gateway's network interface.
To capture traffic from private subnets to the internet through a NAT gateway, you need to enable VPC Flow Logs on the NAT gateway's elastic network interface (option C). Additionally, you can create a VPC Flow Log for the VPC and filter by the NAT gateway's network interface (option B) to capture the same traffic. Option A is incorrect because VPC Flow Logs on the internet gateway capture traffic that reaches the internet gateway, but traffic from private subnets goes through the NAT gateway, not directly through the internet gateway. Option D is incorrect because a Site-to-Site VPN is not used for outbound internet traffic from private subnets; it is for connecting to on-premises networks. Option E is incorrect because AWS CloudTrail logs API calls, not network traffic.
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.
- ✗
Enable VPC Flow Logs on the internet gateway.
Why it's wrong here
Internet gateway does not have network interfaces for flow logs.
- ✓
Create a VPC Flow Log for the VPC and filter by the NAT gateway's network interface.
- ✓
Enable VPC Flow Logs on the NAT gateway's elastic network interface.
- ✗
Set up an AWS Site-to-Site VPN to route traffic through a third-party logging appliance.
Why it's wrong here
This is overkill and not necessary for auditing.
- ✗
Enable AWS CloudTrail for the NAT gateway.
Why it's wrong here
CloudTrail records API calls, not network traffic.
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.
Visual reference
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 Management and Operations — This question tests Network Management and Operations — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create a VPC Flow Log for the VPC and filter by the NAT gateway's network interface. — To capture traffic from private subnets to the internet through a NAT gateway, you need to enable VPC Flow Logs on the NAT gateway's elastic network interface (option C). Additionally, you can create a VPC Flow Log for the VPC and filter by the NAT gateway's network interface (option B) to capture the same traffic. Option A is incorrect because VPC Flow Logs on the internet gateway capture traffic that reaches the internet gateway, but traffic from private subnets goes through the NAT gateway, not directly through the internet gateway. Option D is incorrect because a Site-to-Site VPN is not used for outbound internet traffic from private subnets; it is for connecting to on-premises networks. Option E is incorrect because AWS CloudTrail logs API calls, not network traffic.
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.
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Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 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. The public subnets have a NAT gateway for outbound internet access. The private subnets route all 0.0.0.0/0 traffic to the NAT gateway. The network team wants to centrally log all outbound internet traffic from the private subnets. They enable VPC Flow Logs and publish them to Amazon S3. However, they notice that the flow logs are capturing only traffic between instances within the VPC, not the NAT gateway traffic. What should the team do to capture outbound internet traffic?
easy- ✓ A.Enable VPC Flow Logs specifically for the NAT gateway's elastic network interface.
- B.Enable VPC Flow Logs for all subnets in the VPC.
- C.Use AWS CloudTrail to log NAT gateway traffic.
- D.Enable VPC Flow Logs for the VPC and publish to CloudWatch Logs instead of S3.
Why A: VPC Flow Logs capture traffic at the network interface level. Traffic from private subnets to the NAT gateway is captured by flow logs on the private subnet instances' ENIs, but the NAT gateway's outbound traffic goes through its own ENI. To log the actual outbound internet traffic, you must enable flow logs on the NAT gateway's ENI. Option A correctly identifies this. Option B would not capture NAT gateway egress because flow logs are per-ENI. Option C (CloudTrail) logs API calls, not network traffic. Option D is incorrect because the destination (S3 vs CloudWatch) does not affect what traffic is captured.
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Last reviewed: Jun 20, 2026
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