The answer is VPC Flow Logs and AWS Network Firewall. VPC Flow Logs capture all IP traffic at the network interface level, including DNS queries and responses, making them a straightforward choice for monitoring any traffic to an on-premises DNS resolver over a VPN. AWS Network Firewall can also capture and log DNS traffic by applying stateful rule groups that specifically inspect DNS protocol traffic, logging the queries regardless of the resolver’s location. On the ANS-C01 exam, this question tests your understanding of which AWS services operate at the network packet layer versus the application layer—a common trap is confusing Route 53 Resolver query logs, which only capture queries directed to Route 53’s managed DNS, not to a custom on-premises resolver. Another trap is assuming CloudTrail or CloudWatch can capture raw traffic; they log API calls and metrics, not packets. Memory tip: think “Flow and Firewall for full packet capture” to remember that only these two services see the actual DNS query packets traversing the VPN.
ANS-C01 Network Management and Operations Practice Question
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. The network team wants to monitor DNS queries from EC2 instances in private subnets to a custom DNS resolver on-premises over a VPN. Which TWO services can capture this traffic?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VPC Flow Logs
Option A is correct because VPC Flow Logs capture all IP traffic including DNS. Option D is correct because AWS Network Firewall can capture and log DNS traffic. Option B is incorrect because Route 53 Resolver query logs capture queries to Route 53, not custom resolvers. Option C is incorrect because CloudTrail logs API calls. Option E is incorrect because CloudWatch does not capture traffic directly.
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.
✗
Amazon Route 53 Resolver query logs
Why it's wrong here
Resolver query logs capture queries to Route 53, not custom on-premises resolvers.
✗
Amazon CloudWatch
Why it's wrong here
CloudWatch is for monitoring metrics and logs, not capturing traffic directly.
✓
VPC Flow Logs
Why this is correct
Flow logs capture all IP traffic, including DNS queries.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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 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: VPC Flow Logs — Option A is correct because VPC Flow Logs capture all IP traffic including DNS. Option D is correct because AWS Network Firewall can capture and log DNS traffic. Option B is incorrect because Route 53 Resolver query logs capture queries to Route 53, not custom resolvers. Option C is incorrect because CloudTrail logs API calls. Option E is incorrect because CloudWatch does not capture traffic directly.
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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Question Discussion
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