Quick Answer
The answer is VPC Flow Logs. This AWS service captures metadata about IP traffic flowing to and from network interfaces in your VPC, allowing you to analyze the logs to detect packet loss, rejected connections, or asymmetric routing between your EC2 instances. When troubleshooting connectivity between EC2 instances in the same VPC, especially across different subnets, VPC Flow Logs provide the granular, per-flow data needed to pinpoint where packets are being dropped, even when security groups and network ACLs appear correctly configured. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this question tests your ability to differentiate between logging services and network connectivity tools—a common trap is confusing VPC Flow Logs with CloudTrail, which logs API calls, not network traffic. Remember: Flow Logs = flow of packets; CloudTrail = trail of API calls.
This PAS-C01 practice question tests your understanding of operations and maintenance. 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.
An SAP system running on AWS is experiencing intermittent connectivity issues between the application server and the database server. Both servers are in the same VPC but different subnets. The security groups and network ACLs are correctly configured. Which AWS service can help diagnose the network path and identify packet loss?
AWS Direct Connect
Why wrong: Direct Connect is a dedicated network connection, not a diagnostic tool.
VPC Flow Logs
VPC Flow Logs capture network traffic information for analysis.
AWS CloudTrail
Why wrong: CloudTrail records API activity, not network traffic.
AWS Site-to-Site VPN
Why wrong: VPN is for secure connections, not diagnostics.
Answer choices
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
VPC Flow Logs capture IP traffic metadata and can be analyzed to detect packet loss or rejected connections. Option D is correct. Option A is wrong because CloudTrail logs API calls. Option B is wrong because Direct Connect is for on-premises connectivity. Option C is wrong because VPN is also for external connectivity.
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
For each option: why learners choose it and why it is or isn't the right answer here.
AWS Direct Connect
Why it's wrong here
Direct Connect is a dedicated network connection, not a diagnostic tool.
VPC Flow Logs
Why this is correct
VPC Flow Logs capture network traffic information for analysis.
Related concept
CIDR notation defines the prefix length.
AWS CloudTrail
Why it's wrong here
CloudTrail records API activity, not network traffic.
AWS Site-to-Site VPN
Why it's wrong here
VPN is for secure connections, not diagnostics.
Common exam traps
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
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.
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
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
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Operations and Maintenance — study guide chapter
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FAQ
Operations and Maintenance — This question tests Operations and Maintenance — CIDR notation defines the prefix length..
The correct answer is: VPC Flow Logs — VPC Flow Logs capture IP traffic metadata and can be analyzed to detect packet loss or rejected connections. Option D is correct. Option A is wrong because CloudTrail logs API calls. Option B is wrong because Direct Connect is for on-premises connectivity. Option C is wrong because VPN is also for external connectivity.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
CIDR notation defines the prefix length.
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Same concept, more angles
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. An SAP system on AWS is experiencing intermittent network connectivity issues between the application servers and the database server. Both are in the same VPC but different subnets. The security groups allow all traffic between them. What should the administrator check next?
hardWhy A: Network ACLs are stateless and must allow both inbound and outbound traffic. If NACLs block return traffic, connectivity fails intermittently. VPC Flow Logs can help diagnose but are not the first check. Route tables are typically correct within a VPC. The issue is likely at the NACL level.
Variation 2. An SAP system running on EC2 is experiencing intermittent connectivity issues between application servers and the database server. The network team suspects that the security group rules are too restrictive. What is the best approach to identify which traffic is being blocked?
mediumWhy D: Option A is correct because VPC Flow Logs capture traffic metadata and can show accepted and rejected traffic. Option B is wrong because CloudTrail logs API calls, not network traffic. Option C is wrong because CloudWatch metrics do not provide per-packet detail. Option D is wrong because the question is about network traffic, not application logs.
Variation 3. An SAP system on AWS is experiencing intermittent connectivity issues between the application servers and the HANA database. The network team has confirmed that the VPC and subnets are configured correctly. What should the operations team check NEXT?
hardWhy C: Option B is correct because security group rules for HANA database default deny inbound traffic; if not properly configured, they can block application traffic. Option A is wrong because NACLs are stateless and less likely to cause intermittent issues. Option C is wrong because route tables typically do not change. Option D is wrong because DNS resolution is not the likely cause of intermittent connectivity.
Last reviewed: Jun 20, 2026
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