The answer is that the security group does not allow inbound traffic from the NLB's private IP addresses. This is because Network Load Balancer health checks originate from the NLB’s own elastic network interface IPs within the subnet, not from the client IPs or the subnet CIDR range. Even if the security group permits traffic from the NLB’s subnet CIDR, the actual source IP of the health check probe is the NLB’s private IP, which may fall outside that CIDR block. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this question tests your understanding of how NLB health checks differ from Application Load Balancer checks and the specific security group rules required for SAP workloads. A common trap is assuming that allowing the subnet CIDR is sufficient, but the NLB’s IPs are assigned from the subnet and are distinct. Memory tip: think “NLB probes come from its own IP, not the subnet range”—so always add a rule for the NLB’s private IPs, not just the CIDR.
PAS-C01 Operations and Maintenance Practice Question
This PAS-C01 practice question tests your understanding of operations and maintenance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 uses a Network Load Balancer (NLB) to distribute traffic to SAP application servers. The application servers are in private subnets. The operations team notices that the health checks are failing for one of the application servers. The health check is configured to use TCP on port 3200. The application server's security group allows inbound traffic on port 3200 from the NLB's subnet CIDR. The network ACL allows inbound and outbound traffic on ephemeral ports. What is the most likely cause of the health check failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The security group does not allow inbound traffic from the NLB's private IP addresses.
Option C is correct because the NLB health checks originate from its own IP addresses, not from the client IPs. The security group must allow traffic from the NLB's private IP addresses. Option A is wrong because the application may be listening correctly. Option B is wrong because NACLs are properly configured. Option D is wrong because the NLB communicates with targets using their private IPs.
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.
✓
The security group does not allow inbound traffic from the NLB's private IP addresses.
Why this is correct
Health checks come from NLB's IPs, not client IPs.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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 PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Operations and Maintenance — This question tests Operations and Maintenance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The security group does not allow inbound traffic from the NLB's private IP addresses. — Option C is correct because the NLB health checks originate from its own IP addresses, not from the client IPs. The security group must allow traffic from the NLB's private IP addresses. Option A is wrong because the application may be listening correctly. Option B is wrong because NACLs are properly configured. Option D is wrong because the NLB communicates with targets using their private IPs.
What should I do if I get this PAS-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 PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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