The answer is that network ACLs do not have rules to allow ephemeral ports for return traffic, which is the most likely cause of intermittent SAP connectivity issues during peak hours. This occurs because network ACLs are stateless, meaning they require explicit inbound and outbound rules for every traffic flow, unlike security groups which automatically track connection state. When SAP application servers initiate connections to the database server, the return traffic uses high-numbered ephemeral ports; if the outbound NACL rule for the database subnet does not explicitly allow these ports, the response packets are dropped, especially under load when many concurrent connections are established. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this question tests your understanding of the critical difference between stateful security groups and stateless network ACLs, a common trap where candidates assume both behave identically. A helpful memory tip: think of NACLs as needing a “round-trip ticket” for every conversation—if you only book the outbound flight, the return flight gets denied.
PAS-C01 Technology Practice Question
This PAS-C01 practice question tests your understanding of technology. 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 running on AWS is experiencing intermittent connectivity issues between the SAP application servers and the database server. Both are in the same VPC but different subnets. The security groups and network ACLs are correctly configured. The issue occurs only during peak hours. Which of the following is the most likely cause?
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
✓
Network ACLs do not have rules to allow ephemeral ports for return traffic.
Option D is correct because network ACLs are stateless and require explicit rules for both inbound and outbound traffic, and ephemeral ports are often missed. Option A is wrong because NACL rules are evaluated before security groups. Option B is wrong because VPC peering is not mentioned. Option C is wrong because security groups are stateful and would not cause asymmetric traffic issues.
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.
✗
Security group outbound rules are blocking return traffic.
Why it's wrong here
Security groups are stateful; return traffic is allowed regardless of outbound rules.
✗
The VPC peering connection is throttling traffic.
Why it's wrong here
No VPC peering is mentioned; both servers are in the same VPC.
✓
Network ACLs do not have rules to allow ephemeral ports for return traffic.
Why this is correct
NACLs are stateless; failing to allow ephemeral ports can cause intermittent connectivity during high traffic.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Security groups are stateful; if outbound is allowed, return traffic is automatically allowed.
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 PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Technology — This question tests Technology — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Network ACLs do not have rules to allow ephemeral ports for return traffic. — Option D is correct because network ACLs are stateless and require explicit rules for both inbound and outbound traffic, and ephemeral ports are often missed. Option A is wrong because NACL rules are evaluated before security groups. Option B is wrong because VPC peering is not mentioned. Option C is wrong because security groups are stateful and would not cause asymmetric traffic issues.
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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