The correct answer is that the network ACL for the HANA instance's subnet is missing an outbound rule to allow return traffic on ephemeral ports. This is because network ACLs are stateless, meaning they require explicit rules for both inbound and outbound traffic; while the inbound rule permits SQL traffic on port 39013, the outbound response from HANA back to the application server uses a random ephemeral port (typically 1024-65535), and without a corresponding outbound allow rule, the return packets are dropped. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of the critical difference between stateful security groups and stateless network ACLs—a common trap is assuming that allowing all inbound traffic in the NACL is sufficient, but the outbound ephemeral port rule is often overlooked. For a memory tip, remember: "NACL is stateless—if it lets something in, you must also let the reply out."
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 administrator is troubleshooting an issue where an application cannot connect to an SAP HANA database running on an EC2 instance. The security group for the HANA instance allows inbound traffic on port 39013 (SQL) from the application server's security group. The network ACLs for the subnet allow all traffic. What could be the cause of the connectivity issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The network ACL for the HANA instance's subnet is missing an outbound rule to allow return traffic on ephemeral ports.
Option C is correct: The network ACL is stateless and must allow both inbound and outbound traffic; the outbound rule for ephemeral ports may be missing. Option A is incorrect because the security group allows the port. Option B is incorrect because the NACL allows all inbound traffic. Option D is incorrect because the security group allows the application server's security group.
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 for the HANA instance does not allow inbound traffic on port 39013 from the application server's IP address.
Why it's wrong here
A is wrong: the security group allows from the application server's security group.
✗
The network ACL for the application server's subnet does not allow outbound traffic on port 39013.
Why it's wrong here
B is wrong: the NACL allows all traffic.
✓
The network ACL for the HANA instance's subnet is missing an outbound rule to allow return traffic on ephemeral ports.
Why this is correct
C is correct: NACLs are stateless; outbound rules for return traffic are required.
The security group for the application server does not allow outbound traffic on port 39013.
Why it's wrong here
D is wrong: security groups are stateful; outbound is allowed by default.
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: The network ACL for the HANA instance's subnet is missing an outbound rule to allow return traffic on ephemeral ports. — Option C is correct: The network ACL is stateless and must allow both inbound and outbound traffic; the outbound rule for ephemeral ports may be missing. Option A is incorrect because the security group allows the port. Option B is incorrect because the NACL allows all inbound traffic. Option D is incorrect because the security group allows the application server's security group.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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