The correct step is to review the network ACL rules for both the public and private subnets. This is because network ACLs are stateless, meaning they require explicit inbound and outbound rules for traffic to flow in both directions; if a maintenance window updated the NACLs, they may have inadvertently blocked the ephemeral ports or return traffic needed for SAP connectivity between subnets. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of the difference between stateful security groups and stateless network ACLs—a common trap is assuming security group verification alone resolves the issue, when NACLs operate at the subnet boundary and can silently drop traffic. Remember the memory tip: "NACLs need two-way streets; security groups need one-way doors."
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 operations team manages an SAP ERP system on AWS that uses a single EC2 instance for the SAP central services (SCS) and multiple instances for application servers. The system is running in a VPC with both public and private subnets. The team notices that the SCS instance is unreachable from the application servers after a maintenance window where network ACLs were updated. The application servers are in private subnets, and the SCS instance is in a public subnet. The team has verified that the security groups allow the required traffic. Which step should the team take to resolve 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
✓
Review the network ACL rules for both the public and private subnets.
Option C is correct because network ACLs are stateless and require both inbound and outbound rules. During maintenance, the NACL might have been modified to block required traffic. Option A is wrong because security groups are already verified. Option B is wrong because route tables affect routing, not connectivity if they are within the same VPC. Option D is wrong because the issue is not about Elastic 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.
✓
Review the network ACL rules for both the public and private subnets.
Verify that the route tables have a route to the internet gateway.
Why it's wrong here
Route tables are for subnet routing, not direct connectivity between instances in the same VPC.
✗
Assign an Elastic IP to the SCS instance.
Why it's wrong here
Elastic IPs are for internet connectivity, not internal communication.
✗
Check the security group rules on the application servers.
Why it's wrong here
Security groups have already been verified.
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.
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: Review the network ACL rules for both the public and private subnets. — Option C is correct because network ACLs are stateless and require both inbound and outbound rules. During maintenance, the NACL might have been modified to block required traffic. Option A is wrong because security groups are already verified. Option B is wrong because route tables affect routing, not connectivity if they are within the same VPC. Option D is wrong because the issue is not about Elastic 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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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