The answer is the route tables are not correctly configured for cross-AZ traffic. In a single VPC, instances in different Availability Zones communicate via the VPC’s implicit router, which relies on route table entries to direct traffic between subnets. If the route tables lack explicit routes for the destination subnet’s CIDR block, packets may be dropped, causing intermittent connectivity between SAP application and database servers. This scenario tests your understanding of VPC routing fundamentals on the AWS Certified SAP on AWS Specialty PAS-C01 exam, where a common trap is assuming cross-AZ issues require complex solutions like Transit Gateway or VPC Peering. Remember, within the same VPC, no additional networking constructs are needed—the problem is almost always a missing or misconfigured route table entry. Memory tip: “Same VPC, different AZ? Check the route table first.”
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 network connectivity issues between the application server and the database server. Both servers are in the same VPC but in different Availability Zones. The network ACLs and security groups are properly configured. What is the most likely cause and solution?
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 route tables are not correctly configured for cross-AZ traffic; verify and update route tables
Option B is correct because an AWS Transit Gateway is not needed; the issue is likely due to missing route table entries for cross-AZ traffic. Option A is incorrect because NACL changes are not needed if properly configured. Option C is incorrect because security groups are stateful. Option D is incorrect because VPC Peering is not needed within the same VPC.
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 groups are stateful and blocking return traffic; use network ACLs instead
Why it's wrong here
Security groups are stateful and allow return traffic automatically.
✓
The route tables are not correctly configured for cross-AZ traffic; verify and update route tables
Use AWS Transit Gateway to connect the subnets in different AZs
Why it's wrong here
Transit Gateway is for connecting multiple VPCs, not subnets within a VPC.
✗
The network ACLs are blocking traffic between Availability Zones; update the NACLs
Why it's wrong here
NACLs are stateless but if properly configured, they should allow traffic.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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 route tables are not correctly configured for cross-AZ traffic; verify and update route tables — Option B is correct because an AWS Transit Gateway is not needed; the issue is likely due to missing route table entries for cross-AZ traffic. Option A is incorrect because NACL changes are not needed if properly configured. Option C is incorrect because security groups are stateful. Option D is incorrect because VPC Peering is not needed within the same VPC.
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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