The answer is that the security group attached to the SAP instance does not allow inbound RFC traffic. Security groups act as a stateful, instance-level firewall on AWS, and when an SAP RFC connection is refused, it typically indicates that the target EC2 instance is actively rejecting the connection attempt, which is exactly what a missing inbound rule for the RFC port (usually 33xx or 48xx) does. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this question tests your ability to distinguish between security group rules and other network components like NACLs or route tables; a common trap is confusing a connection refusal (security group) with a timeout (NACL or bandwidth issue). Remember that a security group denies by default, so if you see "connection refused" during an SAP migration over VPN, think "SG first." Memory tip: Refused = Rules (security group), Timeout = Transit (NACL or bandwidth).
PAS-C01 Migration Practice Question
This PAS-C01 practice question tests your understanding of migration. 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.
During a migration of an SAP system to AWS, the SAP application team reports that batch jobs are failing with an error 'RFC connection refused'. The on-premises system and AWS are connected via a VPN. What 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
✓
The security group attached to the SAP instance does not allow inbound RFC traffic
Security groups act as a virtual firewall for EC2 instances. If inbound RFC ports are not allowed, connections will be refused. Option A (NACL) operates at subnet level, but SG is more common for instance-level. Option C (Route table) is for routing, not security. Option D (Bandwidth) would cause timeouts, not immediate refusal.
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 attached to the SAP instance does not allow inbound RFC traffic
Why this is correct
Security group rules control inbound traffic to the instance.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The VPN bandwidth is insufficient causing timeouts
Why it's wrong here
Insufficient bandwidth would cause timeouts, not immediate refusal.
✗
The network ACLs are blocking the RFC ports
Why it's wrong here
NACLs are stateless and might be an issue, but SGs are more likely.
✗
The route table does not have a route to the on-premises network
Why it's wrong here
Would cause 'destination unreachable', not 'connection refused'.
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.
Migration — This question tests Migration — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The security group attached to the SAP instance does not allow inbound RFC traffic — Security groups act as a virtual firewall for EC2 instances. If inbound RFC ports are not allowed, connections will be refused. Option A (NACL) operates at subnet level, but SG is more common for instance-level. Option C (Route table) is for routing, not security. Option D (Bandwidth) would cause timeouts, not immediate refusal.
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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