- A
Modify the VPC subnet to use a smaller CIDR range to ensure the IP is available.
Why wrong: This does not help; the IP may still be taken by another instance.
- B
Create a new AMI from the failed instance and use that AMI to launch a new instance, specifying the same private IP in the subnet.
Why wrong: Private IPs are assigned automatically; you cannot guarantee the same IP unless you use an ENI.
- C
Assign an Elastic IP to the instance and update the VPN configuration to use the Elastic IP.
Why wrong: Elastic IP is a public IP, not private; the VPN uses private IPs.
- D
Create an Elastic Network Interface (ENI) with the desired private IP, attach it to the instance, and after failure, detach it from the old instance and attach to the new instance.
ENI retains the private IP and can be moved to another instance.
Quick Answer
The answer is to create an Elastic Network Interface (ENI) with the desired private IP, attach it to the instance, and after failure, detach it from the old instance and attach to the new one. This works because an ENI retains its private IP address, subnet, and security group settings independently of the EC2 instance’s lifecycle, allowing you to preserve the private IP after EC2 failure using ENI for SAP by simply reattaching the same ENI to a replacement instance. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of network interface persistence versus ephemeral instance attributes—a common trap is confusing an Elastic IP (which handles public IPs) with an ENI’s ability to fix a private IP. Remember the mnemonic: “ENI locks the LAN, EIP locks the WAN.”
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.
A small business runs its SAP Business One on a single EC2 instance in AWS. The database is SAP HANA, and the application is also on the same instance. The company wants to ensure that in the event of an instance failure, they can quickly restore the system from backups. They take daily EBS snapshots of the root volume and the data volume. One day, the instance fails and becomes unreachable. The IT administrator attempts to launch a new instance from the most recent AMI, but the new instance does not have the same private IP address, causing connectivity issues for the company's on-premises systems that use VPN to connect to the SAP server. The company uses a Site-to-Site VPN connection to the VPC. What should the administrator do to ensure that the private IP address is preserved after recovery?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Create an Elastic Network Interface (ENI) with the desired private IP, attach it to the instance, and after failure, detach it from the old instance and attach to the new instance.
Option B is correct because an ENI with a fixed private IP can be detached from the failed instance and attached to the new instance. Option A is wrong because Elastic IP is for public IPs. Option C is wrong because creating a new AMI does not preserve the private IP. Option D is wrong because modifying the VPC is unnecessary.
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.
- ✗
Modify the VPC subnet to use a smaller CIDR range to ensure the IP is available.
Why it's wrong here
This does not help; the IP may still be taken by another instance.
- ✗
Create a new AMI from the failed instance and use that AMI to launch a new instance, specifying the same private IP in the subnet.
Why it's wrong here
Private IPs are assigned automatically; you cannot guarantee the same IP unless you use an ENI.
- ✗
Assign an Elastic IP to the instance and update the VPN configuration to use the Elastic IP.
- ✓
Create an Elastic Network Interface (ENI) with the desired private IP, attach it to the instance, and after failure, detach it from the old instance and attach to the new instance.
Why this is correct
ENI retains the private IP and can be moved to another instance.
Related concept
CIDR notation defines the prefix length.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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.
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FAQ
Questions learners often ask
What does this PAS-C01 question test?
Technology — This question tests Technology — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create an Elastic Network Interface (ENI) with the desired private IP, attach it to the instance, and after failure, detach it from the old instance and attach to the new instance. — Option B is correct because an ENI with a fixed private IP can be detached from the failed instance and attached to the new instance. Option A is wrong because Elastic IP is for public IPs. Option C is wrong because creating a new AMI does not preserve the private IP. Option D is wrong because modifying the VPC is unnecessary.
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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Last reviewed: Jun 20, 2026
This PAS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PAS-C01 exam.
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