- A
Auto mode VPCs cost more per subnet than custom mode
Why wrong: VPC networking costs are based on traffic and peering, not the VPC mode — auto and custom mode have the same pricing structure.
- B
Custom mode allows full control over which regions have subnets and what CIDR ranges are used
In custom mode, the team creates subnets explicitly, choosing regions and CIDRs. This avoids CIDR conflicts with on-premises networks and prevents unnecessary subnet sprawl.
- C
Auto mode VPCs cannot be used with GKE clusters
Why wrong: GKE clusters can be deployed in both auto mode and custom mode VPCs.
- D
Custom mode VPCs support more IP addresses per subnet than auto mode
Why wrong: The VPC mode doesn't restrict subnet IP capacity — both modes support the same CIDR sizes.
Quick Answer
The answer is custom mode VPC because it gives you full control over which regions have subnets and what CIDR ranges are used. Unlike auto mode, which automatically creates a subnet in every region using a fixed /20 range, custom mode lets you define your own IP address space and deploy subnets only where needed. This is critical when you must avoid overlapping CIDRs with on-premises networks or other VPCs, or when you need to restrict subnets to specific regions for compliance or cost reasons. On the Google Associate Cloud Engineer exam, this distinction tests your understanding of network planning and scalability—auto mode is convenient for quick labs but dangerous in production due to rigid, unpredictable IP allocation. A common trap is assuming auto mode is always simpler; in reality, it can cause conflicts that custom mode prevents. Memory tip: think “Custom = Control,” because you choose every subnet and CIDR, while “Auto = Automatic, but also Automatic problems.”
Google ACE Deploying and implementing a cloud solution Practice Question
This ACE practice question tests your understanding of deploying and implementing a cloud solution. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 network team is creating a new VPC and must decide between auto mode and custom mode. Why would they choose custom mode?
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
Custom mode allows full control over which regions have subnets and what CIDR ranges are used
Custom mode VPCs give the network team full control over the IP address range (CIDR block) and the ability to create subnets in any region, unlike auto mode VPCs which automatically create subnets in every region with a fixed /20 range per region. This is essential when you need to avoid overlapping CIDRs with on-premises networks or other VPCs, or when you want to restrict subnets to specific regions for compliance or cost reasons.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Auto mode VPCs cost more per subnet than custom mode
Why it's wrong here
VPC networking costs are based on traffic and peering, not the VPC mode — auto and custom mode have the same pricing structure.
- ✓
Custom mode allows full control over which regions have subnets and what CIDR ranges are used
Why this is correct
In custom mode, the team creates subnets explicitly, choosing regions and CIDRs. This avoids CIDR conflicts with on-premises networks and prevents unnecessary subnet sprawl.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Auto mode VPCs cannot be used with GKE clusters
Why it's wrong here
GKE clusters can be deployed in both auto mode and custom mode VPCs.
- ✗
Custom mode VPCs support more IP addresses per subnet than auto mode
Why it's wrong here
The VPC mode doesn't restrict subnet IP capacity — both modes support the same CIDR sizes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that auto mode VPCs are more expensive or have IP limitations, when in fact the key differentiator is control over subnet placement and CIDR range, not cost or capacity.
Detailed technical explanation
How to think about this question
Under the hood, auto mode VPCs use a predefined /20 CIDR block (10.128.0.0/9) and automatically create a /24 subnet in each region, which can lead to IP exhaustion if many regions are used. Custom mode VPCs start with no subnets, allowing you to define any RFC 1918 CIDR (e.g., 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) and create subnets only where needed, which is critical for hybrid cloud scenarios where you must avoid overlapping with on-premises networks. A real-world scenario is a multi-region deployment where you need to use non-overlapping 10.x.x.x ranges across VPCs for peering or VPN connectivity.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
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FAQ
Questions learners often ask
What does this ACE question test?
Deploying and implementing a cloud solution — This question tests Deploying and implementing a cloud solution — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Custom mode allows full control over which regions have subnets and what CIDR ranges are used — Custom mode VPCs give the network team full control over the IP address range (CIDR block) and the ability to create subnets in any region, unlike auto mode VPCs which automatically create subnets in every region with a fixed /20 range per region. This is essential when you need to avoid overlapping CIDRs with on-premises networks or other VPCs, or when you want to restrict subnets to specific regions for compliance or cost reasons.
What should I do if I get this ACE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 30, 2026
This ACE practice question is part of Courseiva's free Google Cloud 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 ACE exam.
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