- A
Create a firewall rule with priority 2000 denying ingress from 0.0.0.0/0 and a rule allowing ingress from 10.0.0.0/16 on port 443 with priority 1000.
Why wrong: Incorrect: The default rules still exist and allow internet ingress; the deny rule has lower priority (higher number) than default allow rules (priority 65535), so the default rules take effect.
- B
Create a firewall rule with priority 1000 allowing ingress from 0.0.0.0/0 on port 443 and deny all other traffic.
Why wrong: Incorrect: This still allows traffic from the internet on port 443.
- C
Delete all default firewall rules and create a rule allowing ingress from the VPC's subnet range (e.g., 10.0.0.0/16) on port 443.
Correct: Deleting default rules removes internet ingress and the default allow-all-internal rule. New rule restricts internal communication to port 443.
- D
Modify the default-allow-internal rule to only allow port 443.
Why wrong: Incorrect: The default-allow-internal rule cannot be modified; it must be recreated with the desired ports.
Google ACE Configuring Access and Security Practice Question
This ACE practice question tests your understanding of configuring access and security. 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 security engineer needs to ensure that Compute Engine instances in a VPC can only communicate with each other on port 443 and cannot receive traffic from the internet. The VPC has a default network with default firewall rules. What should the engineer do?
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
Delete all default firewall rules and create a rule allowing ingress from the VPC's subnet range (e.g., 10.0.0.0/16) on port 443.
The default VPC includes default firewall rules that allow ingress from the internet and allow all internal traffic. To restrict communication, the engineer must first delete the default ingress rule that allows all traffic from the internet (allow-ssh, allow-icmp, allow-rdp, and allow-http/https can be deleted), then create a new rule that allows ingress only from the VPC's IP range on port 443. The default internal rule allows all traffic within the network; to restrict to port 443, a new rule with higher priority can override it, or the default rule can be deleted and a new one created.
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.
- ✗
Create a firewall rule with priority 2000 denying ingress from 0.0.0.0/0 and a rule allowing ingress from 10.0.0.0/16 on port 443 with priority 1000.
Why it's wrong here
Incorrect: The default rules still exist and allow internet ingress; the deny rule has lower priority (higher number) than default allow rules (priority 65535), so the default rules take effect.
- ✗
Create a firewall rule with priority 1000 allowing ingress from 0.0.0.0/0 on port 443 and deny all other traffic.
Why it's wrong here
Incorrect: This still allows traffic from the internet on port 443.
- ✓
Delete all default firewall rules and create a rule allowing ingress from the VPC's subnet range (e.g., 10.0.0.0/16) on port 443.
Why this is correct
Correct: Deleting default rules removes internet ingress and the default allow-all-internal rule. New rule restricts internal communication to port 443.
Related concept
CIDR notation defines the prefix length.
- ✗
Modify the default-allow-internal rule to only allow port 443.
Why it's wrong here
Incorrect: The default-allow-internal rule cannot be modified; it must be recreated with the desired ports.
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 ACE subnetting questions on CIDR, address ranges, and subnet selection.
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Configuring Access and Security — study guide chapter
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FAQ
Questions learners often ask
What does this ACE question test?
Configuring Access and Security — This question tests Configuring Access and Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Delete all default firewall rules and create a rule allowing ingress from the VPC's subnet range (e.g., 10.0.0.0/16) on port 443. — The default VPC includes default firewall rules that allow ingress from the internet and allow all internal traffic. To restrict communication, the engineer must first delete the default ingress rule that allows all traffic from the internet (allow-ssh, allow-icmp, allow-rdp, and allow-http/https can be deleted), then create a new rule that allows ingress only from the VPC's IP range on port 443. The default internal rule allows all traffic within the network; to restrict to port 443, a new rule with higher priority can override it, or the default rule can be deleted and a new one created.
What should I do if I get this ACE 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 ACE subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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Last reviewed: Jul 4, 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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