- A
Create a VPC firewall rule with priority 1000 to deny ingress on port 22 from 0.0.0.0/0.
Why wrong: Creating a VPC firewall rule with priority 1000 to deny ingress on port 22 from 0.0.0.0/0 would technically work because priority 1000 is higher than the default rule's priority of 65534, so the deny rule would take precedence. However, the simplest and most standard practice is to remove the unnecessary allow rule as in option D.
- B
Configure a route to drop traffic destined to the instances on port 22.
Why wrong: Routes do not filter traffic. A route can direct traffic but cannot drop it, so this option is incorrect.
- C
Remove the SSH public key from the instance metadata.
Why wrong: Removing the SSH public key from instance metadata does not block network traffic; it only removes the ability to authenticate using that key. The firewall still allows SSH connections.
- D
Disable or delete the default-allow-ssh firewall rule in the VPC.
Disabling or deleting the default-allow-ssh firewall rule directly stops SSH traffic from the internet because that rule is what permits it. This is the correct action.
Google ACE Practice Question: A small business has a single Google Cloud…
This ACE practice question tests your understanding of ace exam topics. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 has a single Google Cloud project with a few Compute Engine instances running a web application. The instances are all in the same VPC and subnet. The security team wants to ensure that only HTTP (port 80) and HTTPS (port 443) traffic from the public internet is allowed to the instances, and that all other inbound traffic is blocked. They have already configured Cloud Armor for the load balancer. However, they notice that SSH traffic (port 22) is still reaching the instances from the internet, even though they do not have any explicit firewall rules allowing SSH. The project was just created and uses the default VPC network. What should they do to resolve this?
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
Disable or delete the default-allow-ssh firewall rule in the VPC.
The correct answer is D. The default VPC includes a 'default-allow-ssh' firewall rule that allows TCP port 22 from 0.0.0.0/0. Disabling or deleting this rule directly stops SSH traffic from the internet. Option A (creating a deny rule with priority 1000) would technically work because 1000 is a higher priority than the default rule's priority (65534), but the simplest and most standard practice is to remove the unnecessary allow rule. Option B is incorrect because routes do not filter traffic. Option C is incorrect because removing SSH keys does not block network traffic.
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 VPC firewall rule with priority 1000 to deny ingress on port 22 from 0.0.0.0/0.
Why it's wrong here
Creating a VPC firewall rule with priority 1000 to deny ingress on port 22 from 0.0.0.0/0 would technically work because priority 1000 is higher than the default rule's priority of 65534, so the deny rule would take precedence. However, the simplest and most standard practice is to remove the unnecessary allow rule as in option D.
- ✗
Configure a route to drop traffic destined to the instances on port 22.
Why it's wrong here
Routes do not filter traffic. A route can direct traffic but cannot drop it, so this option is incorrect.
- ✗
Remove the SSH public key from the instance metadata.
- ✓
Disable or delete the default-allow-ssh firewall rule in the VPC.
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.
Visual reference
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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FAQ
Questions learners often ask
What does this ACE question test?
CIDR notation defines the prefix length.
What is the correct answer to this question?
The correct answer is: Disable or delete the default-allow-ssh firewall rule in the VPC. — The correct answer is D. The default VPC includes a 'default-allow-ssh' firewall rule that allows TCP port 22 from 0.0.0.0/0. Disabling or deleting this rule directly stops SSH traffic from the internet. Option A (creating a deny rule with priority 1000) would technically work because 1000 is a higher priority than the default rule's priority (65534), but the simplest and most standard practice is to remove the unnecessary allow rule. Option B is incorrect because routes do not filter traffic. Option C is incorrect because removing SSH keys does not block network traffic.
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: Jun 23, 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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