- A
Create a VPC firewall rule with priority 1000 to deny ingress on port 22 from 0.0.0.0/0.
Why wrong: The default-allow-ssh rule has priority 65534, but since it is an allow rule, a lower-priority deny rule will not override it; the allow rule will still match first.
- B
Configure a route to drop traffic destined to the instances on port 22.
Why wrong: Routes do not filter traffic; they control the path packets take. Firewall rules are used to permit or deny traffic.
- C
Remove the SSH public key from the instance metadata.
Why wrong: This prevents SSH key-based authentication but does not block the network port; SSH connections would still reach the instance and be rejected at the application layer.
- D
Disable or delete the default-allow-ssh firewall rule in the VPC.
This rule allows SSH from anywhere; disabling it stops SSH traffic from the internet.
Google ACE Configuring access and security Practice Question
This ACE practice question tests your understanding of configuring access and security. 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.
Option B is correct because the default VPC includes a default-allow-ssh firewall rule that allows SSH traffic from any source (0.0.0.0/0) on port 22. Disabling this rule will block SSH traffic. Option A is incorrect because creating a deny rule with a lower priority does not override the existing allow rule (allow rules take precedence if a matching allow rule exists). Option C is incorrect because removing SSH keys does not block network traffic. Option D is incorrect because routes control packet forwarding, not firewall filtering.
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
The default-allow-ssh rule has priority 65534, but since it is an allow rule, a lower-priority deny rule will not override it; the allow rule will still match first.
- ✗
Configure a route to drop traffic destined to the instances on port 22.
Why it's wrong here
Routes do not filter traffic; they control the path packets take. Firewall rules are used to permit or deny traffic.
- ✗
Remove the SSH public key from the instance metadata.
Why it's wrong here
This prevents SSH key-based authentication but does not block the network port; SSH connections would still reach the instance and be rejected at the application layer.
- ✓
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.
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: Disable or delete the default-allow-ssh firewall rule in the VPC. — Option B is correct because the default VPC includes a default-allow-ssh firewall rule that allows SSH traffic from any source (0.0.0.0/0) on port 22. Disabling this rule will block SSH traffic. Option A is incorrect because creating a deny rule with a lower priority does not override the existing allow rule (allow rules take precedence if a matching allow rule exists). Option C is incorrect because removing SSH keys does not block network traffic. Option D is incorrect because routes control packet forwarding, not firewall filtering.
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
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