The answer is to update the existing Cloud Armor security policy by adding a deny rule for the IP range with priority 1000. This is the most efficient way to block requests from a specific IP range during a DDoS attack because it applies the filter at the edge of Google’s network, directly at the HTTP Load Balancer, without requiring a new policy attachment or reconfiguration. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of Cloud Armor’s rule priority system—lower numbers are evaluated first, so a priority of 1000 ensures the deny rule is processed before any allow rules. A common trap is confusing Cloud Armor with VPC firewall rules, which operate at the network layer and cannot block HTTP-level traffic, or assuming Cloud CDN can handle IP blocking. Remember the mnemonic: “Deny first, priority low—block the IP, stop the show.”
PCSE Practice Question: Managing operations in a cloud solution environment
This PCSE practice question tests your understanding of managing operations in a cloud solution environment. 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 company uses Cloud Armor to protect their HTTP Load Balancer. They want to block requests from a specific IP range during a DDoS attack. What is the most efficient way to implement this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Update the existing security policy by adding a deny rule for the IP range with priority 1000.
Option B is correct because updating the existing security policy by adding a deny rule is the quickest and most efficient way to block the IP range during an active attack. Option A is less efficient as it requires creating a new policy and reconfiguring the attachment. Option C is incorrect because firewall rules operate at the network layer and cannot block HTTP-level requests. Option D is incorrect because Cloud CDN does not provide IP blocking capabilities.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 new Cloud Armor security policy and attach it to the backend service.
Why it's wrong here
Creating a new policy is less efficient and may cause a brief gap in protection.
✗
Modify the load balancer's firewall rule to deny traffic from that IP range.
Why it's wrong here
Firewall rules affect network layer, not HTTP layer, and cannot be used to block specific requests on the load balancer.
✗
Use Cloud CDN to cache responses and block the IP at the edge.
Why it's wrong here
Cloud CDN does not have IP blocking capabilities; it only caches content.
✓
Update the existing security policy by adding a deny rule for the IP range with priority 1000.
Why this is correct
Adding a deny rule to the existing policy is immediate and efficient.
Related concept
Standard ACLs match source addresses.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCSE ACL questions on filtering logic and placement.
Managing operations in a cloud solution environment — This question tests Managing operations in a cloud solution environment — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Update the existing security policy by adding a deny rule for the IP range with priority 1000. — Option B is correct because updating the existing security policy by adding a deny rule is the quickest and most efficient way to block the IP range during an active attack. Option A is less efficient as it requires creating a new policy and reconfiguring the attachment. Option C is incorrect because firewall rules operate at the network layer and cannot block HTTP-level requests. Option D is incorrect because Cloud CDN does not provide IP blocking capabilities.
What should I do if I get this PCSE question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCSE ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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