The answer is to check the rule direction—specifically whether it is set to ingress or egress. This is correct because a firewall rule configured to allow HTTP traffic from a source IP range will only apply to incoming requests if its direction is ingress; if the rule is accidentally set to egress, it governs outbound traffic leaving the VPC network, leaving the incoming HTTP requests blocked by the implied deny ingress rule. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of how VPC firewall rule direction controls traffic flow, a common trap where engineers focus on source IPs or ports while overlooking the direction toggle. A frequent mistake is assuming an allow rule applies universally, but direction is the gatekeeper. Remember the memory tip: "Ingress is for guests coming in, egress is for guests leaving."
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network 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 company has configured a VPC firewall rule to allow HTTP traffic from a specific source IP range 203.0.113.0/24. However, HTTP requests from that range are being denied. Which initial verification should the security engineer perform?
Check if the source range overlaps with a deny rule
Why wrong: Overlapping ranges could cause issues, but the first step is to confirm the direction is correct.
B
Check if the target instances have the correct network tag
Why wrong: If the rule has no target tags, it applies to all instances. Tags are not the primary issue here.
C
Check the rule priority
Why wrong: Priority affects order but a higher priority allow rule should override a lower priority deny. Typically priority is not the first thing to check.
D
Check the rule direction (ingress vs egress)
A firewall rule must be ingress to allow incoming traffic. If it is egress, it won't allow inbound connections.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check the rule direction (ingress vs egress)
Option D is correct because the rule is configured to allow HTTP traffic, but if the rule direction is set to egress instead of ingress, it will not apply to incoming HTTP requests from the source IP range. In Google Cloud VPC firewall rules, direction determines whether the rule applies to inbound (ingress) or outbound (egress) traffic; an egress rule only controls traffic leaving the VPC network, so HTTP requests arriving from the internet would be denied by the implied deny ingress rule.
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.
✗
Check if the source range overlaps with a deny rule
Why it's wrong here
Overlapping ranges could cause issues, but the first step is to confirm the direction is correct.
✗
Check if the target instances have the correct network tag
Why it's wrong here
If the rule has no target tags, it applies to all instances. Tags are not the primary issue here.
✗
Check the rule priority
Why it's wrong here
Priority affects order but a higher priority allow rule should override a lower priority deny. Typically priority is not the first thing to check.
✓
Check the rule direction (ingress vs egress)
Why this is correct
A firewall rule must be ingress to allow incoming traffic. If it is egress, it won't allow inbound connections.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that firewall rules are automatically bidirectional or that source IP range alone guarantees traffic flow, when in fact the direction attribute must match the traffic path (ingress for incoming requests).
Detailed technical explanation
How to think about this question
Google Cloud VPC firewall rules are stateful and evaluated based on direction, priority, and match conditions. An ingress rule with source range 203.0.113.0/24 and allow tcp:80 will permit HTTP requests, but if the rule is mistakenly created as egress, it will only apply to outbound traffic from VMs to that range, leaving the default implicit deny ingress rule to block the incoming requests. This is a common misconfiguration because the console defaults to egress when creating rules, and engineers often overlook the direction field.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Configuring network security — This question tests Configuring network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Check the rule direction (ingress vs egress) — Option D is correct because the rule is configured to allow HTTP traffic, but if the rule direction is set to egress instead of ingress, it will not apply to incoming HTTP requests from the source IP range. In Google Cloud VPC firewall rules, direction determines whether the rule applies to inbound (ingress) or outbound (egress) traffic; an egress rule only controls traffic leaving the VPC network, so HTTP requests arriving from the internet would be denied by the implied deny ingress rule.
What should I do if I get this PCSE 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.
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Question Discussion
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