The answer is that firewall rules are evaluated from highest priority to lowest, meaning the rule with the lowest priority number (0 to 65535) is applied first. This priority-based evaluation order ensures that the most specific rule takes precedence because administrators can assign a higher priority (lower number) to a narrowly scoped rule, making it evaluate before broader, lower-priority rules. In the Google Professional Cloud Network Engineer exam, this concept tests your understanding of how GCP resolves rule conflicts—a common trap is assuming rules are evaluated in a top-down list order or that a deny rule always overrides an allow rule. Instead, remember that once a rule matches traffic, its action is definitive and no further rules are evaluated for that traffic. A useful memory tip is to think of priority numbers like a race: the smallest number wins the race to match the traffic first, and once it does, the race is over.
PCNE Practice Question: Designing, planning, and prototyping a GCP network
This PCNE practice question tests your understanding of designing, planning, and prototyping a gcp network. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 a VPC with three subnets and multiple firewall rules. They want to ensure that the most specific firewall rule takes precedence when there is a conflict. What is the default evaluation order of firewall rules?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The rule with the highest priority (lowest priority number) is evaluated first.
In Google Cloud Platform (GCP) VPC firewall rules, the default evaluation order is based on priority. Each rule is assigned a priority number from 0 to 65535 (lower number = higher priority), and rules are evaluated from highest priority (lowest number) to lowest priority. When multiple rules match traffic, the rule with the highest priority (lowest priority number) is applied first, and its action (allow/deny) is definitive; lower-priority rules are not evaluated for that traffic.
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.
✗
Egress rules are evaluated before ingress rules.
Why it's wrong here
Ingress and egress are separate rule sets; within each, priority determines order.
✓
The rule with the highest priority (lowest priority number) is evaluated first.
Why this is correct
Lower priority number = higher priority; rules are evaluated from high to low priority.
Related concept
Read the scenario before looking for a memorised answer.
✗
The more restrictive rule (with smaller IP range) is applied first.
Why it's wrong here
Specific IP range does not determine precedence; priority does.
✗
Rules are evaluated in the order they were created.
Why it's wrong here
Creation order is irrelevant; priority is the sole determinant.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that firewall rules are evaluated based on specificity (most restrictive wins) or creation order, but GCP explicitly uses a numeric priority system where lower numbers take precedence, not the breadth of the rule's match criteria.
Detailed technical explanation
How to think about this question
Under the hood, GCP firewall rules are implemented as distributed stateful packet inspection rules within the VPC network. The priority field (0–65535) is mandatory and directly maps to the order in which rules are installed in the forwarding pipeline; a lower number means the rule is inserted earlier in the chain. In a real-world scenario, if you have a broad deny-all rule with priority 1000 and a specific allow rule for a single IP with priority 500, the allow rule (higher priority) is evaluated first, permitting that IP before the deny rule can block it—this is critical for correctly implementing least-privilege access without accidentally blocking necessary traffic.
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.
Designing, planning, and prototyping a GCP network — This question tests Designing, planning, and prototyping a GCP network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The rule with the highest priority (lowest priority number) is evaluated first. — In Google Cloud Platform (GCP) VPC firewall rules, the default evaluation order is based on priority. Each rule is assigned a priority number from 0 to 65535 (lower number = higher priority), and rules are evaluated from highest priority (lowest number) to lowest priority. When multiple rules match traffic, the rule with the highest priority (lowest priority number) is applied first, and its action (allow/deny) is definitive; lower-priority rules are not evaluated for that traffic.
What should I do if I get this PCNE 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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