- A
Modify the existing deny rule to include an exception for the VPN IP in the source IP field.
Why wrong: Firewall rules do not support exceptions in source IPs; you need multiple rules.
- B
Delete the deny rule and create a single rule that denies all IPs except the VPN IP using the 'except' option.
Why wrong: Firewall rules do not have an 'except' source IP option; you must use multiple rules.
- C
Create a new allow rule with priority 500, source IP 203.0.113.1/32, target 'web-server', and action allow.
This allow rule has higher priority (lower number) than the deny rule, so traffic from the VPN IP will be allowed before the deny rule applies.
- D
Change the priority of the existing deny rule to 1 and create an allow rule with priority 2 for the VPN IP.
Why wrong: Priority 1 would deny everything first, making the allow rule at priority 2 ineffective.
PCNE Implementing VPC Instances Practice Question
This PCNE practice question tests your understanding of implementing vpc instances. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 network engineer needs to create a firewall rule that blocks all ingress traffic from the internet to Compute Engine instances tagged 'web-server', except for traffic from the organization's VPN gateway at IP 203.0.113.1. The engineer creates a rule with priority 1000, deny ingress, source IP ranges 0.0.0.0/0, and targets 'web-server'. To allow the VPN IP, what should the engineer do?
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
Create a new allow rule with priority 500, source IP 203.0.113.1/32, target 'web-server', and action allow.
Firewall rules are evaluated in order of priority (lower number = higher priority). The deny rule at priority 1000 will deny all IPs. To allow the VPN IP, a higher priority (lower number) allow rule must be created for that specific IP, before the deny rule is evaluated. The correct approach is to create an allow rule with priority 100 (or any lower number) for source IP 203.0.0.0/8 (or the specific IP) targeting web-server.
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.
- ✗
Modify the existing deny rule to include an exception for the VPN IP in the source IP field.
- ✗
Delete the deny rule and create a single rule that denies all IPs except the VPN IP using the 'except' option.
Why it's wrong here
Firewall rules do not have an 'except' source IP option; you must use multiple rules.
- ✓
Create a new allow rule with priority 500, source IP 203.0.113.1/32, target 'web-server', and action allow.
Why this is correct
This allow rule has higher priority (lower number) than the deny rule, so traffic from the VPN IP will be allowed before the deny rule applies.
Related concept
Standard ACLs match source addresses.
- ✗
Change the priority of the existing deny rule to 1 and create an allow rule with priority 2 for the VPN IP.
Why it's wrong here
Priority 1 would deny everything first, making the allow rule at priority 2 ineffective.
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
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 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 PCNE ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this PCNE question test?
Implementing VPC Instances — This question tests Implementing VPC Instances — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Create a new allow rule with priority 500, source IP 203.0.113.1/32, target 'web-server', and action allow. — Firewall rules are evaluated in order of priority (lower number = higher priority). The deny rule at priority 1000 will deny all IPs. To allow the VPN IP, a higher priority (lower number) allow rule must be created for that specific IP, before the deny rule is evaluated. The correct approach is to create an allow rule with priority 100 (or any lower number) for source IP 203.0.0.0/8 (or the specific IP) targeting web-server.
What should I do if I get this PCNE 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 PCNE ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
About these practice questions
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Last reviewed: Jul 4, 2026
This PCNE 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 PCNE exam.
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