- A
Create an ingress rule with source 0.0.0.0/0, protocol tcp:0-65535, and target tags 'web-server'.
Why wrong: This would allow all TCP ports, which is overly permissive.
- B
Create an egress rule with source 0.0.0.0/0, tcp:80, and target tags 'web-server'.
Why wrong: Egress rules control outbound traffic; for incoming traffic, ingress rule is needed.
- C
Create an ingress rule with source 0.0.0.0/0, tcp:80, and target tags 'web-server'.
This single ingress rule allows HTTP from any source to instances tagged 'web-server'.
- D
Create an ingress rule for each subnet with source 0.0.0.0/0, tcp:80, and target tags 'web-server'.
Why wrong: Unnecessary duplication; a single global rule with target tags applies to all matching instances.
Question 736 of 982
PCNE Implementing VPC Instances Practice Question
This PCNE practice question tests your understanding of implementing vpc instances. 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.
You need to configure firewall rules to allow HTTP (TCP 80) traffic from the internet to instances in a VPC. The instances are in different subnets and have a network tag 'web-server'. You want to minimize the number of rules. Which rule configuration is correct?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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 an ingress rule with source 0.0.0.0/0, tcp:80, and target tags 'web-server'.
Firewall rules are global, so one ingress rule can apply to all instances with the tag 'web-server' regardless of subnet. The direction must be ingress, source 0.0.0.0/0, protocol tcp:80, and target tags 'web-server'.
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 an ingress rule with source 0.0.0.0/0, protocol tcp:0-65535, and target tags 'web-server'.
Why it's wrong here
This would allow all TCP ports, which is overly permissive.
- ✗
Create an egress rule with source 0.0.0.0/0, tcp:80, and target tags 'web-server'.
Why it's wrong here
Egress rules control outbound traffic; for incoming traffic, ingress rule is needed.
- ✓
Create an ingress rule with source 0.0.0.0/0, tcp:80, and target tags 'web-server'.
- ✗
Create an ingress rule for each subnet with source 0.0.0.0/0, tcp:80, and target tags 'web-server'.
Why it's wrong here
Unnecessary duplication; a single global rule with target tags applies to all matching instances.
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
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.
Visual reference
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 PCNE subnetting questions on CIDR, address ranges, and subnet selection.
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Implementing VPC Instances — study guide chapter
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FAQ
Questions learners often ask
What does this PCNE question test?
Implementing VPC Instances — This question tests Implementing VPC Instances — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create an ingress rule with source 0.0.0.0/0, tcp:80, and target tags 'web-server'. — Firewall rules are global, so one ingress rule can apply to all instances with the tag 'web-server' regardless of subnet. The direction must be ingress, source 0.0.0.0/0, protocol tcp:80, and target tags 'web-server'.
What should I do if I get this PCNE 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 PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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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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