The answer is an ingress firewall rule allowing TCP port 80 from source range 0.0.0.0/0, applied to VMs with the target tag 'web-server'. This is correct because HTTP traffic from the internet must be permitted by an ingress rule, which controls incoming traffic to your VPC; specifying source 0.0.0.0/0 allows any external IP, while targeting the tag 'web-server' ensures only the designated web server VM is exposed on port 80, not every instance in the network. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of VPC firewall rules, specifically the distinction between ingress and egress, and the use of target tags for granular application. A common trap is confusing ingress with egress or omitting the source range—remember, internet traffic always requires an ingress rule with a source of 0.0.0.0/0. Memory tip: "Ingress from the internet, egress to the exit"—if traffic comes from outside, it must be an ingress rule with a wide source.
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. 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 wants to allow HTTP traffic from the internet to a web server running on a Compute Engine VM in a VPC. The web server should only be accessible on port 80. Which firewall rule should be created?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ingress rule: allow tcp:80 from 0.0.0.0/0 (target tags: web-server)
Option B is correct because HTTP traffic from the internet (source 0.0.0.0/0) must be allowed by an ingress firewall rule targeting the web server VM. The rule specifies TCP port 80, which is the standard HTTP port, and uses target tags 'web-server' to apply the rule only to VMs with that tag, ensuring the web server is accessible on port 80 from any source.
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 rule: allow tcp:80 from 0.0.0.0/0 (target tags: web-server)
Why it's wrong here
Egress rules control outgoing traffic, not incoming.
✓
Ingress rule: allow tcp:80 from 0.0.0.0/0 (target tags: web-server)
Why this is correct
Correct: Ingress, port 80, any source, target tag 'web-server'.
Related concept
Read the scenario before looking for a memorised answer.
✗
Ingress rule: allow tcp:443 from 0.0.0.0/0 (target tags: web-server)
Ingress rule: allow tcp:80 from 0.0.0.0/0 (target tags: default)
Why it's wrong here
The 'default' tag is applied to all VMs but may include unintended instances; use a specific tag.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between ingress and egress rules, and the trap here is that candidates may confuse the direction of traffic (ingress for inbound, egress for outbound) or select a rule with the wrong port (e.g., 443 instead of 80) or incorrect target tags (e.g., 'default' instead of 'web-server').
Detailed technical explanation
How to think about this question
In Google Cloud VPC, firewall rules are stateful: if an ingress rule allows traffic, the corresponding egress response traffic is automatically permitted without an explicit egress rule. Target tags provide a flexible way to apply rules to specific VM instances based on their network tags, which are set at instance creation or modification. The source range 0.0.0.0/0 represents all IPv4 addresses, making the web server publicly accessible, which is appropriate for a public-facing HTTP server.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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.
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Ingress rule: allow tcp:80 from 0.0.0.0/0 (target tags: web-server) — Option B is correct because HTTP traffic from the internet (source 0.0.0.0/0) must be allowed by an ingress firewall rule targeting the web server VM. The rule specifies TCP port 80, which is the standard HTTP port, and uses target tags 'web-server' to apply the rule only to VMs with that tag, ensuring the web server is accessible on port 80 from any source.
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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