The answer is to create a packet mirroring policy that copies traffic from the VM to the NIDS instance. This is correct because packet mirroring, also known as VPC Traffic Mirroring, duplicates all ingress and egress traffic from the VM’s elastic network interface (ENI) to the NIDS appliance without altering the original packet flow or impacting VM performance. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of how to perform passive network monitoring in a VPC without introducing a inline bottleneck or single point of failure. A common trap is choosing a proxy or load balancer, which would intercept and modify traffic, whereas packet mirroring is purely a copy operation. Remember the key distinction: mirroring copies, forwarding changes. For exam day, think “mirror = copy, not intercept” to avoid confusing it with a forwarding or routing solution.
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring 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 security team wants to mirror all traffic from a critical VM to a network intrusion detection system (NIDS) appliance running in the same VPC. They need to ensure that the NIDS receives both ingress and egress traffic, and that the original traffic is not impacted. Which solution should they implement?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a packet mirroring policy that mirrors traffic from the VM to the NIDS instance.
Packet mirroring (also known as VPC Traffic Mirroring) is the correct solution because it copies all ingress and egress traffic from the VM's elastic network interface (ENI) to the NIDS instance without affecting the original traffic flow. This is achieved by creating a mirror filter and session that forwards a copy of the packets to the NIDS, ensuring the VM's performance and connectivity remain unchanged.
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.
✗
Apply a network tag to the VM and create a firewall rule to copy traffic to the NIDS.
Configure the VM to use the NIDS as a proxy for all traffic.
Why it's wrong here
Incorrect: proxy changes traffic path and adds latency.
✗
Enable VPC Flow Logs on the VM's subnet and forward logs to the NIDS.
Why it's wrong here
Incorrect: Flow Logs only contain metadata, not full packets.
✓
Create a packet mirroring policy that mirrors traffic from the VM to the NIDS instance.
Why this is correct
Correct: Packet Mirroring copies packets for inspection without affecting live traffic.
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 distinction between traffic mirroring (which copies packets) and flow logs (which only log metadata), leading candidates to mistakenly choose VPC Flow Logs because they assume 'logs' provide full traffic visibility.
Detailed technical explanation
How to think about this question
Packet mirroring works by creating a mirror session that specifies a source (the VM's ENI), a filter (e.g., all traffic or specific protocols), and a target (the NIDS ENI or a Network Load Balancer). The VPC infrastructure uses a packet broker to duplicate packets at the hypervisor level, ensuring zero performance impact on the source VM. In real-world scenarios, this is critical for compliance (e.g., PCI DSS) where full packet capture is required without disrupting production 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
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.
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: Create a packet mirroring policy that mirrors traffic from the VM to the NIDS instance. — Packet mirroring (also known as VPC Traffic Mirroring) is the correct solution because it copies all ingress and egress traffic from the VM's elastic network interface (ENI) to the NIDS instance without affecting the original traffic flow. This is achieved by creating a mirror filter and session that forwards a copy of the packets to the NIDS, ensuring the VM's performance and connectivity remain unchanged.
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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