PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. 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.
A company connects their on-premises data center to Google Cloud via Dedicated Interconnect. They have two VLAN attachments (VLAN-A and VLAN-B) to a single VPC. They use BGP over the VLAN attachments with Cloud Router. Both VLAN attachments are in the same region. They want to use both links for active-active traffic and have redundancy. Which BGP configuration is correct?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the same BGP ASN and same MED for both VLAN attachments, and enable ECMP on Cloud Router.
For active-active traffic with two VLAN attachments to the same VPC in the same region, you must use the same BGP ASN on both sessions and enable ECMP (Equal Cost Multi-Path) on Cloud Router. This allows Cloud Router to install multiple equal-cost routes from both BGP sessions, enabling load balancing across both links. Using the same MED value ensures the routes are considered equal, which is required for ECMP to function correctly.
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.
✗
Use a different BGP ASN for each VLAN attachment.
Why it's wrong here
Incorrect: different ASNs would require different BGP sessions and not achieve ECMP.
✗
Use a single VLAN attachment and rely on link redundancy.
Why it's wrong here
Incorrect: single attachment is not redundant.
✗
Set different MED values for each BGP session to load-balance.
Why it's wrong here
Incorrect: different MED values would prefer one path over the other, not active-active.
✓
Use the same BGP ASN and same MED for both VLAN attachments, and enable ECMP on Cloud Router.
Why this is correct
Correct: this allows equal-cost multipath, active-active.
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 misconception that different BGP ASNs or MED values are needed for load balancing, but in Google Cloud's Dedicated Interconnect with Cloud Router, active-active requires identical ASN and MED plus explicit ECMP enablement.
Detailed technical explanation
How to think about this question
Cloud Router uses BGP multipath (ECMP) to load-balance traffic across multiple VLAN attachments when the BGP routes have the same AS_PATH length, MED, and local preference. Under the hood, Cloud Router installs up to 4 equal-cost paths per prefix, distributing traffic via flow-based hashing (e.g., 5-tuple). In a real-world scenario, if one VLAN attachment experiences higher latency or jitter, ECMP still distributes flows equally, which may require additional tuning like BGP link-bandwidth or traffic engineering for optimal utilization.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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: Use the same BGP ASN and same MED for both VLAN attachments, and enable ECMP on Cloud Router. — For active-active traffic with two VLAN attachments to the same VPC in the same region, you must use the same BGP ASN on both sessions and enable ECMP (Equal Cost Multi-Path) on Cloud Router. This allows Cloud Router to install multiple equal-cost routes from both BGP sessions, enabling load balancing across both links. Using the same MED value ensures the routes are considered equal, which is required for ECMP to function correctly.
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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