The answer is to set the same MED value on both on-premises BGP peers while ensuring identical AS path length. This configuration works because BGP’s best-path selection algorithm on Google Cloud’s active/active Cloud Routers will view both VLAN attachments as equally preferred when the MED and AS path are identical, enabling ECMP load balancing across the Dedicated Interconnect. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of how to force equal-cost multipath over multiple attachments, a common trap being that simply enabling active/active BGP is insufficient without matching these path attributes. A key memory tip is “Same MED, Same AS Path” — think of it as telling the Cloud Router, “These two roads are exactly the same length, so split the traffic evenly.”
PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. 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 is using Dedicated Interconnect to connect their on-premises network to Google Cloud. They have two VLAN attachments configured, each with a separate Cloud Router with active/active BGP. They want to ensure that traffic from their on-premises network to Google Cloud uses both attachments equally. Which configuration 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
✓
Set the same MED value on both on-premises BGP peers, and ensure the AS path length is identical.
Option A is correct because setting the same MED (Multi-Exit Discriminator) value on both on-premises BGP peers ensures that Google Cloud's Cloud Routers, which are configured with active/active BGP, will see both paths as equally preferred. When the AS path length is also identical, the BGP best-path selection algorithm on the Cloud Routers will load-balance traffic across both VLAN attachments, achieving equal utilization. This is the standard method for enabling equal-cost multipath (ECMP) over Dedicated Interconnect with multiple attachments.
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.
✓
Set the same MED value on both on-premises BGP peers, and ensure the AS path length is identical.
Why this is correct
Equal MED and AS path length enables ECMP, balancing traffic across both attachments.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure local preference on the Cloud Router to prefer one attachment, and rely on the other for backup.
Why it's wrong here
This only affects outbound traffic from GCP, not inbound.
✗
Configure a single BGP session on one Cloud Router and use static routing for the other attachment.
Why it's wrong here
This reduces redundancy and does not balance traffic.
✗
Set a higher MED value on one on-premises peer to deprefer that attachment.
Why it's wrong here
This would make one path less preferred, not equalize.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume MED is only for influencing inbound traffic from Google Cloud to on-premises, but in this scenario, the MED values are set on the on-premises peers to influence how Google Cloud selects the return path, and equal MED is required for ECMP to work.
Detailed technical explanation
How to think about this question
Under the hood, BGP ECMP (Equal-Cost Multipath) requires that all path attributes (including MED, AS path length, local preference, and origin code) are identical for the routes to be considered equal. In Google Cloud, Cloud Routers with active/active BGP automatically install multiple paths into the routing table when they meet these criteria, enabling per-packet or per-flow load balancing across VLAN attachments. A real-world scenario where this matters is when an enterprise has two redundant 10 Gbps interconnects and needs to fully utilize both links to avoid underutilization and meet bandwidth demands.
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.
Implementing hybrid interconnectivity — This question tests Implementing hybrid interconnectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set the same MED value on both on-premises BGP peers, and ensure the AS path length is identical. — Option A is correct because setting the same MED (Multi-Exit Discriminator) value on both on-premises BGP peers ensures that Google Cloud's Cloud Routers, which are configured with active/active BGP, will see both paths as equally preferred. When the AS path length is also identical, the BGP best-path selection algorithm on the Cloud Routers will load-balance traffic across both VLAN attachments, achieving equal utilization. This is the standard method for enabling equal-cost multipath (ECMP) over Dedicated Interconnect with multiple attachments.
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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