The answer is to configure MED values on the on-premises router to prefer the us-central1 interconnect. This works because the Multi-Exit Discriminator (MED) is a BGP metric that influences inbound traffic from a neighboring AS, telling it which path to use when multiple entry points exist. By setting a lower MED on the routes advertised via the us-central1 interconnect, the on-premises network will actively send traffic through that link, while the other interconnect remains a backup, only used if the primary fails. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of BGP path selection and how to manipulate inbound traffic without changing outbound routing—a common trap is confusing MED with Local Preference, which controls outbound traffic instead. Remember: MED is for incoming traffic preference, so think “MED for my entry door.”
PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 has two Dedicated Interconnect connections to two separate Google Cloud regions for redundancy. They use Cloud Router with BGP to exchange routes. They want to ensure that traffic from on-premises to a specific VPC in us-central1 uses only the interconnect to us-central1, and the other interconnect is used only as a backup. How can they achieve this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure MED values on the on-premises router to prefer the us-central1 interconnect.
Option A is correct because Multi-Exit Discriminator (MED) is a BGP attribute used to influence inbound traffic from an AS to a specific entry point. By setting a lower MED value on the on-premises router for the routes advertised via the us-central1 interconnect, the on-premises network will prefer that path for traffic destined to the VPC in us-central1. The other interconnect will only be used if the preferred path fails, providing the desired active/backup behavior.
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.
✓
Configure MED values on the on-premises router to prefer the us-central1 interconnect.
Why this is correct
Lower MED on us-central1 interconnect will make on-premises router prefer that path.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure BGP communities on Google Cloud to prefer the us-central1 interconnect.
Why it's wrong here
BGP communities on Google Cloud affect outbound traffic from Google Cloud, not inbound from on-premises.
✗
Configure AS path prepending on the on-premises router to make the us-central1 path longer.
Why it's wrong here
AS path prepending would make the path less preferred, not more.
✗
Use Cloud Router's custom route advertisements to influence path selection.
Why it's wrong here
Cloud Router cannot influence inbound traffic; it only advertises routes to on-premises.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse MED with AS path prepending, thinking that making a path longer (prepending) increases preference, when in fact it decreases it, and they may also mistakenly believe that Google Cloud can directly influence on-premises path selection via communities or custom advertisements.
Detailed technical explanation
How to think about this question
MED is an optional non-transitive BGP attribute that is compared only when paths come from the same neighboring AS. In this scenario, both interconnects connect to Google's AS (15169), so MED values are compared. Setting a lower MED (e.g., 100) on the us-central1 interconnect and a higher MED (e.g., 200) on the other makes the on-premises router prefer the lower MED path. This is a common technique for traffic engineering in multi-homed environments, but note that MED is only considered if the 'bgp always-compare-med' command is not used, as it can cause unexpected behavior.
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.
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: Configure MED values on the on-premises router to prefer the us-central1 interconnect. — Option A is correct because Multi-Exit Discriminator (MED) is a BGP attribute used to influence inbound traffic from an AS to a specific entry point. By setting a lower MED value on the on-premises router for the routes advertised via the us-central1 interconnect, the on-premises network will prefer that path for traffic destined to the VPC in us-central1. The other interconnect will only be used if the preferred path fails, providing the desired active/backup behavior.
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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