PCNE Implementing Hybrid Interconnectivity Practice Question
A company has a Hybrid Connectivity setup using Cloud VPN with dynamic routing (BGP). They notice that traffic from their on-premises network to Google Cloud is intermittently dropping. The on-premises BGP speaker is sending routes with a higher local preference (200) than the Google Cloud router (default 100). What is the most likely cause of the intermittent drops?
⚠ Common exam trap
Google Cloud often tests the misconception that BGP attributes like local preference only affect inbound traffic, when in fact local preference influences outbound path selection from the router's perspective, and a mismatch between on-premises and cloud can cause asymmetric routing that stateful firewalls drop.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Asymmetric routing is causing traffic to be dropped by stateful firewalls
The on-premises BGP speaker is sending routes with a higher local preference (200) than the default on Cloud Router (100). This makes the on-premises route preferred for return traffic from Google Cloud, but the forward traffic from on-premises may still use the Cloud VPN tunnel. This asymmetry causes stateful firewalls (e.g., on-premises firewall or Google Cloud firewall) to drop packets that do not match an existing session, leading to intermittent drops.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AS path prepending is causing route flapping
Why it's wrong here
AS path prepending would affect path selection but not cause intermittent drops directly.
- ✓
Asymmetric routing is causing traffic to be dropped by stateful firewalls
Why this is correct
Higher local preference can cause asymmetric routing, leading to stateful firewall drops.
- ✗
Cloud Router is not configured for ECMP
Why it's wrong here
ECMP is not related to local preference; Cloud Router supports ECMP by default.
- ✗
The BGP MED attribute is misconfigured
Why it's wrong here
MED is used for inbound traffic; local preference affects outbound traffic.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCNE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCNE exam.