PCNE Practice Question: Managing, Monitoring, and Optimising Network Operations
A network engineer is troubleshooting BGP session flaps between a Cloud Router and an on-premises router. The Cloud Router logs show that the session goes down and up repeatedly every few minutes. What is the most common cause of such flapping?
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
✓
The on-premises router is experiencing high CPU load
BGP session flaps often occur due to hold timer expiration caused by network congestion, high CPU on either router, or packet loss. The most common cause in GCP is when the on-premises router does not process keepalives fast enough due to high CPU or memory pressure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
There is a firewall rule blocking BGP port 179
Why it's wrong here
If blocked, the session would not establish at all, not flap.
- ✗
The VLAN attachment is misconfigured
Why it's wrong here
Misconfiguration usually causes persistent down, not intermittent flaps.
- ✓
The on-premises router is experiencing high CPU load
Why this is correct
High CPU can cause delayed keepalives, leading to hold timer expiry and flapping.
- ✗
The Cloud Router's BGP timer values are too low
Why it's wrong here
While possible, the default timers are usually fine.
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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.