350-601 Network Practice Question
After adding a new spine switch to a VXLAN EVPN fabric with OSPF underlay, some leaf switches experience routing instability. Which action could resolve the instability?
⚠ Common exam trap
Cisco often tests the misconception that routing instability is caused by security or timer issues, when in fact it is typically due to unequal cost paths causing SPF thrashing after a new device is added.
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
✓
Increase the OSPF cost on the leaf-to-spine links.
When a new spine switch is added to a VXLAN EVPN fabric with an OSPF underlay, the leaf switches may experience routing instability because the new spine advertises routes with a lower cost, causing traffic to shift abruptly. Increasing the OSPF cost on the leaf-to-spine links makes those paths less preferred, stabilizing the routing table by preventing flapping and ensuring a more gradual convergence.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Increase the OSPF cost on the leaf-to-spine links.
Why this is correct
Higher cost makes the new spine less preferred, stabilizing routing.
- ✗
Configure OSPF neighbor authentication.
Why it's wrong here
Authentication adds security but does not affect stability from equal-cost paths.
- ✗
Decrease the OSPF hello timer.
Why it's wrong here
Decreasing hello timer may increase load and worsen instability.
- ✗
Enable OSPF route summarization on the leaves.
Why it's wrong here
Summarization reduces route size but does not prevent flap from equal-cost paths.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-601 practice question is part of Courseiva's free Cisco 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 350-601 exam.