350-601 Network Practice Question
During a network upgrade, an engineer applies a new OSPF configuration on a Nexus 9000 spine. After the change, several leaf switches lose connectivity to each other. The engineer examines the logs and sees OSPF adjacency flapping. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between 'adjacency flapping' (caused by duplicate RIDs or mismatched authentication) and 'failure to form adjacency' (caused by hello/dead timer or MTU mismatches), so candidates mistakenly choose MTU or timer issues when the symptom is flapping rather than non-formation.
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
✓
Duplicate router IDs.
Duplicate router IDs cause OSPF adjacency flapping because OSPF uses the Router ID (RID) to uniquely identify each router in the OSPF domain. When two routers share the same RID, they reject each other's Hello packets, leading to repeated adjacency resets. In a Nexus 9000 spine-leaf topology, this often occurs when the spine's RID is accidentally configured to match an existing leaf's RID, disrupting the entire fabric's OSPF 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.
- ✓
Duplicate router IDs.
Why this is correct
Duplicate router IDs cause OSPF neighbors to flap.
- ✗
OSPF hello timer mismatch.
Why it's wrong here
Hello timer mismatch would prevent adjacency from forming.
- ✗
MTU mismatch on the fabric links.
Why it's wrong here
MTU mismatch can cause problems but not typically flapping.
- ✗
Incorrect area configuration.
Why it's wrong here
Incorrect area would prevent adjacency entirely.
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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.