This 350-601 practice question tests your understanding of network. 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 network engineer is troubleshooting an OSPF adjacency issue between two Nexus switches. The neighbors are stuck in the EXSTART state. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Hold timer mismatch
Why wrong: Hold timer mismatch causes adjacency to go down, not stuck in EXSTART.
Incorrect area ID
Why wrong: Area ID mismatch prevents neighbor discovery, not EXSTART.
MTU mismatch
MTU mismatch leads to DBD packet rejection, keeping the neighbor in EXSTART.
Duplicate router ID
Why wrong: Duplicate router IDs prevent adjacency formation entirely, not just EXSTART.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
MTU mismatch
An MTU mismatch prevents the exchange of Database Description packets, causing neighbors to remain in EXSTART. Other options cause different adjacency states.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Hold timer mismatch
Why it's wrong here
Hold timer mismatch causes adjacency to go down, not stuck in EXSTART.
Incorrect area ID
Why it's wrong here
Area ID mismatch prevents neighbor discovery, not EXSTART.
MTU mismatch
Duplicate router ID
Why it's wrong here
Duplicate router IDs prevent adjacency formation entirely, not just EXSTART.
Common exam traps
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-601 OSPF questions on adjacency and route selection.
Network — study guide chapter
Learn the concepts, then practise the questions
Network practice questions
Targeted practice on this topic area only
All 350-601 questions
500 questions across all exam domains
Cisco DCCOR / CCNP Data Center Core 350-601 study guide
Full concept coverage aligned to exam objectives
350-601 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise 350-601 questions linked to Network.
Practise 350-601 questions linked to Compute.
Practise 350-601 questions linked to Storage Network.
Practise 350-601 questions linked to Automation.
Practise 350-601 questions linked to Security.
Practise 350-601 questions linked to 350-601 fundamentals.
Practise 350-601 questions linked to 350-601 scenario.
Practise 350-601 questions linked to 350-601 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Network — This question tests Network — OSPF neighbours must agree on key parameters..
The correct answer is: MTU mismatch — An MTU mismatch prevents the exchange of Database Description packets, causing neighbors to remain in EXSTART. Other options cause different adjacency states.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-601 OSPF questions on adjacency and route selection.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
OSPF neighbours must agree on key parameters.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 24, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.