The answer is mismatched hello/dead timers and mismatched area IDs. OSPF adjacency requires that both routers agree on the same hello and dead intervals, as well as the same area ID, because these parameters are included in the Hello packet and must match for neighbor discovery and state progression; if either differs, the routers will remain stuck in the INIT or EXSTART/EXCHANGE state and never reach FULL. On the Cisco DCCOR 350-601 exam, this concept tests your understanding of OSPF neighbor formation fundamentals on Nexus 9000 switches, often appearing as a multi-select troubleshooting scenario where you must identify two common causes from a list that includes MTU mismatch and network type mismatch as distractors. A common trap is assuming that only one parameter can block adjacency, but the exam expects you to recognize that both timer and area mismatches are equally frequent culprits in data center environments. Remember the memory tip: “Timers and areas must match—if either is off, the adjacency will catch.”
350-601 Network Practice Question
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 that fails to reach FULL state between two Nexus 9000 switches. Which TWO are common causes for this issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Mismatched area ID
Option B is correct because OSPF requires that both routers in a neighbor relationship belong to the same area. If the area IDs differ, the routers will not exchange routing information and the adjacency will stall at the EXSTART or EXCHANGE state, never reaching FULL. This is a fundamental OSPF neighbor requirement defined in RFC 2328.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Mismatched OSPF process ID
Why it's wrong here
OSPF process ID is local to each router and does not affect adjacency formation.
✓
Mismatched area ID
Why this is correct
OSPF neighbors must belong to the same area to form an adjacency.
Related concept
Read the scenario before looking for a memorised answer.
✗
Mismatched router ID
Why it's wrong here
Router IDs must be unique, but a mismatch does not prevent adjacency as long as they are unique.
✓
Mismatched hello/dead timers
Why this is correct
Hello and dead timers must match for OSPF neighbors to form adjacency.
Related concept
Read the scenario before looking for a memorised answer.
✗
Mismatched network type
Why it's wrong here
Network type mismatch does not prevent adjacency; timers can be adjusted to match.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that the OSPF process ID must match between neighbors, but it is only locally significant and does not affect adjacency formation.
Detailed technical explanation
How to think about this question
OSPF uses Hello packets to discover neighbors and maintain adjacencies; the Hello packet includes the area ID, and if the received area ID does not match the configured area on the receiving interface, the packet is silently dropped. The dead timer is typically four times the hello interval (default 40 seconds for broadcast networks), and even a one-second mismatch causes the adjacency to fail because routers cannot agree on the hold time for neighbor liveliness.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network — This question tests Network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Mismatched area ID — Option B is correct because OSPF requires that both routers in a neighbor relationship belong to the same area. If the area IDs differ, the routers will not exchange routing information and the adjacency will stall at the EXSTART or EXCHANGE state, never reaching FULL. This is a fundamental OSPF neighbor requirement defined in RFC 2328.
What should I do if I get this 350-601 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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 →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. 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?
medium
A.Hold timer mismatch
B.Incorrect area ID
✓ C.MTU mismatch
D.Duplicate router ID
Why C: An MTU mismatch prevents the exchange of Database Description packets, causing neighbors to remain in EXSTART. Other options cause different adjacency states.
Last reviewed: Jun 24, 2026
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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.
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