The answer is an OSPF network type mismatch between the interfaces. This is the most likely cause of an OSPF adjacency failure when both routers share the same process ID and area, and Layer 3 connectivity is verified, because OSPF uses different hello and dead timers and neighbor discovery mechanisms depending on the configured network type—for example, a point-to-point interface expects a direct neighbor relationship without a DR/BDR election, while a broadcast interface requires a designated router election and uses multicast hellos every 10 seconds, causing a fundamental incompatibility that prevents the routers from reaching the FULL state. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of OSPF operational behavior beyond basic configuration; a common trap is to suspect an MTU mismatch, but that issue only disrupts LSA exchange after the adjacency forms, not the initial neighbor establishment. A reliable memory tip is to remember that network types dictate hello timers and DR election rules—if the timers or election logic don’t match, the adjacency simply won’t form.
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. 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 failure between two directly connected routers, R1 and R2. Both routers are configured with the same OSPF process ID and area. The engineer verifies that the interfaces are up and IP connectivity exists. Which configuration mismatch is most likely causing the adjacency to fail?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
OSPF network type mismatch between the interfaces
Option C is correct because OSPF network type mismatch, such as one side configured as point-to-point and the other as broadcast, prevents adjacency formation. Option A is wrong because an MTU mismatch would cause the adjacency to form but show problems during LSA exchange. Option B is wrong because area mismatch would cause a mismatch in area ID. Option D is wrong because a passive interface would allow the neighbor to be seen but not become full.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
MTU mismatch between the interfaces
Why it's wrong here
MTU mismatch causes OSPF packets to be silently dropped, but the adjacency may still reach the EXCHANGE state before failing.
✗
Passive interface configuration on one router
Why it's wrong here
Passive interface prevents sending hellos, so the neighbor would not be discovered at all.
✗
Area ID mismatch on the interfaces
Why it's wrong here
Area ID mismatch would result in a different area and the adjacency would not form due to area mismatch.
✓
OSPF network type mismatch between the interfaces
Why this is correct
Network type mismatch (e.g., broadcast vs. point-to-point) causes the routers to disagree on DR/BDR election and hello behavior, preventing adjacency.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Common exam trap: OSPF can fail even when IP connectivity looks correct
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
How to think about this question
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.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
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
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.
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 350-501 OSPF questions on adjacency and route selection.
Networking — This question tests Networking — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: OSPF network type mismatch between the interfaces — Option C is correct because OSPF network type mismatch, such as one side configured as point-to-point and the other as broadcast, prevents adjacency formation. Option A is wrong because an MTU mismatch would cause the adjacency to form but show problems during LSA exchange. Option B is wrong because area mismatch would cause a mismatch in area ID. Option D is wrong because a passive interface would allow the neighbor to be seen but not become full.
What should I do if I get this 350-501 question wrong?
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 350-501 OSPF questions on adjacency and route selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
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 →
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.
This 350-501 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 350-501 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.