This 200-301 practice question tests your understanding of ip routing. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: oSPF routers must be configured with the same area ID on a shared interface to successfully form neighbor adjacencies.. 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.
Two OSPF routers connected over Ethernet fail to become neighbors. Their interfaces are up/up and in the same IPv4 subnet. One router uses area 0 and the other uses area 1 on the connecting interfaces. 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.
Mismatched OSPF process IDs
Why wrong: OSPF process IDs are locally significant and do not need to match between neighbors.
Mismatched OSPF areas on the shared link
Correct. The area mismatch is a neighbor-forming failure condition.
Missing default routes
Why wrong: Default routes are not required to establish adjacency.
Different router IDs
Why wrong: Different router IDs are expected; they must be unique, not equal.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Mismatched OSPF areas on the shared link
OSPF neighbors on the same link must agree on key parameters, including the area assigned to that interface. A mismatch prevents the adjacency from forming.
Key principle: OSPF routers must be configured with the same area ID on a shared interface to successfully form neighbor adjacencies.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Mismatched OSPF process IDs
Why it's wrong here
OSPF process IDs are locally significant and do not need to match between neighbors.
When this WOULD be correct
In a scenario where two OSPF routers are configured with the same subnet but have different OSPF process IDs and are also in the same area, a question could ask why they are unable to establish a neighbor relationship. In this case, mismatched process IDs would be the correct answer.
Mismatched OSPF areas on the shared link
Why this is correct
Correct. The area mismatch is a neighbor-forming failure condition.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF routers must be configured with the same area ID on a shared interface to successfully form neighbor adjacencies.
Missing default routes
Why it's wrong here
Default routes are not required to establish adjacency.
When this WOULD be correct
In a scenario where two routers are configured to use OSPF but are unable to reach each other due to missing default routes, a question might ask about the impact of routing on OSPF neighbor formation. In this case, if the routers cannot route packets to each other, the absence of a default route could prevent them from becoming neighbors.
Different router IDs
Why it's wrong here
Different router IDs are expected; they must be unique, not equal.
When this WOULD be correct
In a different question setup, if two OSPF routers were configured in the same area but had mismatched router IDs, the question could ask about issues in OSPF route selection or redundancy. In this case, the option would be correct if the question focused on how router IDs affect OSPF operations.
Option-by-option analysis
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
Why this is correct
Correct. The area mismatch is a neighbor-forming failure condition.
Why this is wrong here
Mismatched OSPF process IDs do not prevent OSPF routers from forming neighbor relationships if they are in the same subnet. The routers can still exchange OSPF packets; however, they will not share routing information if they are in different areas.
★ When this WOULD be the correct answer
In a scenario where two OSPF routers are configured with the same subnet but have different OSPF process IDs and are also in the same area, a question could ask why they are unable to establish a neighbor relationship. In this case, mismatched process IDs would be the correct answer.
Why candidates choose this
Candidates may mistakenly believe that OSPF process IDs are critical for establishing neighbor relationships, leading them to choose this option without fully considering the area configuration requirements.
Why this is wrong here
This option is wrong because missing default routes does not affect OSPF neighbor adjacency directly; OSPF neighbors can still form without default routes as long as they have valid OSPF configurations and are in the same subnet.
★ When this WOULD be the correct answer
In a scenario where two routers are configured to use OSPF but are unable to reach each other due to missing default routes, a question might ask about the impact of routing on OSPF neighbor formation. In this case, if the routers cannot route packets to each other, the absence of a default route could prevent them from becoming neighbors.
Why candidates choose this
Candidates may choose this option because they might confuse general routing issues with OSPF neighbor formation, thinking that routing paths are essential for neighbor relationships, leading to the assumption that missing default routes could be a factor.
Why this is wrong here
Different router IDs do not prevent OSPF routers from forming neighbor relationships; they are only used for OSPF route selection and identification. In this scenario, the routers are in different OSPF areas, which is the actual reason for the failure to become neighbors.
★ When this WOULD be the correct answer
In a different question setup, if two OSPF routers were configured in the same area but had mismatched router IDs, the question could ask about issues in OSPF route selection or redundancy. In this case, the option would be correct if the question focused on how router IDs affect OSPF operations.
Why candidates choose this
Candidates may confuse router IDs with OSPF neighbor relationships, thinking that differing IDs indicate a fundamental misconfiguration. This misunderstanding can lead them to incorrectly select this option when they see OSPF-related issues.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
A common exam trap is assuming that OSPF process IDs must match between neighbors for adjacency to form. Many candidates mistakenly focus on process ID alignment, but OSPF process IDs are locally significant and do not need to match. The real cause of adjacency failure in this scenario is the mismatch in OSPF area IDs on the shared link. This subtle difference often leads to confusion, causing candidates to overlook the critical role of area consistency in neighbor formation and select incorrect answers related to process IDs or router IDs.
Detailed technical explanation
Open Shortest Path First (OSPF) is a link-state routing protocol that establishes neighbor relationships between routers on a shared network segment to exchange routing information. For two OSPF routers to become neighbors, they must agree on several parameters, including the subnet, hello and dead intervals, authentication, and importantly, the OSPF area assigned to the interface. The area ID logically segments the OSPF domain, and routers in different areas do not form adjacencies directly on the same link. When two OSPF routers are connected over Ethernet and their interfaces are up with IP addresses in the same subnet, they still must be configured with the same OSPF area on that interface to form a neighbor adjacency. If one router’s interface is in area 0 and the other’s is in area 1, the routers will detect the mismatch during the OSPF hello packet exchange and will not progress beyond the Init or 2-Way state. This prevents the routers from exchanging link-state advertisements and building a consistent routing database. A common exam trap is confusing OSPF process IDs with areas. Process IDs are locally significant and do not need to match between neighbors, whereas area IDs must match on the shared link. In practical networks, mismatched areas on a shared segment cause adjacency failures and routing blackholes, so verifying area configuration consistency is critical for OSPF neighbor formation and stable routing.
Key takeaway
OSPF routers must be configured with the same area ID on a shared interface to successfully form neighbor adjacencies.
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 routers must be configured with the same area ID on a shared interface to successfully form neighbor adjacencies., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — study guide chapter
Learn the concepts, then practise the questions
IP Routing practice questions
Targeted practice on this topic area only
All 200-301 questions
1,819 questions across all exam domains
CCNA 200-301 v2 study guide
Full concept coverage aligned to exam objectives
200-301 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 200-301 questions linked to Network Infrastructure and Connectivity.
Practise 200-301 questions linked to Switching and Network Access.
Practise 200-301 questions linked to IP Routing.
Practise 200-301 questions linked to Network Services and Security.
Practise 200-301 questions linked to AI and Network Operations.
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
IP Routing — This question tests IP Routing — OSPF routers must be configured with the same area ID on a shared interface to successfully form neighbor adjacencies..
The correct answer is: Mismatched OSPF areas on the shared link — OSPF neighbors on the same link must agree on key parameters, including the area assigned to that interface. A mismatch prevents the adjacency from forming.
Review oSPF routers must be configured with the same area ID on a shared interface to successfully form neighbor adjacencies., then practise related 200-301 questions on the same topic to reinforce the concept.
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 routers must be configured with the same area ID on a shared interface to successfully form neighbor adjacencies.
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 →
Keep practising
Last reviewed: May 17, 2026
This 200-301 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 200-301 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.