Quick Answer
The answer is a hello and dead timer mismatch, as this is the most common cause of an OSPF neighbor being stuck in the INIT state. When R1 sees R2’s Hello packets but cannot move to 2-WAY, it means R1 received the packets but found a mismatch in a required OSPF parameter—most frequently the hello or dead interval. Unlike MTU mismatches, which halt adjacency during the Exstart/Exchange phase, timer mismatches prevent the initial neighbor relationship from forming at all. On the CCNA 200-301 v2 exam, this question tests your ability to differentiate between OSPF states and their associated failure points; a common trap is confusing INIT with EXSTART or EXCHANGE problems. Remember that INIT means “I heard you, but you don’t match my settings.” A quick memory tip: “INIT = I Need It Timed” — if timers don’t match, you stay stuck in INIT.
This 200-301 practice question tests your understanding of ip routing. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: oSPF routers must have matching hello and dead timers on interfaces 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.
R1 G0/0: ip 10.1.12.1/30, ip ospf hello-interval 10, ip ospf dead-interval 40 R2 G0/0: ip 10.1.12.2/30, ip ospf hello-interval 5, ip ospf dead-interval 20 Both interfaces are up/up and in area 0.
R1 and R2 are directly connected via Ethernet on interface G0/0. Both interfaces are in the same subnet and configured for OSPF area 0. After enabling OSPF, R1's G0/0 is stuck in the INIT state in the OSPF neighbor table. 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.
R1 G0/0: ip 10.1.12.1/30, ip ospf hello-interval 10, ip ospf dead-interval 40 R2 G0/0: ip 10.1.12.2/30, ip ospf hello-interval 5, ip ospf dead-interval 20 Both interfaces are up/up and in area 0.
MTU mismatch
Why wrong: Distractor.
Hello and dead timer mismatch
Correct choice.
Missing router ID on both routers
Why wrong: Distractor.
A duplicate static route to 10.1.12.0/30
Why wrong: Distractor.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Hello and dead timer mismatch
Being stuck in the INIT state means R1 has received Hello packets from R2 but has not transitioned to the 2-WAY state. This most often occurs when critical OSPF parameters like the hello and dead timers do not match. An MTU mismatch, while problematic, would cause the adjacency to fail during database exchange (Exstart/Exchange), not during initial neighbor formation. Missing router IDs are not a real issue because routers auto-generate them, and a duplicate static route to the connected subnet would not affect OSPF neighbor discovery.
Key principle: OSPF routers must have matching hello and dead timers on interfaces 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.
MTU mismatch
Why it's wrong here
Distractor.
When this WOULD be correct
In a different scenario where the question specifies that both routers are configured with different MTU sizes, and the OSPF packets exceed the smaller MTU, this option would be correct. For example, if R1 has an MTU of 1500 and R2 has an MTU of 1400, this could lead to adjacency issues.
Hello and dead timer mismatch
Why this is correct
Correct choice.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF routers must have matching hello and dead timers on interfaces to successfully form neighbor adjacencies.
Missing router ID on both routers
Why it's wrong here
Distractor.
A duplicate static route to 10.1.12.0/30
Why it's wrong here
Distractor.
When this WOULD be correct
In a scenario where the question specifies that R1 and R2 are using static routing instead of OSPF, and both routers have a duplicate static route configured for the same destination, this could lead to routing conflicts. The question would need to focus on static routing behavior rather than OSPF adjacency.
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 choice.
Why this is wrong here
An MTU mismatch would typically prevent OSPF packets from being successfully transmitted, but it does not directly cause an adjacency failure. OSPF can still establish adjacency if the MTU is mismatched, as long as the packets are small enough to be transmitted.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that both routers are configured with different MTU sizes, and the OSPF packets exceed the smaller MTU, this option would be correct. For example, if R1 has an MTU of 1500 and R2 has an MTU of 1400, this could lead to adjacency issues.
Why candidates choose this
Candidates may choose this option because they associate MTU mismatches with connectivity issues in networking, leading them to believe it could be a plausible cause for OSPF adjacency failures.
Why this is wrong here
This option is wrong because a missing router ID does not prevent OSPF adjacency formation; it only affects OSPF routing. OSPF can still establish adjacencies without a router ID, as it will generate a default one if not configured.
★ When this WOULD be the correct answer
In a different question, if the scenario described routers that were configured to use OSPF but had no router ID set, and the question asked why OSPF routes were not being advertised, then this option would be correct as it directly impacts OSPF operation.
Why candidates choose this
Candidates may choose this option because they associate router IDs with OSPF functionality and believe that a missing router ID would inherently disrupt OSPF operations, leading to adjacency issues.
Why this is wrong here
A duplicate static route to 10.1.12.0/30 would not prevent R1 and R2 from forming an OSPF adjacency, as OSPF does not rely on static routes for neighbor relationships. OSPF adjacency issues are typically related to configuration mismatches rather than routing table entries.
★ When this WOULD be the correct answer
In a scenario where the question specifies that R1 and R2 are using static routing instead of OSPF, and both routers have a duplicate static route configured for the same destination, this could lead to routing conflicts. The question would need to focus on static routing behavior rather than OSPF adjacency.
Why candidates choose this
Candidates might choose this option because they associate routing issues with static routes and believe that any routing conflict could disrupt OSPF operations, even though this is not the case.
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 selecting MTU mismatch or missing router IDs as the cause of OSPF adjacency failure. While MTU mismatches can cause adjacency issues during database exchange, they do not prevent the initial neighbor relationship from forming. Missing router IDs do not block adjacency because routers automatically generate IDs if none are configured. Another trap is confusing static routes with neighbor discovery; static routes do not influence OSPF adjacency. The key is to focus on timer mismatches, as hello and dead intervals must be identical for routers to recognize each other as neighbors and establish adjacency.
Detailed technical explanation
OSPF (Open Shortest Path First) is a link-state routing protocol that relies on neighbor adjacencies to exchange routing information. Routers send hello packets at regular intervals to discover neighbors and maintain adjacency. The hello interval defines how often these packets are sent, while the dead interval specifies how long a router waits without receiving a hello before declaring the neighbor down. Both timers must match on connected interfaces for adjacency to form. When two OSPF routers connect on a broadcast or point-to-point network, they compare several parameters during the neighbor discovery process, including hello and dead timers, area ID, subnet, and authentication settings. If any of these parameters differ, the routers will not establish an adjacency. The hello and dead timer mismatch is a common cause because these timers control neighbor liveness detection. If one router expects hellos every 10 seconds but the other sends them every 30 seconds, the adjacency will fail. Exam candidates often mistake other issues such as MTU mismatch or missing router IDs as causes for adjacency failure. While MTU mismatches can delay adjacency in some cases, they do not typically prevent it outright. Router IDs are automatically assigned if not configured, so missing IDs do not block adjacency. Static routes are unrelated to neighbor formation. Understanding that hello and dead timer consistency is mandatory helps avoid these traps and ensures reliable OSPF neighbor relationships in practical networks.
Key takeaway
OSPF routers must have matching hello and dead timers on interfaces 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 have matching hello and dead timers on interfaces to successfully form neighbor adjacencies., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
IP Routing — This question tests IP Routing — OSPF routers must have matching hello and dead timers on interfaces to successfully form neighbor adjacencies..
The correct answer is: Hello and dead timer mismatch — Being stuck in the INIT state means R1 has received Hello packets from R2 but has not transitioned to the 2-WAY state. This most often occurs when critical OSPF parameters like the hello and dead timers do not match. An MTU mismatch, while problematic, would cause the adjacency to fail during database exchange (Exstart/Exchange), not during initial neighbor formation. Missing router IDs are not a real issue because routers auto-generate them, and a duplicate static route to the connected subnet would not affect OSPF neighbor discovery.
Review oSPF routers must have matching hello and dead timers on interfaces 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 have matching hello and dead timers on interfaces to successfully form neighbor adjacencies.
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Last reviewed: May 17, 2026
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