- A
The OSPF hello and dead intervals on R2 do not match those of other routers on the segment.
Why wrong: Mismatched timers prevent OSPF neighbor adjacency entirely. If this were the case, R2 would never have become BDR in the first place, because it would not have formed a full adjacency with R1. The issue is DR election, not adjacency.
- B
R2 has an OSPF priority of 255.
Why wrong: An OSPF priority of 255 is the highest possible and would make R2 the first choice for DR in any election. This would not prevent R2 from becoming DR; it would cause R2 to be elected DR if a new election occurs, exactly the opposite of the observed behavior.
- C
The OSPF network type on the segment was changed to point-to-point.
Why wrong: If the network type had been changed to point-to-point, there would be no DR or BDR at all, and R2 would never have been the BDR. The scenario clearly describes a broadcast segment with an existing DR/BDR relationship.
- D
R2 has an OSPF priority of 0.
On a broadcast OSPF network, a priority of 0 makes a router ineligible for DR or BDR election. Even though R2 was the BDR, its priority of 0 prevents it from taking over as DR when R1 fails. Consequently, a new DR election is triggered among the remaining eligible routers, and a router other than R2 becomes the new DR.
CCNA IP Routing Practice Question
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. 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 technician is troubleshooting an OSPF network. On a broadcast segment, R1 is the DR and R2 is the BDR. R1's interface GigabitEthernet0/0 is shut down for maintenance. The technician expects that R2 will assume the DR role, but instead a new DR election occurs and another router is elected DR. 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.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
R2 has an OSPF priority of 0.
When the DR fails on a broadcast OSPF network, the BDR normally takes over as DR and a new BDR is elected. However, if the BDR's OSPF priority is set to 0, the router is ineligible to become DR or BDR. With the DR down and the BDR ineligible, the remaining routers must hold a fresh election, and the router with the highest non-zero priority (or highest router-ID if priorities tie) becomes the new DR. Therefore, R2's priority of 0 explains why it did not become DR and a new election was triggered.
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.
- ✗
The OSPF hello and dead intervals on R2 do not match those of other routers on the segment.
Why it's wrong here
Mismatched timers prevent OSPF neighbor adjacency entirely. If this were the case, R2 would never have become BDR in the first place, because it would not have formed a full adjacency with R1. The issue is DR election, not adjacency.
- ✗
R2 has an OSPF priority of 255.
Why it's wrong here
An OSPF priority of 255 is the highest possible and would make R2 the first choice for DR in any election. This would not prevent R2 from becoming DR; it would cause R2 to be elected DR if a new election occurs, exactly the opposite of the observed behavior.
- ✗
The OSPF network type on the segment was changed to point-to-point.
Why it's wrong here
If the network type had been changed to point-to-point, there would be no DR or BDR at all, and R2 would never have been the BDR. The scenario clearly describes a broadcast segment with an existing DR/BDR relationship.
- ✓
R2 has an OSPF priority of 0.
Why this is correct
On a broadcast OSPF network, a priority of 0 makes a router ineligible for DR or BDR election. Even though R2 was the BDR, its priority of 0 prevents it from taking over as DR when R1 fails. Consequently, a new DR election is triggered among the remaining eligible routers, and a router other than R2 becomes the new DR.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
Option-by-option analysis
Why each answer is right or wrong
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.
✓R2 has an OSPF priority of 0.Correct answer▾
Why this is correct
On a broadcast OSPF network, a priority of 0 makes a router ineligible for DR or BDR election. Even though R2 was the BDR, its priority of 0 prevents it from taking over as DR when R1 fails. Consequently, a new DR election is triggered among the remaining eligible routers, and a router other than R2 becomes the new DR.
✗The OSPF hello and dead intervals on R2 do not match those of other routers on the segment.Wrong answer — click to see why▾
Why this is wrong here
Neighbor adjacency failure due to timer mismatch would have prevented R2 from becoming BDR at all.
✗R2 has an OSPF priority of 255.Wrong answer — click to see why▾
Why this is wrong here
High priority increases the chance of being elected DR, not decrease it.
✗The OSPF network type on the segment was changed to point-to-point.Wrong answer — click to see why▾
Why this is wrong here
Point-to-point networks do not have DR/BDR elections, so R2 could not have been BDR.
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
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.
Trap categories for this question
Scenario analysis trap
If the network type had been changed to point-to-point, there would be no DR or BDR at all, and R2 would never have been the BDR. The scenario clearly describes a broadcast segment with an existing DR/BDR relationship.
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 200-301 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 200-301 question test?
IP Routing — This question tests IP Routing — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: R2 has an OSPF priority of 0. — When the DR fails on a broadcast OSPF network, the BDR normally takes over as DR and a new BDR is elected. However, if the BDR's OSPF priority is set to 0, the router is ineligible to become DR or BDR. With the DR down and the BDR ineligible, the remaining routers must hold a fresh election, and the router with the highest non-zero priority (or highest router-ID if priorities tie) becomes the new DR. Therefore, R2's priority of 0 explains why it did not become DR and a new election was triggered.
What should I do if I get this 200-301 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 200-301 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.
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Last reviewed: Jun 14, 2026
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