Question 311 of 2,152

OSPF Troubleshooting (v2/v3) →hardMultiple ChoiceObjective-mapped

300-410 OSPF Troubleshooting (v2/v3) Practice Question

This 300-410 practice question tests your understanding of ospf troubleshooting (v2/v3). 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 OSPFv2 adjacency issue between two routers across a Frame Relay network. R1 and R2 are connected via a point-to-point subinterface. The engineer configures 'ip ospf network point-to-point' on both subinterfaces. However, the adjacency does not form. 'show ip ospf interface' on R1 shows the interface is up and OSPF is enabled, but no neighbors are seen. 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.

Question 1hardmultiple choice

Review the full OSPF breakdown →

A
The OSPF network type is set to broadcast, causing a DR/BDR election that fails on a point-to-point subinterface.
Why wrong: The engineer set it to point-to-point, so this is not the issue.
B
The subinterface is not configured with an IP address.
Why wrong: If there were no IP address, OSPF would not be enabled on the interface.
C
The Frame Relay map is missing or the DLCI is not assigned to the subinterface.
Without a proper DLCI mapping, the router cannot send Layer 2 frames to the neighbor, preventing OSPF hello packets from being exchanged.
D
The OSPF hello and dead timers are mismatched between R1 and R2.
Why wrong: While timer mismatch can cause adjacency issues, it is less likely than a Layer 2 problem, and the stem does not indicate any timer configuration.

Full breakdown with real-world context →

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

✓

The Frame Relay map is missing or the DLCI is not assigned to the subinterface.

On Frame Relay point-to-point subinterfaces, the OSPF network type should be point-to-point, but the adjacency may still fail if the Layer 2 mapping is incorrect. The subinterface must be mapped to the correct DLCI. If the 'frame-relay interface-dlci' command is missing or misconfigured, the router cannot send packets to the neighbor, even though OSPF is enabled. The engineer should verify the DLCI mapping.

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 network type is set to broadcast, causing a DR/BDR election that fails on a point-to-point subinterface.
Why it's wrong here
The engineer set it to point-to-point, so this is not the issue.
✗
The subinterface is not configured with an IP address.
Why it's wrong here
If there were no IP address, OSPF would not be enabled on the interface.
✓
The Frame Relay map is missing or the DLCI is not assigned to the subinterface.
Why this is correct
Without a proper DLCI mapping, the router cannot send Layer 2 frames to the neighbor, preventing OSPF hello packets from being exchanged.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The OSPF hello and dead timers are mismatched between R1 and R2.
Why it's wrong here
While timer mismatch can cause adjacency issues, it is less likely than a Layer 2 problem, and the stem does not indicate any timer configuration.

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.

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 300-410 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 300-410 question test?

OSPF Troubleshooting (v2/v3) — This question tests OSPF Troubleshooting (v2/v3) — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The Frame Relay map is missing or the DLCI is not assigned to the subinterface. — On Frame Relay point-to-point subinterfaces, the OSPF network type should be point-to-point, but the adjacency may still fail if the Layer 2 mapping is incorrect. The subinterface must be mapped to the correct DLCI. If the 'frame-relay interface-dlci' command is missing or misconfigured, the router cannot send packets to the neighbor, even though OSPF is enabled. The engineer should verify the DLCI mapping.

What should I do if I get this 300-410 question wrong?

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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