Question 1,210 of 2,152

EIGRP Troubleshooting →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the subinterface is configured as multipoint instead of point-to-point. This is the most likely cause of the adjacency failure because on a Frame Relay point-to-point subinterface, the default interface type is non-broadcast, meaning multicast EIGRP hellos are not automatically sent. When the subinterface is set to multipoint, it expects a broadcast-capable environment, but without the proper frame-relay map statements or broadcast keyword, EIGRP cannot deliver its multicast hellos to the neighbor, preventing adjacency formation. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how EIGRP interacts with non-broadcast multi-access (NBMA) networks, specifically the requirement for point-to-point subinterfaces to be explicitly configured as such. A common trap is assuming a physical interface being up/up and a correct network statement guarantees adjacency; instead, the subinterface type dictates multicast behavior. Memory tip: "Point-to-point needs a point; multipoint misses the multicast."

300-410 EIGRP Troubleshooting Practice Question

This 300-410 practice question tests your understanding of eigrp troubleshooting. 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.

An engineer is troubleshooting an EIGRP issue where a router is not forming an adjacency with a neighbor over a Frame Relay point-to-point subinterface. The physical interface is up/up, and the subinterface is configured with an IP address. The engineer checks the EIGRP configuration and sees that the network statement includes the subnet of the subinterface. What is the most likely cause of the adjacency failure?

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

Study the full EIGRP explanation →

A
The subinterface is not configured with the 'frame-relay interface-dlci' command.
Why wrong: Incorrect because the DLCI is needed for Frame Relay, but the adjacency failure is more likely due to the interface type not supporting multicast.
B
The subinterface is configured as multipoint instead of point-to-point.
Correct because multipoint subinterfaces require additional configuration (like 'frame-relay map' for multicast) to support EIGRP, while point-to-point subinterfaces work with multicast by default.
C
The EIGRP hello timer is set to 0 on the subinterface.
Why wrong: Incorrect because setting the hello timer to 0 would disable hellos, but this is not a common misconfiguration.
D
The IP address on the subinterface is not in the same subnet as the neighbor.
Why wrong: Incorrect because if the subinterface is point-to-point, the IP addresses do not need to be in the same subnet; Frame Relay point-to-point links can use different subnets.

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 subinterface is configured as multipoint instead of point-to-point.

On Frame Relay point-to-point subinterfaces, the default interface type is non-broadcast, and EIGRP by default uses multicast hellos. If the interface is not configured as a point-to-point type, or if the multicast capability is not enabled, EIGRP will not send hellos, and adjacency will not form.

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 subinterface is not configured with the 'frame-relay interface-dlci' command.
Why it's wrong here
Incorrect because the DLCI is needed for Frame Relay, but the adjacency failure is more likely due to the interface type not supporting multicast.
✓
The subinterface is configured as multipoint instead of point-to-point.
Why this is correct
Correct because multipoint subinterfaces require additional configuration (like 'frame-relay map' for multicast) to support EIGRP, while point-to-point subinterfaces work with multicast by default.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The EIGRP hello timer is set to 0 on the subinterface.
Why it's wrong here
Incorrect because setting the hello timer to 0 would disable hellos, but this is not a common misconfiguration.
✗
The IP address on the subinterface is not in the same subnet as the neighbor.
Why it's wrong here
Incorrect because if the subinterface is point-to-point, the IP addresses do not need to be in the same subnet; Frame Relay point-to-point links can use different subnets.

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?

EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The subinterface is configured as multipoint instead of point-to-point. — On Frame Relay point-to-point subinterfaces, the default interface type is non-broadcast, and EIGRP by default uses multicast hellos. If the interface is not configured as a point-to-point type, or if the multicast capability is not enabled, EIGRP will not send hellos, and adjacency will not form.

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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