Question 1,210 of 2,152

EIGRP Troubleshooting →hardMultiple ChoiceObjective-mapped

EIGRP Frame Relay Adjacency Troubleshooting

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.

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 →

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."

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 a Frame Relay point-to-point subinterface, EIGRP expects the interface to be treated as a point-to-point link, which automatically disables split horizon and uses unicast hellos. If the subinterface is accidentally configured as multipoint, EIGRP treats it as a multi-access network, requiring a different neighbor discovery mechanism and often causing adjacency failures because the router does not receive hellos from the neighbor over the single DLCI. The correct answer is B because a multipoint configuration on a point-to-point subinterface breaks the expected EIGRP behavior.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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
Read the scenario before looking for a memorised answer.
✗
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: answer the scenario, not the keyword

Cisco often tests the distinction between point-to-point and multipoint subinterfaces in Frame Relay, where candidates mistakenly think the DLCI mapping or IP subnet mismatch is the primary issue, overlooking that the subinterface type itself dictates EIGRP's behavior regarding split horizon and neighbor discovery.

Detailed technical explanation

How to think about this question

EIGRP uses different neighbor discovery mechanisms on point-to-point versus multipoint interfaces: on point-to-point, hellos are sent to the multicast address 224.0.0.10 and split horizon is disabled by default, while on multipoint, split horizon is enabled and hellos are also multicast but the router must resolve the next-hop over a single DLCI, which can cause issues if the subinterface is misconfigured. In real-world scenarios, this misconfiguration often occurs when an engineer copies a configuration from a multipoint interface without changing the subinterface type, leading to silent adjacency failures that are hard to diagnose without checking 'show ip eigrp interfaces' or 'show frame-relay map'.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.

Visual reference

Quick reference

Routing Protocol Comparison

Protocol	Metric	Max Hops	Algorithm	Type
RIP v2	Hop count	15	Bellman-Ford	Distance vector
OSPF	Cost (bandwidth)	Unlimited	Dijkstra (SPF)	Link state
EIGRP	Composite metric	Unlimited	DUAL	Hybrid
IS-IS	Cost	Unlimited	Dijkstra	Link state
BGP	Policy / attributes	Unlimited	Path vector	Path vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 300-410 question test?

EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The subinterface is configured as multipoint instead of point-to-point. — On a Frame Relay point-to-point subinterface, EIGRP expects the interface to be treated as a point-to-point link, which automatically disables split horizon and uses unicast hellos. If the subinterface is accidentally configured as multipoint, EIGRP treats it as a multi-access network, requiring a different neighbor discovery mechanism and often causing adjacency failures because the router does not receive hellos from the neighbor over the single DLCI. The correct answer is B because a multipoint configuration on a point-to-point subinterface breaks the expected EIGRP behavior.

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

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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?

Read the scenario before looking for a memorised answer.

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