Question 1,434 of 2,152

EIGRP Troubleshooting →mediumMultiple ChoiceObjective-mapped

EIGRP Stub Router: Neighbor Not Learning Routes

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 learning any routes from a neighbor, but the neighbor adjacency is up. The engineer checks the EIGRP topology table on the local router and sees that the neighbor is listed, but no routes from that neighbor are present. The engineer also verifies that the neighbor has routes to advertise. 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.

A
The neighbor is configured as an EIGRP stub router.
Correct because a stub router only advertises connected and summary routes by default, so if the neighbor has other routes, they will not be advertised.
B
The local router has a distribute-list out applied to the neighbor.
Why wrong: Incorrect because a distribute-list out would filter routes going out to the neighbor, not incoming routes.
C
The EIGRP metric weights are different on the two routers.
Why wrong: Incorrect because mismatched metric weights prevent adjacency formation, not route advertisement after adjacency is up.
D
The local router has a route-map applied to the EIGRP process that is filtering all routes.
Why wrong: Incorrect because a route-map applied to the EIGRP process would affect redistribution, not the reception of routes from a neighbor.

Full breakdown with real-world context →

Quick Answer

The answer is that the neighbor is configured as an EIGRP stub router. When a router is configured as an EIGRP stub, it restricts the types of routes it advertises to its neighbors, typically sending only connected and summary routes while withholding all other learned routes. This explains why the adjacency is up—the neighbor relationship forms normally—but no routes appear in the topology table, even though the neighbor has routes to advertise. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of EIGRP stub behavior and its impact on route propagation, often appearing as a troubleshooting trap where candidates mistakenly blame distribute-lists or authentication issues. A common memory tip is to remember that a stub router is a "quiet neighbor"—it listens but only speaks a few specific route types, so if you see an up adjacency with zero received routes, think "stub first."

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 neighbor is configured as an EIGRP stub router.

When an EIGRP neighbor adjacency is up but no routes are received from the neighbor, the most likely cause is that the neighbor is configured as an EIGRP stub router. A stub router advertises only a default route or its directly connected and summary routes, depending on the stub setting, and does not advertise all learned routes. Since the engineer confirmed the neighbor has routes to advertise, the stub configuration on the neighbor would prevent those routes from being sent, even though the adjacency remains established.

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 neighbor is configured as an EIGRP stub router.
Why this is correct
Correct because a stub router only advertises connected and summary routes by default, so if the neighbor has other routes, they will not be advertised.
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 local router has a distribute-list out applied to the neighbor.
Why it's wrong here
Incorrect because a distribute-list out would filter routes going out to the neighbor, not incoming routes.
✗
The EIGRP metric weights are different on the two routers.
Why it's wrong here
Incorrect because mismatched metric weights prevent adjacency formation, not route advertisement after adjacency is up.
✗
The local router has a route-map applied to the EIGRP process that is filtering all routes.
Why it's wrong here
Incorrect because a route-map applied to the EIGRP process would affect redistribution, not the reception of routes from a neighbor.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between conditions that prevent adjacency formation (like mismatched K values or AS numbers) versus conditions that allow adjacency but suppress route advertisement (like stub configuration), leading candidates to incorrectly select metric weight mismatches when the adjacency is already up.

Detailed technical explanation

How to think about this question

EIGRP stub routing is commonly used in hub-and-spoke topologies to prevent spoke routers from acting as transit routers. When a router is configured as a stub (e.g., with the 'eigrp stub' command), it sends a special stub flag in its hello packets, and the hub router will not query the stub for alternate routes, while the stub only advertises a default route or its connected/summary routes depending on the 'receive-only', 'connected', 'static', or 'summary' keywords. This behavior is defined in RFC 7868 and is a common cause of missing routes when the stub router has other learned routes it could advertise.

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.

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 neighbor is configured as an EIGRP stub router. — When an EIGRP neighbor adjacency is up but no routes are received from the neighbor, the most likely cause is that the neighbor is configured as an EIGRP stub router. A stub router advertises only a default route or its directly connected and summary routes, depending on the stub setting, and does not advertise all learned routes. Since the engineer confirmed the neighbor has routes to advertise, the stub configuration on the neighbor would prevent those routes from being sent, even though the adjacency remains established.

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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