Question 1,447 of 2,152

EIGRP Troubleshooting →easyMultiple ChoiceObjective-mapped

Quick Answer

The answer is a distribute-list in applied on the local router that filters the specific route. This is correct because when only one EIGRP route is missing from a neighbor while all other routes from that same neighbor are learned successfully, the issue is almost always a targeted inbound filter. The distribute-list in command, often paired with an access-list or prefix-list, blocks only the matched prefix from entering the routing table, leaving the rest of the routes unaffected. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to distinguish between global neighbor issues and route-specific filtering; a common trap is to assume the neighbor is not advertising the route, but the topology table confirms the route is absent only locally. A quick memory tip: if the route is missing from the topology table but present on the neighbor, think “filter in, not out”—the distribute-list in is blocking the inbound update.

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 learning a specific route from a neighbor, but other routes from the same neighbor are being learned. The engineer checks the EIGRP topology table and sees that the route is not present. The engineer also checks the neighbor's routing table and confirms that the route exists. 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 1easymultiple choice

Study the full EIGRP explanation →

A
A distribute-list in is applied on the local router that filters the specific route.
Correct because a distribute-list can filter specific routes based on prefix or other criteria.
B
The neighbor is configured as a stub router.
Why wrong: Incorrect because a stub router would not advertise any routes except connected and summary, so all routes would be missing, not just one.
C
The route is a summary route that is being suppressed by the 'summary-address' command.
Why wrong: Incorrect because summary-address creates a summary route, it does not suppress a specific route.
D
The EIGRP metric for the route is too high, so it is not considered feasible.
Why wrong: Incorrect because if the route is not in the topology table at all, it is not being received, not that it is being ignored due to metric.

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

✓

A distribute-list in is applied on the local router that filters the specific route.

If only one route is missing from a neighbor, the issue is likely that the route is being filtered by a distribute-list or route-map on the receiving router. Since other routes are received, the filter is specific to that route.

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.

✓
A distribute-list in is applied on the local router that filters the specific route.
Why this is correct
Correct because a distribute-list can filter specific routes based on prefix or other criteria.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The neighbor is configured as a stub router.
Why it's wrong here
Incorrect because a stub router would not advertise any routes except connected and summary, so all routes would be missing, not just one.
✗
The route is a summary route that is being suppressed by the 'summary-address' command.
Why it's wrong here
Incorrect because summary-address creates a summary route, it does not suppress a specific route.
✗
The EIGRP metric for the route is too high, so it is not considered feasible.
Why it's wrong here
Incorrect because if the route is not in the topology table at all, it is not being received, not that it is being ignored due to metric.

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: A distribute-list in is applied on the local router that filters the specific route. — If only one route is missing from a neighbor, the issue is likely that the route is being filtered by a distribute-list or route-map on the receiving router. Since other routes are received, the filter is specific to that route.

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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Same concept, more angles

1 more ways this is tested on 300-410

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A network engineer is troubleshooting a routing issue in an EIGRP network. Router R1 is not learning a specific route from its neighbor R2, even though R2 has the route in its routing table. The engineer checks the EIGRP topology table on R1 and does not see the route. The output of 'show ip eigrp neighbors' shows that R1 and R2 are adjacent. What should the engineer check next?

medium

✓ A.Check if a distribute-list in or out is applied under the EIGRP process on R1.
B.Check if the route is being summarized on R2.
C.Check if the EIGRP metric for the route is too high.
D.Check if the route is a connected route on R2.

Why A: If the neighbor adjacency is up but the route is not in the topology table, the issue is likely that the route is being filtered by a distribute-list configured under the EIGRP process on the receiving router.

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