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BGP Troubleshooting →hardMultiple ChoiceObjective-mapped

300-410 BGP Troubleshooting Practice Question

This 300-410 practice question tests your understanding of bgp troubleshooting. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 configures mutual redistribution between OSPF and EIGRP without route tagging. After convergence, some routes oscillate between the two protocols. What is the most likely explanation?

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
Routes redistributed from OSPF into EIGRP are re-redistributed back into OSPF, and the OSPF route is preferred over the original due to administrative distance, causing a loop.
Without tagging, the router cannot distinguish between the original and redistributed route, leading to feedback loops.
B
The seed metric for EIGRP is not set, so redistributed routes are dropped.
Why wrong: Missing seed metric would cause routes to not be redistributed, not oscillation.
C
OSPF has a higher administrative distance than EIGRP, so OSPF routes are always preferred.
Why wrong: EIGRP has a lower AD (90) than OSPF (110), so EIGRP routes are preferred, but this does not cause oscillation.
D
The 'redistribute ospf' command under EIGRP automatically sets a tag, preventing loops.
Why wrong: Automatic tagging is not enabled by default; manual configuration is required.

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

✓

Routes redistributed from OSPF into EIGRP are re-redistributed back into OSPF, and the OSPF route is preferred over the original due to administrative distance, causing a loop.

Without route tagging, redistributed routes can be re-injected back into the original protocol, creating a routing loop. The administrative distance comparison can cause the route to be preferred from the wrong protocol, leading to oscillation.

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.

✓
Routes redistributed from OSPF into EIGRP are re-redistributed back into OSPF, and the OSPF route is preferred over the original due to administrative distance, causing a loop.
Why this is correct
Without tagging, the router cannot distinguish between the original and redistributed route, leading to feedback loops.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The seed metric for EIGRP is not set, so redistributed routes are dropped.
Why it's wrong here
Missing seed metric would cause routes to not be redistributed, not oscillation.
✗
OSPF has a higher administrative distance than EIGRP, so OSPF routes are always preferred.
Why it's wrong here
EIGRP has a lower AD (90) than OSPF (110), so EIGRP routes are preferred, but this does not cause oscillation.
✗
The 'redistribute ospf' command under EIGRP automatically sets a tag, preventing loops.
Why it's wrong here
Automatic tagging is not enabled by default; manual configuration is required.

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?

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

What is the correct answer to this question?

The correct answer is: Routes redistributed from OSPF into EIGRP are re-redistributed back into OSPF, and the OSPF route is preferred over the original due to administrative distance, causing a loop. — Without route tagging, redistributed routes can be re-injected back into the original protocol, creating a routing loop. The administrative distance comparison can cause the route to be preferred from the wrong protocol, leading to oscillation.

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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