Question 607 of 2,152

NetFlow and Flexible NetFlow →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is that the redistributed routes are not tagged, so they are re-redistributed back into the original protocol, creating a loop. This occurs because mutual redistribution between OSPF and EIGRP without route tagging allows a route learned from one protocol to be injected into the other, then re-learned and redistributed back, forming a feedback loop. The loop is sustained when the administrative distance of the redistributed route is lower than the original—for instance, if an OSPF external route (AD 110) is redistributed into EIGRP and then re-redistributed into OSPF as an internal route (AD 110), or if an EIGRP internal route (AD 90) is redistributed into OSPF and then back into EIGRP as an internal route, the lower AD causes the router to prefer the looped path. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of redistribution mechanics and the critical role of route tagging to prevent loops. A common trap is assuming that different ADs alone prevent loops, but without tags, the redistributed route can appear as a better (lower AD) path. Memory tip: “No tag, loop drag”—always tag redistributed routes to break the redistribution cycle.

300-410 NetFlow and Flexible NetFlow Practice Question

This 300-410 practice question tests your understanding of netflow and flexible netflow. 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. After the configuration, routing loops occur. The engineer checks the routing tables and sees that the same prefix is learned from both protocols with different administrative distances. Which 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
The redistributed routes are not tagged, so they are re-redistributed back into the original protocol, creating a loop.
Without route tagging, there is no way to prevent the redistributed route from being sent back to the original protocol, causing a routing loop.
B
The administrative distance of EIGRP is lower than OSPF, so the redistributed route is preferred and causes a loop.
Why wrong: EIGRP internal routes have AD 90, which is lower than OSPF's 110, but this alone does not cause a loop; it can cause suboptimal routing but not necessarily a loop.
C
The seed metric is not configured, so the redistributed route has an infinite metric and is not installed.
Why wrong: If the seed metric is missing, the route may not be redistributed at all, which would prevent loops but also break connectivity.
D
The OSPF process is configured with 'default-information originate always', which injects a default route and causes a loop.
Why wrong: This could cause a loop if the default route points back to the same router, but the scenario describes mutual redistribution of specific prefixes, not default routes.

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 redistributed routes are not tagged, so they are re-redistributed back into the original protocol, creating a loop.

Mutual redistribution without proper route tagging can cause routing loops. When a route redistributed from OSPF into EIGRP is then redistributed back into OSPF, it can be preferred if the administrative distance (AD) of the redistributed route is lower than the original. By default, OSPF external routes have AD 110, and EIGRP external routes have AD 170. However, if the redistributed route is learned as an OSPF internal route (AD 110) vs EIGRP internal (AD 90), the loop can occur. A common edge case is when the route is redistributed with a metric that makes it appear as an internal route in the other protocol, causing a lower AD and thus a loop.

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 redistributed routes are not tagged, so they are re-redistributed back into the original protocol, creating a loop.
Why this is correct
Without route tagging, there is no way to prevent the redistributed route from being sent back to the original protocol, causing a routing loop.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The administrative distance of EIGRP is lower than OSPF, so the redistributed route is preferred and causes a loop.
Why it's wrong here
EIGRP internal routes have AD 90, which is lower than OSPF's 110, but this alone does not cause a loop; it can cause suboptimal routing but not necessarily a loop.
✗
The seed metric is not configured, so the redistributed route has an infinite metric and is not installed.
Why it's wrong here
If the seed metric is missing, the route may not be redistributed at all, which would prevent loops but also break connectivity.
✗
The OSPF process is configured with 'default-information originate always', which injects a default route and causes a loop.
Why it's wrong here
This could cause a loop if the default route points back to the same router, but the scenario describes mutual redistribution of specific prefixes, not default routes.

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.

Trap categories for this question

Scenario analysis trap
This could cause a loop if the default route points back to the same router, but the scenario describes mutual redistribution of specific prefixes, not default routes.

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?

NetFlow and Flexible NetFlow — This question tests NetFlow and Flexible NetFlow — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The redistributed routes are not tagged, so they are re-redistributed back into the original protocol, creating a loop. — Mutual redistribution without proper route tagging can cause routing loops. When a route redistributed from OSPF into EIGRP is then redistributed back into OSPF, it can be preferred if the administrative distance (AD) of the redistributed route is lower than the original. By default, OSPF external routes have AD 110, and EIGRP external routes have AD 170. However, if the redistributed route is learned as an OSPF internal route (AD 110) vs EIGRP internal (AD 90), the loop can occur. A common edge case is when the route is redistributed with a metric that makes it appear as an internal route in the other protocol, causing a lower AD and thus a loop.

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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