- A
Routes are being re-redistributed due to missing route tags; a route-map with 'set tag' should be used to prevent loops.
Correct because route tags allow filtering to prevent redistribution loops.
- B
The OSPF process has a 'default-information originate' command that is injecting a default route into EIGRP.
Why wrong: Incorrect because this would inject a default route, not affect metrics.
- C
The EIGRP process has a 'variance' command that is causing unequal-cost load balancing.
Why wrong: Incorrect because variance affects load balancing, not redistribution metrics.
- D
The route-map applied to redistribution is missing a 'match tag' statement to filter out redistributed routes.
Why wrong: Incorrect because the issue is re-redistribution, not filtering of specific tags.
Quick Answer
The answer is missing route tags, which allow a route-map with 'set tag' to prevent redistribution loops. When OSPF and EIGRP mutually redistribute without tagging, a route learned from one protocol can be re-injected back into its source, causing a loop that inflates metrics and creates suboptimal paths. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of redistribution loop prevention using route-map and tag—a common trap is assuming metric manipulation alone solves the issue, when in fact tagging breaks the cycle by marking routes so they are not re-redistributed. Remember the memory tip: "Tag it once, loop it none."
300-410 Route Maps and Route Filtering Practice Question
This 300-410 practice question tests your understanding of route maps and route filtering. 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.
A network engineer is troubleshooting a redistribution loop between OSPF and EIGRP. Router R7 is redistributing EIGRP routes into OSPF, and also redistributing OSPF routes into EIGRP. The engineer notices that some OSPF routes are appearing in the EIGRP topology table with a higher metric than expected, causing suboptimal routing. 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.
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 are being re-redistributed due to missing route tags; a route-map with 'set tag' should be used to prevent loops.
Redistribution loops can cause routes to be re-injected with different metrics. The most common fix is to use route-maps with tags to prevent re-redistribution. Without proper tagging, routes can loop between the two protocols.
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 are being re-redistributed due to missing route tags; a route-map with 'set tag' should be used to prevent loops.
Why this is correct
Correct because route tags allow filtering to prevent redistribution 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 OSPF process has a 'default-information originate' command that is injecting a default route into EIGRP.
Why it's wrong here
Incorrect because this would inject a default route, not affect metrics.
- ✗
The EIGRP process has a 'variance' command that is causing unequal-cost load balancing.
Why it's wrong here
Incorrect because variance affects load balancing, not redistribution metrics.
- ✗
The route-map applied to redistribution is missing a 'match tag' statement to filter out redistributed routes.
Why it's wrong here
Incorrect because the issue is re-redistribution, not filtering of specific tags.
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?
Route Maps and Route Filtering — This question tests Route Maps and Route Filtering — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Routes are being re-redistributed due to missing route tags; a route-map with 'set tag' should be used to prevent loops. — Redistribution loops can cause routes to be re-injected with different metrics. The most common fix is to use route-maps with tags to prevent re-redistribution. Without proper tagging, routes can loop between the two protocols.
What should I do if I get this 300-410 question wrong?
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.
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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Last reviewed: Jun 18, 2026
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