- A
The redistribution metric is too low, causing the route to be preferred over the OSPF path, but the loop is due to missing route tagging and filtering on redistribution.
The route-map sets a tag, but without a corresponding filter on the OSPF side (e.g., deny routes with tag 100), the route can be redistributed back into OSPF, creating a loop.
- B
The EIGRP metric values are incorrect; the delay value of 100 is too high, causing the route to be considered unreachable.
Why wrong: The metric values are valid; a delay of 100 microseconds is acceptable and does not cause loops.
- C
The route-map is applied in the wrong direction; it should be applied to the redistribute command under OSPF instead of EIGRP.
Why wrong: The route-map is correctly applied to the redistribution from OSPF into EIGRP.
- D
R3 has a static route for 192.168.1.0/24 pointing to R1, overriding the dynamic route.
Why wrong: No static route is mentioned; the loop is due to redistribution dynamics.
Quick Answer
The root cause is missing route tagging and filtering to prevent the redistributed OSPF routes from being re-advertised back into OSPF, creating a feedback loop. When R1 redistributes OSPF into EIGRP with a route-map that sets tag 100, the tag alone does nothing unless inbound filtering is applied on the EIGRP side or on any mutual redistribution point. Without a distribute-list or a route-map that denies tagged routes on re-redistribution, Router R3—if it also runs OSPF—can learn the EIGRP route and redistribute it back into OSPF, causing R1 to see a better metric for 192.168.1.0/24 via OSPF from R3, thus looping traffic between R1 and R3. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of redistribution loop prevention using administrative distance manipulation or, more reliably, route tagging with filtering. A common trap is assuming a low metric alone causes the loop, but the real issue is the absence of a filter that blocks tagged routes from re-entering OSPF. Memory tip: “Tag it, then block it—if you tag without a lock, the loop will mock.”
300-410 Device Management Practice Question
This 300-410 practice question tests your understanding of device management. 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 redistributes OSPF routes into EIGRP on Router R1. After redistribution, Router R3, which is an EIGRP neighbor of R1, starts experiencing routing loops for the 192.168.1.0/24 network. R1 configuration: router eigrp 100, redistribute ospf 1 metric 10000 100 255 1 1500, route-map RM-OSPF-to-EIGRP. The route-map sets tag 100. R3 shows: 'show ip route 192.168.1.0' points to R1, but traceroute shows packets looping between R1 and R3. What is the root cause?
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 redistribution metric is too low, causing the route to be preferred over the OSPF path, but the loop is due to missing route tagging and filtering on redistribution.
The redistribution injects OSPF routes into EIGRP with a metric that may be suboptimal. However, the key issue is that the route-map sets a tag, but without filtering, the redistributed routes may be re-advertised back into OSPF if mutual redistribution is configured elsewhere, causing a loop. In this case, the loop occurs because R1 redistributes into EIGRP, and R3, which may also have OSPF, redistributes the route back, creating a feedback loop. The fix is to use route tagging and filtering to prevent redistribution loops.
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 redistribution metric is too low, causing the route to be preferred over the OSPF path, but the loop is due to missing route tagging and filtering on redistribution.
- ✗
The EIGRP metric values are incorrect; the delay value of 100 is too high, causing the route to be considered unreachable.
Why it's wrong here
The metric values are valid; a delay of 100 microseconds is acceptable and does not cause loops.
- ✗
The route-map is applied in the wrong direction; it should be applied to the redistribute command under OSPF instead of EIGRP.
- ✗
R3 has a static route for 192.168.1.0/24 pointing to R1, overriding the dynamic route.
Why it's wrong here
No static route is mentioned; the loop is due to redistribution dynamics.
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?
Device Management — This question tests Device Management — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The redistribution metric is too low, causing the route to be preferred over the OSPF path, but the loop is due to missing route tagging and filtering on redistribution. — The redistribution injects OSPF routes into EIGRP with a metric that may be suboptimal. However, the key issue is that the route-map sets a tag, but without filtering, the redistributed routes may be re-advertised back into OSPF if mutual redistribution is configured elsewhere, causing a loop. In this case, the loop occurs because R1 redistributes into EIGRP, and R3, which may also have OSPF, redistributes the route back, creating a feedback loop. The fix is to use route tagging and filtering to prevent redistribution loops.
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.
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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