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300-410 Practice Question: Is troubleshooting a redistribution issue between…
A network engineer is troubleshooting a redistribution issue between OSPF and EIGRP. Router R1 redistributes OSPF into EIGRP, and Router R2 redistributes EIGRP into OSPF. After configuration, some routes are missing, and routing loops occur. R1 has: router eigrp 100 redistribute ospf 1 metric 10000 100 255 1 1500 route-map OSPF-to-EIGRP. R2 has: router ospf 1 redistribute eigrp 100 subnets route-map EIGRP-to-OSPF. Show ip route on R1 shows an OSPF route 172.16.1.0/24 learned via R2, but also an EIGRP route for the same prefix with a better administrative distance. What is the root cause?
⚠ Common exam trap
Cisco often tests the concept of mutual redistribution and route feedback loops, where candidates mistakenly focus on metric or administrative distance adjustments instead of recognizing that a route-map filter is required to break the redistribution cycle.
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 route-map OSPF-to-EIGRP on R1 should include a match clause to filter out routes learned from R2 via OSPF, preventing feedback.
The route-map OSPF-to-EIGRP on R1 is not filtering out the OSPF route 172.16.1.0/24 that was originally redistributed from EIGRP into OSPF by R2. This creates a routing feedback loop: R1 learns the prefix via OSPF (from R2) and then redistributes it back into EIGRP, causing R2 to see an EIGRP route with a better administrative distance (90 vs. 110) and prefer it, leading to missing routes and loops. The route-map should include a match clause to deny routes that were originally EIGRP (e.g., via a tag or prefix-list) to prevent mutual redistribution.
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 route-map OSPF-to-EIGRP on R1 should include a match clause to filter out routes learned from R2 via OSPF, preventing feedback.
Why this is correct
Adding a match route-map that tags routes from R2 and denies them, or using a tag-based filter, stops the redistribution loop.
- ✗
The redistribute command on R2 should have a metric-type 1 to avoid suboptimal routing.
Why it's wrong here
Metric type does not prevent loops; it only affects OSPF path selection.
- ✗
The administrative distance of OSPF should be changed to 85 on R1 to prefer OSPF over EIGRP.
Why it's wrong here
Changing AD may hide the symptom but does not fix the loop; the loop will still exist and may cause other issues.
- ✗
The EIGRP metric on R1 should be set to a higher value to make the redistributed route less preferred.
Why it's wrong here
Higher metric does not prevent redistribution of the route back into OSPF; the loop persists.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
BGP Prefix Filtering
BGP Prefix Filtering is the practice of controlling which network routes (prefixes) a router accepts or advertises to its BGP neighbors, preventing unwanted or harmful routes from spreading across the internet.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.