hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures mutual redistribution…
An engineer configures mutual redistribution between OSPF and EIGRP on a router. After the configuration, a routing loop occurs for a specific prefix. The engineer checks and confirms that route tagging is not used. What is the most likely explanation?
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 is not filtered, so the same prefix is redistributed back and forth, causing a loop.
Without route tagging, mutual redistribution can cause a routing loop when the same prefix is redistributed back and forth. The edge case is that OSPF and EIGRP have different administrative distances (AD). OSPF external routes have AD 110, and EIGRP external routes have AD 170. If the prefix is learned via both protocols, the router prefers the lower AD (OSPF external). However, if the router redistributes the EIGRP route into OSPF, and then receives it back via OSPF, it may prefer the OSPF route and cause a loop. The loop is exacerbated if the redistribution is not filtered.
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 is not filtered, so the same prefix is redistributed back and forth, causing a loop.
Why this is correct
Without route tagging or filtering, mutual redistribution can lead to a feedback loop where a route redistributed from OSPF to EIGRP is then redistributed back into OSPF, creating a loop.
- ✗
The 'default-metric' command is missing in both protocols, causing the seed metric to be inconsistent.
Why it's wrong here
Missing seed metric prevents redistribution from occurring at all, as the routes are not injected. This would not cause a loop.
- ✗
The 'subnets' keyword is missing in the OSPF redistribution command.
Why it's wrong here
Missing the 'subnets' keyword only affects classful networks; it does not cause routing loops.
- ✗
The 'distance' command is used to change AD, causing OSPF and EIGRP to have the same AD.
Why it's wrong here
While equal AD can cause issues, the question states no tagging is used, and the loop is due to redistribution feedback, not AD equality.
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.
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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.