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300-410 Practice Question: An engineer configures mutual redistribution…
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?
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.
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.
- ✗
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.
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.