hardMultiple Choice
300-410 Practice Question: An experienced network engineer configures mutual…
An experienced network engineer configures mutual redistribution between OSPF and EIGRP on a router. Both protocols have routes to the same prefix, but after redistribution, a routing loop occurs. The engineer did not use route tagging. Which is the most likely explanation?
⚠ Common exam trap
300-410 often tests the misconception that redistribution is a simple one-way operation; candidates forget that without route tagging or filtering, routes can be re-advertised back into the source protocol, creating a loop.
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 redistribute command without route-map or tag allows routes to be re-advertised back into the source protocol, creating a loop.
When mutual redistribution is configured without route tagging or filtering, routes learned from OSPF can be redistributed into EIGRP and then redistributed back into OSPF (and vice versa). Because each protocol treats the redistributed route as a new external route, the metric and administrative distance can cause the router to prefer the re-injected path, creating a feedback loop. Route tagging (with a route-map that denies routes carrying the tag) is the standard method to prevent this two-way redistribution 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 seed metric for EIGRP was not configured, causing routes to be rejected.
Why it's wrong here
A missing EIGRP seed metric causes redistributed routes to be dropped, producing missing routes rather than a loop. The engineer's loop stems from routes re-entering each routing domain untagged. Seed metrics matter when injecting routes into EIGRP and must be set explicitly, but their absence yields rejection, not looping.
- ✓
The redistribute command without route-map or tag allows routes to be re-advertised back into the source protocol, creating a loop.
Why this is correct
Without tags or a route-map filter, routes learned from OSPF are redistributed into EIGRP and then redistributed straight back into OSPF, and vice versa. Each protocol re-advertises the other's routes as its own, so the same prefix oscillates between domains, producing the mutual redistribution loop described.
- ✗
OSPF has a lower administrative distance than EIGRP, so OSPF routes are always preferred.
Why it's wrong here
Administrative distance only breaks ties between routes to the same prefix from different sources; it cannot create a loop, because each protocol still installs the redistributed route. The loop arises from routes being fed back and forth without tagging. AD comparison is relevant when selecting between competing routes, not during mutual redistribution.
- ✗
EIGRP stub configuration on the redistributing router prevents routes from being advertised.
Why it's wrong here
EIGRP stub restricts which routes the router advertises, but stub sites still advertise connected and summary routes, so mutual redistribution loops persist regardless. It is tempting because stub reduces query scope, and would be correct for limiting spoke advertisements in hub-and-spoke topologies, not for preventing redistribution loops.
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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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.