hardMultiple Choice
300-410 Practice Question: An engineer configures mutual redistribution…
An engineer configures mutual redistribution between OSPF and EIGRP on a router. After a few minutes, the router's CPU spikes and routes start flapping. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the concept that mutual redistribution inherently causes loops unless explicit filtering or tagging is applied, and candidates mistakenly focus on missing metrics or administrative distance instead of the re-redirection 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 redistribution is creating a routing loop because there is no route tagging or filtering to prevent re-redistribution.
Mutual redistribution without route tagging or filtering causes the redistributed routes to be re-injected back into the original routing protocol, creating a routing loop. This loop leads to continuous route updates, CPU spikes, and route flapping as the router repeatedly processes and advertises the same prefixes.
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 creating a routing loop because there is no route tagging or filtering to prevent re-redistribution.
Why this is correct
Without route tags or distribute-lists, each protocol re-advertises routes learned from the other, so prefixes oscillate between domains and never converge. The CPU spike and flapping stem from this mutual feedback loop, not from timers or metrics.
- ✗
The seed metric is not configured, so the routes are not redistributed.
Why it's wrong here
A missing seed metric causes routes to be omitted from redistribution entirely, producing silent route loss rather than flapping and CPU spikes. It is tempting because seed metrics are a common redistribution pitfall, yet the symptom here is instability, which points to routes being redistributed back and forth between the two domains.
- ✗
The administrative distance is set too low, causing the router to prefer the wrong route.
Why it's wrong here
Administrative distance controls route preference between sources, not redistribution loops; a low AD would cause suboptimal path selection, not CPU spikes from flapping. It is tempting because AD governs route selection, but mutual redistribution loops arise from routes fed back between protocols without filtering or tag-based denial.
- ✗
The OSPF process ID is the same on both routers.
Why it's wrong here
OSPF process IDs are locally significant and need not match between routers, so identical IDs cause no redistribution problem. It is tempting because mismatched area or process identifiers do break OSPF adjacencies, but process ID mismatch is irrelevant here; the flapping stems from routes looping between the two protocols.
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 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.