Question 35 of 2,011
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 a few minutes, routing loops occur. The engineer did not configure route tagging. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the misconception that administrative distance differences alone prevent loops, but the real danger is route feedback when redistribution is bidirectional and untagged.
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 router redistributes routes from OSPF into EIGRP, and then those routes are redistributed back into OSPF, creating a loop.
Without route tagging, when the router redistributes OSPF routes into EIGRP, those routes are learned by EIGRP neighbors. If the same router (or another router) then redistributes those EIGRP-learned routes back into OSPF, OSPF will accept them because they appear as external routes with a lower administrative distance than the original OSPF intra-area routes. This creates a mutual redistribution loop, causing routing instability and loops.
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 router redistributes routes from OSPF into EIGRP, and then those routes are redistributed back into OSPF, creating a loop.
Why this is correct
Without tagging, the router cannot prevent re-redistribution of its own routes, leading to a loop.
- ✗
The seed metric is not configured, causing EIGRP to reject the redistributed routes.
Why it's wrong here
Missing seed metric would prevent redistribution, not cause loops.
- ✗
OSPF has a lower administrative distance than EIGRP, causing route preference issues.
Why it's wrong here
AD differences do not cause loops in redistribution; loops are caused by feedback.
- ✗
The router is running both protocols on the same interface, causing a conflict.
Why it's wrong here
Running both protocols on the same interface is possible and does not inherently cause 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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Last reviewed: Jul 4, 2026
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