hardMultiple Choice
300-410 Practice Question: An engineer configures mutual redistribution…
An engineer configures mutual redistribution between OSPF and EIGRP on a router that is part of an IPsec site-to-site VPN. After the configuration, routing loops occur intermittently. The engineer has not used any route tagging. What is the most likely cause of the routing loops?
⚠ Common exam trap
Cisco often tests the concept that mutual redistribution without route tagging or filtering is the primary cause of routing loops, and candidates mistakenly focus on metric or administrative distance differences instead of the re-injection mechanism.
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
✓
Routes redistributed from OSPF into EIGRP are re-distributed back into OSPF because there is no route tagging to identify them as OSPF-originated.
Without route tagging, routes redistributed from OSPF into EIGRP are not marked as OSPF-originated. When EIGRP redistributes these routes back into OSPF, OSPF accepts them as external routes, creating a mutual redistribution loop. This occurs because OSPF has no mechanism to distinguish between its own routes and those learned from EIGRP without explicit tagging (e.g., using a route-map with a tag).
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 redistribution is set to a low value, causing EIGRP routes to be preferred over OSPF routes.
Why it's wrong here
Without route tags, redistributed routes re-enter their originating domain and are re-advertised, creating feedback loops; the seed metric only affects preference, not the loop itself. It is tempting because metric manipulation does influence path selection, and setting a high seed metric would be correct when preventing suboptimal routing between domains.
- ✓
Routes redistributed from OSPF into EIGRP are re-distributed back into OSPF because there is no route tagging to identify them as OSPF-originated.
Why this is correct
Without route tagging, EIGRP cannot distinguish OSPF-originated routes from its own native entries, so it advertises them back into OSPF during mutual redistribution. OSPF then reinstalls them, creating a feedback loop between the two protocols. Tagging each domain's routes with distinct administrative tags prevents this redistribution cycle.
- ✗
The IPsec tunnel is using transport mode, which causes routing protocol packets to be dropped.
Why it's wrong here
Transport mode encrypts only the payload, leaving the original IP header intact, so routing protocols still form adjacencies; it does not drop them. Transport mode is chosen when the tunnel endpoints are the actual communication hosts, not for site-to-site gateway tunnels, which require tunnel mode.
- ✗
The OSPF process has a higher administrative distance than EIGRP, causing route flapping.
Why it's wrong here
Administrative distance governs which protocol's route is installed when both offer the same prefix; it does not cause flapping here. EIGRP's internal distance of 90 already beats OSPF's 110, so this ordering is normal. Distance manipulation is used to prefer one protocol deliberately, not to prevent mutual 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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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.