hardMultiple Choice
300-410 Practice Question: Configures mutual redistribution between EIGRP…
A network engineer configures mutual redistribution between EIGRP and OSPF on a DMVPN hub router. The EIGRP domain includes the DMVPN tunnel network, and OSPF includes a corporate backbone. Unexpectedly, after a few minutes, the routing table on the hub shows oscillating routes between EIGRP and OSPF for the same prefix, causing intermittent connectivity. Which is the most likely explanation?
⚠ Common exam trap
300-410 often tests redistribution loop scenarios; candidates may blame interface configuration or metrics instead of recognizing the classic feedback loop caused by mutual redistribution without filtering.
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 mutual redistribution creates a routing loop because the redistributed routes are re-injected into the original protocol without proper filtering, causing the hub to prefer the redistributed route with a lower AD.
Mutual redistribution between EIGRP and OSPF without proper filtering or tag-based loop prevention causes routes to be redistributed back into their original protocol. The hub may then prefer the redistributed route due to a lower administrative distance, creating a feedback loop that manifests as oscillating routes and intermittent connectivity.
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 mutual redistribution creates a routing loop because the redistributed routes are re-injected into the original protocol without proper filtering, causing the hub to prefer the redistributed route with a lower AD.
Why this is correct
Without route tagging, a route redistributed from EIGRP into OSPF (AD 110) and then back into EIGRP (AD 170) may be preferred over the original EIGRP internal route (AD 90) if the AD is misconfigured, but typically the original internal route has lower AD. However, if the route is external in EIGRP, the AD is 170, so the OSPF route (110) is preferred, causing a loop.
- ✗
The DMVPN tunnel interface is not included in the OSPF process, causing the redistributed routes to have an incorrect next-hop that points to the tunnel interface.
Why it's wrong here
Redistribution does not depend on the tunnel interface joining OSPF; the oscillation stems from each protocol advertising the other's routes back, with no tag or filter breaking the loop. It is tempting because next-hop reachability does matter on multipoint tunnels, but that produces unreachable routes, not flapping.
- ✗
The EIGRP and OSPF processes are using different metric styles, causing the redistributed routes to have infinite metrics and be ignored.
Why it's wrong here
Different metric styles are expected in mutual redistribution and are handled by seed metrics and default-metric commands; infinite metrics cause routes to be omitted, not to oscillate. It is tempting because metric incompatibility is a genuine redistribution pitfall, but the flapping here comes from routes being fed back between the two domains.
- ✗
The hub router's routing table is overloaded due to the DMVPN tunnel being a multipoint interface, causing route flapping.
Why it's wrong here
A multipoint tunnel interface does not overload the routing table or cause flapping; oscillation arises from each routing protocol redistributing the other's routes back without loop prevention. It is tempting because DMVPN multipoint behaviour complicates next-hop handling, but that yields reachability problems rather than repeated route changes.
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 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
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