hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An enterprise is redistributing EIGRP into OSPF…
An enterprise is redistributing EIGRP into OSPF on router R1. R1 has the following configuration: router eigrp 100 redistribute ospf 1 metric 10000 100 255 1 1500 route-map RMAP-OSPF. Router R2 (OSPF-only) shows: 'show ip route 10.1.1.0' as an O E2 route with metric 20, but 'show ip ospf database external 10.1.1.0' shows the forwarding address is 0.0.0.0. Router R3 (also OSPF) cannot reach 10.1.1.0. What is the root cause?
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 redistributed route's next-hop is not reachable via OSPF, causing the forwarding address to be 0.0.0.0, but R1's router ID is not reachable from R3 due to a missing OSPF network statement.
When redistributing into OSPF, if the redistributed route's next-hop is not reachable via OSPF (e.g., it is an EIGRP-learned route with a next-hop that is not in the OSPF domain), the forwarding address is set to 0.0.0.0. This causes other OSPF routers to try to reach the originating router (R1) as the next-hop. However, if R1's OSPF router ID is not reachable or if there is a filtering issue, the route may be installed but unreachable. In this scenario, the route-map RMAP-OSPF may be filtering the route or setting incorrect metrics, but the forwarding address issue suggests that the next-hop is not being advertised correctly. The root cause is likely that the redistributed route's next-hop is not in the OSPF domain, so R1 should use a route-map to set the forwarding address to itself (e.g., set forwarding-address 0.0.0.0 is default, but if the next-hop is reachable, it should be set to the router's own interface IP).
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 redistributed route's next-hop is not reachable via OSPF, causing the forwarding address to be 0.0.0.0, but R1's router ID is not reachable from R3 due to a missing OSPF network statement.
Why this is correct
If the next-hop is not in OSPF, the forwarding address is set to 0.0.0.0, meaning the packet should be sent to the advertising router (R1). If R1's router ID is not reachable (e.g., R1's OSPF interfaces are not advertised correctly), R3 cannot reach the route.
- ✗
The route-map RMAP-OSPF is setting the metric to 20, which is too high and causes the route to be suppressed.
Why it's wrong here
The metric 20 is the default for E2 routes and does not suppress the route.
- ✗
The EIGRP process on R1 has a distribute-list blocking the route.
Why it's wrong here
The route is being redistributed (shown in OSPF database), so EIGRP is not blocking it.
- ✗
The OSPF process on R1 has a route-map applied inbound that filters the route.
Why it's wrong here
The route is in the OSPF database, so it is not filtered inbound.
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
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