300-410 Layer 3 Technologies Practice Question
A network administrator is troubleshooting a route redistribution issue on a Cisco router running both EIGRP and OSPF. The router is redistributing EIGRP routes into OSPF, but the routes are not appearing in the OSPF domain. The administrator has configured redistribution with a seed metric of 20. Which additional configuration is required to ensure the routes are advertised?
⚠ Common exam trap
The trap here is assuming that setting a seed metric is sufficient for redistribution, overlooking the need for the subnets keyword to handle subnetted routes.
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
✓
Configure the subnets keyword under the redistribute command.
The subnets keyword is necessary when redistributing routes into OSPF to include subnetted routes. Without it, only classful networks are redistributed, which is why the EIGRP routes are missing. The seed metric alone does not ensure subnetted routes are advertised. Metric-type and route maps are unrelated to this requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set the metric-type to 1 under the redistribute command.
Why it's wrong here
The metric-type (E1 or E2) determines how the cost is calculated for external routes, but it does not affect whether subnetted routes are redistributed. Even with metric-type 1, routes without the subnets keyword will not be advertised if they are subnetted. Thus, this does not solve the problem of missing routes.
- ✗
Enable OSPF on the interface connecting to the EIGRP domain.
Why it's wrong here
OSPF must be enabled on interfaces where OSPF adjacencies are formed, but redistribution occurs between routing protocols on the same router. The interface connecting to the EIGRP domain does not need OSPF enabled unless OSPF is also running there. Redistribution is a process-level configuration, so this is not required.
- ✗
Configure a route map to match the EIGRP routes.
Why it's wrong here
A route map can filter or modify routes, but it is not required to redistribute subnetted routes. The absence of the subnets keyword is the likely cause. While a route map could be used to selectively redistribute, it does not address the fundamental issue of classful redistribution.
- ✓
Configure the subnets keyword under the redistribute command.
Why this is correct
When redistributing routes into OSPF, the subnets keyword is required to include subnetted routes. Without it, only classful networks are redistributed, so routes with subnet masks are not advertised. Since the scenario involves redistributing EIGRP routes, which are often subnetted, the subnets keyword ensures they are included in OSPF LSAs.
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.
Go deeper
Related to this question
Learn chapter
EIGRP Route Summarization and Filtering
Key term
Route Redistribution Between Protocols
Route redistribution between protocols is the process of taking routes learned from one routing protocol and injecting them into another routing protocol so that networks using different protocols can communicate.
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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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