hardMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting a route redistribution issue…
A network engineer is troubleshooting a route redistribution issue between OSPF and BGP. Router R1 runs both OSPF and BGP, and redistributes OSPF routes into BGP. The engineer notices that OSPF external routes are not appearing in the BGP table on R1. The show ip bgp command does not list these prefixes. The redistribute ospf 1 match external command is configured under BGP. What is the most likely 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 redistribute ospf 1 match external command under BGP is missing the subnets keyword.
When redistributing OSPF into BGP, the subnets keyword is required to redistribute classless subnets. Without it, only classful networks are redistributed, which may cause many routes to be missing.
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 redistribute ospf 1 match external command under BGP is missing the subnets keyword.
Why this is correct
Correct: Without subnets, only classful networks are redistributed, causing missing routes.
- ✗
OSPF has a higher administrative distance than BGP.
Why it's wrong here
Administrative distance affects route selection, not redistribution.
- ✗
The OSPF process on R1 has a distribute-list blocking these routes.
Why it's wrong here
While possible, the missing subnets keyword is a more common and likely cause.
- ✗
BGP requires the network command to advertise routes, not redistribution.
Why it's wrong here
Redistribution is a valid method to inject routes into BGP.
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
Introduction to ENARSI Exam and Network Fundamentals
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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