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300-410 Router R1 and R2 are running OSPF and BGP Practice Question
Router R1 and R2 are running OSPF and BGP. R1 is an ASBR redistributing BGP routes into OSPF. R2 is an ABR between area 0 and area 1. R2 has 'distance ospf external 150' configured. R3 in area 1 learns a BGP-redistributed route 10.0.0.0/8 via R2 with AD 150. R3 also learns the same prefix via a different path from R4 (another ABR) with AD 110 (default OSPF external). R3's 'show ip route 10.0.0.0' shows the route via R4. 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
✓
R2's 'distance ospf external 150' makes the external route less preferred than the default AD 110 from R4.
OSPF administrative distance can be set per route type. With 'distance ospf external 150', the external routes from R2 have AD 150, while routes from R4 have default AD 110. R3 prefers the route with lower AD (110 via R4). This is expected behavior, but the question might imply that the route via R2 should be preferred due to some other reason. The correct answer is that the configuration on R2 increases the AD for external routes, making them less preferred.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
R2's 'distance ospf external 150' makes the external route less preferred than the default AD 110 from R4.
Why this is correct
Higher AD means less trust; R3 chooses the lower AD route.
- ✗
R4's route is an inter-area route (AD 110) while R2's route is external (AD 150), so inter-area is preferred.
Why it's wrong here
Both are external type-5; the AD difference is due to configuration.
- ✗
R3 has a route-map that prefers routes from R4.
Why it's wrong here
No route-map mentioned.
- ✗
The route from R2 is not in the OSPF database due to a filter.
Why it's wrong here
R3 learns it but with higher AD.
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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JA
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.