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300-410 Practice Question: Router R1 and R2 are iBGP peers in the same AS
Router R1 and R2 are iBGP peers in the same AS. R1 learns a route 172.16.1.0/24 from an eBGP peer with AS_PATH 100 200. R2 learns the same prefix from another eBGP peer with AS_PATH 100. Both routers redistribute the route into OSPF with default administrative distance. R3, an OSPF internal router, sees two OSPF external routes for 172.16.1.0/24: one from R1 (type-5, metric 20) and one from R2 (type-5, metric 30). R3's 'show ip route 172.16.1.0' shows the route via R1. What is the root cause of R3 preferring the route via R1?
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
✓
R3 prefers the route with the lower metric (20) over the higher metric (30), which is correct OSPF behavior.
OSPF prefers external routes based on metric (cost) first for type-5 routes. The route from R1 has metric 20, R2 has metric 30, so R1 is preferred. However, if the administrative distance of OSPF external routes is changed via 'distance ospf external 150', then the route with lower AD is chosen. The correct answer is that the default AD for OSPF external is 110, so metric decides. The question implies a trick: the route from R2 might have a higher metric but lower AD due to a configuration, but the default is unchanged.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
R3 prefers the route with the lower metric (20) over the higher metric (30), which is correct OSPF behavior.
Why this is correct
OSPF external routes are compared by metric first when the same type; lower metric wins.
- ✗
R3 has a static route with AD 1 that overrides both OSPF routes.
Why it's wrong here
No static route mentioned.
- ✗
The route from R1 is an OSPF inter-area route (AD 110) while from R2 is external (AD 110), so they are equal; metric decides.
Why it's wrong here
Both are external type-5.
- ✗
R3's OSPF process has 'distance 150' configured, making all OSPF routes AD 150, but the route from R2 is redistributed from BGP with a lower AD.
Why it's wrong here
No evidence of distance change.
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
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.