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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?
⚠ Common exam trap
The trap is overcomplicating the scenario with administrative distance or route-type confusion — candidates may chase AD values or assume inter-area vs. external distinctions matter, when the question is simply testing that OSPF E2 external routes are selected by lowest external metric.
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.
When two OSPF external (type-5) LSAs describe the same prefix with the same forwarding metric type (both E2 by default), R3 compares the external metric carried in the LSA — 20 versus 30 — and installs the lower-metric path via R1. This is standard OSPF E2 route selection behavior, so the route via R1 is preferred purely on metric.
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 selects among multiple external type-5 routes to the same prefix by comparing metric when forwarding addresses and route types match. R3 therefore installs the R1 path with metric 20, which is standard OSPF behaviour, not a fault.
- ✗
R3 has a static route with AD 1 that overrides both OSPF routes.
Why it's wrong here
R3's output shows the route learned via OSPF, so no static route with AD 1 exists for 172.16.1.0/24; a static would have suppressed both type-5 entries. Static routes are tempting because AD 1 beats OSPF's 110, but the stem's two external routes prove none is installed.
- ✗
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 routes are type-5 externals, not inter-area, so the AD-110 comparison is irrelevant; R3 selects on external metric, and R1's 20 beats R2's 30. Inter-area versus external AD is tempting because it matters when OSPF internal and external paths compete, which is not this case.
- ✗
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
Changing OSPF distance to 150 would not make R3 prefer R1, and AD is not compared between two routes from the same OSPF process; the type-5 metric decides. Distance manipulation is tempting when mixing protocols, but here both candidates arrive as OSPF externals.
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 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
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.