- A
The route from R1 is an inter-area route (type-3) while the route from R2 is an external route (type-5); OSPF prefers inter-area over external.
Why wrong: Incorrect because both R1 and R2 generate type-5 LSAs, not type-3.
- B
R3 has a static route with AD 1 that points to R1.
Correct. The static route with AD 1 is more preferred than OSPF routes.
- C
The route from R2 has a higher administrative distance because R2 is an ASBR.
Why wrong: Incorrect because administrative distance is not affected by whether a router is an ASBR.
- D
R3's OSPF process has 'distance ospf external 200' configured, making R2's route less preferred.
Why wrong: Incorrect because configuring 'distance ospf external 200' would affect all external routes equally, making both OSPF routes have AD 200, but the static route still has AD 1, so R3 would still prefer the static route; moreover, the type-5 LSAs would still be compared by metric, leading to R2 if no static route.
OSPF Route Preference: Why Inter-Area Routes Are Chosen Over External
This 300-410 practice question tests your understanding of administrative distance. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. A key principle to apply: administrative Distance. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Router R1 and R2 are iBGP peers. R1 learns a route 10.10.10.0/24 from an eBGP peer with local preference 200. R2 learns the same route from another eBGP peer with local preference 150. Both routers redistribute the route into OSPF with default settings. R3, an OSPF router, receives two type-5 LSAs for 10.10.10.0/24: one from R1 with metric 20, one from R2 with metric 10. R3's 'show ip route 10.10.10.0' shows the route via R1. What is the root cause?
Quick Answer
The answer is that OSPF prefers inter-area routes over external routes, which is why R3 chooses the route via R1 even though R2’s type-5 LSA has a lower metric. In OSPF, the route selection order is intra-area (O) first, then inter-area (O IA), and finally external (O E1/E2 or N1/N2). When R1, acting as an ABR, redistributes the iBGP-learned prefix into OSPF, it generates a type-3 inter-area LSA, while R2’s redistribution produces a type-5 external LSA. Since inter-area routes are inherently preferred over external routes regardless of metric, R3 installs the route via R1. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of OSPF route preference hierarchy and the subtle distinction between redistribution behavior on an ABR versus a non-ABR. A common trap is assuming metric alone decides the winner, but OSPF’s LSA type precedence overrides cost. Memory tip: “I before E, except after C” — Inter-area beats External, and cost only matters within the same LSA type.
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 has a static route with AD 1 that points to R1.
R3 prefers the route via R1 because it has a static route pointing to R1 with administrative distance 1. The static route (AD 1) is preferred over OSPF routes (AD 110). Even though OSPF learns two type-5 LSAs with metrics 20 and 10, the static route overrides them. Therefore, 'show ip route' shows the route via R1.
Key principle: Administrative Distance
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 route from R1 is an inter-area route (type-3) while the route from R2 is an external route (type-5); OSPF prefers inter-area over external.
Why it's wrong here
Incorrect because both R1 and R2 generate type-5 LSAs, not type-3.
- ✓
R3 has a static route with AD 1 that points to R1.
Why this is correct
Correct. The static route with AD 1 is more preferred than OSPF routes.
Related concept
- ✗
The route from R2 has a higher administrative distance because R2 is an ASBR.
Why it's wrong here
Incorrect because administrative distance is not affected by whether a router is an ASBR.
- ✗
R3's OSPF process has 'distance ospf external 200' configured, making R2's route less preferred.
Why it's wrong here
Incorrect because configuring 'distance ospf external 200' would affect all external routes equally, making both OSPF routes have AD 200, but the static route still has AD 1, so R3 would still prefer the static route; moreover, the type-5 LSAs would still be compared by metric, leading to R2 if no static route.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates may assume that the lower OSPF metric determines the route, overlooking the possibility of a static route with lower administrative distance.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Administrative Distance
- Static Route
- OSPF External Route
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Administrative Distance
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
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.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
Administrative Distance — This question tests Administrative Distance — Administrative Distance.
What is the correct answer to this question?
The correct answer is: R3 has a static route with AD 1 that points to R1. — R3 prefers the route via R1 because it has a static route pointing to R1 with administrative distance 1. The static route (AD 1) is preferred over OSPF routes (AD 110). Even though OSPF learns two type-5 LSAs with metrics 20 and 10, the static route overrides them. Therefore, 'show ip route' shows the route via R1.
What should I do if I get this 300-410 question wrong?
Review administrative Distance, then practise related 300-410 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Administrative Distance
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Last reviewed: Jun 18, 2026
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