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300-410 Practice Question: Router R1 and R2 are connected via a serial link…
Router R1 and R2 are connected via a serial link running OSPF. R1 has 'ip ospf network point-to-point' configured on the interface, while R2 has default broadcast network type. R1's 'show ip ospf neighbor' shows R2 in FULL state, but R2's 'show ip ospf neighbor' shows R1 in FULL state. However, R1's routing table does not contain a route to a subnet 10.10.10.0/24 that is advertised by R2 via a type-3 LSA. R2's 'show ip route 10.10.10.0' shows it as connected. 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
✓
The network type mismatch causes R1 to not install the type-3 LSA because the LSA has a DR field that is not valid for point-to-point networks.
Network type mismatch on a point-to-point link can cause OSPF adjacency to form but may affect LSA propagation. With point-to-point, R1 expects no DR/BDR election and uses a different LSA format. R2, with broadcast, expects DR/BDR. The adjacency forms because both see each other as neighbors, but the type-3 LSA from R2 might be generated incorrectly or R1 may not accept it due to network type mismatch. The correct answer is that the network type mismatch causes R1 to ignore type-3 LSAs from R2 because R1 expects the link to be point-to-point and R2's LSA includes a DR field that R1 does not process.
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 network type mismatch causes R1 to not install the type-3 LSA because the LSA has a DR field that is not valid for point-to-point networks.
Why this is correct
OSPF network type mismatch can lead to LSA filtering; point-to-point interfaces ignore LSAs with DR information.
- ✗
R2's OSPF process has 'distance 150' set, making the route unreachable.
Why it's wrong here
AD does not affect LSA installation; it affects route preference.
- ✗
R1 has a distribute-list blocking the 10.10.10.0/24 route.
Why it's wrong here
No distribute-list mentioned.
- ✗
The subnet 10.10.10.0/24 is not in R2's OSPF database due to a missing network command.
Why it's wrong here
R2 shows it as connected, but OSPF must be enabled on that interface.
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.