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300-410 Practice Question: Two routers R1 and R2 are connected via Ethernet
Two routers R1 and R2 are connected via Ethernet. R1 has:
interface GigabitEthernet0/0 ip ospf network point-to-point
R2 has default OSPF network type (broadcast). R1 shows:
R1# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.2.2.2 0 FULL/ - 00:00:35 10.1.1.2 GigabitEthernet0/0
R2 shows:
R2# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.1 1 FULL/DR 00:00:30 10.1.1.1 GigabitEthernet0/0
R1 is not installing OSPF routes from R2. 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
✓
OSPF network type mismatch prevents proper LSA exchange, causing R1 to ignore routes from R2.
OSPF network type mismatch: R1 is point-to-point, R2 is broadcast. On the point-to-point side, R1 expects no DR/BDR election and uses a different LSA format. The broadcast side sees R1 as DR (because R1's priority is 0? Actually R1 has priority 0? Output shows R1's neighbor has priority 0, but R2 shows R1 as DR. This inconsistency causes adjacency but routes are not exchanged properly due to LSA type mismatch. The fix is to match network types.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
OSPF network type mismatch prevents proper LSA exchange, causing R1 to ignore routes from R2.
Why this is correct
R1 is configured as point-to-point, R2 as broadcast. This causes R1 to not process Type 2 LSAs from R2.
- ✗
R1 has a higher OSPF priority, causing it to become DR and not accept routes.
Why it's wrong here
R1's priority is 0 (shown in neighbor output), so it cannot be DR.
- ✗
The dead timer mismatch causes adjacency to be unstable.
Why it's wrong here
Dead timers are consistent (35 and 30 seconds are within tolerance).
- ✗
R2 is not configured with the same OSPF process ID.
Why it's wrong here
Process ID does not need to match for adjacency.
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
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