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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 link, but OSPF adjacency is not forming. Router R1 has the following relevant configuration: interface GigabitEthernet0/0 ip address 10.1.1.1 255.255.255.252 ip ospf network point-to-multipoint ip ospf 1 area 0 Router R2 shows: show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:35 10.1.1.2 GigabitEthernet0/0 But R2's configuration: interface GigabitEthernet0/0 ip address 10.1.1.2 255.255.255.252 ip ospf network broadcast ip ospf 1 area 0 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
✓
Network type mismatch; change both to point-to-point or broadcast.
OSPF network type mismatch: R1 is configured as point-to-multipoint, which does not elect DR/BDR and uses multicast 224.0.0.5 for all neighbors. R2 is broadcast, expecting DR/BDR election and using 224.0.0.6 for DR/BDR communication. This mismatch prevents proper adjacency formation, though R2 sees R1 as FULL due to unidirectional hello. The correct 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.
- ✓
Network type mismatch; change both to point-to-point or broadcast.
Why this is correct
Point-to-multipoint and broadcast have different hello and DR election behaviors, causing adjacency failure.
- ✗
The subnet mask is /30, which is not supported with point-to-multipoint.
Why it's wrong here
Point-to-multipoint works with any subnet mask.
- ✗
The OSPF area is mismatched; both are area 0.
Why it's wrong here
Area is same, so not the issue.
- ✗
The IP addresses are on different subnets; both are 10.1.1.0/30.
Why it's wrong here
IPs are on same subnet.
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.