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300-410 Practice Question: Is troubleshooting an OSPFv2 adjacency issue…
A network engineer is troubleshooting an OSPFv2 adjacency issue between two directly connected routers, R1 and R2, both running IOS-XE. The link is a point-to-point Ethernet link. The engineer issues 'show ip ospf neighbor' on R1 and sees no neighbors. 'show ip ospf interface GigabitEthernet0/0' on R1 shows 'Network Type BROADCAST', but the link is actually a point-to-point link. Both routers have 'ip ospf 1 area 0' configured on the interface. What is the most likely cause of the adjacency not forming?
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 routers have duplicate OSPF router IDs.
The default OSPF network type on Ethernet interfaces is BROADCAST, which requires a DR/BDR election and uses multicast 224.0.0.5 and 224.0.0.6. On a point-to-point link, if both routers do not agree on the network type, they may not form an adjacency because the hello packets are sent differently. However, since both are BROADCAST, they should form an adjacency. The real issue is likely a mismatch in OSPF network type if one side is manually set to POINT-TO-POINT, but here both are BROADCAST. A more common cause is that the interface is administratively down or there is a Layer 1 issue, but the stem indicates the interface is up. Another common cause is that the router IDs are not configured, leading to OSPF not starting. The most likely cause in this scenario is that the routers have duplicate router IDs, which prevents adjacency formation. The stem does not mention router IDs, so the best answer is that the engineer should check for duplicate router IDs.
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 OSPF network type mismatch between the two routers (one is BROADCAST, the other is POINT-TO-POINT).
Why it's wrong here
Both show BROADCAST, so no mismatch.
- ✓
The routers have duplicate OSPF router IDs.
Why this is correct
Duplicate router IDs prevent OSPF adjacency from forming; each router must have a unique router ID.
- ✗
The interface is configured with 'ip ospf passive-interface'.
Why it's wrong here
Passive interface would still allow the router to receive hellos but not send them, but the neighbor list would show the neighbor in INIT state, not absent.
- ✗
The OSPF process is not enabled globally; 'router ospf 1' is missing.
Why it's wrong here
If 'ip ospf 1 area 0' is configured on the interface, the process is automatically created if not already present.
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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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.