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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 routers connected via a VLAN trunk. R1 and R2 are in different VLANs but are connected through a Layer 2 switch. The engineer has configured 'ip ospf 1 area 0' on the subinterfaces. The adjacency forms but is stuck in INIT state. What is the most likely 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 routers have the same OSPF router ID.
The INIT state indicates that the router has received a hello packet from the neighbor but the neighbor has not seen its own router ID in the hello packet. This is often due to a mismatch in the OSPF network type or a unicast communication issue. In a VLAN trunk scenario, if the subinterfaces are not in the same VLAN, the routers may not be able to communicate at Layer 2. However, the most common cause is that the routers are using the same router ID, which causes the hello packet to be ignored because the router sees its own router ID in the neighbor list.
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 routers have the same OSPF router ID.
Why this is correct
When a router receives a hello packet with its own router ID, it ignores it, causing the adjacency to stay in INIT.
- ✗
The OSPF hello interval is mismatched between the two routers.
Why it's wrong here
A hello interval mismatch would cause the adjacency to not form at all, not to be stuck in INIT.
- ✗
The subinterfaces are in different VLANs, preventing Layer 2 communication.
Why it's wrong here
If they were in different VLANs, the routers would not receive each other's hellos, so no adjacency would form.
- ✗
The OSPF network type is set to point-to-point on one side and broadcast on the other.
Why it's wrong here
A network type mismatch would cause the adjacency to be stuck in EXSTART or EXCHANGE, not INIT.
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.