300-410 Layer 3 Technologies Practice Question
A network engineer is troubleshooting a flapping OSPFv2 adjacency between two Cisco IOS-XE routers on a broadcast segment. The log shows repeated %OSPF-5-ADJCHG messages with reason 'Dead timer expired'. The engineer confirms that both routers are in Area 0, have identical hello/dead intervals, and are not configured with authentication. Which action most likely resolves the issue?
⚠ Common exam trap
The trap here is assuming that any adjacency problem is caused by OSPF configuration mismatches, when a dead timer expiration often points to a Layer 2 forwarding issue.
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
✓
Check for a Layer 2 loop or unidirectional link on the segment, because hellos are being lost in one direction and the dead timer expires.
The repeated 'Dead timer expired' indicates that the router stopped receiving hellos from its neighbor within the dead interval. Since authentication, area, and timers are correct, the issue is at Layer 2—likely a unidirectional link or loop causing hello loss. Checking Layer 2 and interface counters is the correct troubleshooting step. Other options address issues that would produce different symptoms, such as Init or 2-Way states, not a dead timer expiration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Check for a Layer 2 loop or unidirectional link on the segment, because hellos are being lost in one direction and the dead timer expires.
Why this is correct
The 'Dead timer expired' message means hellos are not being received within the dead interval. Since authentication and timers are correct, the most likely cause is that hellos are lost in one direction due to a Layer 2 loop, unidirectional link, or a faulty cable/port. Verifying the Layer 2 path and interface counters will reveal dropped or missing hellos and resolve the flapping.
- ✗
Verify that the OSPF network type matches on both interfaces; a mismatch between broadcast and point-to-point prevents hellos from being processed correctly.
Why it's wrong here
While OSPF network type mismatches can prevent adjacency formation, they typically cause hellos to be ignored or sent as unicast instead of multicast, leading to 'Init' or '2-Way' states rather than 'Dead timer expired'. In this scenario, the adjacency forms and then drops, which is more consistent with a forwarding-plane issue such as MTU or packet loss, not a network type mismatch.
- ✗
Confirm that the OSPF priority is set to 0 on both interfaces, because a priority of 0 prevents the router from sending hellos on broadcast networks.
Why it's wrong here
OSPF priority 0 only prevents a router from becoming a Designated Router or Backup Designated Router; it does not stop the router from sending or receiving hellos. Adjacency can still form between DR-other routers. Therefore, setting priority to 0 would not cause the dead timer to expire, and changing it would not resolve the flapping.
- ✗
Ensure that both routers have the same OSPF router ID, as duplicate router IDs cause the adjacency to continuously reset.
Why it's wrong here
Duplicate router IDs in OSPF can cause instability, but they usually result in the router ignoring hellos from the duplicate or logging specific errors about router ID conflicts. The 'Dead timer expired' message specifically indicates that hellos are not received, not that there is an ID conflict. Changing the router ID would not address the missing hello packets.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.