hardMultiple Choice
300-410 Practice Question: An engineer configures OSPF on two routers…
An engineer configures OSPF on two routers connected via a serial link. Both routers show the neighbor state as EXSTART/EXSTART, and no LSAs are exchanged. The engineer verifies that the OSPF process IDs are the same, areas match, and authentication is correct. Which is the most likely explanation?
⚠ Common exam trap
The trap is picking hello/dead interval mismatches because they are common OSPF issues; however, those cause failures earlier in the adjacency process, while EXSTART specifically points to MTU or DBD exchange problems.
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
✓
MTU mismatch between the two routers
OSPF neighbors stuck in EXSTART/EXSTART indicate a failure during database description (DBD) packet exchange, most commonly caused by an MTU mismatch on the interface. The master/slave negotiation cannot complete because the routers cannot agree on the initial DBD sequence, often due to differing MTU values. The fix is to match MTU on both interfaces or use 'ip ospf mtu-ignore'.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
MTU mismatch between the two routers
Why this is correct
OSPF routers exchange DBD packets in ExStart to elect master/slave and agree on the initial sequence number. An MTU mismatch prevents the DBD exchange from completing, leaving both neighbours stuck in ExStart with no LSAs exchanged, despite matching areas and authentication.
- ✗
OSPF network type mismatch (e.g., point-to-point vs broadcast)
Why it's wrong here
A network type mismatch typically causes the neighbor to get stuck in INIT or 2WAY, not EXSTART.
- ✗
OSPF hello interval mismatch
Why it's wrong here
A hello interval mismatch prevents the neighbor from forming at all; the state would remain DOWN.
- ✗
OSPF dead interval mismatch
Why it's wrong here
A dead interval mismatch also prevents neighbor formation, resulting in DOWN state.
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.