350-501 Networking Practice Question
An OSPF network uses point-to-point links. The engineer notices that LSAs are being flooded every 30 minutes even when no topology changes occur. What is the most likely reason?
⚠ Common exam trap
Cisco often tests the distinction between event-driven LSA flooding (due to topology changes) and periodic LSA refresh (due to the 30-minute timer), leading candidates to incorrectly attribute the behavior to a network issue like flapping interfaces or misconfigured timers.
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 LSA refresh interval has expired.
In OSPF, LSAs have a default refresh interval of 30 minutes (1800 seconds). When this timer expires, the router that originated the LSA re-floods it to maintain database synchronization, even if no topology changes have occurred. This is normal OSPF behavior defined in RFC 2328, and it explains why LSAs are flooded every 30 minutes.
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 are using LSU packets incorrectly.
Why it's wrong here
Incorrect. LSUs are normal for flooding LSAs.
- ✗
There is a flapping interface on the network.
Why it's wrong here
Incorrect. Flapping would cause frequent updates, not a regular 30-minute pattern.
- ✗
The dead timer is set too low.
Why it's wrong here
Incorrect. Dead timer affects neighbor state, not LSA flooding.
- ✓
The LSA refresh interval has expired.
Why this is correct
Correct. OSPF refreshes LSAs every 30 minutes.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 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 350-501 exam.