Cybersecurity-Apprentice Practice Question: A network engineer configures OSPF on a Palo Alto Networks virtual router
A network engineer configures OSPF on a Palo Alto Networks virtual router. Neighbors are stuck in the EXSTART/EXCHANGE state. What is the most likely cause of this issue?
⚠ Common exam trap
The trap is that candidates see 'neighbors stuck' and immediately blame timers or authentication, but those failures prevent adjacency from forming at all — only MTU mismatch lets neighbors reach EXSTART/EXCHANGE and then stall.
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
✓
An MTU mismatch between the OSPF neighbors
OSPF neighbors stuck in EXSTART/EXCHANGE almost always indicate an MTU mismatch between the two routers. During the ExchangeStart phase, routers negotiate the Database Description (DBD) sequence and Master/Slave roles, and if the MTU values differ, the DBD packets are dropped, preventing progression to the Loading and Full states.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A mismatch in OSPF area ID types (e.g., normal vs. stub)
Why it's wrong here
Area ID type mismatches (normal versus stub) block LSA flooding and routing, but neighbours still reach FULL and exchange LSAs; they do not stall at EXSTART/EXCHANGE. That state indicates an MTU mismatch or duplicate router ID preventing database description packet negotiation. Area type configuration would be the answer if adjacencies formed fully but specific routes were missing.
- ✗
Incorrect OSPF hello or dead timer intervals
Why it's wrong here
OSPF checks the hello and dead intervals in every hello packet, and neighbours with different values discard each other's hellos, so they never reach 2-Way, let alone ExStart. On a Palo Alto virtual router these are set in the OSPF interface timer settings. A timer mismatch is a very common OSPF error, which makes the option tempting, but it stops adjacencies much earlier than the database exchange stages described here.
- ✓
An MTU mismatch between the OSPF neighbors
Why this is correct
In ExStart and Exchange, neighbours swap Database Description packets that include the interface MTU. A router rejects DBD packets whose MTU is larger than its own, so the pair retransmits and never moves on to Loading and Full. Match the MTU on both sides, on PAN-OS in the Layer 3 interface or subinterface settings, rather than ignoring the check, which only hides the problem and can drop large packets later.
- ✗
Authentication type or password mismatch
Why it's wrong here
Authentication mismatches prevent adjacency formation at the INIT or 2-WAY stage, before database description packets are exchanged, so neighbours would not reach EXSTART. The EXSTART/EXCHANGE stall instead points to an MTU mismatch between interfaces. Authentication settings are correctly configured when routers must mutually verify OSPF hello packets before any neighbour relationship forms.
Visual reference
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Written and reviewed by Johnson Ajibi, MSc IT Security
Security Systems Architect · founder of Courseiva
Last reviewed September 2026 · checked against the official Palo Alto Networks exam blueprint
This Cybersecurity-Apprentice practice question is part of Courseiva's free Palo Alto Networks 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 Cybersecurity-Apprentice exam.