Quick Answer
The answer is that Area ID, timers, and authentication settings are three critical factors that influence OSPF neighbor adjacency formation. This is correct because OSPF routers must agree on the same Area ID, as it defines the logical segment of the OSPF domain and is carried in Hello packets; a mismatch causes routers to believe they are in different areas, blocking adjacency. Additionally, Hello and Dead timers must match exactly, and authentication settings—such as simple password or MD5—must be identical, or Hello packets will be rejected. On the JNCIA-Junos exam, this concept tests your understanding of OSPF’s neighbor discovery process, often appearing as a multiple-select question where common traps include forgetting that the Router ID does not need to match or that network types must be compatible but are not a direct adjacency requirement. A useful memory tip is “A-T-A”: Area, Timers, Authentication—three pillars that must align for OSPF neighbors to say hello.
This JNCIA-JUNOS practice question tests your understanding of networking fundamentals. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which THREE factors influence OSPF neighbor adjacency formation? (Choose three.)
Area ID
Must match between neighbors.
Router ID
Why wrong: Router IDs must be unique, not the same.
MTU mismatch
Why wrong: MTU must be identical, not different.
Hello and dead intervals
Must match; mismatch prevents adjacency.
Authentication settings
If authentication is enabled, must match.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Area ID
OSPF neighbor adjacency formation requires that both routers agree on the Area ID, because the Area ID defines the logical segment of the OSPF domain and is included in OSPF Hello packets. If the Area ID does not match, the routers will not form an adjacency, as they would consider themselves in different OSPF areas.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Area ID
Why this is correct
Must match between neighbors.
Related concept
Read the scenario before looking for a memorised answer.
Router ID
Why it's wrong here
Router IDs must be unique, not the same.
MTU mismatch
Why it's wrong here
MTU must be identical, not different.
Hello and dead intervals
Why this is correct
Must match; mismatch prevents adjacency.
Related concept
Read the scenario before looking for a memorised answer.
Authentication settings
Why this is correct
If authentication is enabled, must match.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse Router ID uniqueness (required for OSPF operation) with a matching requirement between neighbors, but Router ID only needs to be unique per router, not identical between peers.
Detailed technical explanation
OSPF Hello packets carry the Area ID, Hello interval, Dead interval, and authentication data (if configured). These parameters must match on both sides for the neighbor state to progress beyond 2-Way. The Dead interval is typically four times the Hello interval, and any mismatch causes the neighbor to be stuck in INIT or EXSTART state. In JUNOS, you can verify these with 'show ospf neighbor detail' and 'show ospf interface'.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
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FAQ
Networking Fundamentals — This question tests Networking Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: Area ID — OSPF neighbor adjacency formation requires that both routers agree on the Area ID, because the Area ID defines the logical segment of the OSPF domain and is included in OSPF Hello packets. If the Area ID does not match, the routers will not form an adjacency, as they would consider themselves in different OSPF areas.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This JNCIA-JUNOS practice question is part of Courseiva's free Juniper 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 JNCIA-JUNOS exam.
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