The answer is both A and C, because an iBGP route becomes active when the OSPF route is withdrawn or when the OSPF preference is raised above 170. In Junos, the routing table selects the active route based on the lowest preference value, not the metric, when protocols differ. OSPF’s default preference of 10 is far lower than iBGP’s 170, so OSPF wins by default. However, if the OSPF route disappears or its preference is manually increased beyond 170, the iBGP route immediately becomes active. On the JNCIA-Junos exam, this question tests your understanding of route selection logic and the distinction between preference and metric—a common trap is confusing metric comparison with preference comparison. Remember: preference decides between protocols; metric only breaks ties within the same protocol. A useful memory tip is “preference first, metric later”—if preferences differ, metric never matters.
JNCIA-JUNOS Routing Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of routing 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.
A router is running OSPF and iBGP. Both protocols learn a route to 10.0.0.0/8. The OSPF route is in the routing table with a preference of 10, and the iBGP route has a preference of 170. Which event would cause the iBGP route to become active?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Both A and C.
If the OSPF route is withdrawn, the iBGP route becomes active. Also, if the OSPF preference is increased above 170, iBGP wins. So both A and C are valid. Option B does not apply because metric is not compared when preferences differ.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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The OSPF route is withdrawn.
Why it's wrong here
This alone would cause iBGP to become active, but there is another correct option.
✓
Both A and C.
Why this is correct
Either withdrawing the OSPF route or increasing its preference above 170 allows the iBGP route to become active.
Metric is not considered when preferences differ; preference is primary.
✗
The OSPF route's preference is changed to 180.
Why it's wrong here
This alone would cause iBGP to become active, but there is another correct option.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related JNCIA-JUNOS OSPF questions on adjacency and route selection.
Routing Fundamentals — This question tests Routing Fundamentals — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Both A and C. — If the OSPF route is withdrawn, the iBGP route becomes active. Also, if the OSPF preference is increased above 170, iBGP wins. So both A and C are valid. Option B does not apply because metric is not compared when preferences differ.
What should I do if I get this JNCIA-JUNOS question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related JNCIA-JUNOS OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.