- A
Decrease the OSPF cost on interface ge-0/0/0.0 to 1.
Why wrong: If the cost is already equal, reducing to 1 may work, but if it is already 1, it cannot be decreased further. Also increasing cost on LTE is more direct.
- B
Configure a static route to 10.99.99.99/32 with next-hop referencing the T1 interface and a lower preference than OSPF.
Why wrong: A static route with preference 5 would override OSPF (10), but it is not flexible and could cause issues. Best practice is to adjust OSPF metrics.
- C
Set the OSPF priority on ge-0/0/0.0 to 128 to influence the designated router election.
Why wrong: OSPF priority affects DR/BDR election, not route preference or cost.
- D
Increase the OSPF cost on interface lte-0/0/0.0 to a value higher than the cost on ge-0/0/0.0.
This makes the T1 path lower cost, so it will be the only active route. The LTE path becomes a backup if the T1 fails.
Quick Answer
The answer is to increase the OSPF cost on interface lte-0/0/0.0 to a value higher than the cost on ge-0/0/0.0. This is correct because OSPF cost path selection is based on the cumulative cost to a destination, where lower cost is preferred; by raising the cost on the LTE interface, the T1 path becomes the sole active route, breaking the equal-cost multipath (ECMP) condition that caused the spoke router to load-share traffic. On the JNCIA-Junos exam, this scenario tests your understanding of OSPF metric manipulation and how interface cost directly influences route preference, often appearing in troubleshooting questions where unintended ECMP occurs. A common trap is assuming that adjusting the reference bandwidth or using static routes is the fix, but the most precise and scalable method is adjusting the cost at the interface level. Remember the mnemonic: "Lower cost, lower latency—raise the cost to break the tie."
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 network engineer is managing a hub-and-spoke OSPF network for a retail company. The hub router (hub01) is at the data center with a loopback address 10.99.99.99. The spoke router (spoke01) is at a branch office and connects to hub01 via two links: a primary T1 link on interface ge-0/0/0.0 and a backup LTE link on interface lte-0/0/0.0. Both links are in area 0. Recently, the spoke router began sending traffic to the hub's loopback over the LTE link instead of the T1 link, causing higher latency and data charges. The engineer checks the routing table on spoke01 and sees that the route to 10.99.99.99/32 has two equal-cost next-hops: one via ge-0/0/0.0 and one via lte-0/0/0.0. The engineer wants to ensure that only the T1 link is used under normal conditions, with the LTE link as a backup. Which action should the engineer take to achieve this?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"primary"Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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
Increase the OSPF cost on interface lte-0/0/0.0 to a value higher than the cost on ge-0/0/0.0.
The correct answer is A. By increasing the OSPF cost on the LTE interface, the path via LTE becomes higher cost, making the T1 path the only active route (since ECMP will break). Option B may not work if the T1 cost is already at the minimum (1). Option C uses a static route, which would override OSPF but is not best practice and could cause routing loops. Option D affects DR election, not route selection. Hence, A is the best course of action.
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.
- ✗
Decrease the OSPF cost on interface ge-0/0/0.0 to 1.
Why it's wrong here
If the cost is already equal, reducing to 1 may work, but if it is already 1, it cannot be decreased further. Also increasing cost on LTE is more direct.
- ✗
Configure a static route to 10.99.99.99/32 with next-hop referencing the T1 interface and a lower preference than OSPF.
Why it's wrong here
A static route with preference 5 would override OSPF (10), but it is not flexible and could cause issues. Best practice is to adjust OSPF metrics.
- ✗
Set the OSPF priority on ge-0/0/0.0 to 128 to influence the designated router election.
Why it's wrong here
OSPF priority affects DR/BDR election, not route preference or cost.
- ✓
Increase the OSPF cost on interface lte-0/0/0.0 to a value higher than the cost on ge-0/0/0.0.
Why this is correct
This makes the T1 path lower cost, so it will be the only active route. The LTE path becomes a backup if the T1 fails.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
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.
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
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: Increase the OSPF cost on interface lte-0/0/0.0 to a value higher than the cost on ge-0/0/0.0. — The correct answer is A. By increasing the OSPF cost on the LTE interface, the path via LTE becomes higher cost, making the T1 path the only active route (since ECMP will break). Option B may not work if the T1 cost is already at the minimum (1). Option C uses a static route, which would override OSPF but is not best practice and could cause routing loops. Option D affects DR election, not route selection. Hence, A is the best course of action.
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.
Are there clue words in this question I should notice?
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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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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