- A
The OSPF route is withdrawn.
Correct. Withdrawal of the OSPF route removes the route with lower preference (10), allowing the iBGP route (preference 170) to become active.
- B
Both A and C.
Why wrong: Incorrect. This option claims both A and C are correct, but C is false. A lower metric in iBGP does not override the higher-preference OSPF route; preference is evaluated first.
- C
The iBGP route's metric is lower.
Why wrong: Incorrect. A lower metric in iBGP is irrelevant because OSPF has a better preference (10 vs 170). Metric is only considered when preferences are equal.
- D
The OSPF route's preference is changed to 180.
Correct. Changing the OSPF preference to 180 makes it worse than iBGP's 170, so the iBGP route becomes active.
Question 377 of 514
When iBGP Route Becomes Active: OSPF Withdrawn or Preference Raised | JNCIA-Junos
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?
Quick Answer
The answer is both A and C, because an iBGP route becomes active when the OSPF route is withdrawn or when the OSPF preference is raised above 170.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.
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 OSPF route is withdrawn.
In Junos, the active route is determined by the lowest preference value. OSPF has a default preference of 10, while iBGP has 170. The iBGP route can become active only if the OSPF route is removed from the routing table (withdrawal, option A) or if its preference is increased above 170 (e.g., changed to 180, option D). Both events cause the iBGP route to have the best preference. Option C is incorrect because metric is only considered when preferences are equal, which is not the case here.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
- ✗
Both A and C.
- ✗
The iBGP route's metric is lower.
- ✓
The OSPF route's preference is changed to 180.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse metric with preference, thinking a lower metric in iBGP can override a higher-preference OSPF route, but in Junos, preference is always evaluated before metric.
Detailed technical explanation
How to think about this question
Junos uses a two-step route selection process: first, the route with the lowest preference is chosen; if preferences are equal, then metric (cost) is compared. OSPF's default preference of 10 is much lower than iBGP's 170, so the OSPF route always wins unless its preference is manually altered or the route is withdrawn. This behavior is defined in RFC 4271 for BGP and RFC 2328 for OSPF, and Junos implements it via the 'route preference' parameter, which can be modified per protocol or per route using policy.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
Routing Fundamentals — This question tests Routing Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The OSPF route is withdrawn. — In Junos, the active route is determined by the lowest preference value. OSPF has a default preference of 10, while iBGP has 170. The iBGP route can become active only if the OSPF route is removed from the routing table (withdrawal, option A) or if its preference is increased above 170 (e.g., changed to 180, option D). Both events cause the iBGP route to have the best preference. Option C is incorrect because metric is only considered when preferences are equal, which is not the case here.
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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