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.
Exhibit
inet.0: 3 destinations, 4 routes (3 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.10.10.0/24 *[OSPF/10] 00:10:00, metric 1, via 10.0.0.1
[OSPF/150] 00:05:00, metric 20, via 10.0.0.2
Refer to the exhibit. Why is the route via 10.0.0.1 selected as the active route?
Exhibit
inet.0: 3 destinations, 4 routes (3 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.10.10.0/24 *[OSPF/10] 00:10:00, metric 1, via 10.0.0.1
[OSPF/150] 00:05:00, metric 20, via 10.0.0.2
A
It has a lower metric
Why wrong: Metric is 1 vs 20, but preference decides first.
B
It has a lower cost
Why wrong: Cost is the same as metric; preference is decisive.
C
It is an older route
Why wrong: Route age (00:10:00 vs 00:05:00) does not influence selection when preferences differ.
D
It has a lower preference
Preference 10 is lower than 150, so it is preferred.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It has a lower preference
In Junos, the active route is selected based on the route preference value, where a lower preference is preferred. Since the route via 10.0.0.1 has a lower preference than the other route, it is chosen as active. This is a fundamental Junos routing decision process, distinct from metrics which are used within a single routing protocol.
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.
Cost is the same as metric; preference is decisive.
✗
It is an older route
Why it's wrong here
Route age (00:10:00 vs 00:05:00) does not influence selection when preferences differ.
✓
It has a lower preference
Why this is correct
Preference 10 is lower than 150, so it is preferred.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that metric (or cost) is the primary tiebreaker for route selection across all scenarios, but in Junos, preference is the first criterion for choosing between routes from different protocols or sources.
Detailed technical explanation
How to think about this question
Junos assigns a default preference value to each routing protocol (e.g., OSPF internal routes have preference 10, static routes have preference 5, BGP routes have preference 170). When multiple routes to the same destination exist from different protocols, the route with the lowest preference is installed in the forwarding table as active. This preference-based selection occurs before any metric comparison, which only applies when comparing routes from the same protocol.
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 practitioner preparing for the JNCIA-JUNOS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: It has a lower preference — In Junos, the active route is selected based on the route preference value, where a lower preference is preferred. Since the route via 10.0.0.1 has a lower preference than the other route, it is chosen as active. This is a fundamental Junos routing decision process, distinct from metrics which are used within a single routing protocol.
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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