JN0-106 Routing Fundamentals Practice Question
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 10.0.0.2Refer to the exhibit. Why is the route via 10.0.0.1 selected as the active route?
⚠ Common exam trap
The JNCIA-JUNOS exam 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.
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
✓
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.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It has a lower metric
Why it's wrong here
While the route via 10.0.0.1 indeed has a lower metric (1 versus 20), metric in Junos is only compared after route preference has been evaluated. Two routes from different protocols or with different preference values are never compared by metric; the route with the better (lower) preference is always chosen first. Since the selected route wins on preference, the metric is not the reason it is installed.
- ✗
It has a lower cost
Why it's wrong here
Junos treats 'cost' as a protocol-specific metric (e.g., OSPF interface cost), not an independent route-selection parameter. Even if a lower cost appears attractive, it is considered only as a tie-breaker after preference. Here the route via 10.0.0.1 is preferred because its preference (10) is far lower than the alternative's (150), so any cost difference is irrelevant to the final decision.
- ✗
It is an older route
Why it's wrong here
The route age (00:10:00 versus 00:05:00) is informational only and does not participate in Junos route selection. Junos uses preference, then protocol-specific metrics, and then other tie-breakers like next-hop type or router ID—but never how long a route has been in the table. Therefore, the older route is not chosen because it is older; it is chosen because it has a more preferred protocol source.
- ✓
It has a lower preference
Why this is correct
This is correct: route preference is the first and most decisive factor in Junos active-route selection. Preference is a numeric value assigned to each protocol (for example, static is 5 or 10, OSPF internal is 10, OSPF external is 150). When multiple routes to the same destination exist, Junos installs the one with the lowest preference, so the route via 10.0.0.1 with preference 10 wins over the less-preferred alternative with preference 150.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 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 JN0-106 exam.