JN0-106 Routing Fundamentals Practice Question
A router receives two OSPF routes for 10.10.10.0/24: one intra-area with preference 10 and metric 1, and one external type 2 with preference 150 and metric 20. Which route is selected as active?
⚠ Common exam trap
The trap here is that candidates often focus on metric or route type (intra-area vs external) as the tiebreaker, but Junos strictly uses route preference first, and the large difference (10 vs 150) makes the intra-area route the clear winner regardless of metric values.
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 intra-area route because it has a lower preference
B is correct because Junos uses route preference (administrative distance) as the primary tiebreaker when selecting the active route for a destination. The intra-area OSPF route has a default preference of 10, which is lower than the external type 2 route's preference of 150, so the intra-area route is installed into the routing table regardless of metric values.
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 external route because it is type 2
Why it's wrong here
The OSPF route type (intra-area vs external) affects metric calculation but it does not affect route preference, which is the primary selection criterion in Junos. On Junos, OSPF internal routes have a default preference of 10, while OSPF external routes (both type 1 and type 2) have a default preference of 150. Since the preferences differ, the router selects the route with the lower preference—the intra-area route—regardless of the fact that the external route is type 2. Thus, 'because it is type 2' is an invalid justification: being type 2 only changes how the metric is computed, not the preference.
- ✓
The intra-area route because it has a lower preference
Why this is correct
The intra-area route is the correct choice because Junos selects the route with the lowest preference value among all candidate routes for the same prefix. In this case, the intra-area OSPF route has a preference of 10, while the external OSPF route has a preference of 150; since 10 is lower than 150, the intra-area route is installed as active in the forwarding table. Preference is checked before metric—only when two routes share the same preference does the router compare metrics. Therefore, the lower preference of the intra-area route is the decisive factor, not the route type or metric.
- ✗
The external route because it has a higher metric
Why it's wrong here
The claim that a higher metric makes the external route preferred is incorrect on two counts: Junos prefers a lower metric, not a higher one, and metric comparison only occurs between routes with the same preference. Here, the intra-area route has preference 10 and the external route has preference 150; because these preferences differ, the router does not even examine the metrics, so the external route's metric (higher or lower) is irrelevant. Even if the external route had a very low metric, it would still lose due to its higher preference. Thus, this option misapplies both the metric rule and the order of route selection.
- ✗
The intra-area route because it has a lower metric
Why it's wrong here
Although the intra-area route often has a lower metric than an external route, the lower metric is not why it wins. Junos first evaluates preference; the intra-area route has preference 10 and the external route has preference 150, so the intra-area route is chosen before any metric is considered. If both routes had the same preference (e.g., both were intra-area or both external), then the lower metric would break the tie—but that is not the situation here. Therefore, 'lower metric' is a coincidental observation, not the controlling factor.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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