JN0-106 Routing Fundamentals Practice Question
A Juniper device receives several routes to the same destination prefix from different routing protocols. Which parameter is used first to select the active route?
⚠ Common exam trap
It's easy for candidates to confuse route preference with metric, thinking that a lower metric from one protocol will automatically beat a higher metric from another protocol, but in reality, metric comparisons are only valid within the same routing protocol.
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
✓
Route preference (administrative distance)
When a Juniper device receives multiple routes to the same destination prefix from different routing protocols, the route preference (also known as administrative distance) is the first tiebreaker used to select the active route. Each protocol has a default preference value (e.g., OSPF internal routes have a preference of 10, while static routes have a preference of 5), and the route with the lowest preference is chosen as active. This occurs before any metric or other path attribute is considered.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Route preference (administrative distance)
Why this is correct
Route preference (administrative distance) is the first criterion Junos uses when selecting the best route to a destination among routes from different routing protocols. Each protocol has a default preference value (e.g., OSPF 10, BGP 170), and the route with the lowest preference wins. Because these values are locally defined and universally comparable across protocols, they serve as the primary tie-breaker.
- ✗
Metric
Why it's wrong here
Metric is a protocol-specific cost value, such as OSPF cost or RIP hop count, and is only compared between routes that originate from the same routing protocol. Metrics are not normalized across protocols, so comparing an OSPF metric to a BGP metric is meaningless. Therefore Junos evaluates route preference first, and only if multiple routes come from the same protocol does metric decide the winner.
- ✗
AS path length
Why it's wrong here
AS path length is a BGP path attribute that explicitly records the number of ASes traversed by a route. It is only consulted during the BGP decision process, and only when comparing two or more BGP routes after route preference and other protocol-level checks. At the top-level route selection across different protocols, AS path length is never considered because it is not a property of non-BGP routes.
- ✗
Local preference
Why it's wrong here
Local preference is a BGP well-known discretionary attribute used to influence outbound traffic by prioritizing exit points within an AS. It is evaluated only inside the BGP path selection algorithm, after route preference and after comparing BGP routes against each other. When selecting a route among OSPF, static, and BGP, local preference is irrelevant because it does not exist for non-BGP protocols and is not a global routing parameter.
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
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.