JN0-106 Routing Fundamentals Practice Question
You configure an aggregate route for 172.16.0.0/16. What must exist for this aggregate to be active in the routing table?
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
✓
A contributing route (more specific route within the aggregate range)
The correct option is C: a contributing route (a more specific route within the aggregate range) must exist for the aggregate to become active. In Junos, an aggregate route is only installed into the routing table when at least one more-specific route covered by the aggregate prefix is present in the routing table; for 172.16.0.0/16, that means a route such as 172.16.1.0/24 must be learned or configured. Option A is incorrect because a directly connected interface on the exact aggregate subnet is not required, and a more-specific connected route would itself serve as the contributing route. Option B is incorrect because a static route to the aggregate prefix does not activate the aggregate and would conflict with the aggregate's purpose. Option D is incorrect because aggregate routes are not unconditionally active; they depend on the presence of contributing routes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A directly connected interface on that subnet
Why it's wrong here
A directly connected interface on a subnet within 172.16.0.0/16 would generate a direct route that could serve as a contributor, but it is not a prerequisite for aggregate activation. Junos only requires the presence of any active route whose prefix length is longer than the aggregate's /16 mask, regardless of whether that route was learned via a direct interface, static configuration, or a dynamic protocol. Therefore, demanding a directly connected interface incorrectly imposes a single source where multiple are valid.
- ✗
A static route to the aggregate prefix
Why it's wrong here
Installing a static route to 172.16.0.0/16 would not satisfy the contributor rule because the aggregate's own prefix is not more specific than itself. For an aggregate to become active, the routing table must contain a route that falls inside the aggregate range with a longer prefix length—for example, 172.16.10.0/24—and a static route to the exact /16 simply duplicates the aggregate and fails that test. This redundancy also risks confusion in policy or forwarding, so it is both unnecessary and ineffective as a contributor.
- ✓
A contributing route (more specific route within the aggregate range)
Why this is correct
The one mandatory configuration for an aggregate route is a contributing route: any active route with a prefix that is more specific than 172.16.0.0/16 and whose destination lies within that aggregate's address space. Junos evaluates the routing table for such routes and installs the aggregate with a next hop derived from the selected contributor; without at least one contributor, the aggregate is not installed and cannot be advertised or used for packet forwarding. This requirement ensures the aggregate always has a valid forwarding path rather than becoming a black hole.
- ✗
Nothing; the aggregate is always active once committed.
Why it's wrong here
Committing an aggregate route does not make it inherently active; the route remains inactive until the routing table contains a matching more-specific route. If all contributing routes are withdrawn, the aggregate is removed from the active route table even though its configuration persists, preventing the router from advertising a summary that leads to nowhere. Thus, an aggregate with no contributors is effectively dormant, and relying on 'commit means active' is a common error in aggregate configuration.
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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.