LEARN. PRACTICE. GROW.Concept and mechanism
Route selection and packet-forwarding lookup are related but distinct decisions. Among valid routes for the same prefix, lower Junos preference is favored under the exercise conditions. During forwarding, a destination matching installed /16 and /24 entries uses the more-specific prefix. Do not transfer preference comparison to prefixes of different lengths. A static route also requires a resolvable next hop in the applicable context; lowering preference does not create missing connectivity. Configuration can be syntactically correct while still failing to produce the usable route a project expected.
Guided application
In the fictional example, the team adds a route to inet.0 while the flow belongs to FUNDS.inet.0. Global presence does not prove availability in that instance. Confirm table, entry, next hop, return, and authorized policy. If connectivity sharing is necessary, define only justified scope instead of importing every route for convenience. Static routes offer explicit control for simple cases; dynamic protocols distribute and adapt information while adding state and dependencies that also need observation. To accept a change, use a representative flow and test the relevant degraded condition. Showing a prefix in a console is partial evidence; the aim is to demonstrate that the application uses the intended path without expanding access beyond agreement.
10.40.7.18 uses the installed /24 through B even when an aggregate /16 through A exists.
Common pitfalls
Preference as reachability; global table as all instances; known route as validated traffic; forward path without return.
Related topics: Addressing and capacity · Junos planes and state interpretation · CLI, candidate, and rollback
Follow the flow in the correct table and context.
Reference: Route preferences · JN0-106, effective 2026-04-06; Junos OS 21.2 exam baseline