Network+ routing decisions: longest prefix and default routes
A router selects the most specific matching destination prefix before comparing alternatives for that prefix. A default route is used when no more-specific route applies. The chosen next hop must be usable, and replies need their own return path. Dynamic metrics and route-source preferences answer different questions, so avoid comparing them before checking whether the destination prefixes are equally specific.
How to read the scenario
When a service works in one direction only, inspect the return route and any stateful devices along both paths.
Identify the required outcome, the evidence already provided, and the limits on the technician’s action. Compare every option against those details before deciding. Record why the closest alternative does not meet the stated need.
Original practice example
A router has matching routes for /16 and /24 networks containing the destination. What rule makes it choose the /24 route first?
- Static route
- Longest-prefix match
- Default route
- Dynamic routing
Show the answer and explanation
Longest-prefix match
Routing first selects the most specific matching prefix; other preferences compare routes for the same prefix.
Study questions
Which objective does this guide support?
N10-009, objective 2.1. This independent guide supports original practice and does not replace the full official objectives.
What should I watch for in a scenario?
When a service works in one direction only, inspect the return route and any stateful devices along both paths.
Source and version
CompTIA official N10-009 objectives, objective 2.1. Verified November 5, 2026. Use the exam code when choosing study materials; similarly named certifications can have different objectives.