Cisco Certified Network Associate (CCNA) Practice Exam

Which administrative distance value is used for unknown routes?

1. 170

2. 200

3. 225

4. 255

The correct answer is: 225

When determining the administrative distance for unknown routes in Cisco systems, it is important to recognize that the value assigned for unknown or unreachable routes is standardized. The administrative distance used for unknown routes is 255. This indicates that the route is not reachable or valid, and essentially prevents the route from being used in the routing table. In this case, the higher the administrative distance, the less likely the route will be selected by the router for routing decisions. An administrative distance of 255 effectively means that the route is ignored, ensuring that the router does not attempt to route traffic through an undefined or unknown path. Therefore, the correct answer aligns with the established protocol of assigning an administrative distance of 255 to unknown routes.