What is the Administrative Distance for unknown routes?

The Administrative Distance (AD) is a value that routers use to rank the trustworthiness of different routing sources—lower values indicate more trusted sources. In the case of unknown routes, which include routes that the router cannot directly learn from any routing protocol or static route, the Administrative Distance is assigned a value of 255. This high value essentially tells the router to treat these routes as unreliable and not to use them for routing decisions.

This concept helps ensure that a router prioritizes known good routes over unknown or potentially faulty routes. By assigning unknown routes the AD of 255, routers prevent them from being added to the routing table, thereby safeguarding the network's reliability and performance.