What does an administrative distance indicate in routing?

An administrative distance represents the reliability of a route in the context of routing protocols. It is a value assigned to each routing protocol that indicates the trustworthiness or preference level of the route learned from that protocol. When a router receives routes from multiple routing protocols, it uses the administrative distance to determine which route to install in its routing table. A lower administrative distance indicates a more reliable or preferred route. For example, routes learned through directly connected interfaces have an administrative distance of 0, while routes learned via certain dynamic routing protocols like RIP or OSPF have higher administrative distances.

In contrast, other options like data transmission speed, physical distance between routers, and the cost of a routing path pertain to different aspects of networking and routing. Speed of data transmission is related to bandwidth or latency, physical distance relates to the geographic separation of devices, and cost in routing can refer to metrics utilized by specific protocols, not the administrative distance itself. Thus, the correct understanding of administrative distance focuses on how routers evaluate and trust the routes they learn.