How is "administrative distance" defined in routing protocols?

Administrative distance is defined as a value used by routers to rank the trustworthiness of routes learned from different routing protocols. Each routing protocol has a predefined administrative distance, which helps the router to determine which route to prefer when multiple routes to the same destination exist from different sources. For instance, routes learned through static configuration or directly connected interfaces typically have lower administrative distances compared to routes learned dynamically from routing protocols, such as EIGRP or OSPF. This mechanism allows the router to prioritize more reliable and preferred paths over less reliable ones, ensuring efficient and stable routing decisions in a network.

In contrast, the other options do not accurately describe administrative distance: the size of data packets is not relevant to administrative trust levels, performance metrics focus on different aspects of network health rather than route credibility, and thresholds for security enforcement are unrelated concepts that govern access and policy rather than routing path selection.