Which administrative distance (AD) is the lowest?

The administrative distance for directly connected routes is the lowest value, which is 0. This means that any route learned from a directly connected interface is considered the most reliable and trusted source of routing information. In networking, administrative distance is a value used by routers to choose the best path to a destination based on the trustworthiness of the route source. Directly connected routes represent the immediate paths from routers to their interfaces, and since these routes are directly part of the routing device, they have the highest level of confidence assigned to them.

In comparison, the administrative distances for other types of routes are higher: static routes have an AD of 1, eBGP (External Border Gateway Protocol) has an AD of 20, and EIGRP (Enhanced Interior Gateway Routing Protocol) has an AD of 90 for internal routes. Therefore, directly connected routes are prioritized over these other options due to their lower administrative distance, confirming their reliability as the first choice for routing decisions.