In terms of administrative distance, which routing protocols are considered the most reliable?

Static routes are considered the most reliable in terms of administrative distance because they are manually configured and do not depend on any complex algorithms or the state of the network to determine optimal paths. The administrative distance (AD) value for static routes is 1, making them the most trusted source of routing information for a router.

Since static routes are pre-defined by the network administrator, the router will always prefer them over dynamically learned routes from protocols like RIP, IGRP, or OSPF. The administrative distances for these dynamic protocols are greater than that of static routes—RIP has an AD of 120, IGRP has an AD of 100, and OSPF has an AD of 110. This means that in a routing decision, if both a static route and a route learned through one of these dynamic protocols exist, the static route will always be chosen because it has a lower administrative distance, ensuring reliable and predictable routing behavior.