What is used to compare routes learned via different routing protocols?

Administrative Distance (AD) is the value used to compare routes learned via different routing protocols in networking. Each routing protocol is assigned a default AD value, which indicates the trustworthiness of that protocol in terms of route selection. When a router learns multiple routes to the same destination from different protocols, it uses the AD to determine which route to prefer. For example, routes learned via a directly connected interface have an AD of 0, while routes learned from protocols like OSPF have an AD of 110, and routes from RIP have an AD of 120. The lower the AD, the more trustworthy the route, leading the router to select the route with the lowest AD when a route to a particular destination is available from multiple sources.

This mechanism allows routers to make informed decisions about which paths to use when forwarding packets, ultimately optimizing the network’s routing efficiency. Understanding AD is critical for network professionals, as it directly influences routing decisions and the overall behavior of the network.