What is the default administrative distance of OSPF?

Administrative distance is the first criterion that a router uses to determine which routing protocol to use if two protocols provide route information for the same destination. It is a measure of the trustworthiness of the source of the routing information. Keep in mind that administrative distance has only local significance; it is not advertised in routing updates.

Note: The smaller the administrative distance value, the more reliable the protocol. For example, if a router receives a route to a certain network from both Open Shortest Path First (OSPF) (default administrative distance – 110) and Interior Gateway Routing Protocol (IGRP) (default administrative distance – 100), the router will choose IGRP because it is more reliable. This means the IGRP version of the route would be added to the routing table.

If you lose the source of the IGRP-derived information (for example, because of a power shutdown), the software uses the OSPF-derived information until the IGRP-derived information reappears.