4.1.4. Administrative Distance

Administrative Distance (AD) is a measure of trustworthiness of a routing source. Lower AD = more trusted. Used when multiple routing sources provide routes to the same destination. Only the lowest-AD route is installed; the losing source keeps its route in its own database, so if the winner is withdrawn the next-best route is installed automatically (the principle behind floating static routes).

In show ip route the bracketed pair is [AD/metric]: in O 10.0.0.0/8 [110/20], 110 is OSPF's AD and 20 is the route's metric (for OSPF, the summed interface cost, not a hop count).