The AD (Administrative Distance) is used when the router has learned about a prefix and has to decide which entry to install in the routing table. For example, let’s say a router is running both OSPF and EIGRP and learns about network 192.168.1.0/24. Which source do we trust more? OSPF or EIGRP? In this case, the AD is the tie breaker, the lower the value the more reliable the source is. OSPF has an AD of 110 while EIGRP (internal) has an AD of 90, which means that the information from EIGRP will be installed in the routing table. These lessons explain more about the administrative distance or show you how to manipulate the AD.