Administrative Distance
Many companies and organizations use a single routing protocol. However, in some cases, a company needs to use multiple routing protocols. For example, if two companies connect their networks so that they can exchange information, they need to exchange some routing information. If one company uses OSPF, and the other uses EIGRP, on at least one router, both OSPF and EIGRP must be used. Then, that router can take routes learned by OSPF and advertise them into EIGRP, and vice versa, through a process called route redistribution.
Depending on the network topology, the two routing protocols might learn routes to the same subnets. When a single routing protocol learns multiple routes to the same subnet, the metric tells it ...
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