Dynamic routes are typically learned by enabling the RIP, OSPF, IS-IS or BGP protocols, and are also learned from ICMP redirects exchanged with other routers. These routes are called dynamic routes because they are not a permanent part of the configuration. The routes are learned when the router starts up and are dynamically updated as the network changes. Older dynamic routes are aged out of the tables when an update for the network is not received for a period of time, as determined by the routing protocol.
Once a routing protocol is configured, dynamic routes require no configuration and are automatically updated as the network changes.