Routers add entries to routing table with the help of routing protocols. The commonly used routing protocols are,
Routing Information Protocol(RIP):-
It is used to advertise the current status and information in the routing table, including the routes to the rest of the routers in every 30 seconds.
Open Shortest Path First(OSPF):-
It is used to determine the shortest path, otherwise known as the lowest cost path among the nodes of different networks.