Routing table updating methods

Routers use routing table entries to make forwarding decisions. There are three ways to update the routing table entries: automatic, manual, and dynamic.

In the automatic method, the router automatically adds routing information to the routing table from the IP configuration we assign to its interfaces. The routes the router adds from the IP configuration of interfaces are called the directly connected and local routes. It uses the directly connected routes to reach the network connected to the interface. It uses the local route to reach the interface.

In the manual method, we manually add routing information to the routing table. The routes we manually add to the routing table are known as static, floating static, and default routes.

In the dynamic method, we configure a routing protocol on all routers of the network. The routing protocol automatically discovers all routes from the network and adds them to the routing table of each router.

This tutorial is part of the tutorial series "Understanding route types in the routing table.". Other parts of this series are the following.

Chapter 1 The show IP route command on Routers

Chapter 2 Routing table updating methods

Chapter 3 Directly connected routes and Local routes

Chapter 4 Static and Floating Static Routes Explained

Chapter 5 Static and Dynamic routes in the routing table

Chapter 6 Default Route in the Routing Table

Chapter 7 Network Routes and Host Routes Explained

Chapter 8 CCNA Exam Practice Question with Answer 1

The following table compares the methods a router can use to build the routing table.

ParameterAutomatic Manual Dynamic
Speed It is a fast method. The router adds the routes to the routing table as soon as we start the interface having the IP configuration. It is a normal method. The router adds the route to the routing table when we configure it. It is a slow method. The router depends on the routing protocols. Different routing protocols take different times to discover network routes.
Configuration The router automatically learns the routes from the IP configuration we assign to the interfaces. We do not need to change any additional settings for it. The router learns the routes from the routes we configure in global configuration mode. The router learns the routes from the routing protocol we configure on it.
Update The router automatically updates these routes when we update the IP configuration on interfaces. To update these routes in the routing table, we need to manually change the related route in global configuration mode. The routing protocol updates these routes in the routing table.
RemoveThe router automatically removes these routes when we shut down the related interfaces. To remove these routes from the routing table, we have to manually remove the related route in global configuration mode. If any route goes down, the routing protocol removes them from the routing table. To remove these routes from the routing table, we have to manually remove the related route in global configuration mode.
ManagementThe management is easy. The management is simple. The management is complex.

routing table update method

Key points:-

  • Routers use the routing table to make forwarding decisions.
  • There are three ways to add entries to the routing table.
  • In the automatic method, the router automatically learns routes from the IP configuration we make on interfaces.
  • In the manual method, we manually add routes to the routing table.
  • In the dynamic method, we configure a routing protocol, and the routing protocol learns, adds, and manages all network routes.

ComputerNetworkingNotes CCNA Study Guide Routing table updating methods