What is a Routing Table?

A Routing Table is an electronic document that stores the routes to the various nodes in a computer network. The nodes may be any kind of electronic device connected to the network.

The Routing Table is usually stored in a router or networked computer in the form of a database file. When data needs to be sent from one node to another on the network, the routing table is referred to in order to find the best possible route for the transfer of information.

Hop-by-hop Routing is a common routing method used in networks wherein for each node in the network, the address of the next node leading to the destination is listed. So when a data packet arrives at a particular node, it then refers to the routing table to find the address of the next hop destination. Once it reaches that node, it again refers to the routing table for the address of the next hop and so on, until it reaches the final destination.

For a large network consisting of a number of nodes and routers, the routing tables in all the routers need to be consistent, failing which, routing loops can often develop. This can create problems especially in networks that use the hop-by-hop routing model in which the data packets can end up being sent in an endless loop. Routing loops have always been a recurring problem in networks and one of the major goals of designing routing protocols is the careful avoidance of these routing loops.

Routing tables can generally be maintained manually when the network is small and static. The routing tables for all static network devices never change unless and until the administrator of the network changes them manually. In dynamic routing, the devices themselves automatically build and maintain their own routing tables. They do this by exchanging information regarding the network topology using routing protocols. This enables the devices in the network to automatically adapt to the changes in the network like device failures and network congestion as and when they occur.