Routing Table Definition

A routing table is a database in a router that stores and updates the locations (addresses) of other network devices and the most efficient routes to them. It is used to directing routing.

A router is a network layer electronic device and/or software that connects at least two networks, such as two LANs (local area networks) or WANs (wide area networks) or a LAN and its ISP's (Internet service provider's) network, and forwards packets (the fundamental unit of data transport on modern computer networks) among them. The network layer, the third layer from the bottom in the OSI (Open Systems Interconnection) seven layer model, is the layer at which IP (Internet protocol) operates, and it is responsible for routing, which is moving packets across the network using the most appropriate paths. Routers regularly share data with each other in order to their routing tables current.

The fields in a typical IP routing table are destination, network mask, next hop, interface and metric. The destination can be either an IP address or a class-based, subnetted or supernetted network ID. A hop is the number of links or routers that are crossed en route to the destination.

A metric consists of any value used by routing algorithms to determine the best route among multiple routes to a destination. Metrics can be based on such information as bandwidth, hop count, path cost, delay, load, MTU (maximum transmission unit), reliability and communications cost.

Created October 9, 2005.
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