Metric Definition

A metric is a measurement of performance in some product or system, such as a program or a network.

Although often used interchangeably with measurement, the term is also sometimes used to mean a composite of two or more independent measures, typically in the form of a ratio. There is no relation to metric as used in metric system.

Routers use metrics to make routing decisions, and metric is one of the fields in a typical routing table. A router is an electronic device and/or software that connects at least two networks, such as two LANs (local area networks) or WANs (wide area networks), and forwards packets among them. 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.

In this case, the metric consists of any value used by routing algorithms to determine the best route among multiple routes to a destination. It is typically based on such information as bandwidth, hop count, path cost, delay, load, MTU (maximum transmission unit), reliability and communications cost. A hop is the number of links or routers that are crossed en route to the destination. MTU is the largest packet size, measured in bytes, that can be transmitted over a network.

Created October 13, 2005.
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