Metrics (networking)

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Routing metrics are configuration values used by a router to make routing decisions. A metric is typically one of many fields in a routing table. Router metrics help the router choose the best route among multiple feasible routes to a destination. The route will go in the direction of the gateway with the lowest metric.

A router metric is typically based on information such as path length, bandwidth, load, hop count, path cost, delay, maximum transmission unit (MTU), reliability and communications cost.

A metric can include:

• measuring link utilization (using SNMP)
• number of hops (hop count)
• speed of the path
• packet loss (router congestion/conditions)
• network delay
• path reliability
• path bandwidth
• throughput [SNMP - query routers]
• load
• maximum transmission unit (MTU)
• administrator configured value

In EIGRP, metrics is represented by an integer from 0 to 4,294,967,295 (The size of a 32-bit integer). In Microsoft Windows XP routing it ranges from 1 to 9999.

A metric can be considered as:^[1]

• additive - the total cost of a path is the sum of the costs of individual links along the path,
• concave - the total cost of a path is the minimum of the costs of individual links along the path,
• multiplicative - the total cost of a path is the product of the costs of individual links along the path.

Router metrics are metrics used by a router to make routing decisions. It is typically one of many fields in a routing table.

Router metrics can contain any number of values that help the router determine the best route among multiple routes to a destination. A router metric is typically based on information like path length, bandwidth, load, hop count, path cost, delay, MTU, reliability and communications cost.

• Administrative distance, indicates the source of routing table entry and is used in preference to metrics for routing decisions^[2][3][4]

• Survey of routing metrics