Metrics (networking) explained

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.

Examples

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.

Service level metrics

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.

See also

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

External links

• Survey of routing metrics

Notes and References

1. 10.1016/j.comnet.2004.11.003 . Distributed dynamic QoS-aware routing in WDM optical networks . 2005 . Rao . S. Dharma . Murthy . C. Siva Ram . Computer Networks . 48 . 4 . 585–604 .
2. Web site: Administrative Distance and Metric . 2021-12-23 . 2021-11-22 . https://web.archive.org/web/20211122173400/http://etutorials.org/Networking/Integrated+cisco+and+unix+network+architectures/Chapter+8.+Static+Routing+Concepts/Administrative+Distance+and+Metric/ . live .
3. Web site: Understand the significance of administrative distance and metrics when working with routers . 19 May 2005 . 2021-12-23 . 2021-12-23 . https://web.archive.org/web/20211223222331/https://www.techrepublic.com/article/understand-the-significance-of-administrative-distance-and-metrics-when-working-with-routers/ . live .
4. Web site: Administrative distance & metric . 26 January 2016 . 2021-12-23 . 2021-12-23 . https://web.archive.org/web/20211223222332/https://study-ccna.com/administrative-distance-metric/ . live .