Metrics (networking)

Short description: Field in a routing table used to make routing decisions

Router 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.

## Contents

* 1 Examples
* 2 Service level metrics
* 3 See also
* 4 References
* 5 External links

## 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 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]

## References

1. ↑ Rao, S. Dharma; Murthy, C. Siva Ram (2005). "Distributed dynamic QoS-aware routing in WDM optical networks". Computer Networks 48 (4): 585–604. doi:10.1016/j.comnet.2004.11.003.
2. ↑ "Administrative Distance and Metric". https://etutorials.org/Networking/Integrated+cisco+and+unix+network+architectures/Chapter+8.+Static+Routing+Concepts/Administrative+Distance+and+Metric/.
3. ↑ "Understand the significance of administrative distance and metrics when working with routers". https://www.techrepublic.com/article/understand-the-significance-of-administrative-distance-and-metrics-when-working-with-routers/.
4. ↑ "Administrative distance & metric". https://study-ccna.com/administrative-distance-metric/.

## External links

* Survey of routing metrics

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