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Modifying the Interface Metric

All IS-IS interfaces have a cost, which is a routing metric that is used in the IS-IS link-state calculation. Routes with lower total path metrics are preferred over those with higher path metrics. When there are several equal-cost routes to a destination, traffic is distributed equally among them.

The cost of a route is described by a single dimensionless metric that is determined using the following formula:



cost = reference-bandwidth/bandwidth

reference-bandwidth is the reference bandwidth. If the reference bandwidth is not configured, all interfaces have a default metric of 10 (with the exception of the lo0 interface, which has a default metric of 0).

To modify the reference bandwidth, include the reference-bandwidth statement:




reference-bandwidth reference-bandwidth;

For a list of hierarchy levels at which you can configure this statement, see the statement summary section for this statement.

For example, if you set the reference bandwidth to 1 Gbps (that is, reference-bandwidth is set to 1,000,000,000), a 100-Mbps interface has a default metric of 10.

For more information about IS-IS route metrics, see Modifying the IS-IS Metric.

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