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Modifying the Interface Metric

All OSPF interfaces have a cost, which is a routing metric that is used in the link-state calculation. Routes with lower total path metrics are preferred over those with higher path metrics.

When several equal-cost routes to a destination exist, 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. Its default value is 100 Mbps (which you specify as 100,000,000), which gives a metric of 1 for any bandwidth that is 100 Mbps or greater.

To modify the metric for routes advertised from an interface, include the metric statement:



(ospf | ospf3) {


area area-id interface interface-name {

metric metric;
}


}

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



(ospf | ospf3) {

reference-bandwidth reference-bandwidth;
}

For a list of hierarchy levels at which you can configure these statements, see the statement summary sections for these statements.

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.

By default, the loopback interface (lo0) metric is 0. No bandwidth is associated with the loopback interface.

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