reference-bandwidth (Protocols IS-IS)

Syntax

Hierarchy Level

Description

Optimize routing based on bandwidth by setting the reference bandwidth used in calculating the default interface cost.

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. Tweak the reference bandwidth to route traffic across the fastest interface.

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

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 routing metric of 10.

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. By default, IS-IS has a metric of 10. Modify the configured reference bandwidth to increase the cost of an interface in order to avoid a slow route or you can modify the reference bandwidth value to decrease the cost of a preferred interface. A route that has a lower cost is selected over a high cost route. Note that fractional metric values are not allowed. Therefore, if you configure a reference bandwidth that is higher than the actual bandwidth, which results in a fractional metric value then IS-IS takes the metric value as 1 because fractional metric values are not allowed.

Options

reference-bandwidth—Reference bandwidth value in bits per second.

• Range: 9600 through 4,000,000,000,000 bps

• Default: None

Required Privilege Level

routing—To view this statement in the configuration.

routing-control—To add this statement to the configuration.

Release Information

Statement introduced before Junos OS Release 7.4.