18. July 2012 · Comments Off on How To Calculate OSPF Cost · Categories: Cisco · Tags: , , ,

As a CCNA / CCNP candidate you are expected to understand how to set and interpret the OSPF cost function on your Cisco devices

During your career as a Cisco network engineer you will have to deal with setting and manipulating the OSPF costs on an interface.

OSPF uses a metric called “Cost” to calculate the metric of path. The cost is a cumulative value which is an incremental metric.

The cost is as a default based on the bandwidth of the interface. The Higher the interface bandwidth the lower the cost that is associated to that interface, to see the cost that is assigned to any given interface which is participating in OSPF issue the following command:

Router# show ip ospf interface

The output of this command will show the current cost given to this interface. The costs of the interface is calculated by taking the bandwidth of the interface and dividing this number by a value known as the “auto-cost reference-bandwidth”. This auto-cost reference-bandwidth is an integer used to calculate a standard metric across OSPF and is set to 100,000,000. The cost is calculated as follows:

100,000,000/BW More »