If multiple routes to a destination are known, routes learned through the protocol with the better administrative distance are preferred.
If more than one route to a destination is learned through the preferred protocol, then the preference of routes is based on the metric of the routes.
Routes with the better metric are preferred.
Open Shortest Path First (OSPF) uses cost as the metric calculated, based on the bandwidth of the link.
The cost of a link is calculated by dividing the reference bandwidth (100 Mbps by default) by the interface bandwidth.
The total cost to a destination is the cost of the individual links in the path to the destination.
The cost of the outbound interface toward the destination is used.
The OSPF cost for an interface is explicitly specified or set.
This is done by changing the reference bandwidth.
To explicitly specify the cost of an interface, issue the ip ospf cost command in interface configuration mode.
To control how OSPF calculates the default metrics for the interface (based on the reference bandwidth), issue the auto-cost command in OSPF router configuration mode.
For more information refer to:
How do I change the reference bandwidth in OSPF?
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