The principles of calculating the cost of an OSPF interface are as follows: The cost configured on the interface is preferred. If no cost is configured on the interface, the formula for calculating the cost of the interface is as follows: 

Cost = Reference bandwidth/Interface bandwidth. The default reference bandwidth of OSPF is 100 Mbit/s.

For example, the cost of a 10 Mbit/s Ethernet interface = 100 Mbits per second/10 Mbits per second = 10. If the calculation result is smaller than 1, the cost is set to 1. For example, the cost of a GE interface is 100 Mbits per second/1000 Mbits per second = 0.1, which is less than 1. Therefore, the cost of this interface is 1.


The default cost on the loopback interface, which is a virtual interface, is 0.

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