The OSPF cost shown is 1 for a Gigabit Ethernet interface. What does this indicate?
- The interface bandwidth is configured incorrectly
- The cost has been manually configured on the interface
- OSPF is using the default reference bandwidth of 100 Mbps
- The auto-cost reference-bandwidth has been modified
Explanation: According to the sources, OSPF uses a default reference bandwidth of 100 Mbps for cost calculation.
The cost of an interface is determined by dividing the reference bandwidth by the interface bandwidth.
Since the cost cannot be less than 1, both Fast Ethernet (100 Mbps) and Gigabit Ethernet (1000 Mbps) interfaces will have an identical cost of 1 by default.
Therefore, a cost of 1 on a Gigabit Ethernet interface indicates that the router is still using the default 100 Mbps reference value.
To differentiate costs for interfaces faster than 100 Mbps, the auto-cost reference-bandwidth command must be used to increase the reference bandwidth.
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