What link costs are

Link costs let you prioritize which data center site provides a requested service when two or more data center sites exist. You can adjust link costs to reflect latency between sites.

The diagram shows a three site grid that has link costs configured between sites:
Conceptual diagram for link costs between data centers
Link costs are arbitrary relative numbers with no specific unit of measure. For example, a link cost of 50 is used less preferentially than a link cost of 25. The table shows commonly used link costs.
Link Link cost Notes
Between physical data center sites 25 (default) Data centers connected by a WAN link.
Between logical data center sites at the same physical location 0 Logical data centers in the same physical building or campus connected by a LAN.