This read-write value, from 1 to 200000000 (with 0 meaning auto-select based on link speed), assigns the cost Spanning Tree uses for this port's link when calculating the best path to the root bridge. An admin sets a lower cost on the link that should be preferred as the primary path, letting higher-cost links serve only as standby routes. For example, giving the primary fiber uplink a lower path cost than a slower copper backup link ensures STP always prefers the fiber path when both are available.