% man 8 ifconfig
.......
ifpriority interface value
Set the Spanning Tree priority of interface to value. The
default is 128. The minimum is 0 and the maximum is 240.

ifpathcost interface value
Set the Spanning Tree path cost of interface to value. The
default is calculated from the link speed. To change a previ-
ously selected path cost back to automatic, set the cost to 0.
The minimum is 1 and the maximum is 200000000.