This read-write INTEGER, though its source description is empty, sits among this port's spanning tree fields alongside sifStPriority and sifState and represents the per-port Spanning Tree path cost assigned to this port. An administrator raises it on a slower link to steer spanning tree away from that port whenever a faster alternative is available. For example, the admin raises sifPortCost on a slower backup uplink so spanning tree prefers the faster primary port whenever both are available.