dot1dStpPortPathCost : The contribution of this
port to the path cost of paths towards the spanning
tree root which include this port. 802.1D-1990
recommends that the default value of this parameter
be in inverse proportion to the speed of the
attached LAN. Writing value zero to this object
sets path cost to a default value which automatically
changes according to port speed. Reading value zero
indicates an unknown path cost value because port
speed cannot be determined due to speed auto sense
in progress.