This option can take a value of 0,1,2,3... with the lower the value the more leverage it has. The value of this property decides the priority of the device. This parameter has significance only while routing packets. For example, if you have two Ethernet cards and you want to forcibly make your machine use one card over the other in sending the data. Then you can set the Metric value of the Ethernet card which you favor lower than that of the other Ethernet card. I am told that in Linux, setting this value using ifconfig has no effect on the priority of the card being chosen as Linux uses the Metric value in its routing table to decide the priority.