How do I change the speed, duplex, or other parameters on an Ethernet card?

Depending on which type of Ethernet card is installed on the system, there are usually one of two utilities that can configure the network card speed, duplex (half or full), and other options: ethtool or mii-tool. Some Ethernet cards will not work with ethtool, if this is the case, then try mii-tool and vice versa. First, check to make sure t...