A device that automatically configures the high speed (100 Mbps) port of a switch both physically and logically is provided. For physical configuration, the device determines the transmit pair conductor and the receive pair conductor interconnecting a switch port and Data Terminal Equipment (DTE). The switch port can be termed “Primary” while the connected DTE is termed “Secondary” or vice versa. For logical configurations, the device makes the determination. The device includes a switching relay, a controller and impedance matching transformers. The controller switches the connections between the relay and the transformer so that the impedance is substantially constant even though the output from the high speed port is feeding different resistive transmission lines.