(Medium Dependent Interface port) Also called an "uplink port," it is a port on a network hub or switch used to connect to other hubs or switches without requiring a crossover cable. The MDI port does not cross the transmit and receive lines, which is done by the regular MDI-X ports that connect to end stations (the X stands for "crossed"). The MDI port connects to the MDI-X port on the other device. There are typically one or two ports on a device that can be toggled between MDI (not crossed) and MDI-X (crossed).

Automatic MDI/MDI-X
Gigabit Ethernet introduced automatic line sensing in the ports, which detects whether the crossover is needed or not. Referred to as "auto MDI/MDI-X," "universal cable recognition" and "auto sensing," it eliminates having separate MDI and MDI-X ports, selector switches and special crossover cables on the equipment. See crossover cable.