Auto-MDI/MDIX feature

Auto-MDI/MDIX is a feature that eliminates the need for crossover cabling by performing an internal crossover when a straight cable is detected during the auto-negotiation phase. The feature is enabled by default with auto-negotiation on RJ-45 interfaces and requires either speed or duplex to be set to auto-negotiate. If you explicitly set both the speed and duplex to a fixed value, thus disabling auto-negotiation for both settings, then Auto-MDI/MDIX is also disabled. For Gigabit Ethernet, when the speed and duplex are set to 1000 and full, then the interface always auto-negotiates; therefore Auto-MDI/MDIX is always enabled and you cannot disable it.