Prerequisites for Auto-MDIX
If the interface is in Layer 3 mode and you want to want to configure Layer 2 parameters, you must first change the interface to Layer 2 mode. Enter the switchport interface configuration command without any parameters, to change the interface to Layer 2 mode. This shuts down the interface and then re-enables it, which may generate messages on the device to which the interface is connected. When you change an interface from Layer 3 mode to Layer 2 mode, previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration.