Examples include connecting an external physical layer device to a media access control device by determining a mode of a communications link between the external physical layer device and the media access control device; and when the mode of the communications link is serial gigabit media independent interface (SGMII), enabling an inter-integrated circuit (I2) interface between the external physical layer device and the media access control device, and setting a destination for management data input/output (MDIO) transactions to the external physical layer device.