Canon EOS 6D Instruction Manual page 17

Connecting with an Interface Cable
When [Wi-Fi] under the [53] tab is set to [Enable], interface cable
connection is disabled. Set it to [Disable] to connect the interface cable.
When the camera is connected to a computer, printer, GPS receiver, or
any other devices via an interface cable, the settings for [Wi-Fi] cannot
be changed. Disconnect the interface cable and then configure settings.
Using an Eye-Fi card
When [Wi-Fi] under the [53] tab is set to [Enable], image transfer using
an Eye-Fi card is disabled.
Basic Operation and Settings
17