Reason has two different systems for configuring MIDI sources. When you connect a keyboard controller to lay Reason's instruments, the DAW assumes the connected device as the master. As such, it directs all the MIDI to the selected track or device. Therefore, the only thing required to use the controller with Reason is the MIDI controller itself, the DAW, and the preferred output devices.
Reason also has a separate direct MIDI routing system for patching incoming MIDI channels to devices in the Rack. The method is great for using the Reason Rack as a multitimbral sound module or connecting an external sequencer. In this case, you’ll require an external sequencer as well.