It's possible to sync a Dante network to an external clock source, such as a master/house clock unit (e.g. an Apogee Big Ben). Only one device on the Dante network should be synced externally in this manner, that device will then become the master for the rest of the Dante network (attempting to sync multiple Dante devices externally can cause problems and should be avoided).
To change the sync source of a Red/RedNet product click the Tools menu for that unit in RedNet Control and select the desired sync source (e.g. Word Clock, Loop Sync, ADAT, MADI etc):
Once that's done, the 'Sync to External' option for that device should be ticked in Dante Controller's "Clock Status" window automatically. As long as the Preferred Master option isn't selected for any other device then the externally sync'd device will automatically become the master for the network (passing on the master clock signal it's receiving to all Dante devices on the network):