Got the Deco M5 with three units.  Have xfinity 300mbps.  tried setup with all three as master and each time, end up with red-light and "not connected to internet." error.  network cable is fine and works with my netgear router.  I have tried all the troubleshooting tips from the web site ( power up sequence, etc). and nothing works!  This is getting very frustrating and thinking of just returning the item unless someone has additional ideas.  Thanks