does that router support Unifi ?
i meant,support those VLAN tagging and everything
DIR-615 is not like any other ordinary router out there.Eventho it's a crappy router, but the main purpose of it's are to control those VLAN tagging and everything.
so u have to make sure your router supports the function
and also, you cant just simply plug in your BTU & STB RJ-45 cable on any port as each port are assigned with their own VLAN .