Ooma Telo and Netgear Nighthawk X6 R8000

[firefox111]

Hello! I recently cancelled my own ISP and now piggy-backing on my son's cable Internet with a Nighthawk X4 R7500.  My X6 WAN port is connected to one of the LAN port of his X4.  I have good Internet connection.  My previous setup has the Ooma Telo connected directly to my ISP's modem, which makes the Ooma Telo works flawlessly.  Now that I have moved the Ooma Telo connection to my X6, it does not call out anymore.  It gives me a busy tone after about 6 seconds of silence after dialing a number.  But incoming calls do come in!  My workaround is to install a dumb Gig switch between my son's X4 and my X6 WAN port, with the Ooma Telo connected to one of the ports of the dumb switch.  I can now dial out with this setup.  My conclusion is that somehow the X6 is causing the call out problem! Does anyone of you know how to configure the X6 so that outgoing calls from the Ooma Telo will work?  Thanks in advance.