Modem Ethernet ports not communicating.

I have an Arris TG1682 Telephony Gateway about 5 years old.  Phone and WiFi functions are working fine.  For some reason the four ethernet ports on the modem have stopped working.  I can no longer get internet on from my external WiFi router, a configuration that was working fine until recently.  On the modem I do get a solid green light when the ethernet cable is plugged into any port on the modem.  There are no amber illuminated lights that come on.  On my external Linksys WiFi router I get a solid green light and solid amber light with the ethernet cable plugged in.  If there was communication between the modem and router I should see the router amber light blinking.  All four of the Arris modem ethernet ports give the same result.  I have tried using an older backup WiFi router to see if the Linksys router might be the problem but saw no change.  I'm believing that the four ethernet ports on the Arris Modem have failed and I need a new/replacement modem/WiFi router from Comcast/xfinity?  Or is there something else I can try to restore communications from ethernet ports to my external WiFi router?