I am using the GX450 modem using firmware 4.8.1. The modem is setup to use a private APN and DMNR is configured. I am unable to ping the Verizon assigned IP address but DMNR is up and I can ping devices connected to the modem. Cannot ping WAN address but can ping devices on APN.
You need to update the firmware version along with the bios set up. The thing is that firmware is very important for the modem to run and that is why you have to update the firmware. You can do the update from windows modules installer worker