HELP WITH MY MODEM AND ROUTER 🥺

[Taken21x]

Hello im coming here for some support, i have optimum wifi and recently got the altice 1gig fiber plan and they came and setup their wifi and i have now a GPON fiber connection cable connected to their supplied router/modem combo the Altice FiberGateway GR140DG, i have that bridged to my nighthawk x6 ac3200 model r8000. I have a few questions: 1) i want to replace their modem with a 3rd party modem i dont like not being able to access my Mac adress and change it and ect so what are some good modems that are accessible with the fiber GPon connection wire. 2) is this router compatible with Fiber if i was to bridge my modem to this router?

[FURRYe38]

You'll need to ask the ISP if it's possible to replace there Fiber gateway with something different or user owned. They will have this information. There are fiber ONTs that don't have built in routers. 

This would be a double NAT condition which isn't recommended. https://kb.netgear.com/30186/What-is-Double-NAT
https://kb.netgear.com/30187/How-to-fix-issues-with-Double-NAT
Couple of options,
1. Configure the modem for transparent bridge or modem only mode. Then use the NG router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the NG router gets from the modem.
3. Or disable all wifi radios on the modem and connect the NG router to the modem, LAN to LAN configure AP mode on the NG router.
https://kb.netgear.com/24104/How-do-I-change-my-Nighthawk-router-to-AP-mode-after-I-ve-already-run-s...