Orbi RBR 750 issues with Netgear AC1750 cable modem

What Firmware version is currently loaded?
What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too? Built in router here by chance? This would be a double NAT (two router) 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 Orbi 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 Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, configure AP mode on the Orbi router. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point and https://www.youtube.com/watch?v=H7LOcJ8GdDo&app=desktop

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Gmurakami wrote:
i recently switched out Spectrum modem with Netgear AC 1750 and have Orbi connected as older cement brick house. Now Orbi speed test won't work and Netgear keeps telling me firmware needs to be upgraded, but I can't access router login site. Considering all devices are netgear I cannot figure out why not working. Considering returning cable modem for Arris modem. Please help with any advice.

Thanks in advance for any help

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Why do you want to just eliminate the Netgear AC 1750 router all together and just connect the Orbi router to the Spectrum modem, and set the Orbi router in router mode? 

Or are you referring to a different Netgear router?