Netgear c7000v2 with external router

[Trunk_Monkey]

Hello!

I upgraded my internet plan from Xfinity a few months ago and have gone over my monthly limit every month since. I wanted to monitor bandwidth usage by device to see what the culprit was, but this was not possible with my Nighthawk c7000v2 -AC1900 cable modem/router.

I read on a separate post here that I could use the c7000 as a modem only. I decided to try that and purchased the ASUS RT-AC86U to use as my dedicated router.

I connected from the WAN port on the ASUS to the LAN on the Nighthawk for setup. I used the same SSID for ASUS thinking that it would provide a smooth transition from Nighthawk to ASUS for all 20 home devices when I turned off the router mode on Nighthawk.

Unfortunately, turning off router mode in nighthawk admin tools stopped all wifi signal. I thought I would still have internet access through the ASUS, but this doesnt seem to be the case. I turned router mode back on with my computer that is connected to another LAN on Nighthawk. Then, I thought I could just disable the SSID broadcast from Nighthawk but that seems to affect the ASUS projection too... i.e, I turn off 2ghz from Nighthawk admin panel and I just can't see the 2ghz from ASUS even though it's admin panel says it is broadcasting.

I then switched the ASUS from router to AP, but this removed my capability of seeing data usage by device.

With router mode enabled on Nighthawk and ASUS set to router also, some devices appear in the ASUS admin page, but some are still in the Nighthawk page.

I set up a DMZ on the Nighthawk for the IP of the WAN on the ASUS and most devices migrated over, not all. Still in double NAT, which at this point I'm not sure I even care about unless that will also somehow use MORE data?

Sorry if this post is bogged down with unnecessary details, or not enough specific ones. I've been at this for the past 6 hours and I'm frustrated lol, Obviously very new to networking. I just don't want to keep going over my data plan. Any help is appreciated!

[plemans]

when you turn on modem only mode, it literally becomse just a modem.

Meaning the isp needs to reassign the public IP address it assigns. 

So when you switch the netgear to modem only mode, it needs to be powered off and rebooted in the proper sequence to reassign that ip address.. Make sure everything is disconnected from it and power it off. 

Then wait 2 minutes. (have the asus off  and starting from factory too)

Power the netgear back on and give it a couple minutes to fully boot. 

then connect lan port 1 to the asus's wan port. 

boot up the asus and wait a couple minutes. 

Attempt setup on the asus.