R6900v2 DNS Not Working

Modem is a SB8200

ipv6 is disabled 

If I manually set one of the devices dns to point to the dns it works, but I have 50+ devices I don't want to have to change each one. Pihole is only seeing the devices I manually changed the DNS on

Your devices will show the 192.168.1.1 as dns server. Thats expected as the router is the initial contact point for your devices but it refers the dns to the pihole. Mine does to. And I've done it with that same modem and a multitude of different routers. 

So we need to determine what your actual pihole settings are and what your router settings are. 

Click on DNS at the pihole and get a screen snip of that page so we can see what your settings are for the pihole. 

You put the internet settins page one time that showed the .243 in the primary dns.

Put your piholes address into both the primary dns and secondary dns. 

i'm also a little uncertain why you're pihole ipv4 address is showing as 192.168.1.243/24

mine has its straight ip address. (not a pihole expert but got the basics down)

the \24 tells pihole its using a 24 bit subnet mask 255.255.255.0

with the router 192.168.1.1 as a dns the pihole is only blocking 1% of the actaul request, and it makes it impossible to see what ip address is the blockage is happening on. with my linksys and tplink routers they both would tell the devices the dns is 192.168.1.243 and i'd be able to see each device on pihole and what ip was getting things blocked on. now it just shows 192.168.1.1 is the only ip 

1. thing you can try. try downgrading the r6900v2's firmware 1 version. there's been some concerns with the latest firmware and DNS not working properly. 

2. if that doesn't work, I'd open a post on the pi-hole forum. I'm not an expert on it and mines running in a docker container so my settings might be slightly different. I know it works but can be finicky with how you setup the pihole. Its challenging to troubleshoot off the occassional screen snip.

From the routers perspective. I've only ever needed to plug in my IPv4 info on the internet setup, dns server page. And its worked. It was a bit more challenging when I enabled IPv6 but not a bunch. And i've used it on/off for a couple years. 

At this point its looks like it's going to better to just throw this netgear away and go back to my tplink. I already tried the Firmware Version 1.1.0.24 and the router isn't telling the devices the correct dns. See the screenshot, hooked my tplink back up and restarted the whole network and it does exactly what its supposed to do

I have my pihole configured to provide both DNS and DHCP. That way you get more info and the DHCP service provides the DNS address to each device via DHCP rather then the router's IP address. Works great and never down. Using a Raspberry PI 3.