That shows your RPi to have IPv6 connectivity (deduced by a 2600: prefix), but not IPv4 (by lack of 192.168.1.<x>).
What is your RPi using as gateway?
We can find that out by executing:
ip route
Its output should contain a line starting with:
default via
What is the IP address that immediately follows after via?
You have to reset your router.
According to the manual, there should be a button for it in the back that you need to press for 10 seconds:
When done, you have to go through customisation of your DHCP settings again.
In addition, try to find the DHCP lease reservation option in your router to reserve an IP address for your RPi. Actual naming may vary, so it may be labeled as fixed or static IP adress assignment or similar in your router.
Argggggg ... now the router won't reset. Called ATT. They think there's a router problem. Service person scheduled for Friday evening. I'll also ask about setting up a static reservation for the router.
When's the best time for us to regroup? I don't see getting anything accomplished until the router reset.
You've been very helpful and patient. Don't despair, this just has to be an unusual situation.
Frankly, your router/modem is not very capable (which is unfortunate), the best and easiest option is to ask ATT if they can provide you with a router/modem that is capable of the following
- turning off DHCP
- ability to manually set DNS
Sorry if this is not really helpful, just wanted to say it outright so you don't spend long time trying to figure this out, since this is a trick, it might not work very well.
I'll sure hang around, but am based in Europe, and not on a fixed schedule.
Just post again once you're ready, and usually you'll be picked up pretty quickly, even it is not guaranteed that it'll be me who does.
Folks tend all to be friendly and helpful around here 
Ok. Replaced router (same att5268ac) installed and operable.
Two questions. First attempts to access pih admin page fails (192.168.1.251 and pi.hole/admin) time out. How do I verify the pihole admin address to be sure it's correct.
Second, when attempt to use pih by manually changing DNS server field on each device, which field is the DNS server field ... DNS1/DNS2/IPv4 Gateway? Certainly not the IP Address. I thought that I would run a single device test, but obviously need the ph server address.
I also installed a Dlink ac1900 as an addition router as a supplement to the Att router. Therefore adding two new network addresses. Maybe this will permit the DNS and DHCP setting issues, but I want to be cautious and try the DNS Server field change test first.
Thanks for your help.
I have cable connected the rp to the LAN port of the att router.
Note that introducing another router into your setup will complicate matters, possibly partially or even completely invalidating our previous efforts.
Furthermore, I can only provide sensible advice for configuring Pi-hole itself, and possibly guide you unto the right path for making your router play nicely with Pi-hole.
Integrating your new router with your existing one is beyond me (and certainly beyond the scope of Pi-hole).
The recommendation for your single ATT router setup remain as before:
Restrict its DHCP range and have Pi-hole run as DHCP and DNS server.
But before you start a new attempt, please establish how you can set a DHCP lease reservation (aka reserved or fixed or static address assignment, or similar) on your ATT5268ac.
Then just configure an IP address via DHCP lease reservation for your Pi-hole - do not touch any other router setting yet.
Once set, disconnect and reconnect your Pi-hole to acquire the newly fixed IP.
Verify you can ping Pi-hole's IP address from your Windows machine, and report back once you succeeded.
Have disconnected the 2nd router. I thought that it could be an alternative to the ATT router, since I'm not sure that it permits DHCP changes as needed for the PI-Hole. The last time we changed it, the ATT router failed . . . maybe coincidental, or problematic (See Below):
So, being "nervous" about possibly repeating the potential router failure, I thought that we'd try just changing the Gateway address (IPv4 Gateway) in my Desktop to the PI-Hole address and see if that connects to the PI-Hole (The documentation suggests this as an alternative when the router fails to permit the settings normally assumed by PI-Hole):
However, to do this, I need the PI-Hole IP address. Previously I'd use http://pi.hole/admin or 192.168.1.112/admin, for access, but it can't be found. It doesn't connect in any of my devices, or different OS. However, when activating the Raspberry Pi and mouse-over the internet I see two addresses ... 192.168.1.78 (lan0) for use with the router's network address (ATT6wQa4EC) and 168.254.54.155 (eth0). Does this help? Not sure what the 168.254.54.155 IP address relates to the network.
I'm suspicious that the PIH address has changed. I tried the ipconfig for info, but didn't help. Here's the ipconfig on my desktop:
Tried "ping -a pi-hole" with nothing found.
So, with your infinite wisdom, (1) does using the pihole address as the gateway make sense on an individual device? (2) how do I get the http://pi.hole/admin and/or pi.hole ip address?
By the way, any problems with the coronova virus where you live? We're basically immobile here in the U.S.
This is crucial:
Did you manange to set a fixed IP address for Pi-hole?
Ok. We're out of synch. I recited where there might be an opportunity to create a fixed address for the ATT5268ac
on the previous email, with a screen capture of were that might happen:
but also concern of whether it contributed to the subsequent router failure. If you'll remember, we tried that.
So, I suggested a link to the PIH directly from my desktop, changing the Gateway IP 192.168.1.254 to the PIH address, looking for your comments, but also don't have the PIH address and cannot seem to load the pi.hole/admin page, so I'm stuck.
It likely did, as your WIndows PC seemed to have grabbed the singular DHCP lease from your router. Assigning a DHCP lease reservation for Pi-hole will avoid the latter.
Those above screenshots of yours are showing DHCP range definition; they are not concerned with DHCP lease reservations / fixed or static IPaddress assignment at all.
Assigning your Pi-hole with a fixed IP address on your router would have to look similar to the equivalent section on Pi-hole's DHCP option pane:
You'd have to find the appropriate corresponding settings in your ATT5268ac router to configure a fixed IP address for your Pi-hole.
P.S.:
It's starting to hit hard in Europe - goverments are steering towards a complete halt of all public affairs.
I don't see those settings. So, let's give-up on the router and modify the devices.
Attached is a copy of an email that I attempted to send to you last night before receiving your email this morning. It was an attempt to start a new email stream but, unfortunately, it was rejected. So, I've attached it to this email.
(Attachment PIHEmailStatus.pdf is missing)
The attachment was rejected.All of the following was completed before your email this morning. I attempted to send it twice, Once it had an incorrect email address to you. Second, it rejected the PDF attachment.
So, I'll recreate it here:
I've now successfully executed pihole reconfigure in RP and have:
Also have "Use as static network IP 192.168.1.70/24 and Gateway 192.168.1.254". And have "configure devices to
use PIH as DNS 192.168.70"
The documentation also states that:
"If your router does not support setting the DNS server, you can use Pi-hole's built-in DHCP server; just be sure to
disable DHCP on your router first (if it has that feature available).
As a last resort, you can always manually set each device to use Pi-hole as their DNS server." To me, this is the next
step. It avoids the need to deal with the Desktop Router configuration issues.
So, does that mean that I change just my Desktop network of ATT6wQa4EC with IPv4 Gateway of 192.168.1.254
below to 192.168.168.70 and all future traffic via ATT6wQa4EC on my desktop will flow through PIH? And that I'll see
that traffic under the "Network View" in the PIH/Admin?
That router is a moody beast indeed 
I can see how this might be a really frustrating ordeal for you. I'd be teeming with it by now. I know you are trying any availale angle to solve the problem at your end while keeping me updated. And then, dealing with competing settings from your explorations and my suggestions plus an obvious time zone difference all do not make it any easier
You are correct to assume that turning to modify the devices should be the next approach.
This should be pretty straight forward, as you'd just have to enter Pi-hole's IP addresses in the right places of your clients.
Note that you don't need Pi-hole as DHCP if you enter DNS settings per each client, so switch it off when going down that lane.
However, there are two caveats:
a) Some devices may not allow entering a DNS server manually
b) Whenever your Pi-hole's IP address changes, you'd have to walk to each and any of your clients and reconfigure accordingly
You'd have to decide whether manual-per-client-configuration is feasible for you, based on the devices in your network and your router's IP assignment behaviour.
I sincerely hope that your router does not mess up b) by disregarding Pi-hole's IP address preference (which we tried to avoid by setting a DHCP lease reservation, to no avail).
When you installed Pi-hole, did you answer Do you want to use your current network settings as a static address? with yes?
If not, it may be best to switch off Pi-hole's DHCP, revert your router to defauklt DHCP settings and reinstall Pi-hole.
Yes, the PIH address is static. Why would it change if it's static? Next, is the DNS1 field the correct field to placing the PIH IP address? That would be in the DNS1 now 192.168.1.254 in the below screen shot from my cell phone?
It wouldn't, but your router may disagree with your Pi-hole taking it and refuse to forward traffic to it.
To avoid this, I would normally recommend to pick an IP address outside of your router's DHCP range for static IP addresses.
But I wouldn't touch it if it is working for you the way it is now.
Yes, those are the correct entries.
If your device allows, put Pi-hole in both slots.
Otherwise, it might bypass Pi-hole every now and then by using DNS2 as well.
