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Expected Behaviour:
Pi-hole should be blocking ads from all devices connected to my home network. (I implemented it by pointing a Netgear R8500 router to it for DNS resolution).
Actual Behaviour:
Pi-hole worked perfectly for about 2 days, blocking ads on my iPad, iPhone and computer, all of which use the router as gateway (and DNS resolution). Then suddenly yesterday Pi-hole began blocking all traffic to the internet. It doesn't affect traffic that stays within my home network, just internet outbound traffic. I get the 404 error on every page I visit, no matter what site or device.
I noticed that the query log had grown to over 150,000 entries and thought that might need flushing, so I did that from the web interface; no change in behavior.
It's worth noting that this is the second time this problem has happened (Pi-hole blocking all internet traffic). The first time it happened (almost a week ago), I uninstalled Pi-hole using 'pihole uninstall' and unwittingly screwed up my Raspberry Pi install (I think by saying Yes to uninstall all dependencies in the Pi-hole uninstall routine -- I'm new to Linux and wasn't aware it would uninstall components the O/S needs). So I reinstalled the RPi and then Pi-hole.
One thing worth noting in that first effort. After Pi-hole began blocking all traffic to the internet, I checked the query log and it reported that queries were being forwarded on requests that I know did not make it to the internet. So from the web interface, you would never know that no requests were making it to the internet. That seemed odd to me.
Another oddity that I noticed when I submitted the debug log from my laptop. Even though I removed the Raspberry Pi from the DNS entry for my router yesterday, in the Pi-hole web interface under query logs there are entries from today, including the tricorder.pi-hole.net domain used to upload the debug log. I checked my laptop and it still points to the router as gateway, and the router still has 8.8.8.8, 8.8.4.4 for DNS resolution. I don't know how Pi-hole is getting any traffic.