Can't ping any host from pi-hole, even IPs

[Andrew9]

The issue I am facing:
My pi-hole suddenly stopped working. I've traced the problem to the fact that the computer can't ping any host or IP, even the router to which it's connected. However I can connect to the pi-hole no problem; both to the admin panel and through an SSH connection.

Details about my system:
Installed on Peppermint OS, on an old 32-bit netbook. No deviations from installation.
On my router I've reserved the IP address of the netbook.

What I have changed since installing Pi-hole:
Nothing else.

When I first installed pi-hole, I didn't switch over my router's DNS settings to use it; I manually switched the DNS settings on some devices on my network to use pi-hole, and they worked just fine for a few days. Then I decided to switch my router's DNS settings to the pi-hole, and it stopped working. I switched the router's DNS settings back to its previous values but the pi-hole computer continues to not work.

I've tried bringing the network interface down then up, no effect. I've tried restarting the computer, no effect.

If I try to ping anything, even IP addresses, I get the error "Destination Host Unreachable".

I've generated a debug log but can't upload it automatically because of course the netbook doesn't have an Internet connection.

[Andrew9]

I managed to get it working again by first switching the router's DNS settings back to automatic, then unplugging the cable from the netbook, waiting a bit and plugging it back in. Sometimes I would have to do it a few times in order to make it work.

But it seems the problem is very consistent. As soon as I set the router/modem's DNS to point to the pihole, it breaks. If I leave the DNS settings on the modem/router alone, and instead change the DNS settings on my individual devices, pihole works.

So I'm guessing there's a problem with my modem/router?

[nprampage]

It may be that you're setting your router's DNS under the WAN settings instead of the DNS for the local LAN. Several routers need a public DNS for the WAN settings, and allow you to set whatever you like for the DHCP-provided DNS LAN settings (my Synology 2600 is among these).

I'll bet if you provide a debug log, one of the devs can point you in the right direction.