Assuming you are configuring Pi-hole via your router or Pi-hole’s built in DHCP server it may be one of several things.
- Rebind Protection
You just need to disable it to make it work. Only some routers are affected.
Another common mistake we see if people setting Pi-hole as their WAN DNS server, which will cut off Internet since Pi-hole isn’t an authoritative DNS server. You need to instead set this under the LAN DNS server, or in the DHCP options section.
If your gateway on your Pi-hole is not configured correctly, you cannot get out to the Internet. Since all devices query the Pi-hole, it needs to be able to reach the Internet to find upstream servers, but if it can’t get out through the default gateway, the Internet will appear to be offline