For routers that do not allow DNS change, Pi Hole proposes to position itself as a DHCP server. So you have to think about deactivating the DHCP server of the box. Its working very well, but if pi hole does not start then there will be an error, the devices on the network will no longer be able to work?
To understand the situation, start thinking what would happen if the router is the DHCP server.
In this case, if the router doesn't start, there will be no DHCP server on your network.
With Pi-hole is the same.
ok how to avoid this, it will be necessary that if pi hole does not start the box takes over