Pihole wrong client IP & DHCP not detected

[deHakkelaar]

@Samy

Router DHCP OFF, pihole DHCP ON (this config does not work)

nmap --script broadcast-dhcp-discover -e enp2s0

Starting Nmap 7.60 ( https://nmap.org ) at 2020-01-31 11:59 CET
WARNING: No targets were specified, so 0 hosts scanned.
Nmap done: 0 IP addresses (0 hosts up) scanned in 10.31 seconds

Try run nmap from a client PC.
Running nmap from the same host thats serving DHCP is going to fail.

@Samy

Because everyone recommends to activate pihole DHCP instead of router DHCP to solve this issue, I did it, then only my static IP devices were able to keep internet connection and no DHCP client were able to find pihole DHCP server

Sounds like rebind protection:

Why won't Pi-hole work with DNS rebind protection enabled?

What is DNS rebind protection? If your router has an option called DNS rebind protection enabled, you may run into issues when trying to use Pi-hole as your DNS server. The reasons for this are quite technical, but to summarize what this option does in one sentence: DNS rebind protection does not allow DNS queries to be answered with a local IP address. Why does this interfere with Pi-hole? DNS rebind is meant to be a countermeasure to an attack on your network. So in many cases, it's actu…

Try enable DHCP on Pi-hole,
connect a client PC, with network settings set to auto, directly to Pi-hole without router in between and
run below one on the client to check if resolves:

nslookup pi.hole