Pi-hole DHCP

Pi-hole can also do DHCP. However, the GUI only allows for a single range. On a large network you’ll need multiple ranges. You do this by editing the config files directly.

Interface-Based Ranges

In this setup, you have a separate interface per LAN. Easy to do in a virtual or VLAN environment, but you’ll have to define each in the /etc/network/interfaces file.

Let’s create a range from 192.168.0.100-200 tied to eth0 and a range of 192.168.1.100-200 tied to eth1. We’ll also specify the router and two DNS servers.

vim /etc/dnsmasq.d/05-dhcp.conf

dhcp-range=eth0,192.168.0.100,192.168.0.200,24h
dhcp-option=ens161,option:router,192.168.0.1
dhcp-option=ens161,option:dns-server,192.168.0.2,192.168.0.3

dhcp-range=eth1,192.168.1.100,192.168.1.200,24h
dhcp-option=ens161,option:router,192.168.1.1
dhcp-option=ens161,option:dns-server,192.168.1.2,192.168.1.3

# Shared by both
dhcp-option=option:netmask,255.255.0.0

# Respond immediately without waiting for other servers 
dhcp-authoritative

# Don't try and ping the address before assigning it
no-ping

dhcp-lease-max=10000
dhcp-leasefile=/etc/pihole/dhcp.leases

domain=home.lan

These settings can be implicit - i.e. we could have left out ethX in the range, but explicit is often better for clarity.

Note - the DHCP server (dnsmasq) is not enabled by default. You can do that in the GUI under Settings –> DHCP

Relay-Based Ranges

In this setup, the router relays DHCP requests to the server. Only one system network interface is required, though you must configure the router(s).

When configured, the relay (router) sets the relay-agent (giaddr) field, sends it to dnsmasq, which (I think) understands it’s a relayed request when it sees that field, and looks at it’s available ranges for a match. It’s also sets a tag that to be used for assigning different options, such as the gateway, per range.

dhcp-range=tag0,192.168.0.100,192.168.0.250,255.255.255.0,8h
dhcp-range=tag1,192.168.1.100,192.168.1.250,255.255.255.0,8h
dhcp-range=tag2,192.168.2.100,192.168.2.250,255.255.255.0,8h

dhcp-options=tag0,3,192.168.0.1
dhcp-options=tag1,3,192.168.1.1
dhcp-options=tag2,3,192.168.2.1

Sources

https://discourse.pi-hole.net/t/more-than-one-conditional-forwarding-entry-in-the-gui/11359

Troubleshooting

It’s possible that the DHCP part of dnsmasq doesn’t scale to many thousands of leases¹