this post was submitted on 05 May 2025
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You specifically shouldn’t run two DHCP servers on the same network. It can cause IP conflicts when two servers assign the same address to different devices. Because the device doesn’t care which DHCP server gave it an address; It just listens to whichever one happens to respond first. And each DHCP server will have its own table of reserved/in-use addresses. And if those tables don’t match, IP conflicts can occur.
Device 1 connects to the network, and requests an IP address. DHCP server 1 checks its table of available addresses, and responds with “your address is 192.168.1.50.” It marks that address as in-use, so it won’t assign it to anything else in the meantime. Device 2 connects to the network, and requests an address. DHCP server 2 checks its table of available addresses (which doesn’t match server 1’s table) and responds with “your address is 192.168.1.50.” Now you have two devices occupying the same IP address, which breaks all kinds of things.
The largest reason to run two is because DNS queries are split amongst the primary and secondary DNS servers. If you only have a primary pihole, you’ll still occasionally get ads when devices use their secondary DNS servers.
Sorry, uh.. I didn’t mean run them at the same time. I had to have a DHCP server stand in for it when I had to take that device itself down (the pi). That was ages ago. But I was still starting out!