Pi-Hole on RPi, different ip on eth0 and wlan0-- Issues?

[dherrenvt]

I made up a Raspberry Pi 4 running Pi-Hole for a friend's home. His router demands that if you force the ip address for the DNS server (through DHCP), that you MUST specify 2 distinct ip addresses. They cannot be the same ip and neither can be 0.0.0.0. It will not allow just a single DNS server ip address.

I don't really want to build 2 RPis, so I thought I'd try doing a DHCP reservation for both the eth0 interface as well as the wlan0 interface, using consecutive addresses. I'm testing this on my own installation (even though my router doesn't enforce the 2 DNS situation, it will accept a second one).

I haven't seen anything wonky in the past 3 days. Do you think this is a reasonably safe way of working around the router's limitations?

[jfb]

Have you considered putting an unused IP from the LAN range in spot 2?

[dherrenvt]

That's also a possibility. I was somewhat concerned that if a client did a request to an ip address that happened to be taken through DHCP that it might mess up the client.

Also I wonder what happens if a request gets sent to an ip address and there's nothing there, what happens.

Nothing "bad" seems to be happening by having the Rpi listening on both interfaces on my system here at home (as near as I can tell). I haven't yet gone back to his house (way the bloody hell up in the mountains…) to change his configuration.

[jfb]

@dherrenvt

I was somewhat concerned that if a client did a request to an ip address that happened to be taken through DHCP that it might mess up the client.

Set the DHCP range to less than the pool of available IP's on the LAN, then use an IP outside of the DHCP range. No client will be using that. Even if a client were to use the "unused" IP, unless the client has a DNS server listening on port 53, no DNS traffic will be answered.

IP range 1-254. DHCP set from 100-200. Use IP 225 in the router, for example.

Using an unused IP is not functionally different than using 0.0.0.0 in the router settings. Neither will get a DNS response.

Another option (and perhaps a better solution) is to disable DHCP on the router (or limit it to a single IP, the IP of the Pi, if the router does not allow disabling DHCP), and use Pi-hole as the DHCP server on the network.

How do I use Pi-hole's built in DHCP server (and why would I want to)?

Using Your Existing Router For Network-wide Ad Blocking You might not need to use Pi-hole's DHCP server: In many home environments, your router also functions as your DHCP server. In this case, you can often set Pi-hole to be the DNS server for your network clients in the router's DHCP (or LAN) settings page, which allows all of your network clients to block ads simply by connecting to the network. Setting it up this way is also what makes Pi-hole very powerful for network-wide ad blocking. …

[dherrenvt]

I haven't found a need to run DHCP on the Pihole. AT least in my personal configuration (a Peplink router doing DHCP and the Pi doing DNS), things are running perfectly smoothly.

I will try resetting the DHCP ranges on his router as well.