How can the Pi Zero (connected over WiFi) be set as the DNS resolver for your WiFi router (instead of say 8.8.8.8)?

Question

I'm an experienced SO'r but am a Pi n00b so please forgive my ignorance if you will.

I badly want a low-effort Pi-hole. A Pi Zero seems the optimal setup for it except that I can't see how what seems to be the suggested setup like this example:

   Cable Modem
        |
        | <Ethernet>
        |
   WiFi router @ 192.168.0.1
        |
        | <WiFi>
        |
——————————————————
| | | ...        |
devices...     Pi Zero (acting as DNS server for router) @ 192.168.0.2

Can possibly work.

...wait a minute, do you just set the router's DNS server to be 192.168.0.2? It just feels wrong somehow for the router to be using its own WiFi client for DNS requests…?

2 more quick questions ! :

1. do you think that running the Pi ←→ WiFi Router leg over WiFi* will be appreciably slower than running it over Ethernet?
2. would you recommend a beefier Pi than the Pi Zero W when employed as a busy DNS server? I have ~60 devices going through my router.

Many, many thanks.

*I see that you can get Micro USB ←→ Pi Zero RJ45 adapters

Answer 1

First you have to install a DNS server program on the Pi0W. Its ip address doesn't matter. It doesn't have anything to do with the router. You only have to ensure that its ip address is given to any device on the local network, either by manual setup or by the DHCP server.

It depends what you want to have. If you do not need to manage your own private DNS domain, maybe with dynamic DNS, then you can use a simple caching only DNS server. Have a look at dnsmasq for this. Otherwise you have to use a full featured DNS server like bind9. Both programs are available from the default Raspberry Pi OS repository. How to setup them is out of scope here, but you will find many examples on the internet.

Because DNS requests are only short messages and not very heavy asked I would say a Pi0W is sufficient if it only serves DNS.