Router Using Backup DNS After New Pi-hole Install

[pbeeks]

Expected Behaviour:

Pi Hole is used as the primary DNS for all devices on my network as configured on my router.

Actual Behaviour:

After a short timeout the backup DNS is being used to resolve queries.

Details:

Original OS:
Raspbian GNU/Linux 9 (stretch)

Current OS:
PRETTY_NAME="Raspbian GNU/Linux 10 (buster)"
NAME="Raspbian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=raspbian
ID_LIKE=debian

Hardware:
Raspberry Pi 3

I had pi hole running on my network for over a year and had added a bunch of blocklists that no longer existed/they moved/I typed them wrong so I wanted to do a refresh. I did this by running pihole -r and choosing the the Reconfigure option. After doing this the backup DNS was being used (I assume this because the number of queries wasn't increasing). I noticed this:
*** [ DIAGNOSING ]: Networking
[✗] No IPv4 address(es) found on the eth0 interface.

[✗] No IPv6 address(es) found on the eth0 interface.

[i] Default IPv4 gateway: 10.0.0.1

• Pinging 10.0.0.1...
  ping: Warning: source address might be selected on device other than eth0.
  [✗] Gateway did not respond. (Why is a default gateway important for Pi-hole?)

and assumed I had done something wrong during the setup and after finding no answers to fix this I formatted the pi and reinstalled raspbian.

After reinstalling pi hole I have the same issue. The IP of the pi is set as the primary DNS in the router's settings, I am able to ssh to it, and reach the admin console from a browser.

nslookup result from a computer on the network:
$ nslookup pi.hole
*** Request to www.routerlogin.com timed-out
Server: www.routerlogin.com
Address: 10.0.0.1

DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.

Debug Token:

https://tricorder.pi-hole.net/fjbyjtw9sq

[jfb]

@pbeeks

After a short timeout the backup DNS is being used to resolve queries.

There should not be a "backup" DNS server. Pi-hole should be the only DNS server available to clients.

Why should Pi-hole be my only DNS server?

Reduced Ad Blocking Capability The main reason you should Pi-hole as your only DNS server is that you will see increased performance in the blocking of ads. If you have two DNS servers (Pi-hole and something else), your network clients may not always query Pi-hole for name resolution. If a query happens to be answered from a non-Pi-hole DNS server, your block lists will not apply (since that DNS server doesn't know about them). All Queries Need To Go Through Pi-hole First Since other DNS se…

*** [ DIAGNOSING ]: Networking
[✗] No IPv4 address(es) found on the eth0 interface.

[✗] No IPv6 address(es) found on the eth0 interface.

[i] Default IPv4 gateway: 10.0.0.1
   * Pinging 10.0.0.1...
[✗] Gateway did not respond. (https://discourse.pi-hole.net/t/why-is-a-default-gateway-important-for-pi-hole/3546)

You have a connectivity problem on the Pi. Resolve this and Pi-hole should work fine.

[pbeeks]

Yea I would only have the pi hole as the single DNS but unfortunately I get this

The connectivity problem is what I'm trying to troubleshoot.
I have connectivity to the internet:
pi@raspberrypi:~ $ ping www.google.com
PING www.google.com (216.58.192.132) 56(84) bytes of data.
64 bytes from ord36s01-in-f4.1e100.net (216.58.192.132): icmp_seq=1 ttl=118 time=19.8 ms
64 bytes from ord36s01-in-f4.1e100.net (216.58.192.132): icmp_seq=2 ttl=118 time=19.0 ms
64 bytes from ord36s01-in-f4.1e100.net (216.58.192.132): icmp_seq=3 ttl=118 time=21.10 ms
^C
--- www.google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 201ms
rtt min/avg/max/mdev = 19.043/20.290/21.989/1.255 ms

But connecting to the gateway fails. I haven't found any good information/don't know the search terms for the error I'm seeing.

[yubiuser]

The secondary can't be 0.0.0.0 set the same IP (the one of Pihole) for primary and secondary.

[pbeeks]

I tired that as well, they thought of everything.

[pbeeks]

Figured it out.

I had incorrectly configured the install of pi hole to use eth0 instead of wlan0 because I set it up while still connected to ethernet. Once I switched to wifi it was looking for eth0 for pi hole.

Running pihole -r then reconfiguring it to use wlan0 fixed the problem.

[yubiuser]

Glad it's working now.