Inconsistent DNS Resolution

Help
1

Expected Behaviour:

I am consistently getting DNS lookups that fail consistently across the environment (example below). There does not seem to be consistent timing / behavior for when they file. Based on other issues I ran "pihole repair" and retested but am still seeing consistent failures. This instance has been up and functional for a long time but this behavior seems to have become prevalent after a I switched to an Eero based Wifi system. I have configured Eero with Custom DNS specifying the PiHole IP Address (192.168.0.127).

PS C:\Users\Matt> nslookup discourse.net
DNS request timed out.
timeout was 2 seconds.
Server: UnKnown
Address: 192.168.0.127

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.
*** Request to UnKnown timed-out

Debug Token:

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

2

From this same client, what are the outputs of the following from the client terminal:

nslookup pi.hole 192.168.0.127

ipconfig /all

3 
PS C:\Users\Matt> nslookup pi.hole 192.168.0.127
Server:  pi.hole
Address:  192.168.0.127

Name:    pi.hole
Addresses:  fd8c:5cb6:4b50:2624:bc09:d702:e415:8b1e
          192.168.0.127

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Intel(R) Ethernet Controller (3) I225-V
   Physical Address. . . . . . . . . : D8-BB-C1-9F-18-29
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes
   IPv6 Address. . . . . . . . . . . : fd8c:5cb6:4b50:2624:887a:1934:e8d1:b319(Preferred)
   Temporary IPv6 Address. . . . . . : fd8c:5cb6:4b50:2624:88ed:59b4:f0c0:9140(Deprecated)
   Link-local IPv6 Address . . . . . : fe80::7e16:c4d6:b7ec:17c8%4(Preferred)
   IPv4 Address. . . . . . . . . . . : 192.168.0.2(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.0.0
   Default Gateway . . . . . . . . . : 192.168.0.1
   DHCPv6 IAID . . . . . . . . . . . : 265862081
   DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-2B-4A-7E-9E-D8-BB-C1-9F-18-29
   DNS Servers . . . . . . . . . . . : 192.168.0.127
   NetBIOS over Tcpip. . . . . . . . : Enabled
4

I am not sure where the IPV6 is getting picked up. I'm on Windows 11 but have tried to disable IPV6 on Eero and PiHole

5

Disable IPv6 on the Windows client and see if that improves things. It's in the internet properties panel.

6

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8

This is the behavior I am seeing consistently - for some amount of time no resolution will occur and then shortly after it will pick up just fine. Not sure where to look to understand what is happening within PiHole at this time.

9

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This is the only entry in FTL.log at the time.

10

Ethernet adapter Ethernet:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Intel(R) Ethernet Controller (3) I225-V
Physical Address. . . . . . . . . : D8-BB-C1-9F-18-29
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IPv4 Address. . . . . . . . . . . : 192.168.0.2(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Lease Obtained. . . . . . . . . . : Friday, August 1, 2025 8:12:22 AM
Lease Expires . . . . . . . . . . : Friday, August 1, 2025 4:12:21 PM
Default Gateway . . . . . . . . . : 192.168.0.1
DHCP Server . . . . . . . . . . . : 192.168.0.1
DNS Servers . . . . . . . . . . . : 192.168.0.127
NetBIOS over Tcpip. . . . . . . . : Enabled

11

I have disabled IPv6 on the client machine but am still seeing nslookup failures consistently.

12

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13

I am seeing increased CPU usage on the Pihole device during the timeframes that DNS lookups are failing.

Any suggestions for next steps?

14

It seems obvious in hindsight what the issue was. As much as I tried to disable ipv6 throughout my environment I was unsuccessful. I ended up adding the ipv6 address to my Eero Custom DNS (Primary ipv6) and this resolved my issue.

Commenting here in case anyone else finds themselves in the same situation.