PiHole as a Upstream DNS

[yubiuser]

@Protheus

[2020-10-11 20:39:34.543 1710/F1619] EDNS(0) pheader[22] = 0xbf
[2020-10-11 20:39:34.543 1710/F1619] EDNS(0) requestor's UDP payload size: 512 bytes
[2020-10-11 20:39:34.543 1710/F1619] EDNS(0) code 10, optlen 8 (bytes 4 - 12 of 12)
[2020-10-11 20:39:34.543 1710/F1619] EDNS(0) COOKIE (client-only): 7E42C3CE46C86ABF

Compare to what I see using dnsmasq with add-mac and add-subnet option

@yubiuser

[2020-08-16 22:26:16.521 22669M] EDNS(0) pheader[32] = 0x54
[2020-08-16 22:26:16.521 22669M] EDNS(0) requestor's UDP payload size: 512 bytes
[2020-08-16 22:26:16.522 22669M] EDNS(0) code 65001, optlen 6 (bytes 4 - 10 of 22)
[2020-08-16 22:26:16.522 22669M] EDNS(0) MAC address (BYTE format): 00:25:d3:c4:d6:a4

Your server is using ENS0, but sending a DNS cookie which does not contain the mac of the client. I'm not sure, if DNS cookies can be used to send client identifier (IP/Mac) or if Pihole capable of dealing with DNS cookies at all. Pinging @DL6ER

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Add : if I understand correctly, you need the subscriber version of bind to use the ECS feature

BIND 9 Significant Features Matrix