Second DNS Server Pihole doesn't respond to DNS queries

Hi,

I'm currently using two Piholes synced with vmstan/gravity-sync (that I love as a tool!) but the second Pihole designed as my second DNS server on my router doesn't seems to work as intended

When the second Pihole is set as the only DNS server, none of the queries seems to pass the test

Here's the setup of the second Pihole :

  • Ubuntu 20.04.5 LTS VM on Synology Virtual Machine Manager
  • Two NICS attached to the VM (CIDRs 192.168.1.x and 172.16.0.x)
  • Docker installed on Linux
  • Pihole container set as Host with the same variables adapted to the 2nd Pihole
    ** FTLCONF_LOCAL_IPV4, VIRTUAL_HOST and INTERFACE all listed
    ** DNSMASQ_LISTENING = all
    ** DNSMASQ_USER = root
  • Added a /etc/pihole/dnsmasq.d/98-interfaces.conf file with the second NIC as an interface
  • Using unbound container as a resolver with both Pihole DNS resolvers set to address 127.0.0.1#5335

I did test command "dig pi-hole.net @127.0.0.1" from inside the Linux VM and the results are positive:

> ; <<>> DiG 9.16.1-Ubuntu <<>> pi-hole.net @*127.0.0.1*
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53517
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;pi-hole.net. IN A
;; ANSWER SECTION:
pi-hole.net. 267 IN A 3.18.136.52
;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Wed Jan 25 02:41:09 UTC 2023
;; MSG SIZE rcvd: 56

But when I try to indicate the complete LAN IP instead of 127.0.0.1, there's a connection timed out error

Unbound seems to work as intended with both addresses SERVFAIL and NOERROR working as mentioned here

Here's the debug LOG: https://tricorder.pi-hole.net/K20bophS/

Do you have any idea what would be the source of that problem?

Thanks in advance and regards!