AdGuard Home DNS requests timing out on Ubuntu Server

AdGuard Home DNS requests timing out on Ubuntu Server

Hi everyone,

I'm trying to set up AdGuard Home on Ubuntu Server, but DNS queries through AdGuard Home keep timing out.

AdGuard Home starts correctly and listens on port 53, and the web dashboard is accessible.

However:

dig .168.0.100 google.com 

returns:

;; communications error to 192.168.0.100#53: timed out ;; no servers could be reached 

The same happens locally:

dig u/127.0.0.1 google.com 

Interestingly, the Ubuntu server itself can resolve DNS normally through the router. I confirmed with tcpdump that DNS requests to the router receive valid responses.

UFW is also inactive.

The AdGuard Home logs show that the upstream DNS is timing out. I initially configured Quad9:

https://dns10.quad9.net/dns-query 

The logs contain:

exchanging with 9.9.9.10:53 over udp: read udp ...: i/o timeout 

and also errors about the IPv6 Quad9 addresses being unreachable.

So it seems like:

Ubuntu → router DNS works

but:

AdGuard Home → upstream DNS does not work

What could cause AdGuard Home to be unable to reach the upstream DNS servers while Ubuntu itself can resolve DNS normally?

I'm running AdGuard Home directly on Ubuntu Server, not Docker.

Thanks!