------- Original Message ------- El domingo, 28 de mayo de 2023 a las 07:23, David Gibson <david(a)gibson.dropbear.id.au> escribió:So, we have some special cases related to port 53 - aimed at allowing the container to contact a nameserver outside. I don't think we thought much about the case of a DNS server inside the container. So my first guess would be that those special cases have an error that's interfering with your use case. If it's possible to try running your server on a port other than 53 temporarily that would be interesting to try.Thanks for the suggestion. I've tried moving the listening port of this service (AdguardHome) to 54 and surprisingly it was still not working on UDPv6. Testing with a different DNS service (unbound) works fine even when using port 53. So this is a problem with this specific service. I don't understand why it's not working, as the service listens on the :: address. Maybe it's using a socket option that it's causing this? I need to investigate this further. # netstat -putan Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 :::3003 :::* LISTEN 2/AdGuardHome tcp 0 0 :::54 :::* LISTEN 2/AdGuardHome udp 0 0 :::54 :::* 2/AdGuardHome # cat /proc/net/udp6 sl local_address remote_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops 4718: 00000000000000000000000000000000:0036 00000000000000000000000000000000:0000 07 00000000:00000000 00:00000000 00000000 0 0 38510801 2 0000000073476783 0We also attempt to auto-configure those cases from the host's resolv.conf, so if you could share that it might shed some extra light.resolv.conf looks correct: # Host: nameserver 192.168.7.1 nameserver fddc:f797:78ef:70::1 search lan # Container: search lan nameserver 192.168.7.1 Thank you.