I spun up an azure instance and tested, and indeed tcp port 53 appears completely missing from any tcpdump, but only for packets sent to the upstream nameserver. TCP sent to port 53 on *any* other ip address does make it out, but tcp port 53 to the nameserver does not. There are no routing rules or ip routes or iptables I could find that might be blocking the packets, so I'm not sure why the packets aren't being sent out, but that's the cause of the failure here to fallback to TCP DNS.
So 1) we do need to fix upstream systemd to use >512 byte edns0 udp with upstream nameservers, and also 2) something is wrong with the azure instances that is blocking TCP DNS to the upstream nameserver. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1886128 Title: systemd-resolved does not resolve address due to udp payload size. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1886128/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
