Comment 0 for bug 1940908

With systemd v245 (and v247) and systemd-resolved we're seeing frequent problems due to resolved rapidly closing the socket on which it sends out a query before the server has answered. The server answers and then resolved sends an ICMP Destination Unreachable (Port Unreachable) response!

This breaks name lookups frequently. In our case the DNS server is reached via a Wireguard tunnel over a satellite link and latencies can vary.

A typical example captured via tcpdump:

07:22:03.446919 IP6 fddc:7e00:e001:ee00:fffe:f875:a4f3:42b4.45338 > fddc:7e00:e001:ee00::1.53: 2963+ [1au] AAAA? contile-images.services.mozilla.com. (64)
07:22:03.501089 IP6 fddc:7e00:e001:ee00::1.53 > fddc:7e00:e001:ee00:fffe:f875:a4f3:42b4.45338: 2963 1/0/1 AAAA 2a01:7e00:e001:ee64::2278:7366 (92)
07:22:03.501152 IP6 fddc:7e00:e001:ee00:fffe:f875:a4f3:42b4 > fddc:7e00:e001:ee00::1: ICMP6, destination unreachable, unreachable port, fddc:7e00:e001:ee00:fffe:f875:a4f3:42b4 udp port 45338, length 148

The time difference here is only 0.054170 and there is no way to alter the timeout in resolved.

There are recent upstream commits to fix this which ought to be cherry-picked. See:

https://github.com/systemd/systemd/issues/17421

https://github.com/systemd/systemd/pull/17535

https://github.com/systemd/systemd/commit/e03d156f78cb5a0cac85d1e1310d89fdfa4f1b88