Just upgraded to 17.04 from 16.04 and found DNS resolution stopped randomly working.
As it turns out systemd-resolved decided for some obscure reason to switch to google DNS which it can't reach compared to the locally provided recursive resolver which continues to work just fine. In summary in my case it isn't just a privacy concern but actually breaks DNS resolution. Aug 05 11:29:07 dtank0 systemd-resolved[8051]: Switching to system DNS server 10.124.196.1. Aug 05 11:29:07 dtank0 systemd[1]: Started Network Name Resolution. Aug 05 11:33:58 dtank0 systemd-resolved[8051]: Switching to fallback DNS server 8.8.8.8. After the switch to 8.8.8.8 DNS resolution on the host stopped working because 8.8.8.8 is not reachable from the host. Interestingly stopping and disabling systemd-resolved followed by an "resolvconf -u" did not revert the config back to a working configuration. It required removing /run/resolvconf/interface/systemd-resolved by hand (starting systemd-resolved will add that file but not remove on stop). -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/1449001 Title: systemd-resolved: please do not use Google public DNS by default Status in systemd: New Status in systemd package in Ubuntu: Fix Released Status in systemd source package in Zesty: Confirmed Status in systemd source package in Artful: Fix Released Status in systemd package in Debian: Fix Released Bug description: systemd-resolved will fall back to Google public DNS (8.8.8.8, etc.) in the absence of other configured DNS servers. systemd-resolved is not enabled by default in Ubuntu 15.04, but it is installed by default and will behave in this way if enabled by the user. $ cat /etc/systemd/resolved.conf (...) # Entries in this file show the compile time defaults. (...) #FallbackDNS=8.8.8.8 8.8.4.4 2001:4860:4860::8888 2001:4860:4860::8844 This raises privacy concerns since in the event of accidental misconfiguration DNS queries will be sent unencrypted across the internet, and potentially also security concerns given systemd- resolved does not perform DNSSEC validation and is not particularly well hardened against malicious responses e.g. from a MITM (http://www.openwall.com/lists/oss-security/2014/11/12/5). I believe that it would be better to fail safe if no DNS server is configured -- i.e. have DNS lookups fail; it's better that the user is aware of their misconfiguration, rather than silently sending their queries to Google. The user can intentionally opt to use Google public DNS if they wish. Steps to reproduce: 1. Remove existing DNS configuration (from /etc/network/interfaces, /etc/resolv.conf, /etc/resolvconf/resolv.conf.d/*) 2. Reboot, or otherwise clear relevant state 3. sudo service systemd-resolved start 4. Note that Google's servers are listed in /run/systemd/resolve/resolv.conf 5. If systemd-resolved is enabled in /etc/nsswitch.conf (it isn't by default), observe that DNS lookups probably still work, and queries are being sent to one of Google's servers Possible workaround/bugfix: ship a resolved.conf which clears the FallbackDNS parameter. This issue has been discussed in the Debian BTS (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=761658). My interpretation of the Debian package maintainer's position is that a user concerned with the privacy implications shouldn't let systemd get into a state where it uses the fallback DNS servers (quoting Marco d'Itri: "Short summary: have a resolv.conf file or use DHCP"). I would argue that it's safest not to have fallback DNS servers configured at all by default. To manage notifications about this bug go to: https://bugs.launchpad.net/systemd/+bug/1449001/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
