[Bug 1624320] Re: systemd-resolved appends 127.0.0.53 to resolv.conf alongside existing entries

[Bernhard]

Hi,

I just upgraded from Ubuntu 16.10 to 17.04 and observed the following
systemd-resolve behaviour that might be related to this bug:

--> Any domain listed after the "search" keyword in /etc/resolv.conf
stops being resolved by systemd-resolve.

respectively

--> Any domain listed as "DNS Domain:" when querying "systemd-resolve
--status" stops being resolved by systemd-resolve

I confirmed with tcpdump that systemd-resolve will not query my local or
any dnsserver for any subdomains for any domain listed under the
"search" keyword.

Changing the domains after the search keyword in /erc/resolv.conf
immediately changes which domains systemd-resolve will ignore and not
resolve.

The search domain is normally automatically set in response to receiving
an "option domain-name" from the local dhcp server and normally used to
translate requests for www to e.g. www.localdomain.at if localdomain.at
was the domain-name sent by the DHCP server.

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https://bugs.launchpad.net/bugs/1624320

Title:
  systemd-resolved appends 127.0.0.53 to resolv.conf alongside existing
  entries

Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  systemd-resolved, or more precisely the hook script
  /lib/systemd/system/systemd-resolved.service.d/resolvconf.conf, causes
  resolvconf to add 127.0.0.53 to the set of nameservers in
  /etc/resolv.conf alongside the other nameservers.  That makes no sense
  because systemd-resolved sets up 127.0.0.53 as a proxy for those other
  nameservers.  The effect is similar to bug 1624071 but for
  applications doing their own DNS lookups.  It breaks any DNSSEC
  validation that systemd-resolved tries to do; applications will
  failover to the other nameservers, bypassing validation failures.  And
  it makes failing queries take twice as long.

  /etc/resolv.conf should have only 127.0.0.53 when systemd-resolved is
  active.

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