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

[Doug Goldstein]

So this issue bit me in a weird way. I had my bridge called "xenbr0" and
the result of these two interacting gives me absolutely no DNS
resolution since the /etc/resolv.conf just pointed to 127.0.0.53 and
didn't include the DNS server from my "xenbr0". Renaming the bridge to
"renbr0" caused it to work. Why "renbr0"? Because in
/run/resolvconf/interface/ there is a file called systemd-resolved that
I was guessing was stopping combining the files once it hit the systemd-
resolved.

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

Status in systemd package in Ubuntu:
  Incomplete

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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