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

[FFO]

Problem exist with Ubuntu 19.10
The netplan configuration below just works
then after some time (I can't say when) it just stops resolving.
executing netplan apply make the DNS resolution work again.

----------------------------------------------
root at nas:/home/ff# nslookup www.cisco.com
Server:         127.0.0.53
Address:        127.0.0.53#53

** server can't find www.cisco.com: SERVFAIL

root at nas:/home/ff# netplan apply
root at nas:/home/ff# nslookup www.cisco.com
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
www.cisco.com   canonical name = www.cisco.com.akadns.net.
www.cisco.com.akadns.net        canonical name = wwwds.cisco.com.edgekey.net.
wwwds.cisco.com.edgekey.net     canonical name = wwwds.cisco.com.edgekey.net.globalredir.akadns.net.
wwwds.cisco.com.edgekey.net.globalredir.akadns.net      canonical name = e2867.dsca.akamaiedge.net.
Name:   e2867.dsca.akamaiedge.net
Address: 104.69.84.242
Name:   e2867.dsca.akamaiedge.net
Address: 2a02:26f0:e1:391::b33
Name:   e2867.dsca.akamaiedge.net
Address: 2a02:26f0:e1:381::b33


----------------------------------------------

network:
    ethernets:
            eth0:
                    dhcp4: no
            eth1:
                    dhcp4: no
            eth2:
                    dhcp4: no
            eth3:
                    dhcp4: no
    bridges:
        br0:
            interfaces: [eth0, eth1, eth2, eth3]
            macaddress: 00:51:82:f1:f0:02
            dhcp4: no
            addresses: [192.168.0.32/24]
            gateway4: 192.168.0.2
            nameservers:
              addresses: [192.168.0.2]

    version: 2

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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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