[Bug 1384394] Re: /etc/network/interfaces: "dns-nameservers" entries for bridge "br*" interfaces are ignored i.e. they are not listed in "/etc/resolv.conf" when invoking "ifup" command

[Steve Langasek]

Ok.  So the crucial thing shown here is that in addition to the br
interfaces, you have NetworkManager.  NetworkManager sets 'nameserver
127.0.1.1', which by design will redirect DNS requests to a local
dnsmasq proxy, with dnsmasq itself picking up the configured nameservers
instead; and when set, resolvconf will truncate the dns server list
(because 127.*.*.* is special), so you won't see these in
/etc/resolv.conf.

The only thing I can't figure out is why changing the order of
processing of the interfaces has any effect at all for you, since
NetworkManager should still be processed and the 127.0.1.1 should still
take precedence.

So the root problem is that dnsmasq doesn't have an interface that
allows injecting of individual dns servers into its config, which means
it can only interface with a single client at a time - in this case,
NetworkManager, which doesn't know about network interfaces that are
configured via ifupdown.

NetworkManager and ifupdown can coexist rather reasonably together, and
have done so for quite a while, but they can't coexist very well when
dnsmasq is used.

So there are several workarounds you could employ at the configuration level:
 - change /etc/NetworkManager/NetworkManager.conf to not use 'dns=dnsmasq'
 - if you aren't using any interfaces other than the bridges, disable use of NetworkManager altogether.

Regardless, it's a limitation of dnsmasq that it doesn't have a proper
dbus interface for controlling dns servers.

** Package changed: resolvconf (Ubuntu) => dnsmasq (Ubuntu)

** Changed in: dnsmasq (Ubuntu)
   Importance: Undecided => Low

** Changed in: dnsmasq (Ubuntu)
       Status: Incomplete => Triaged

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https://bugs.launchpad.net/bugs/1384394

Title:
  /etc/network/interfaces: "dns-nameservers" entries for bridge "br*"
  interfaces are ignored i.e. they are not listed in "/etc/resolv.conf"
  when invoking "ifup" command

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