Comment 46 for bug 256054

Alexander, please let's make this clearer.

Previously static configuration was achieved by setting address, netmask, network, broadcast and gateway in /etc/network/interfaces and DNS servers where specified as nameserver in /etc/resolv.conf.

My networking was effectively 'broken' for the last couple of days because I (as like many I suspect) had no entry in /etc/network/interfaces for dns-nameservers.

You have mentioned this entry in two posts above:
"dns is gathered from dns-nameservers entry in interfaces for now, like:

  dns-nameservers 192.168.1.1"
and
"in managed=true mode you need dns-nameservers x.y.z.0 in your
interfaces file."

Why dns in not gathered from /etc/resolv.conf I don't know, instead it is now 'written' to /etc/resolv.conf once it is specified in /etc/network/interfaces by dns-nameservers, e.g.:

# Generated by NetworkManager
nameserver 192.168.11.1

but anyway just to reiterate:
Whatever the value for 'managed' in /etc/NetworkManager/nm-system-settings.conf, you won't get proper internet functionality without manually adding e.g. dns-nameservers 192.168.1.1 to /etc/network/interfaces.

Of course the point of NM is that you could set this using the GUI I suppose, but doing so involves this long process:
Right-click on the NM icon -> Edit connections... -> double click on the connection in question ->Click the IPv4 Settings tab -> Enter the server in the box 'DNS Servers' (the mouse-over hint example shows 10.0.0.1, 10.0.0.2 so I suppose multiple servers are to be separated by a comma?) -> Click the 'OK' button.
All to get this error:
Updating connection failed: nm-ifupdown-connection.c.82 - connection update not supported (read-only)..

Oh dear!