no dns resolver when OpenVPN is running

[Paul Smith]

Please be sure to provide information on what version of Ubuntu you're
using.  Here I'll assume a recent version:

On Sat, 2017-10-21 at 18:26 +0200, robert rottermann wrote:
> As long as the VPN is running, the dns resolver does not work any more, and I 
> can not connect to the internet.

These are two different things: is it that DNS is not working (e.g., you
can access systems on the internet but only by their IP address), or is
it that you cannot connect to the internet at all (your network
connection is not up)?

If it's DNS, then probably you don't have your resolver configured
properly... maybe you undid the original network-manager resover
configuration "back in the day"; normally it takes care of things.

Look at your /etc/resolv.conf file.  Is it a file, or a symbolic link? 
If the latter, where is it pointing?

If you want to use network-manager (and I agree, it's extremely handy to
use it for VPN) then you want your /etc/resolv.conf to look like this:

  $ ls -al /etc/resolv.conf 
    <...> /etc/resolv.conf -> ../run/NetworkManager/resolv.conf

That is, it's a symbolic link to the /run/NetworkManager/resolv.conf
file.  When my VPN is running, the contents of this file look like:

  $ cat /etc/resolv.conf 
  # Generated by NetworkManager
  search <vpn-domains>
  nameserver 127.0.1.1

And, there's a dnsmasq instance running on my system:

  $ ps -aef | grep 'dnsmasq.*127\.0\.1\.1'
  nobody    1269  1007  0 Oct18 ?        00:00:01 /usr/sbin/dnsmasq
    --no-resolv --keep-in-foreground --no-hosts --bind-interfaces
    --pid-file=/var/run/NetworkManager/dnsmasq.pid
    --listen-address=127.0.1.1 --cache-size=0 --conf-file=/dev/null
    --proxy-dnssec --enable-dbus=org.freedesktop.NetworkManager.dnsmasq
    --conf-dir=/etc/NetworkManager/dnsmasq.d