16.10 fail to resolve DNS

DNS behavior during OpenVPN connection improved immediately when I followed a suggestion on ubuntuforums:

1. Open /etc/NetworkManager/NetworkManager.conf in an editor with root rights.
2. Delete (or comment out with a hash #) the line that reads dns=dnsmasq
3. Restart NetworkManager via sudo service NetworkManager restart

I experienced similar problems, for example with adding an extra USB wifi dongle. First I disabled dnsmasq in networkmanager as described above and I stopped dnsmasq (service dnsmasq stop)

I noticed that when resolving broke during my VPN connecting, the routing table looks slightly different (output of route command). The name of the Gateway is DD-WRT in the case it does not work and simply 'gateway' when it does work. The output of this did not change:

nmcli device show wlp1s0 | grep IP4.DNS

It kept showing my router IP. A workaround to get it to work for a while is to restart systemd-resolvd:

sudo service systemd-resolved restart

Since dnsmasq is out of the equation, it is either systemd-resolvd that is the cause of the issue, or anything changing the routing table.

So this is the only difference I see:

ubuntu@ubuntu-Lenovo-Yoga-2-11:~$ route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         gateway         0.0.0.0         UG    601    0        0 

which works. And this when it does NOT work:

ubuntu@ubuntu-Lenovo-Yoga-2-11:~$ route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         DD-WRT          0.0.0.0         UG    601    0        0 wlp1s0

And the same name difference on the VPN line :

vpn-dns.name gateway         255.255.255.255 UGH   0      0        0 wlp1s0

Who knows what may influence the routing table? It would be great if we can identify this so a bug report can be filed. I am getting seriously sick and tired of pursuing all these bugs, but I would like to get them fixed so future users and us will be happy :).

[update] It seems stopping systemd-resolved may fix this and not negatively impact other stuff. You can try that and let it know if it does break stuff. I saw when running systemd-resolvd in debug when it broke:

Removing scope on link wlp1s0, protocol llmnr, family AF_INET
Removing scope on link wlp1s0, protocol llmnr, family AF_INET6
Removing scope on link *, protocol dns, family *

To disable:

sudo systemctl disable systemd-resolved.service

I updated the Ubuntu report with suggestions. [/update] Add: Note: the bug report : https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1624317 has a patch for 17.04 for some issues. Please check the bug report and if possible test the patch. Thank you!

[update]

Please check the above mentioned bug report, the issue seems to be resolved for 17.10 and with a simple command DNS leakage can be disabled too.

[/update]

Ran into the same issue. Somehow I must have installed DNSmasq with some application. Simply removing dnsmasq solved the issue for me.

sudo apt-get remove dnsmasq 

Since then, no more disconnects or some sites not being able to load anymore (I've had an issue loading gmail, i.e. all of the sudden it couldn't connect to gmail, though other sites worked).