The following would revert dns resolution to back the way it was handled in 16.04 (using dnsmasq):

Install dnsmasq:

sudo apt-get install dnsmasq

Disable the systemd-resolved service:

sudo systemctl stop systemd-resolved
sudo systemctl disable systemd-resolved

Check if dnsmaq is running:

systemctl status dnsmasq

You should see a line starting with the following:

Active: active (running)

Updated the ‘‘/etc/NetworkManager/NetworkManager.conf’’ config file, and add ‘‘dns=dnsmasq’’ to the main section as such:

[main]
dns=dnsmasq

Restart the Network Manager:

sudo systemctl restart NetworkManager

And finally ‘‘/etc/resolv.conf’’ should be replaced by a symlink to ‘‘/var/run/NetworkManager/resolv.conf’’:

sudo rm /etc/resolv.conf; sudo ln -s /var/run/NetworkManager/resolv.conf /etc/resolv.conf